Subject: GLOWBUGS digest 442

From: [email-masked]
Date: Mon, 10 Feb 1997 23:09:40 GMT

GLOWBUGS Digest 442

Topics covered in this issue include:

  1) synchronous AM detection using tubes <repost>
	by Dan Kerl <[email-masked]>
  2) Back on line
	by Conard Murray <[email-masked]>
  3) Arcusfivus vfos at 24vdc revisited.....
	by [email-masked]
  4) Re: synchronous AM detection using tubes
	by [email-masked]

----------------------------------------------------------------------

Date: Mon, 10 Feb 1997 08:58:04 -0600
From: Dan Kerl <[email-masked]>
To: [email-masked]
Subject: synchronous AM detection using tubes <repost>
Message-ID: <[email-masked]>

<sorry if this shows up twice. I posted it last Thursday and
 never saw hide nor hair of it - DK >

Since I enjoy listening to short-wave programming on tube
receivers, I'm contemplating the details of a project to build
a synchronous AM add-on detector using no semiconductors.
While information on some of the details hasn't been too
difficult to find (variable reactance-tuned oscillator for a
VCO, etc.), I have trouble visualizing how to make a decent
phase detector.  I would also like to incorporate adaptive
loop filtering, with wide bandwidth out-of-lock and narrow
bandwidth in-lock.  I intend to use one of those 6JH8
sheet-beam tubes that AES has on sale as the detector.

Are there any commercial examples of tube-based AM synchronous
detectors that I can use for ideas?  How does a tube color TV
phase-lock its colorburst oscillator with the back-porch
reference burst and could this technique be adapted?  Mapping
modern semiconductor equivalents of common PLL functions onto
a tube environment can get out of hand.

                                Thanks,

                                Dan Kerl
                                [email-masked]

------------------------------

Date: Mon, 10 Feb 1997 10:32:35 -0600
From: Conard Murray <[email-masked]>
To: [email-masked]
Subject: Back on line
Message-ID: <[email-masked]>

Hi Guys,
The server was having problems last week as I am sure most of you know. If
you posted anything last week that you want to repost, please do so. I tried
to forward what I could from the error messages I got from the server, but
most of the stuff just bounced right back at me.
I would rather have it in the digests twice as to never seeing it at all!
73,
Conard
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
. Conard Murray  WS4S    Glowbugs listowner .
.  217 Dyer Avenue        [email-masked]  .
.   Cookeville, TN  38501  615-526-4093     .
.    <><  Wise men still seek Him  <><      .
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

------------------------------

Date: Mon, 10 Feb 1997 13:12:10 -0500 (EST)
From: [email-masked]
To: [email-masked], [email-masked]
Cc: [email-masked] ()
Subject: Arcusfivus vfos at 24vdc revisited.....
Message-ID: <[email-masked]>

Over the weekend I played some more with several arcusfivus rigs as
cheap vfo's for Boatanchor and Glowbug use.  Basically, every arc-5
I tried worked fine at 24vdc on the plates as a stable vfo.  There
were a couple of gotchas, tho.   1) some 1625's don't work well
at low voltages, and were prone to pulling the oscillator under load
so that they would chirp slightly if the oscillator was keyed.  The
fix was to replace one or both 1625's and carefully tweak up the
plate padding capacitor so that it was correctly in line for a
plate dip.  Mine were off enough that I had to tweak them just to
be sure.  2) at very high power (like approaching the 500 watt input
range) rf feedback into the oscillator was a problem.  This was with
the AN/SRT-14 being driven by the arc-5 vfo, into an end fed antenna
(worked fine into a dummy load).  Even bypass caps on the power and
key lines did not really cure the problem.  More stringent choking
will probably be required on the 24vdc power line to the vfo.  The
vfo will work fine at powers of 200 watts or less input in the driven
rig, which is where most glowbug and boatanchor rigs that need a vfo
are (typically the novice class transmitters).  Basically the arc-5
worked great as a vfo keyed or vox-sequenced, at any voltage from
12vdc up to 450vdc on the plates of the amplifier.  At the higher plate
voltages the link had to be uncoupled as much as possible to keep the
driving rf voltages to the rigs down in the 2-5 volt range.  At 12 or
24 vdc, the link had to be coupled as much as possible for the same
2-5 rf volts of drive.  This was just using the link with minimum
roller inductor for output.

