[R-390] Dynamic Range Measurements

Tue, 13 Aug 2002 22:41:39 -0400

Hi,

The other problem is that having done the measurements you then have to
convince the world that you did them right. Getting 120+ db of isolation
between any two things is a matter careful technique. The equipment isn't
much of a problem and the tests are pretty straightforward. If you look at
what the ARRL uses none of it is very fancy stuff. The thing you hope is
that they do it right each time.

Having the time to haul everything out and run the tests is a bit of a
problem. Having enough time to run them on enough stuff to be sure you are
right when you run them is a bigger problem. About the only way to be sure
you are doing everything right is if all of your data matches published
information.

As an example - if you talk to Bob at Sherwood Engineering about their
R-390A data he more or less comes back with "that was from quite a while
back and it may not be as accurate as the more recent data". At least that
was his statement about two years back when I asked ...

Again none of this is any kind of knock on what anybody does or does not do.
There are a lot of people out there that can run these kind of measurements.
The point is that in order to be believed you need to do more than just one
or two tests on one radio.

All that said if somebody wants to set up to do all this I'd be happy to
help out. At the very least I can probably calibrate a lot of the stuff you
would be using.

    Take Care!

            Bob Camp
            KB8TQ

----- Original Message -----
From: "Bob Tetrault" <[email protected]>
To: <[email protected]>
Sent: Tuesday, August 13, 2002 9:20 PM
Subject: [R-390] Dynamic Range Measurements

> 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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