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Author Topic: What is the best SW antenna ?  (Read 42214 times)
AA1UY
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Posts: 17




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« Reply #30 on: July 17, 2012, 04:40:21 PM »

One that is immune or almost immune from vertically polorized man made noise.
Suggestions?................

A small receiving loop. The Kaito KA33 is an inexpensive example. Due to their very narrow bandwidth,  noise is tuned-out.

At my QTH, I could no longer use my 4BTV vertical on or around 7 MHz (40/49 meters) as I started to get a consistent S7 noise all across that band. At first it was only in the evenings (right at 5:00 pm) but then it became pretty much 24x7. I replaced the 4BTV with an MFJ 1788 small transmitting (and receiving) loop and the S7 noise is gone completely (same co-ax feed-line).

Small loops are not very good for scanning due to the very narrow bandwidth (i.e. you have to tune them to the frequency (not just band) of interest in order to peak the signal), but that works to your advantage in noise suppression.
« Last Edit: July 17, 2012, 04:43:34 PM by AA1UY » Logged
W0BTU
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« Reply #31 on: July 20, 2012, 05:47:19 PM »

  Due to their very narrow bandwidth,  noise is tuned-out.

Really? How does that work?
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KB2VWM
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Posts: 3




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« Reply #32 on: July 21, 2012, 11:27:48 AM »

I've had a few different SW antennas over the years. A T2FD that I made, a few different long wires, and Alpha Delta Sloper.
They were all great on some bands, noisy on others and in some cases deaf on other bands.
Last year I decided to try something different and started looking into active antennas. My research led me to Wellbrook and Clifton Labs.
I ended up buying a Z1501 active antenna from Clifton Labs and I couldn't be happier, great reception on all bands and extremely quiet.

I've read great things about Wellbrook loops too but can't give first hand experience.

In any case I'm convinced that high quality active antennas are the way to go.
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W8XLR
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Posts: 11




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« Reply #33 on: July 21, 2012, 07:20:13 PM »

After extensive experimentation with my own antenna farm, Ive found for general SWL use my Drake R8A likes the 80 meter delta loop, fed with home made 450 ohm ladder line through a cheap MFJ-949E tuner best. I also have an Ameco PT-2 preamp in line which is sometimes usefull, sometimes not...

I agree that the beverage is the way to go for receive antennas, but I dont have the real estate for one...

"ILLIGITIMUS NON CARBORUNDUM", Thats allways been my motto!

73 de W8XLR/Phil
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HFCRUSR
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Posts: 139




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« Reply #34 on: July 21, 2012, 08:58:46 PM »

I am in a 10-unit apartment building on the top floor (3rd) here in western San Francisco and I am blessed to be permitted to run a swl antenna and a d130j discone.
I run a PAR EF-SWL but with a 100' #12 coated wire that is configured as a horizontal "L" and it is up at 40'. I am about a mile and a half from the ocean here, so as you can imagine, I have a lot of fun hunting the bands:)
That PAR magic box likes the 100' wire just fine. It did ok with the 44-footer that came with it but naturally, more is better.
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K0OD
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Posts: 2557




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« Reply #35 on: July 23, 2012, 04:08:40 AM »

Quote
I run a PAR EF-SWL but with a 100' #12 coated wire that is configured as a horizontal "L" and it is up at 40'. I am about a mile and a half from the ocean here, so as you can imagine, I have a lot of fun hunting the bands:)
That PAR magic box likes the 100' wire just fine. It did ok with the 44-footer that came with it but naturally, more is better.

I think the Beach Boys long ago distilled the only thing that matters:

"If everybody had an ocean...

Across the U.S.A. "

"Everybody's gone Dxin'

DXin U.S.A. "

---------------
I once worked a KH6 on 60 meters who was using a 90 foot wire hanging from a tree 50 feet from the Pacific. He was S-9 plus 10dB in Missouri running the then-legal-limit of 50 watts... about 30 dB louder than any other Hawaiian I've heard on that band. The gauge of his antenna wire or whether it was coated didn't count for beans.
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HFCRUSR
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Posts: 139




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« Reply #36 on: July 23, 2012, 08:33:58 AM »

Quote
I run a PAR EF-SWL but with a 100' #12 coated wire that is configured as a horizontal "L" and it is up at 40'. I am about a mile and a half from the ocean here, so as you can imagine, I have a lot of fun hunting the bands:)
That PAR magic box likes the 100' wire just fine. It did ok with the 44-footer that came with it but naturally, more is better.