I also did some testing of straight arc-5 rigs direct into the antenna,
as a normal rig.  At 400-450 volts on the plates of the amplifier, and
the usual 20K ohm screen dropping resistor, and 15K oscillator dropping
resistor with 100K to gnd, it put out a comfortable 12 watts into the
antenna with two types of feed, 1) roller inductor minimum and feed
to a normal antenna tuner with 50 ohm coax just like any other rig, or
2) roller inductor at half to full (tuned for max) with a 100pf series
capacitor to the antenna.  To get the best stable operation, it was
important to make sure the final was properly aligned in its padder
capacitor setting for a plate dip (or max power out).  IT TENDED TO
BE SOMEWHAT CHIRPY UNLESS PROPERLY PEAKED IN THE FINAL AMPLIFIER.
This is best done by centering the capacitor adjustment trim arm in
its position and locking the trim arm holddown screw on the underchassis
amplifier padder capacitor.  THEN, loosen the setscrews on the arm and
physically rotate the capacitor for the plate dip (max current out).
Since we are only running these things on the ham bands, or have converted
the out-of-band models to run down in the ham bands, it really does not
matter that you do a proper alignment per the manual.  It DOES matter that
you make the plate circuit properly resonate.  So, I would highly recommend
that you properly dip your plates in the amplifiers.  Also, make sure the
under chassis selector keying relay is set to make the oscillator plate power
before the amplifier cathodes are keyed.  That is a must, even with the
amplifier properly tuned, to minimize chirp.

If you want to run 50 ohm coax on your arc-5, you can, but you should
still use the series tuned coil/capacitor network for optimizing the
match to the coax.  In this case, take a 100pf capacitor (50-150pf will
probably work fine) and insert it in the antenna output circuit such
that the link+rollercoil+capacitor are feeding your coax.  It then
will give the optimum match to the following stage be it an antenna
direct or a rig being driven with the arc-5 as a vfo.  With 24 volts
on the plate, it would give well in excess of 5 volts rf into the 50
ohm line to the rig with very little link coupling (about 2 on its dial).

For simple coaxial feed, you might try the RG-58 test lead that has a
BNC connector on one end and a pair of quick-clips or alligator-clips
on the other end.  Worked fine for me, and was easy to attach to the
series capacitor.

Food for thought.  Happy Glowbugging and Boatanchoring!

73/ZUT DE NA4G/Bob UP

------------------------------

Date: Mon, 10 Feb 97 13:16:16 cst
From: [email-masked]
To: [email-masked]
Subject: Re: synchronous AM detection using tubes
Message-ID: <[email-masked]>

Hey Y'all:

        Y'all probably heard by now that the porch.com had an outage 
last week.  That explains lost messages.

        The PLL from a TV is a good idea.  I don't have any examples.  
There was a big article in 73 Magazine back in the late 60's.  Sorry I 
don't know when.

        A phase detector is the same thing as a DBM.  Any double 
balanced mixer circuit will work as a phase detector.  The 6JH8 would 
be a good start.

Ray Mack
WD5IFS
[email-masked]
Friendswood (Houston), TX

______________________________ Reply Separator _________________________________
Subject: synchronous AM detection using tubes <repost>
<sorry if this shows up twice. I posted it last Thursday and
 never saw hide nor hair of it - DK >

<snip>
While information on some of the details hasn't been too 
difficult to find (variable reactance-tuned oscillator for a 
VCO, etc.), I have trouble visualizing how to make a decent 
phase detector.  I would also like to incorporate adaptive 
loop filtering, with wide bandwidth out-of-lock and narrow 
bandwidth in-lock.  I intend to use one of those 6JH8 
sheet-beam tubes that AES has on sale as the detector.
                                
                                Are there any commercial examples of tube-based 
                                AM synchronous detectors that I can use for 
                                ideas?  How does a tube color TV phase-lock its 
                                colorburst oscillator with the back-porch 
                                reference burst and could this technique be 
                                adapted?  

------------------------------

End of GLOWBUGS Digest 442
**************************