eHam

eHam Forums => SWL (Shortwave Listening) => Topic started by: K0OD on March 17, 2012, 08:08:54 AM



Title: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on March 17, 2012, 08:08:54 AM
For most SWLs an ever-so-simple random end-feed wire is quite adequate. I have used my ham vertical (basically a random wire on most frequencies) to pick up European longwave stations as low as 150 Hz, as well as shortwave broadcast stations on HF and even VHF.

But nothing beats a directional antenna for gain and QRM/noise reduction.  No doubt wideband log periodic yagis work. You'll see them on government and commercials buildings. But most us don't want to put up something as big as a Volkswagen high over our homes. And even log periodics are compromises. This "small" one has a low frequency cut off of 6.5 MHz and its performance within its rated range is dependent on its height above ground.
http://www.antenna.it/military/images%20military/image.c.630-lp10.jpg

More practical small, easily erected, moderate price SWL antennas are available. Loops have been around from the start of radio and sometimes offer excellent noise and QRM reducing nulls. Also available are simple active verticals, beverages and K9AY-type antennas and more recently, arrays of active verticals.

Eham's own W8JI has created this sophisticated 8-element array available from DX Engineering for a few thousand dollars.
http://tinyurl.com/7hsllnt

Phased arrays of active RECEIVE-ONLY antennas offer QRM and noise reduction over a wide range of frequencies. Moreover, they are instantly electronically rotatable. Such arrays are perhaps the ultimate receiving antenna for real-estate restricted listeners.

Anyone here using sophisticated directional SWL antennas?



Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on March 18, 2012, 10:23:16 AM
Hi Jeff,

I would consider my RF Systems DX-1 Pro MK II Active receive antenna to be a sophisticated antenna. It is extremely well designed and is used in many embassies and military installations throughout the world. However, it is more omni-directional than directional and utilizes both vertical and horizontal polarization, so it performs well on multi-path signals. It has a high 2nd and 3rd order intercept point and is very quiet. It is also very sensitive. But it does not come cheap and at $700 is comparable in price to a beam!
I would be interested to hear your views.....

Best Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on March 18, 2012, 11:38:05 AM
Was glancing at the specs yesterday for that $700 Dutch listening antenna. It is said to have "10 db gain." Wow, right? That's about as good as a 5 element Yagi!   

But gain over what wasn't stated. I presume the preamp adds 10dB. So it has 10dB over itself with the preamp turned off... 10 dB over a small hunk of wire, in effect. Not so impressive.
http://www.rf-systems.nl/Shortform-catalog-complete.pdf

As for the military pedigree, it's pretty vague. In one place it says their antenna was "derived" from a military design. They never name the military or show a photo of it at war. Old trick is to donate something to a base ham club and then claim its "used by the military."

Full bore contest stations occupy many acres and have many antennas. Cost is a minor factor. You may be surprised that many of those antennas aren't monsters. They use small, low yagis, dipoles and verticals for spotting purposes and for back up and probably as references for testing the big antennas. They use many receive only antennas. They are constantly looking for an edge.

I'm inclined to think that W0AIH, for example, knows about actives antennas. I've never heard of him or any contest station using any of these SWL "wonder-antennas" (except perhaps in an array of them):
http://www.qth.com/w0aih/images/sunset.jpg
 


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on March 18, 2012, 12:20:39 PM
Thanks for your comments Jeff. They are most interesting. You are correct about the 10dB gain. This is with the accompanying pre-amp active control unit. It can increase the QRN on a signal which is why I seldom use it. However, I think the IP2 and IP3 figures for the antenna are impressive and speak for themselves. The antenna is probably not as good as those used by full bore DX or Contest stations but because of its small size it is convenient for those BCB/SW listeners with small lots.
The mention of military and government users of the antenna could indeed be marketing hype. Maybe specific references to those users would add to the antennas credentials.
However, at the end of the day the proof is in the pudding and I must say the antenna performs well and is comparable to some of the longer beverage antennas I've heard used.
The antenna is particularly good on LW/MW and LF AM.
Indeed, I have heard a lot of great DX with it including some low powered SW stations from the australian outback.
Anyway Jeff, thanks again for your comments. I found them and the links you provided most informative.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on March 19, 2012, 06:20:25 AM
Fred I couldn't recall reading about active antennas in ham literature. For one thing, they're strictly for receiving.  Also for traditional ham frequencies, the "random hunk of wire tossed out a window" is probably as good especially with a wide range tuner. Active antennas do seem to be useful below the AM broadcast band where hams worldwide are getting expanded authorization. 

