|[AMRadio] HRO question for the day|
qedconsultants at embarqmail.com
Thu Dec 17 23:06:19 EST 2009
well, isn't that interesting. I sort of leaned that way, but did not know.
the only problem with the reference is that the diode detectors are not
linear at all. They generate all sorts of stuff that is not there. I am
going to build a precision detector and use in the NBFM slot of the HRO and
75A2. sounds like National did have an idea what they were doing. It
does do a much better job receiving week signals than my ft1000 MarkV.
----- Original Message -----
From: "ROLYNN PRECHTL K7DFW" <k7dfw at clatskanie.com>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Thursday, December 17, 2009 6:09 PM
Subject: Re: [AMRadio] HRO question for the day
> Interesting idea, as in boiling off fewer electrons to pile up around the
> cathode? not clear to me what effect that would have one way or another.
> Found here.....
> "AM DEMODULATOR
> I'm using one of the diodes of the 8B10 as a detector. I found that audio
> fidelity of detected weak radio stations can be improved by using reduced
> heater voltage. This lowers "contact potential" on the diode, which comes
> from stray electrons floating around the hot cathode. Less of this means
> that a weak signal doesn't have to overcome as much of this potential to
> detected linearily. I used a 100 ohm 1 watt resistor across the heater to
> drop the heater voltage from 8.5V to about 7.7V. This resistor divertes
> of the series string current from the tube heater, thus lowering the
> and thus the heat on the diode cathodes (and also the triode cathodes too,
> but the circuits they are in didn't suffer). This is just like the reduced
> heater voltage on detector diodes like the 6H6, 6AL5 or 5896 to improve
> detector performance on weak signals. Less "contact potential" for the
> signal to overcome. This should increase the fidelity of AM detection. The
> 5896 below is a dual diode version"
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