TopBand: Re: Rx amps/noiseless feedback

[km1h @ juno.com]

On Mon, 6 Oct 1997 10:12:48 -0700 Eric Gustafson <n7cl@toontown.mmsi.com>
writes:
>
>>From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
>>Date: Mon, 6 Oct 1997 17:13:38 +0100
>>
>>The Anzac patent on noiseless feedback should have run out by now. I
>>can't find my copy of it, but it's pretty old - back in the 70's. I
>>guess one point to bear in mind is how the amp responds when the tx
>>antenna is radiating. If you don't really need a noise figure in sub 
>3dB
>>area (which I doubt on 160), you could consider using a tube!
>>
>>73
>>
>>Peter G3RZP
>>
>
>
>Peter,
>
>It is true that on 160 or generally on the low bands for that
>matter, the background noise level is moderate to high.  And full
>size beverage antennas although not very effecient, are effecient
>enough that an extremely low noise figure in the preamp is
>probably not necessary.  However, physically small wideband
>(untuned) loop based antennas are very much les effecient than
>even a short beverage.  So these types of antennas (including the
>EWE if sized to preserve pattern up to 7 - 10 MHz) really do
>require a very low noise figure for the preamp that they require.
>The Anzac circuit (or a push pull version of it for balanced
>designs) should be near ideal for use with small wideband loop
>receiving antennas for topband.  Generally, the preamp needs to
>be quiet enough so that you can hear the band noise with the
>antenna.
>
>73,  Eric

Ward, Peter, Eric,  thanks for the feedback.

What I was most concerned about with in-line filters was the phase shift.
Since the RF-1  I assume is only accurate when connected right at the
load ( or feedline transformed thru a Smith chart) any LC series network
will be an unknown. At least in pratical ham style applications.

The stub seems to be the only viable solution for many of us. 

Peter, I quit using tubes in the RX side of the primary station several
years ago.  I have no desire to go back.  However I do have numerous RX
and TX from the 1950's in another room so I'm not totally anti-hollow
state. Tubes can absorb more punishment but as Rhode pointed out they are
generally poor overload performers. Sort of a Catch-22. 

I do not know the status of the Anzac patent. By US law they could have
renewed it for another 7 years and I have not seen it used commercially
yet. 

Eric, I agree about the NF in a loop. I have a 2 turn loop built from 1"
CATV cable. The preamp uses a pair of U-310's in a PP differential amp
that is varactor tuned remotely from the shack. At times it has helped
dig out a call that was in the noise on the Beverages. 

But getting back to the original thread here....any other comments on the
RF-1 ??

Tnx   Carl   KM1H
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