[R-390] Dynamic Range Measurements

Tue, 13 Aug 2002 18:20:54 -0700

Developing the data (retrieving the 390a from a friend, unpacking from the
recent move, bringing 'all systems' online) is simply out of the question
until perhaps next summer. Some of you will groan and perhaps bark, but the
caravan moves on.

The best thing for all concerned is to get your hands on a recent ARRL
Handbook. All the techniques, measurement 'philosophy' and discussion is
there. The 2000 Handbook is good. The 1995 or '98 Handbook is frankly better
and has a discussion of the Minimum Discernable Signal (MDS) sensitivity
test and the Input Intercept test by none other than Dr.Ulrich Rhode, whose
family owns Rhode & Schwarz. He has cogent arguments for how he does the
tests. This portion of the Handbook is not fuzzy, not "tune for minimum
smoke," but completely supported by the strictest engineering rigor. The
actual data collection is not rocket science, though good experimental
technique requires scrupulous attention to detail. Things like double
shielded cables and well shielded instruments are fundamental. Getting a
substantial attenuator with -130dB of leakage is not trivial. Mine is a
Weinschel, with return losses of -25dB from DC to beyond 1.3GHz (the limit
frequency on the network analyzer at work). Building a return loss bridge
with similar matching and 40dB isolation will occupy some evenings, though
you needn't attempt going beyond 150MHz.. Luckily, the Handbook has a
discussion of this aspect of receiver measurements. It is, quite easily, the
best $25 bucks you could spend, other than that pallet of BA's you stumble
over at some geeks yard sale...

Bob

-----Original Message-----
From: Cecil Acuff [mailto:[email protected]]
Sent: Monday, August 12, 2002 8:07 PM
To: Bob Tetrault; Bob Camp; [email protected]
Subject: Re: [R-390] Solid State R-390, Why Not?

Greetings group...

I would be interested in reading more about the methodology...not much
published that I have been able to find....I am sure it's out there...I just
need  to know where to look....

I have the instrumentation......not sure the degree is necessary!  I have
worked with many highly degreed folks... some know how to make use of it,
others get the most mileage out of it as wall decoration!

Cecil Acuff
The R1051 Shop
[email protected]
www.r1051.com

----- Original Message -----
From: Bob Tetrault <[email protected]>
To: Bob Camp <[email protected]>; <[email protected]>
Sent: Monday, August 12, 2002 7:25 PM
Subject: RE: [R-390] Solid State R-390, Why Not?

> I've got the instrumentation and the degree and the methodology. You might
> also read the website of Sherwood Engineering that discusses many
receivers
> and their measured performance. My numbers are consistent with those
> numbers. Sherwood does competent work.
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Bob Camp
> Sent: Monday, August 12, 2002 4:40 PM
> To: [email protected]
> Subject: Re: [R-390] Solid State R-390, Why Not?
>
>
> Hi,
>
> Not saying you are wrong, but those numbers are about 40 db better than
> what's been published elsewhere on the R-390A.
>
>     Bob
>
> ----- Original Message -----
> From: "Bob Tetrault" <[email protected]>
> Cc: <[email protected]>
> Sent: Sunday, August 11, 2002 8:21 PM
> Subject: RE: [R-390] Solid State R-390, Why Not?
>
>
> > Dynamic range is pretty hard to beat:
> > IP3=+10dBm at 10kHz separation
> > IP3=+20dBm at 100kHz separation (the difference is in the tunable front
> end)
> > 4dB noise figure on all bands.
> >
> > One can buy receivers with better IP3 numbers, but they don't have a 4dB
> > noise figure. It's debatable whether or not anyone can use 4dB, since
it's
> > commonly thought that the HF noise level is 10+dB, but that isn't always
> the
> > case...and we watch and wait for those openings...
> >
> > One could experiment with pushing the distortion levels even further
down,
> > but it requires pushing the tubes harder since the standing current
> > determines their threshold of distortion. Turning up the juice means
> they'll
> > exhaust the cathode emission sooner.
> >
> > Having extra modules does give anyone the option to play all they want.
> I've
> > heard that ome people have replaced the first two mixers with 7360
> designs;
> > this is a double balanced tube mixer designed for SSB detection and
> > generation. Rumor has it that they are noisier than the 6C4W, but I've
> never
> > seent the numbers or methodology. How much it improves the front end is
> also
> > anecdotal. There was a considerable body of literature about similar
mods
> to
> > the 75A4, since that receiver was/is(to some, even now) considered one
of
> > the best DX'ing receivers around. Again, my exposure never got beyond
the
> > anecdotal level, though I'd relish a review of all that was published on
> > that topic. If memory serves, there was quite a lot in QST and CQ back
in
> > the 60's and early 70's. Anyone got any numbers on this mod?
> >
> > The drawback to modifying an RF deck is the RF deck, as anyone who has
> ever
> > taken one out will attest.
> >
> > But let's remember that there were 50K of these made, and while there
are
> an
> > uncounted number of them that were lost, stolen, spindled, stapled and
> > mutilated, modifying one is a drop in the bucket.
> >
> > Imagine what a great exciter a 390 would make! Imagine a pushbutton
where
> > the diode load is so that you could zero-beat a carrier.
> >
> > pot-stirring in Portland,
> >
> > Bob
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
> >
> >
> >
>
>
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