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Author Topic: Receiving 630m on a transmit antenna  (Read 464 times)
AE5X
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Posts: 1010




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« on: November 03, 2017, 03:35:54 AM »

Last night I decided to give the transmitter a rest and operate rx-only on 630m WSPR. I know that vertically polarized antennas do not make for good receive antennas but was surprised at just how poorly it performed on receive. I received no more stations using a resonant 630m antenna that when I used a random wire 75 feet long a few weeks ago.

This is sort of confirmed by other stations on the band as well - stations that are both receiving and transmitting almost always are heard by more stations than they themselves hear. Stations that receive only usually copy many more stations than those that are transceiving.

This all led me to wonder what type of antenna rx-only stations are using that allow them to copy so many stations. I would think 'a loop' but loops are directional and most of these stations are copying signals from all around them.

Here's my request to stations that are active on 630m: please update your QRZ.com bio with what you are using. It's great that you have a supportive wife, 3 grandkids and a furry cat that can copy Morse but a description of your station might be useful to those wondering who is doing what on the band with what.  Cheesy
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K0OD
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Posts: 2953




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« Reply #1 on: November 03, 2017, 06:32:05 AM »

But loops are mainly directional on local groundwave signals. They may help when you have interference from a bad powerpole transformer a block away or from lighting in a neighboring house. The more pin-point the source, the better the rejection. Otherwise that random wire hears fine, and for free.

New SWLs see photos of loops on the roofs of embassies and consulates and assume loops must be fabulous antennas, the best money can buy. But embassies are usually in highly urbanized areas. Imagine the nasty RF in downtown Moscow or in some third world capital.   

I have noticed the asymmetry you're mentioning. Note that I'm using a random wire -- 43' feet -- but it's vertically polarized and as you can see from WSPRnet, it hears fine. Others have reported good longwave reception with similar "what you have" antennas, such as a tribander. 
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K0OD
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Posts: 2953




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« Reply #2 on: November 03, 2017, 07:17:38 AM »

Quote
I know that vertically polarized antennas do not make for good receive antennas

btw, I always used verticals for receiving in the many low band contests I've won for the zero district. Beverages and such are better of course, but years ago few contesters used them. The big boys had Yagis on 40. Hard to beat 2-elements at 120'.

My walls are covered with CQWW DX single band high power 40 meter awards... some in the top-five for the country. My best antenna was a 4-square... four phased verticals. It  usually heard as well as small yagis. On 80 I'd use a wire inverted L which is a top loaded vertical. It heard ok for an invisible $10 antenna.

Neither I, nor any other local low band DXer/contester that I know of, used a loop or active antenna (or e-probe) for listening.

Just wanted to put in a plug for the lowly vertical.
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AA2UK
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Posts: 291




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« Reply #3 on: November 03, 2017, 08:15:42 AM »

Loops seen on Embassies are generally used in part as a DC to Daylight counter surveillance system.
In addition some are used to RX LF/MF coded transmissions where there isn't enough land to install an effective antenna.

Some of the best performing stations on 630 meters use a combination of E Probes, Loops and various other unconventional wire antennas. I'm learning many of this stations use external filtering, preselectors, LNAs and when running LNAs they are mostly battery powered.
Unless you have a station that borders on a Wildlife refuge or own 20 acres almost every antenna is a compromise.
Bill, AA2UK
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