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Measuring antenna performance, was "Re: LF: Loops again"

To: [email protected]
Subject: Measuring antenna performance, was "Re: LF: Loops again"
From: [email protected]
Date: Mon, 6 Jan 2003 11:25:56 +0100
Reply-to: [email protected]
Sender: <[email protected]>
Thread-index: AcKqvVSHFNvwmRzOQFG9IshGWthZawKrzoHw
Thread-topic: LF: Loops again
Happy New Year.
What is important for those receiving aerials is the actual S/N in the receiver. One aerial may have higher signal, but also higher noise. So the actual performance may not have been improved at all.

Once did some comparisons between different aerials at P.O. Laboratories at 
Bearley, near Stratford on Avon,
but I couldn't verify that the log.meter worked as it should. So I've had some interest to build a better equipment later.

One possibility is to use two SPM-3 (Pegelmesser's) - one set for 138.8 kHz, 
and the other for reference on
quiet spot of the band.
The other is to measure S/N directly from the signal output from SPM-3 or D2006.

Does somebody know some circuits I could build for reasonable accuracy?

73,
Jan-Martin

N4623-Kristiansand (tel.: +47-380-87178 Home)(38052660 Work 90777126 Mobile)
http://www.laud.no/la6nca/LA8AK/
-----Opprinnelig melding-----
Fra: James Moritz [mailto:[email protected]]
Sendt: 23. desember 2002 20:49
Til: [email protected]
Emne: Re: LF: Loops again


At 16:55 23/12/2002 +0000, you wrote:
With all the loop talk that has been going on since before time began has anyone found a design for a near perfect small loop, suppose its like how long is a piece of string, obviously the bigger the better but then there is the diminishing returns senario, it there much noticeable difference between a 2 meter side square loop and a 4meter.

How much signal power a loop can deliver to the receiver depends on 2 factors - the area, and the Q (or losses). How much you need depends on the overall system design; how good or bad the RX is, whether you want to trade off sensitivity against bandwidth, have a wide tuning range, etc., so yes, it is a "how long is a piece of string" question. But as a rough guide, a 1m^2 tuned loop with a sensibly designed preamp, or with good matching to a low noise receiver will give a noise floor well below the band noise. The signal to noise ratio of the loop is good, but the absolute signal level is much smaller than with a vertical, so the performance of the receiver is much more important. If you double the size to 4m^2, the design becomes a lot less critical because you are picking up 12dB more signal to start with. With very large loops, almost anything will deliver more than adequate signal levels, but then you lose the advantages of a small loop - being able to rotate it for optimum peaking or nulling, and being able to move it to find a location with low noise levels.

Which is better a single turn loop, several turns in series, several turns in parallel and the best method of feed and matching at the loop.

It is largely a matter of convenience of design - Several alternatives have been mentioned; they all work if done properly.

I have a lot of information about all of these loops little and large but never used a very small loop and might try but there is a lot of conflicting info about the various configurations and I do not want to re invent the wheel so if someone has had good practical results it would be useful.

Maybe it would be a good idea not to keep saying how they are all rubbish before you have actually tried them...

I have been watching QRS activity lately while in the shack doing other things and notice a lot of CQ'S from various amateurs around the UK and Europe and sometimes all going at once, the screen is getting cluttered, but only a few result in QSO'S so it would appear obvious to me that the majority are not seeing each other, and that would indicate poor receiving capabilities.

...Or that they worked each other a couple of days ago.

I appear to be receiving all of the activity but my 90 meter perimiter loop is reasonably large and is doing well on receive but not as good as my vertical, however I would like to try a very small loop and compare results, but I dont want to build several small loops varying in design, if someone has already done this and knows which ones to forget about. I know location is also important, good ground, reasonable and poor ground etc under the loop and some use loops to null out qrm but I am not concerned about qrm, this location is rural and as qrm free as one can get, this is why my vertical is also good on receive.
Please dont tell me to read the Comic, I need todays technology.
73 de Mal/G3KEV


If you have no QRM, and adequate sensitivity already, you can't expect to gain much from other types of antennas. Perhaps you need to install more of today's technology - light dimmers, home entertainment systems, compact florescent bulbs, computers etc. etc. so you can really put things to the test!

Cheers, Jim Moritz
73 de M0BMU






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