HF Active antenna:
http://www.sentex.ca/~mec1995/circ/Activ8/activ8.html

LF Active antenna:
http://www.arrl.org/files/file/Technology/tis/info/pdf/0109031.pdf

I still don't understand how a tiny active antenna would work better than a hunk of wire or be worth $700. Here's a kit available for about $70. You'll notice that no extraordinary claims are made for its performance. It's sold mostly for those who can't put up any outside antenna.
http://www.northcountryradio.com/Kitpages/actant.htm

More interesting for hams would be arrays of active antennas now that commercial controller boxes are available. I used a 4-element system with transmitting and receiving capability on the 40 meter band years ago so I know that such arrays hear great.

Also,the major problem with arrays of transmitting verticals is the need for a good radial system under each vertical. With active receiving antennas a simple ground rod under each is all that's required.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on March 20, 2012, 08:05:47 AM
I still don't understand how a tiny active antenna would work better than a hunk of wire or be worth $700. Here's a kit available for about $70. You'll notice that no extraordinary claims are made for its performance. It's sold mostly for those who can't put up any outside antenna.
http://www.northcountryradio.com/Kitpages/actant.htm

That's a good point Jeff!
I have often thought the same thing about my G5RV Jr. when I hear the claims many antenna manufacturers make about their HF antennas!
Personally, I think this active antenna is overpriced which is probably why RF Systems have stopped producing them.
It was much cheaper when I bought it a number of years ago. I certainly wouldn't shell out $700 for it today, that's for sure!
I guess the advantage I have found using it, is that it allows me to pick up weak AM DX without intermodulation distortion or spurious signals.
Indeed when coupled to my Drake R8, it performs extremely well. I am unable to put up long beverage antennas yet I still get the same great receive performance, especially on LW/MW and LF AM.
Having said that, if I had to do it all over again I would probably buy something a bit cheaper! ;D

Best Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on March 20, 2012, 09:49:22 AM
I can think of very few situations where an active antenna would make sense over a $2 hunk of random wire.  Perhaps it might be advantageous to mount an active antenna far outside a very "radio active" building like a factory or hospital, or a structure with lots of other transmitters like an embassy.  An active antenna on a high tower ABOVE such a building might help a lot in reducing crud from below. 

But the vast majority of noise is atmospheric QRN. A single active antenna won't reduce that. You just don't find ham DXers using active antennas much.

Note that DX Engineering sells a $289 hefty active antenna (designed by W8JI). It's only rated down to 100 KHz. It's designed to be used very close to transmitters as in a ham station. I'd trust that model over most of the SWL-targeted wonder-antennas.
http://www.dxengineering.com/ShowRelatedProd.asp?PartNo=DXE-ARAV3-1P

More on active antennas:
http://wiki.radioreference.com/index.php/Active_Antennas_KB6RWX

Which says in part: "Many people have misconceptions about active antennas. Some think that their radio receiver system will be transformed into a highly sensitive “spy grade” radio that will hear everything that is broadcast around the world. This is simply not so."



Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on March 20, 2012, 01:12:34 PM
I can think of one Jeff. When a full size (resonant) antenna or long wire would be too impractical to set up.
You have also mentioned some good instances yourself and provided some excellent links.
I think we may also be talking at cross purposes as you seem to be referring to HAM HF whilst I am referring to LF/MF BCB!
Anyway Jeff, I don't want to hog the topic. It has been an interesting discussion and I'd like to thank you again for your honest replies.
I will now leave it to others to give their 2 cents worth! Take care.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on March 20, 2012, 04:13:39 PM
Resonance is unimportant on receive. Regardless of HF Ham, BCB or LW. 

Otherwise we'd need 500' verticals on cars to hear AM BCB broadcasts. Sure a tiny car antenna has a ludicrously high SWR at say 540 KHz with resulting high coax loss per foot, but the coax is only a few feet long. And that small loss applies equally to the signal you want to hear and the noise you don't want to hear.  I think its fair to say that with a decent receiver you can totally offset those losses.... by turning up the volume control a bit. 

As for using an active antenna on extremely low frequencies, that makes sense in some settings.

--
Anyone else have comments?


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on March 21, 2012, 02:10:57 PM
Resonance is unimportant on receive. Regardless of HF Ham, BCB or LW.  

As there are no takers I will respond.
A receiver antenna is less critical, since inefficiency can be compensated by signal amplification in the receiver, but there is improvement in reception when receiving antennas are tuned to resonance.
Also, amplification that occurs at the front end of a radio is not as good as amplification that occurs at the antenna end or signal source. Adding external gain can actually make the receiver more sensitive, but at the cost of dynamic range which is perfectly acceptable under certain conditions.
A good antenna factor is also needed to prevent overloading.
An active antenna may not be resonant on LF/MF BCB but high performance antennas like the RF Systems DX-1 Pro Mk II work by having a high quality, low noise, amplification circuit in place. They also have high IP2 and IP3 which means less intermodulation distortion and spurious signals.
This together with the use of a good radio receiver can make all the difference when trying to hear weak AM stations or DX on LF/MF!
 


