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Broadband active loop to match my receiver design

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neazoi

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I have designed this receiver **broken link removed** which works satisfactorily for all HF ham bands as some of you already know.
I want to build the attached HF broadband active antenna for it but I want to remove T3 and use the rf preamplifier transistor of my receiver instead (which also works as an AF preamplifier (reflex).
In the attached preamplifier, T3 does not perform any amplification but it is there for impedance matching. But my RX does not need this impedance matching, because the input of the rf preamplifier (2sc9018) is already a high impedance (I think so).

So I was wondering, can I remove T3 and connect instead at this point, the preamplifier of my receiver through a coupling capacitor before the attenuator of course?

Also, will it be better to connect it at the 5v8 point instead of the 2v1 point?
 

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  • sw loop antenna.pdf
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You can pick the signal from the 5v8 point, but on the point where the connection is done right now (2v1) the gain of the circuit is almost 10dB higher than if use point 5v8.
On the other hand, the price of a BF494 transistor is insignificant, so I would let T3 in place, providing some isolation between antenna preamplifier and the regenerative receiver.
 
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    neazoi

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You can pick the signal from the 5v8 point, but on the point where the connection is done right now (2v1) the gain of the circuit is almost 10dB higher than if use point 5v8.
On the other hand, the price of a BF494 transistor is insignificant, so I would let T3 in place, providing some isolation between antenna preamplifier and the regenerative receiver.

Great thanks, I am happy it will work the way I thought!
There are two reasons for not leaving the buffer there. First there is already a preamp in the receiver that lies between the detector and the loop preamp and because simplicity matters here, I want to make it as simple as possible, if there is only a little to be gained from the extra buffer stage. Second the extra mA drawn by the buffer, although not much, may matter in portable operation, drawing current from a pp3 battery which can only supply 250mAh.
Oh, have a merry Christmas!
 

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