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Author Topic: 3.720 Mhz  (Read 6552 times)
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KX5JT
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John-O-Phonic


« on: November 07, 2009, 11:29:36 PM »

So I'm monitoring and calling the occasional CQ on 3.720 AM.  It's 03:30 UTC (10:30 pm Central, 11:30 AM Eastern)

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AMI#1684
KX5JT
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John-O-Phonic


« Reply #1 on: November 07, 2009, 11:53:52 PM »

Don K4KYV found me and has a BOOMING signal! Thanks Don.
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KX5JT
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« Reply #2 on: November 08, 2009, 12:05:41 AM »

Hi Brian,

Yep it's me.  I'm a bit AM challenged for long haul especially.  I'm running a DX-60 into a SB-200 for about 100 watts of unmodulated carrier.  My antenna is a G5RV inverted and fed at only 35 feet.  But I'm early in the AM game and plan on getting a resonant dipole up at closer to 50 feet.  We'll see if it helps!

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ve6pg
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« Reply #3 on: November 08, 2009, 10:15:02 AM »

..don has been on, alot of evenings, on 3725...the band goes long., and he has been on with bernie, w8rpw...great sigs in here...

..sk..
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...Yes, my name is Tim Smith...sk..
Steve - WB3HUZ
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« Reply #4 on: November 08, 2009, 12:58:54 PM »

Nice session on 3720 kHz last night. I missed most of it but still had a good half-hour plus with Don and John. Conditions were pretty good. Don was his usual 30-40 over 9 and John was 10 over. My Southwest receive antenna was out of commission or I'm sure I would have heard John with full quieting. That antenna will get fixed today!
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k4kyv
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Don
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« Reply #5 on: November 09, 2009, 12:18:41 AM »

I have been running a lot "crapstal" control lately.  Have xtals for 3711, 3720, 3725, 3735 and 3743, plus a bunch of frequencies in the 3600-3700 kHz segment, plus many others.  Also have a drawer full of xtals for 160 and 40. I could pretty well get by if my VFO crapped out, until I could fix it.

Something about my oscillator circuit causes the frequency to consistently be about 300-400 Hz higher than the nominal frequency stamped on the crystal holder.  I use the standard tetrode/pentode oscillator circuit, with xtal from grid to ground and a grid leak resistor in parallel, and a tuned circuit at the plate.  The tube is a buzzardly broadcast receiver final audio tube, using the imperfect shielding of the screen grid typical to those types of tubes to achieve feedback. I presently use a type 59.  A 6F6, 6V6, 6K6, 38, 47, 42, etc. would work just as well, but I like the 59 because the suppressor grid comes out in a separate pin allowing me to switch the same tube over to a grounded grid amplifier stage to serve as coupling/buffer stage for my external VFO.  A grounded grid stage will sometimes self-oscillate at rf with tubes that have the suppressor internally connected to the cathode as is the case with most audio pentodes.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
k4kyv
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Don
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« Reply #6 on: November 09, 2009, 02:42:51 PM »

I made several major modifications to the T-368 exciter.  It would be extremely difficult to get it to work in a T-368 ever again.

I changed the output circuit to link coupled, so I could use a coax feed to transmitters located several feet away.  That involved adding an extra wafer to the bandswitch and modifying each output coil by adding a few turns of coupling coil to the slug tuned coil.  It no longer has the superb output linearity across each entire frequency range as it did originally, but tuning it for best performance in the middle of each ham band, I find negligible tracking error within the confines of any of the bands.  Since I don't use it for any non-amateur purposes, the loss of perfect tracking is a non-issue.

I replaced the 6000 tube with a 6AG7, which involved rewiring the octal socket, and run the whole thing at reduced voltage.  The output measures about 200-250 milliwatts into a 50Ω load on all bands.

The oscillator stage runs all the time, 24/7, as long as it is connected to the a.c. mains voltage.  That eliminates the slight warm-up drift at the beginning of every transmission  during a QSO.  I added extra shielding and  filtering, pretty much standard TVI filtering techniques extrapolated to the HF range, so that the running VFO is inaudible in the receiver.

I still had some drift with even the slightest changes in a.c. line voltage, so the oscillator tube runs with regulated DC applied to both the filament and plate.

The tuning rate was too fast, particularly when using the 4th harmonic of the PTO for 40m, so I added a planetary reduction drive to the main tuning control shaft.

I also have a DDS vfo, but rarely use it.  I used it with my 10m rig when the band was open, and it was rock stable, even on 10m, but with the mods the T-368 unit is so stable on 160-40 that I don't really need the DDS unit.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
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