[R-390] R390A Carrier Level Meter Question

Thu Aug 26 19:19:11 EDT 2004

Too bad the whole list could not see it. I guess my 81K JPEG attachment
bounced the system.

Mike WB2UID

----- Original Message -----
From: "David Wise" <David_Wise at Phoenix.com>
To: "Michael Murphy" <mjmurphy45 at comcast.net>; "Bob Camp" <ham at cq.nu>;
"R-390 HF Receiver List" <r-390 at mailman.qth.net>
Sent: Tuesday, August 24, 2004 1:03 PM
Subject: RE: [R-390] R390A Carrier Level Meter Question

BWA-HA-HA-HA I can't stop laughing oh ouch my sides hurt!

Thank you Michael.

<wipes tears away>

73 (what's the code for "still laughing"?)
Dave Wise

> -----Original Message-----
> From: Michael Murphy [mailto:mjmurphy45 at comcast.net]
> Sent: Monday, August 23, 2004 5:49 PM
> To: Bob Camp; David Wise; R-390 HF Receiver List
> Subject: Re: [R-390] R390A Carrier Level Meter Question
>
>
> Stand by for the mod.
>
> Mike Murphy WB2UID
>
>
> ----- Original Message -----
> From: "Bob Camp" <ham at cq.nu>
> To: "David Wise" <David_Wise at Phoenix.com>; "R-390 HF Receiver List"
> <r-390 at mailman.qth.net>
> Sent: Monday, August 23, 2004 6:56 PM
> Subject: Re: [R-390] R390A Carrier Level Meter Question
>
>
> > Hi
> >
> > One of the amazing things about an R-390 is just how accurate the
> > carrier meters are. Every one I have checked has stayed pretty darn
> > close over the whole range above 20 db. They have been
> pretty good at
> > 10 db. When you take a look at what they had to do to make
> that happen
> > there's a lot that went into it.
> >
> > All that said there is another way to go. The good old back panel
> > connector has the AGC voltage on it. No big surprise that the AGC
> > voltage also follows the carrier level. In a number of
> situations the
> > AGC voltage was used instead of the carrier level for
> accurate signal
> > monitoring. If you are going to rig an external setup there
> should be a
> > way to do a LCD display that would show signal level to a
> tenth of a db
> > over a 100 db range. You'd be the only one in town with one of those
> > .....
> >
> > By using the AGC voltage you would also get around the
> normal problems
> > with the carrier meter zero pot. That alone would be worth
> the effort.
> >
> > Enjoy!
> >
> > Bob Camp
> > KB8TQ
> >
> > On Aug 23, 2004, at 2:27 PM, David Wise wrote:
> >
> > > Wondering what will happen if you put in
> > > any old 1mA meter?
> > >
> > > The R-390, R-391, and R-390A use the meter as one
> > > leg of a bridge circuit, and the meter was wound
> > > with unusually heavy wire to get the exact resistance
> > > required to give the correct calibrated response.
> > > Most 1mA meters have coil resistance higher than 17 ohms.
> > > If you install such a meter, the radio won't be harmed,
> > > but the meter will not go upscale as far as it should
> > > for a given carrier level.
> > >
> > > There is info around which explains how to modify the
> > > radio to use a given meter, and other info on building
> > > an amplifier to make a meter compatible with an unmodified
> > > radio.  I don't know if the following is mentioned anywhere.
> > > It probably is, but it doesn't take much space to explain,
> > > and if you can find an appropriate meter it's the "smallest"
> > > mod possible.
> > >
> > > You are not restricted to a 1mA meter per se.  You can
> > > use a more sensitive meter along with a shunt to give
> > > a 1mA full-scale response.  This does not escape the
> > > basic problem of coil resistance, but it does widen your
> > > options a bit.  For example, if you had a 50uA meter with
> > > 340 ohms coil resistance, you could shunt it with 17.9
> > > ohms.  The problem is, 340 ohm 50uA meters are just as
> > > rare as 17 ohm 1mA meters.  Still, you never know what
> > > will pop up in the junk box.
> > >
> > > By the way, there's nothing sacred about the exact 17 ohm
> > > value, that's just what they found would give about the
> > > right cal most of the time.  If you really care about
> > > this and have a signal generator where you can trust
> > > the output level, you can calibrate the meter to match
> > > your particular radio by tweaking its resistance slightly.
> > > On the other hand, this goes against the idea of interchangeable
> > > parts, which was a fundamental tenet of the radio's design.
> > >
> > > 73,
> > > Dave Wise (SWL)
> > >
> > >> -----Original Message-----
> > >> From: Roy Morgan [mailto:roy.morgan at nist.gov]
> > >> Sent: Monday, August 23, 2004 10:16 AM
> > >> To: R-390 at mailman.qth.net
> > >> Subject: Re: [R-390] R390A Carrier Level Meter Question
> > >>
> > >>
> > >> At 08:33 PM 8/22/2004 -0400, Les Locklear wrote:
> > >>>
> > >>> FS = 1 Ma. Full scale 1 Milliamp.
> > >>
> > >>
> > >> Yes, but there's more.
> > >>
> > >> Not just any 1 ma full scale meter of the right size
> will work.  The
> > >> original meters had an internal resistance of 17 ohms or some
> > >> such.  Hard
> > >> to find. Not impossible to have made but they's cost some
> > >> $100 each if we
> > >> ordered over a hundred.
> > >>
> > >> There have been a number of articles and web pages that
> > >> describe how to use
> > >> other meters instead of the original one.
> > >>
> > >> Roy
> > >>
> > >>
> > >> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> > >> 7130 Panorama Drive, Derwood MD 20855
> > >> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> > >> roy.morgan at nist.gov --
> > >>
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