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: KB1GMX on April 03, 2012, 04:18:50 PM
>Resonance is unimportant on receive. Regardless of HF Ham, BCB or LW. 

Not completely but depends on the system goals.  Resonance often yields greater signals
with less noise due to band width reduction.

>Otherwise we'd need 500' verticals on cars to hear AM BCB broadcasts. Sure a tiny car antenna has a ludicrously high SWR at say 540 KHz with resulting high coax loss per foot, but the coax is only a few feet long. And that small loss applies equally to the signal you want to hear and the noise you don't want to hear.  I think its fair to say that with a decent receiver you can totally offset those losses.... by turning up the volume control a bit. 

First car antennas are connected with high impedance low capacitance cables directly to the first tuned circuit.  It's a voltage probe rather than short(end) whip.

>As for using an active antenna on extremely low frequencies, that makes sense in some settings.

Most common example is the WWVB at 60khz, and before it was shutdown the LORAN-C
active antennas at 100Khz.  Any thing bigger on a airplane has high drag costs.

Years (many) ago I used to play in the 1750M band (160-190khz part 15).  Receive
antennas were not restricted so a loop of wire nearly 1000ft long was used(with tuning and matching) and the transmit antenna was limited by rule to 50FT total cable and antenna
so the tx was at the bottom and part of the big load coil(many turns of #8) pumping
a mighty 1W input.  AM modulated signals were good for about 50 miles, SSB more.
We didn't have computers back then so QRSS was not done.

--
>Anyone else have comments?

Ask you get.


Allison



Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: AUSSIE on May 05, 2012, 05:48:20 PM
Hi Rfsytems & Wellbrook active antennas do an excellent job nulling out interference
expensive but u get what u pay for in this hobby..

Regards Lino..


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0JEG on May 06, 2012, 08:07:39 AM
Resonance is unimportant on receive. Regardless of HF Ham, BCB or LW.  

As there are no takers I will respond.
A receiver antenna is less critical, since inefficiency can be compensated by signal amplification in the receiver, but there is improvement in reception when receiving antennas are tuned to resonance.
Also, amplification that occurs at the front end of a radio is not as good as amplification that occurs at the antenna end or signal source.

Proof of this can be found with magnetic loop antennas. When manually tuning them you get a rough adjustment by listening to the loudness of noise or signal and peaking the S-meter.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 06, 2012, 09:07:46 AM
Yes, signal and noise both peak at resonance. An S-meter will rise but the DX station is no easier to copy amid the louder noise.  Low band DXers agonize over many things, but not about tuning their receiving antennas for precise resonance.

For best reception, would you suggest that avid 160m ops put up a bunch of antennas, each tuned to a slightly different frequency on the band? That would be quite a waste.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: AC5UP on May 06, 2012, 10:05:58 AM
Do a little web search and you'll find plans for resonant loops using varactor diodes as the tuning caps. Nice concept as a DC voltage can be superimposed on the feedline and there are no moving parts anywhere north of the control box. Might see a slight reduction in signal due to the DC block on the RX end of the line, but it has been my experience that even a modest loop is capable of bodacious signal levels.

Years ago I experimented with square loops four feet on a side and wound with seven turns of 20 ga solid enameled copper. The target band was AM broadcast and they worked well enough on local stations to overload almost every receiver I tried with them. At night the entire band was S9+ from end to end and LOUD. At first glance this might seem like a good thing, but in reality the quality of reception was much like any consumer radio with a decent ferrite rod antenna - except - the AVC had more margin on fades.

Otherwise it was the same ol' same ol' of three or more simultaneous stations on almost every channel......... A GE SuperRadio II will demonstrate that quality straight out of the box with no need to peak a second knob.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: KR4HV on May 06, 2012, 08:02:11 PM
You folks might want to look at some of the phased arrays that Dallas Lankford designs and uses.  Dallas is one of the SWL radio and antenna gurus and has been for 30 years or more, especially for small phased arrays that one can build.  To my knowledge he does not sell a product.  Also, if you use any older receivers you may want to find and download all the HSN (Hollow State Newletters).  It is now defuct but was published for years.  It was not a HAM specific publication. although there were some Hams involved, but was for SWLs or anyone interested in high performance receivers and dealt only with receivers, receiver accessories and antennas, etc. It was SWL oriented and filled with all sorts of very good technical information regarding vintage (and some newer) receivers and SWL operations.

