[Lowfer] My Active Loop is apparently dead

Eric NO3M no3m at no3m.net
Wed Nov 20 23:22:50 EST 2019


Scratch the simple source follower buffer and impedance comments... head 
is too wrapped up in vertical monopoles lately.  The usual J310 type 
buffer is intended for single ended, ground referenced hi-imped antenna....

So stick with the Trask design or try a homebrew loop per stuff on the web.


On 11/20/19 11:05 PM, Eric NO3M wrote:
> You could homebrew a suitable amplifier:
>
> http://www.home.earthlink.net/~christrask/Wideband%20Loop%20Antenna%20Amplifier.pdf 
>
>
> The Trask design is a bit elaborate, a simpler alternative might be a 
> high-impedance input source follower design (J310....) driving a 
> normal 50 or 75 ohm input preamp (2N5109 single or PP, J310, etc.).
>
> The high impedance part is important for the first stage, so the term 
> "peamp" needs to be used carefully, as a typical low-impedance (50 or 
> 75 ohm input) preamp directly connected to the loop will not work, 
> loading down the antenna and diminishing the available signal 
> voltage.  More appropriate is referring to it as a "buffer"; in most 
> cases, there is actually a net loss, -6dBV being typical.  I don't 
> have any knowledge of the Wellbrook design, but it probably includes a 
> low impedance output amplifier after the buffer stage to boost the net 
> gain.
>
> Yet another alternative is to scrap the Wellbrook and just homebrew a 
> multiturn loop, plenty of designs on the subject on the web (VE7SL, 
> etc.).
>
>
> 73 Eric NO3M


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