[AMRadio] FW: Homebrew receiver

[David Knepper]

Brett, you should do a photoessay on the building of this dream receiver.

Dave, W3ST
Secretary to the Collins Radio Association
Publisher of the Collins Journal
www.collinsra.com
----- Original Message ----- 
From: "Brett Gazdzinski" <brett.gazdzinski at mci.com>
To: <amradio at mailman.qth.net>
Sent: Monday, November 03, 2003 8:34 AM
Subject: RE: [AMRadio] FW: Homebrew receiver


> The ARRL handbook went with those like crazy, in the 1960's.
> I don't think I have any 7360 tubes. I did not look hard
> for them in the junk box. I DID look in the antique electronic supply
> catalog,
> and they wanted about $50.00 each I think!
> 
> I should look in the junk box, since I may have some of these tubes,
> I got a BUNCH of industrial tubes with numbers out of some old
> sat com military stuff, many 7 and 9 pin tubes, the very nice
> black tube shields, and even a bunch of those big triodes(6sa7?).
> 
> I cant say just how quiet those tubes are, since I never used one.
> Anyone know of a receiver that actually uses a 7360 as a mixer???
> 
> 
> In the first home brew receiver I built, I used a 6SA7, but unlike other
> designs, it used a tube with three grids, injecting the antenna
> signal into the control grid, the LO into the suppressor grid.
> 
> Most designs I looked at had 4 grids when separate injection was used,
> and would be in the very noisy category.
> 
> This circuit was based on the Scott SLRM receiver I have.
> 
> Mixer noise seems very very low on the homebrew, lowest of any
> receiver I have ever tried.
> I am not sure how important the noise figure is on 80 and 40 meters,
> on higher bands, I know its important, but I don't go up there.
> 
> On comparison to very weak signals on a very clear quiet band,
> the homebrew will copy someone who is VERY weak, but give clear
> copy, on the R390a, I might not even be able to tell there is a signal
> there!
> 
> I have not compared the homebrew directly to the Scott or the SX17,
> but they have bandwidth problems, going quite wide at 60 db down.
> That will likely add noise.
> 
> For homebrew #2, I went with a 6ah6 in circuit design b in the handbook
> (1961?), control grid gets the antenna signal, the LO is injected
> into the cathode, suppressor grid is grounded, screen grid has
> screen voltage on it.
> Its supposed to be quiet.
> I can also inject both signals into the control grid, I may try
> both designs to see which works best.
> 
> The receiver is moving along well, all the metal is cut, drilled,
> punched, and I will paint the chassis on this receiver.
> 
> The B+W coil stock arrived, the filters arrived, this receiver will
> have selectable bandwidth, 4.5Khz and 5.5Khz.
> 
> The LO coil (B+W coil stock) is mounted in a small metal box along
> with the band switch (shorts out some of the coil) along with
> the 40 meter tune cap, to adjust the 40 meter frequency, so I can
> set it up like homebrew #1, switching between 160, 80 and 40 meters
> has the receiver go to 1880, 3880, and 7290 when I change bands.
> 
> The coil has been tested in the LO circuit for calibration...
> 
> I broke down and bought a dremel tool, easy to make square holes
> for things like relays, power cord plug in (with filter), digital
> frequency display, etc.
> 
> I need to find a good aluminum primer for painting the chassis.
> 
> Brett
> N2DTS
> 
> 
> 
> > -----Original Message-----
> > From: amradio-admin at mailman.qth.net
> > [mailto:amradio-admin at mailman.qth.net]On Behalf Of Donald Chester
> > Sent: Sunday, November 02, 2003 11:02 AM
> > To: amradio at mailman.qth.net
> > Subject: RE: [AMRadio] FW: Homebrew receiver
> >
> >
> >
> > >I am not sure how much the RF amp adds to the noise level.
> > >A well designed rf amp section can actually reduce noise levels.
> > >Noise mostly comes from mixers, and overall tube counts.
> > >All mixers add some noise, some designs are much better than others,
> > >and the more there are, the more noise you get.
> > >
> > >I used single conversion, with a quiet mixer setup, and
> > >used two tuned circuits of very high Q in the input,
> > >along with resonant dipole antennas for 80 and 40 meters,
> > >so I don't get any images or other problems, as signals
> > >out of band are attenuated very much before making it to
> > >the mixer.
> >
> > I think the best mixer designed ever developed used the 7360
> > or similar beam
> > deflection tube.  I'd like other opinions on the subject, if
> > anyone thinks
> > there is anything else that actually surpasses the
> > performance of these
> > tubes in mixer service?
> >
> > Don K4KYV
> >
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