I think the Beach Boys long ago distilled the only thing that matters:

"If everybody had an ocean...

Across the U.S.A. "

"Everybody's gone Dxin'

DXin U.S.A. "

---------------
I once worked a KH6 on 60 meters who was using a 90 foot wire hanging from a tree 50 feet from the Pacific. He was S-9 plus 10dB in Missouri running the then-legal-limit of 50 watts... about 30 dB louder than any other Hawaiian I've heard on that band. The gauge of his antenna wire or whether it was coated didn't count for beans.

I do realize the coating and gauge do not matter, I was just describing what I run. Was there something wrong with that? My point was mainly that being near the ocean helps my reception of points west and southwest of me.
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K0OD
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Posts: 2557




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« Reply #37 on: July 24, 2012, 06:32:18 AM »

Quote
"I do realize the coating and gauge do not matter, I was just describing what I run. Was there something wrong with that?"

I figured you knew that. 98% of us here know that. But some won't. Every time I stop in the CB shop in the truck stop outside of town I'm reminded tho that utter BS sells antennas.  Love those oil filled, "truck spec'd" antennas they sell tons of!
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HFCRUSR
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Posts: 139




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« Reply #38 on: July 24, 2012, 07:58:59 AM »

ah I need to apologize then-I misread your text-I thought I was being B-slapped lol
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K0OD
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Posts: 2557




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« Reply #39 on: July 24, 2012, 01:55:23 PM »

"The Truck Spec antenna’s oil submersed loading coil is 14 turns of enameled copper wire wound over a grooved plastic insulator. The inners are sandwiched between two heavy, chromed metal tapered ends, and fully enclosed in a clear plastic radome that is filled with clear mineral oil. You can move the antenna around and see the small air bubble move around inside so you can quickly tell that there is still oil in it."

Calling the coil enclosure a radome is hilarious! But no doubt effective ad writing given the audience. Those old CB ads never seemed to establish any purpose for that oil.
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HFCRUSR
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Posts: 139




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« Reply #40 on: July 25, 2012, 08:17:35 AM »

That is pretty outragious-I didn't know they were still pimpin' out like that.
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G0DOQ
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Posts: 6




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« Reply #41 on: September 03, 2012, 09:29:26 AM »

The best antenna for me is my $50 102' G5RV @ 50' strung between 3 trees as a horizontal flat top.  Almost invisible and picks up weak stations very very well.  Had it @ 20' and it didn't work nearly as good for SWL, so what ever antenna you use height is truly the key.
I've used G5RVs for years. the 102ft is the full size and is a good SWL antenna, the half size is OK but not as sensitive at LF. they come with either 450 or 300 ohm matching section, go for the 300 ohm. a commercial one will have a 239 connector, snip it off and solder the coax back to the rig, any length. do not put in a balun. This is how I transmit on mine also, but it needs a tuner then.
make your  own- a dipole T piece, each leg 51ft, 29ft 6in 300 ohm, and any length of coax.
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KB5UBI
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Posts: 97




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« Reply #42 on: September 03, 2012, 03:09:52 PM »

Shielded receiving loops don't tune out noise because of their bandwidth. Most man-made noise is electrostatic and a shielded loop blocks electrostatic signals but allows electromagnetic signals to get through. 
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W0BTU
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« Reply #43 on: September 03, 2012, 03:20:50 PM »

Shielded receiving loops don't tune out noise because of their bandwidth.

Precisely. They reject unwanted signals or noise because of their directional pattern. They have a deep null at very low angles at right angles to the plane of the loop; and we can point that null at a local source of interference and reduce it. At higher angles, the null is not as deep.

Quote
Most man-made noise is electrostatic and a shielded loop blocks electrostatic signals but allows electromagnetic signals to get through.

Well, that's another story (that I don't have time to go into). But basically, a small loop is only "magnetic" within a very short distance from the antenna.
See:
http://www.w8ji.com/magnetic_receiving_loops.htm
http://www.w8ji.com/radiation_and_fields.htm
http://www.w8ji.com/receiving.htm
« Last Edit: September 03, 2012, 03:23:56 PM by W0BTU » Logged

KB5UBI
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Posts: 97




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« Reply #44 on: September 03, 2012, 03:35:07 PM »

Notice that I used the term "shielded".
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