Both are very good reading.

Here is one of the links. I don't have the other handy.  http://groups.yahoo.com/group/thedallasfiles/


73, Walt
KR4HV


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 07, 2012, 08:57:18 AM
Ah, now we're getting somewhere. Thanks for the info, Walt  I just signed up for Lankford's Yahoo Group.

Must say I don't understand why many SWL's own stacks of costly HF radios and scanners and yet have them connected to overpriced and overhyped active antennas or worse. For listening, the goal is directivity rather than gain. Generally, a great antenna is one that gets rid of stuff you don't want to hear... QRM and QRN.      

Sophisticated receive antennas that are compact and inexpensive have come out in recent years for ham/swl/lowfer purposes. Interesting that Lankford isn't a fan of Beverages... which is convenient for those of us in the 'burbs.

http://users.eastlink.ca/~jhsmith/JeffSmith/Lankford%20Antenna%20References%20.htm



Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 07, 2012, 03:11:49 PM
... there is improvement in reception when receiving antennas are tuned to resonance. ...

Other than a narrow band mag loop, in what way is there improvement in reception when receiving antennas are tuned to resonance? Not in S/N.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 08, 2012, 03:36:39 AM
... there is improvement in reception when receiving antennas are tuned to resonance. ...

Other than a narrow band mag loop, in what way is there improvement in reception when receiving antennas are tuned to resonance? Not in S/N.

KB1GMX has already stated it correctly. "Resonance often yields greater signals with less noise due to band width reduction".

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 08, 2012, 01:05:36 PM
"Resonance often yields greater signals with less noise due to band width reduction".

Yes, reducing bandwidth can reduce noise. For example, when we're listening on a 2.4 KHz SSB filter and switch to a 500 Hz CW filter, the result is an improved S/N ratio and a lot less noise.

However, we'd have to have a pretty drastic bandwidth reduction by the antenna to eliminate noise coming out of our receiver's speaker. The only antenna I know of that can reduce bandwidth to that extent is a mag loop, and even then it has to be carefully designed with minimum losses to accomplish that. Unless the antenna's bandwidth is extremely narrow (like only a few KHz; in any case narrower than our receiver's built-in filters), bandwidth reduction in the antenna not going to help us one bit.

What usually makes a receiving antenna work for us is reduced noise pickup in unwanted directions and/or gain in the desired direction, and not reduced bandwidth or resonance.

As for the matter of resonance, look at a Beverage antenna. Not only is it not resonant, but the bandwidth is something in the order of 30 MHz! But the Beverage's S/N ratio beats 99% of resonant antennas hands down for hearing signals buried in the noise.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 08, 2012, 01:37:03 PM
Quote
As for the matter of resonance, look at a Beverage antenna. Not only is it not resonant, but the bandwidth is something in the order of 30 MHz! But the Beverage's S/N ratio beats 99% of resonant antennas hands down for hearing signals buried in the noise.

:) You beat me to saying the same thing, Mike. Or a log periodic Yagi which is also popular with the military. Or a T2FD, to go to an extreme. My old 4-square was incredibly broad on 40 (and well outside that band). I have a wall of certificates and about 330 countries on 40 to prove it heard well.

What sort of resonance are we discussing? Would an antenna with 1.0 to 1 SWR hear better than one with a 1.1 or 1.2 ?  You need to tell the Multi/Multi guys stations about that!   

Main advantage I see in a resonant receiving antenna would be if you live next door to a Voice of America site or you listen on a crystal set, where any extra molecule of selectivity would be welcome.

Learn about antennas from what the world's most competitive DXers use to win, and not from ads aimed at separating SWLs (or hams) from their cash.   


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 08, 2012, 02:04:28 PM
Quote
As for the matter of resonance, look at a Beverage antenna. Not only is it not resonant, but the bandwidth is something in the order of 30 MHz! But the Beverage's S/N ratio beats 99% of resonant antennas hands down for hearing signals buried in the noise.


Learn about antennas from what the world's most competitive DXers use to win, and not from ads aimed at separating SWLs (or hams) from their cash.  

Mike, think of what a Beverage antenna would be like if it were resonant and didn't have a 30 MHz band width!

Jeff, this is what I have learned from studying antenna theory. If you don't believe me check it out!

Here is a link you may both find useful:
 
http://www.rp-photonics.com/spotlight_2009_07_21.html

Take care

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 08, 2012, 02:05:51 PM
'


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 08, 2012, 03:39:02 PM
Quote
"Mike, think of what your antenna would be like if it were resonant and didn't have a 30 MHz band width? Try it!"

All antennas are resonant... somewhere.  
If it makes you happy, resonant Beverages can be built although resonance would offer little benefit and would vary immensely after every rain.

