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Author Topic: Anyone Using Sophisticated SWL Antennas?  (Read 40230 times)
KR4HV
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Posts: 6




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« Reply #15 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
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K0OD
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Posts: 2539




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« Reply #16 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

« Last Edit: May 07, 2012, 09:50:28 AM by K0OD » Logged
W0BTU
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« Reply #17 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.
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EI4GMB
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Posts: 166




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« Reply #18 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
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'You can never plan the future by the past'

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Edmund Burke (1729-1797)
W0BTU
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« Reply #19 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.
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K0OD
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« Reply #20 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.

Smiley 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.   
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EI4GMB
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« Reply #21 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
« Last Edit: May 08, 2012, 03:29:50 PM by EI4GMB » Logged

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Edmund Burke (1729-1797)
EI4GMB
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« Reply #22 on: May 08, 2012, 02:05:51 PM »

'
« Last Edit: May 08, 2012, 02:08:22 PM by EI4GMB » Logged

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'Those who don't know history are destined to repeat it.'

Edmund Burke (1729-1797)
K0OD
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« Reply #23 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.
« Last Edit: May 13, 2012, 03:24:27 AM by K0OD » Logged
EI4GMB
Member

Posts: 166




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« Reply #24 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
« Last Edit: May 09, 2012, 05:19:01 AM by EI4GMB » Logged

'You can never plan the future by the past'

'Those who don't know history are destined to repeat it.'

Edmund Burke (1729-1797)
W0BTU
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« Reply #25 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?  Roll Eyes  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.
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EI4GMB
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Posts: 166




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« Reply #26 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?  Roll Eyes  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. Wink
 
Kind Regards

Fred EI4GMB
« Last Edit: May 09, 2012, 12:40:27 PM by EI4GMB » Logged

'You can never plan the future by the past'

'Those who don't know history are destined to repeat it.'

Edmund Burke (1729-1797)
K0OD
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Posts: 2539




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« Reply #27 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?  Huh?
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EI4GMB
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« Reply #28 on: May 09, 2012, 02:37:39 PM »

Don't knock it till you try it, Jeff !  Grin
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Edmund Burke (1729-1797)
W0BTU
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« Reply #29 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.
« Last Edit: May 09, 2012, 03:22:01 PM by W0BTU » Logged

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