Re: [Discuss-gnuradio] lfrx+loop antenna

[Matt Ettus]

konvak wrote:
> hello all, 
>               I am thinking about building loop antenna for 3-6 MHz to
> receive some DRM stations. As I understand it the loop antenna is parallel
> resonant circuit so without any amplifier the parallel res. circuit should
> look into big impedance(~1 MOhm) to get high Q. Lfrx has 50 Ohm input due to
> the resistor at diff. amplifier. My question is, would it be possible to
> remove this resistor and put there 1MOhm and connect it to the loop antenna
> with coax. Would it work?
>
>   

You can remove that resistor, but then the input impedance will be 348 
ohms.  You can increase that up to maybe 2K by changing out all of the 
348 Ohm resistors surrounding the diff amp with 2K ones.  However, if 
you really need a 1 MOhm input resistance you are better off using a 
buffer amplifier.  Usually loop antennas like this for receiving (like 
you would get at Radio Shack) will have their own buffer for just this 
reason.  Besides, you will want to have some additional gain in front of 
the LFRX board. 

I think Chuck Swiger did something with a loop antenna and a USRP a 
while ago.  You might check out his web pages.

Matt