I ask, what sort of narrow bandwidth antenna are you thinking of? Yes, I guess a simple antenna with 2.5 KHz 60 dB bandwidth might be nice for the 75 meter guys who "own" their favorite frequency.  Can you tell us how to build one?

--------
BTW, in the real world,  the S/N improvement from going extremely narrow with traditional modes (AM, SSB, CW) is offset by distortion of the signal especially over long DX paths. I rarely use a filter of less than 2.4 KHz on SSB or less than 250 Hz on CW Hz, although my Flex can create almost any bandwidth. Many experienced ops prefer to use their brain as their main filter.

Frankly I think most hams are wasting money with these superduper filters from firms like Sherwood.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 09, 2012, 05:13:41 AM
All antennas are resonant... somewhere.  
If it makes you happy, resonant Beverages can be built although resonance would offer little benefit and would vary immensely after every rain.

I ask, what sort of narrow bandwidth antenna are you thinking of? Yes, I guess a simple antenna with a 500 Hz 60 dB bandwidth might be nice for the 75 meter guys who "own" their favorite frequency.  Can you tell us how to build one?

--------
BTW, in the real world,  the S/N improvement from going extremely narrow with traditional modes (AM, SSB, CW) is offset by distortion of the signal especially over long DX paths. I rarely use a filter of less than 2.4 Hz on SSB or less than 250 Hz on CW Hz, although my Flex can create almost any bandwidth. Many experienced ops prefer to use their brain as their main filter.

Frankly I think most hams are wasting money with these superduper filters from firms like Sherwood.

Jeff,

Instead of making sweeping generalizations maybe you should study modern antenna theory more. Some of your statements go against the facts.
One only needs the band width of the operating band to notice an improvement in the performance of an antenna.
A Beverage antenna offers a good compromise to most people who would find it impractical to set up a resonant antenna, especially for LW/MW BCB.
The signal to noise difference occurs first at the antenna-end before it reaches the filters of your radio which only help in further reducing the noise.
That is why it is important to have an efficient antenna and good receiver when SWL'ing.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 09, 2012, 07:23:10 AM
A Beverage antenna offers a good compromise to most people who would find it impractical to set up a resonant antenna, especially for LW/MW BCB.

A Beverage antenna is a compromise?  ::)  It is a well-established fact that a Beverage will enable you to hear extremely weak DX signals that are buried in noise or covered up by other interference, that simply cannot be heard on a vertical or dipole.

Why don't you try one and see? Instructions for making one are at http://www.w0btu.com/Beverage_antennas.html.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 09, 2012, 12:31:26 PM
A Beverage antenna offers a good compromise to most people who would find it impractical to set up a resonant antenna, especially for LW/MW BCB.

A Beverage antenna is a compromise?  ::)  It is a well-established fact that a Beverage will enable you to hear extremely weak DX signals that are buried in noise or covered up by other interference, that simply cannot be heard on a vertical or dipole.

Why don't you try one and see? Instructions for making one are at http://www.w0btu.com/Beverage_antennas.html.

Actually Mike, most antennas are a compromise. The Beverage antenna is no different, especially on LW/MW BCB. This is due to the fact that most antennas are not long or high enough for these bands. To be so would require many hundreds of feet often an impractical consideration for most people.
On 160m and the higher bands your average Beverage is probably a good antenna ,and offers, as you say, some gain and directionality for improved reception.
I have been a BCB Dx'er for many years and my antenna of choice because of limited space is an omni-directional vertical- the RF Systems DX-1 Pro MK II. IMHO it gives comparable  results to a Beverage.
I know many serious DX'ers who obtain good results from Beverages.
Personally, I've nothing against these antennas but like all antennas they are a compromise and have their limitations too. ;)
 
Kind Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 09, 2012, 02:15:23 PM
Quote
I have been a BCB Dx'er for many years and my antenna of choice because of limited space is an omni-directional vertical- the RF Systems DX-1 Pro MK II. IMHO it gives comparable  results to a Beverage.

Uh?  ????


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 09, 2012, 02:37:39 PM
Don't knock it till you try it, Jeff !  ;D


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 09, 2012, 03:05:53 PM
Jeff, we are wasting our time. Someday, I'm going to make some audio and video recordings of my Beverages compared to other antennas. One I've always wanted to record was switching between four different directions, and hearing a different radio station in each of those directions on the same frequency.

I should lengthen them sometime. That would improve things, as 580' is kind of short for the low end of the AM BCB and even more so for the European AM stations between 100 and 200 kHz.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 09, 2012, 03:27:58 PM
Jeff, we are wasting our time.

