[R-390] Call for measurements - 100dB carrier reading

[David Wise]

Thanks for the data point, Graham.  It is close
to what I expected from my carrier meter mockup
and the original carrier meter circuit in my radio.
On the other hand, your AGC is sharper than
mine, even with my sharpest 6DC6.  At 100mV in,
I average in the low 13's.  I must have
unusually wide-cutoff tubes, or gobs more gain
somewhere.  I wish you were local so we could
swap stuff around.  If others duplicate your
findings, then my cute trick is a fluke.  It's
still worthwhile, but most people will have
to go inside their IF deck.  I'll start modifying
the writeup.

Thanks,
Dave Wise
SWL in Portland Oregon

PS: I tried all bands last night and found that
0 and 1MC have the least AGC for a given input.
I also confirmed that 8 and up require noticeably
more AGC due to having one less gain-controlled
tube in the chain.  Although the meter reads higher,
this doesn't mean the gain is up, nor the signal.

> -----Original Message-----
> From: grahambaxterdelphe at googlemail.com
> [mailto:grahambaxterdelphe at googlemail.com]On Behalf Of Graham Baxter
> Sent: Wednesday, August 22, 2007 2:09 AM
> To: David Wise
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] Call for measurements - 100dB carrier reading
> 
> 
> Hi Dave
> 
> EAC R-390A SN 189
> 
> HP8640B generator, cable through terminated with 50 ohm load at
> an HP 3400 rms meter. Short coax to balanced input, one side grounded.
> DC Meter 10 Meg input resistance
> 
> 100mV 99dB 11.18
> 
> 10 mV  84dB 9.60V
> 
> 1 mV  69 dB 7.41V
> 
> Voltage for 100dB = 11.20 ish but the meter reading  is very
> compressed in this region
> 
> Graham
> G8OAD
> 
> On 22/08/07, David Wise <David_Wise at phoenix.com> wrote:
> > I'm working on a writeup of a mod I did to my R-390A
> > a few years ago to improve the carrier zero adjust pot.
> > It worked beautifully, but as I gathered data and did
> > more experiments, I realized that it implicitly relies
> > on a characteristic of my radio that seems at variance
> > with the manual.  Before I send it to Perry Sandeen,
> > I'd like to find out if it's worth the paper it's
> > printed on.  If my radio's the only one it works on,
> > there's no sense in putting it out.
> >
> > A while ago I asked for AGC measurements on an R-390.
> > Now I'm looking for similar info on the R-390A.  Specifically:
> >
> > - Zero your carrier meter
> > - Apply 1450KC to the balanced antenna input
> > - Tune the radio to the signal, including antenna trim
> > - Set the input amplitude to 100mV
> > - Tell me the carrier meter reading
> > - If you feel like it, measure the AGC with a VTVM
> > - For extra credit, set the gen for 100dB carrier indication
> >  and tell me the AGC voltage
> >
> > Be careful that you are actually putting in 100mV -
> > the radio's impedance varies all over the place.
> > I teed an RF voltmeter into the line.
> >
> > I hope I hear a lot of "Couldn't read it, it was pinned."
> > Then I can pull off a great trick.  If not, then I can't
> > get away with it and have to settle for merely good.
> >
> > Why 1450?  Because it's what I happened to use.  This
> > week I'll try some other frequencies.
> >
> > Roger, you've seen thousands of these radios.  Do you
> > think I have a chance?
> >
> > Thanks,
> 
> > Dave Wise
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