40 meters plate modulated... on the air!

[ka1tdq]

I finally pulled all the lose ends together and got my 40 meter station running.  The band is totally dead right now (around 2:30 in the afternoon Arizona time) but someone did come back to me!  Whoever he was, he was deep in the static and I couldn't pull him out.  BUT, someone did come back to me!

My audio distortion problem I mentioned before might have been a phantom one.  My voice peaks were distorted only because the receiver I was listening on got overloaded.  I put a receive relay in-line with the receive antenna and the problem was fixed.  I can now listen to myself in the headphones and it does sound good.

One problem I did find with my car audio amplifier modulating the single-tube transmitter though was that the computer power supply would crap out on voice peaks.  The computer power supply (shown in the photo) would sag in voltage since it supplies all the 12 volts in the shack for my exciter, relays, fans, etc.  I built a separate power supply for the audio amp in a lunch box cooler (also shown in the pictures) and everything works fine.

I asked the wife about buying a good commercial 13.8 vdc power supply but she didn't want to spend the $100 and asked if I could build it. 

So, I'm going to get on the air tonight and see what I can drum up for QSO's.  The NS-40 exciter happens to pull my 7.290 MHz crystal down to 7.289.10 MHz.  A real bummer for crystal people, but my carrier is wide enough that nobody should notice. 

Also, power... Tuning for maximum power my transmitter can dish out gives me 600 watts out of the amp.  I've backed the carrier down to 200 watts though for plenty of headroom.

Jon
KA1TDQ

[KA2DZT]

Jon

I have the same cooler, but mine has soda in it.

I just put together a 13.8 volt 25 amp supply.  I used two old 5 volt 25 amp supplies. I adjusted them to 6.9 volts each and put them is series, works FB.  I also built another 13.8 volt 8amp supply.  I used half of one of those -15-+15 volt supplies.  Both are rack mounted with a fan on the 8 amp one.

Fred

[ka1tdq]

...and it works.  I had a nice long conversation with David, WD4PLI in Burbank, CA.  I ran 200 watts carrier and I was coming in 10 over 9 from Phoenix.  He said the audio sounded really good too.

Anyway, this has been a really long project and thanks to all for the technical advice along the way to get this stuff on the air.

Now for the next project...

Jon
KA1TDQ

[VE3LYX]

Best 12 to 13.8 v power supply usually has four wheel headlights and a horn. A cable with a cigar lighter type plug will plug into your car easily. Here I have a solar panel charging an RV battery. Most of the time it cant even feel the power drain for the hour or so I might use it. Not to mention of course it is nice "quiet " power. 12volt automotive style battery =6 cells, 2,.2 volts per cell when fully charged. 660 CCA (1000CCA is available. ) 7.9KW for a minute at least. So an hour or so with 5 or 10 amp draw  would be a walk in the park.
don