You are also wasting the time of others. Learn the theory first guys before you do the practicals !  ;)

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 11, 2012, 04:20:58 PM
Quote
I have been a BCB Dx'er for many years and my antenna of choice because of limited space is an omni-directional vertical- the RF Systems DX-1 Pro MK II. IMHO it gives comparable results to a Beverage.

Is this the antenna you're talking about that you claim is as good as any Beverage on the BCB?: http://www.universal-radio.com/catalog/sw_ant/1246.html

Oh, BTW, is that a resonant antenna?

And what BCB (that is, frequency range) are you referring to?

I just want to make sure we're on the same page.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 12, 2012, 06:40:39 AM
I know serious DX'ers who have achieved similar results to average sized beverages using the DX-1 Pro antenna.
Their logs are a testament to this.
If you look back on this thread you will see that I have already given an explanation about how this antenna works.
If you have any further questions please feel free to ask.
BTW, I also missed one of your previous edits. A 580 foot beverage would be a good antenna on MW provided it was also a good height above the ground.
It would have a big capture area for receiving signals. However, with a 30 MHz band-width its signal to noise ratio could be improved upon.

Fred EI4GMB



Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 12, 2012, 09:10:02 AM
I use an active rotatable Flag antenna and a 7' rotatable active loop. Neither come anywhere close to my 4 Beverages.

Could you explain why a 30MHz bandwidth of a Beverage (of course, it does not function as  a Beverage over 30MHz) yields a poor S/N  ratio. My engineering background in noise theory tells me the S/N of a received signal is totally dependent upon the bandwidth of the receiver channel.
And the narrow front lobe of a Beverage is far superior to other antennas in rejecting noise- see W8JI on RDF- receive directivity factor.

Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 12, 2012, 01:28:33 PM
Dale,

Optimum S/N is achieved at antenna resonance or minimum band-width. From the theory I've studied the signal to noise difference occurs first at the antenna end before it reaches your radio. In other words the RF noise is dependent on the capture area of your antenna. The filters of your radio only further help in reducing that noise.
Of course the antenna needs to be matched to your radio.
A simple experiment is to twiddle the controls of your ATU and you will see the difference in S/N when your antenna is matched or not.
Of course I am no expert but I have studied antenna theory. As you are an expert in noise theory maybe you could give us a more comprehensive explanation. I stand to be corrected.

Kind Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 12, 2012, 06:31:01 PM
Hi Fred,

With all due respect, I don't think you have a handle on the math behind either noise/stochastic processes or information theory.
Resonance has nothing to do with S/N. Yes, signals will be stronger- and so will the noise- unless   you can explain to me how a given  antenna "knows" the difference between signals and noise or point me to a professional article that verifies this.

The antenna bandwidth has absolutely nothing to do with the ultimate received signal to noise- that is 100% a function of the front end noise figure (in the case of VHF and up) and the channel bandwidth.
If I were to believe the above then a 3-30MHz log periodic antenna with say 8dbD gain on 14MHz and F/B of 20dB would not receive (or TX) as well as a Yagi designed specifically for 14MHz that had the SAME gain and F/B. Obviously, such is  NOT the case.

As for an omni active electric field probe performing as well as a Beverage, please review ON4UN's text on section on receive antennas or the W8JI site at:
http://www.w8ji.com/receiving.htm

I think you would  be well served to get a text on information theory or review some of the writings of W8JI.

Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 13, 2012, 06:23:55 AM

...Resonance has nothing to do with S/N.

...The antenna bandwidth has absolutely nothing to do with the ultimate received signal to noise.

...I think you would  be well served to get a text on information theory or review some of the writings of W8JI.


S/N has everything to do with antenna resonance. At resonance or minimum band-width an antenna captures less noise. This is self evident and doesn't require a handle on math.

I have read Tom W8JI's work and he is indeed an expert in the field. He is also on here from time to time. Perhaps he could clear up this obvious difference of opinion.

Regards

Fred EI4GMB





Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 13, 2012, 07:37:43 AM
Resonance has nothing to do with S/N. Yes, signals will be stronger- and so will the noise- unless   you can explain to me how a given  antenna "knows" the difference between signals and noise or point me to a professional article that verifies this.

The antenna bandwidth has absolutely nothing to do with the ultimate received signal to noise- that is 100% a function of the front end noise figure (in the case of VHF and up) and the channel bandwidth. ...
As for an omni active electric field probe performing as well as a Beverage, please review ON4UN's text on section on receive antennas or the W8JI site at:
http://www.w8ji.com/receiving.htm

I think you would  be well served to get a text on information theory or review some of the writings of W8JI.

Very well said, Dale! That's one thing people overlook: as far as an antenna, receiver, etc. is concerned, there is no difference between noise and the desired signals.

