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Date: Thu, 19 Jul 2018 15:10:24 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: TX > RX isolation test
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Hi Paul,

Am 19.07.2018 14:42, schrieb N1BUG:
>> will give useful supports, they don't lower the RX signal much (at
>> LF/MF). You just need some wire, a capacitor, a small ferrite core.
>> That's all! With that you can build a resonated loop with a 50 Ohm
>> output to feed your existing preamp. I would even recommend to start
>> with this project first! You will be surprised! Done in 1 day. And you
>> can transmit on that antenna with say 5W (when using good capacitors
>> such as WIMA FKP-1).
>>      
> A loop is even easier i find. And it is very quickly done. And the trees
> Hmm, I don't think we are meaning the same thing when we say loop. I
> was thinking something like this:
>
> http://qsl.net/ve7sl/loop.html
>    
...This is a luxury version of course. It is rotatable, which is helpful.

My thought was a single turn loop using normal wire, no RF litz. 
Something that is quickly build out of existing components but still 
giving good results. For example a square with >= 3 m side length. 
Should be no problem for you. It will not have such a high Q like the RF 
litz version and you will need a preamp but on the other side you have 
more bandwidth which may be even helpful because the noiseblanker can 
work more effective.
I have no link to a nice webpage like the above but the design is so 
simple, it will not be necessary.
If you are at home now, give it a try and in 1 hour you will have a 
first impression. Just use a capacitor like 22 nf or 47 nF and search 
the resonance frequency (scope + signal generator). Wind 3 turns of the 
loop wire (say 1mm diameter) on a e.g. N30 ferrite core (Al ~ 4 uH) and 
20 turns secondary of thin wire on the 50 Ohm side. Then connect the 
RG58 or RG59. Connect it to the scope. Then use a signal generator and a 
small coupling loop and inject a detectable signal. After finding the 
peak, you can calculate the necessary C for 137 kHz....
And so on :-)

73, Stefan