Re: Dumb Question of the Week: Loop Antennas


John H. Bryant <bjohnorcas@...>
 

Nick,

Thanks very much for your thoughtful remarks.  I was hoping that you would be intrigued.  What you say about the high impedance input to the mixer makes sense to me....  however, I'm hoping that the Wavemagnet III Crate Antenna/E100 might just be a winner.  Kevin was able to think his was through to the fact that we need to vary the inductance of the Crate rather than messing with a tuning cap (why didn't I think o' that!)   I think that we are gonna make several tries by the empirical method that you and I both love.

John B.





Hi John,

One difference between the All-American 5 and most latter day radios
is that the loop antenna was directly connected to the high impedance
input of the mixer tube. So you had nice sharp tuning, and no
loading down of the loop antenna, which meant solid signal strength.
(Sort of equivalent to the FET amplifiers used with the Sanserino and
NRC loops)

Most solid state radios that use a tuned tank coil on a ferrite bar
have a pickup loop or a tap to a low impedance first stage. I'll
speculate that because AM radio design over the last few decades has
usually been about picking up locals, that the coupling is not
optimized for most effective signal pickup by the tank coil. Generally
the tuning is broader than with the old All American 5 loops. (the
2010's untuned loop is remarkably effective given its design)

I haven't been keeping track I'm afraid, but it would appear the E100
uses a high impedance front end with a parallel tuned tank coil(one
tank coil only, and varying its inductance affects the tuning), so in
theory you should be able to substitute a small air core loop of the
right inductance for its native ferrite loop, but I'm not sure what
would be gained by that, that you're not already getting with the
Slider loop? I suspect you'd be more likely to pick up the E100's
microprocessor noise with a nearby air loop than a ferrite loop does,
but I've been proven wrong before.

Nick

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