When you increase the signal by bringing an antenna or tuner into resonance, the levels of both the signal and noise coming out of our speakers or headphones increase at exactly the same rate. The noise doesn't get "left behind" at a lower level than the desired signal. Their relative levels (the S/N ratio) remain the same.

I know a guy who thinks that he is going to reduce unwanted noise (and therefore increase his S/N ratio) by taking down his ordinary dipole and replacing it with a certain design of of folded dipole, which he claims is a "quieter" antenna. Ain't gonna happen. Oh, there may be differences in the antenna that may reduce corona discharge, or the feedline of one antenna may be less susceptible to noise pickup, but unless he changes the pattern of the antenna, he's wasting his time. But nothing anyone has said to him will convince him otherwise.

As for Tom, I don't believe that he has been on either eHam or QRZ since March. But he speaks of using separate non-resonant antennas for receiving on his site. If resonant antennas helped improve the S/N ratio, I think he would state it.

At http://www.w8ji.com/receiving.htm he very nicely explains how low-noise receiving antennas really work. He states that "... as a general rule, the ratio of peak response in the direction of the signal to average response in all directions is the dominant factor in determining how good an antenna works for receiving. In virtually all installations without clearly dominant direction or directions of noise arrival, RDF (receiving directivity factor) very accurately predicts receiving antenna performance."

Nowhere does he mention resonance helping the S/N ratio, because it doesn't.

BTW, I love those homebrew projects of yours on your web site, Dale!


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 13, 2012, 12:35:36 PM
For best reception it is necessary to ensure that the performance of the RF antenna design is optimum.

I don't think a beverage antenna fully meets this requirement. How would it? It is not even matched to your radio.

The S/N (dB) is the difference between the noise and signal of the receiver channel when it is connected to a matched source !

I happen to believe that an antenna that is matched on its band of operation is less noisy than an antenna which is not. That's all !

I am not making any wild claims just giving some observations based on my own antenna experience.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 13, 2012, 02:03:26 PM
For best reception it is necessary to ensure that the performance of the RF antenna design is optimum.

I don't think a beverage antenna fully meets this requirement. How would it? It is not even matched to your radio.

The S/N (dB) is the difference between the noise and signal of the receiver channel when it is connected to a matched source !

I happen to believe that an antenna that is matched on its band of operation is less noisy than an antenna which is not. That's all !

I am not making any wild claims just giving some observations based on my own antenna experience.

73,

Fred EI4GMB

This will be my last post on the subject as I can see others have posted the same concepts.

First, the Beverage is a travelling wave antenna- resonance is not an issue, nor is it desirable. The Beverage is however matched to the receiver by a transformer. The gain is quite low, thus the matching. One might also note that the active antennas are also nowhere close to being resonant- they are a very high Z electric field probe whose impedance is brought  down via  a source follower or emitter follower.

Matching an antenna to the receiver (at HF) means more signal (and noise in an equal amount) is received. However, efficiency is not an issue at HF. Our noise floor is determined by:
1. Atmospheric noise
2. Galactic noise
3. Manmade noise

If you doubt this, turn your radio on to  any HF frequency with no signals, then disconnect your antenna. If the noise level does NOT drop, then there is something wrong with your receiver.

Isn't it odd that the top receive antennas for 160M are all non-resonant, have very low gain, but do have excellent patterns and therefore high RDF?

Beverages
Multiple/phased  Beverages
EWE's
Flags
Pennants
Receive 4 squares and their ilk- i.e short E field phased verticals

NONE of these antennas are anywhere close to being resonant and yet the world's top  DXers all prefer them Hmmmmm.

Check out K7TJR's site of low band receive antennas. For the uninformed,  RDF is the figure of merit here- the higher the RDF, the better the antenna (i.e. its ability to reject noise from unwanted directions). Note that the WORST of the lot is a resonant inverted Vee at an RDF of 0.6:
http://www.k7tjr.com/rx1comparison.htm

As soon as you find someone to agree with your "resonance is best for RX antennas",  let us know Fred. Tom, W8JI is always available to offer his thoughts.

73,

Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 13, 2012, 03:28:27 PM
Dale,

You have described the beverage antenna as a travelling wave antenna yet have said nothing about how this title effects performance.

You have also stated that a beverage antenna is matched to your radio via a transformer.  What type? and how does this effect antenna performance?

A receiver channel needs to be connected to a matched source i.e antenna, to determine SNR.

S/N is dependent on many things. I believe matching your antenna to the band of operation does help.

Finally, there would appear to be a lack of expertise around the whole issue of resonance on both sides of this debate.

I am prepared to wait for a more knowledgeable and scientific explanation.

Best Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 14, 2012, 07:44:21 AM
Hi Guys,

I have discussed this subject with my good friend, Steve G3TXQ of Hexbeam fame.
He reliably informs me that matching an antenna to a receiver won't have any discernible effect on noise because we are generally externally noise limited at HF. So I stand corrected.
Things are different at VHF/UHF (and sometimes on 10m) were we are typically limited by the front-end noise of the RX, in those situations getting the maximum signal transferred from the antenna to the RX by correctly matching the two is important.
On the other hand, the Beverage is not a 'typical' HF antenna !
By virtue of the way it works close to the ground it is quite lossy; its gain might be as low as -25dB.
So you do have to be careful that it is reasonably well matched to the RX to ensure the S/N ratio is not determined by radio front-end noise.
It's also important that the Beverage is terminated correctly in order for it to act as a transmission line and provide directivity.

Anyway, I just thought I would add this post to the record of the thread.
There seems to be plenty of information here for us all to consider.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 15, 2012, 06:25:04 AM
What did Steve say about resonance affecting S/N ratio?

Here's what W8JI said about it: http://www.eham.net/ehamforum/smf/index.php/topic,80266.msg567904.html#msg567904


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 15, 2012, 10:29:46 AM
Makes perfect sense. Thanks for the link to Tom.
Again, to think that resonance has anything to do with S/N at HF is to assume that the antenna must "know" the difference between a signal and noise on the channel. To think that an antenna's bandwidth limits sensitivity is also wrong as it is the following stages that determine the ultimate S/N. The only exception I can think of is that if the receiver's IP3 is so poor that the wide range of a broad band antenna might overload the front end. Then again, simple wire antennas are a VERY POOR filter even if narrow band, and modern receivers are not prone to overload.

In addition, Fred has commented that resonance implies  a match (which implies maximum power transfer). As we know, even EWE's, Pennants, and Beverages with their very low gain, still are plenty sensitive for HF. I do amplify my Beverages but only to bring their overall level up to that of my TX antennas, making on-air  comparisons easy.

Back to resonance. Resonance simply means the lack of reactance and has zero to do with a good match or VSWR except for a very small class of antennas.
Imagine, if you will,  a resonant end fed half wave antenna. It's end Z is a function  of conductor diameter and height above ground- but for wire antennas at HF will be somewhere in the 2K--> 4K range. This  is a VSWR of 40:1 up to 80:1.
So it is not only true that a resonant antenna has nothing to do with S/N but also does not guarantee a match or low VSWR.

Aside from dipoles at certain heights, Moxons, closed waveguides with a 1/4 wave probe,  and Half Squares, most antennas are not resonant and/or do not present a 50 Ohm match without requiring  require some sort of matching if they will be used for TX. For RX, it's a non-issue.

Finally, measure the input Z of your HF RX. You will find in most cases, it is anything but 50 Ohms resistive over its spectrum
Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 15, 2012, 12:22:59 PM
What did Steve say about resonance affecting S/N ratio?

That resonance wouldn't have any affect on S/N.
As proof of that you could place a 10dB attenuator between the antenna feed and the input of the RX on 40m and you wouldn't change the S/N ratio because both signal and noise would drop by the same 10dB.
I accept the expert opinions of Steve G3TXQ and Tom W8JI and stand corrected.

Best Regards

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: K0OD on May 15, 2012, 01:14:04 PM
Scientists and laymen have had such debates since the beginning of time... 5,700 years ago.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 15, 2012, 02:04:50 PM

Hi Fred,
While you're in contact with Steve run by him your theory that a broadband antenna will yield  a poorer receiver  S/N than a narrow band antenna.

Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 15, 2012, 02:34:11 PM
Dale,

Looks like you haven't got the good grace to accept you weren't completely right either.
But then again good manners is not an american virtue.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W4OP on May 15, 2012, 03:05:15 PM
I was simply interested in Steve's answer as there were 2 issues in your posts I disagreed with:
1. Resonance improves S/N
2. A narrow band antenna would yield a better S/N than a broadband antenna.

Perhaps you could tell me what part of my posts were in error though.

Dale W4OP


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: W0BTU on May 15, 2012, 04:06:10 PM
I was simply interested in Steve's answer ...

It's on the previous page in this thread, Dale. I think we're all in agreement now, gentlemen, and that's good to see.


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: EI4GMB on May 15, 2012, 05:00:36 PM
ooops! Sorry guys! Looks like there may have been a misunderstanding.

73,

Fred EI4GMB


Title: RE: Anyone Using Sophisticated SWL Antennas?
Post by: N0SYA on July 12, 2012, 06:59:12 PM
I use a loop of wire fed with cable tv coax as a sophisticated swl antenna.