Re: Yep. I built it.
- From: "BretLudwig" <bratzirules@xxxxxx>
- Date: Sat, 24 May 2008 18:57:50 -0500
Audio > Audio Tubes > Yep. I built it..."
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Yep. I built it.
by Ty Unes <riverty@xxxxxxxxx> May 24, 2008 at 04:48 AM
I built this:
http://www.vacuumtuberadio.com/AM_Transmitter/
Mine looks like this:
http://2xl.homelinux.com/riverty/dscn1643.jpg
- and -
http://2xl.homelinux.com/riverty/dscn1642.jpg
It works. Doesn't sound very good and is not very powerful, but it works.
I'm trying to diagnose if I have a problem - or - if I need to modify it
to
make it work better!
Tuning is weird. Using my best radio, a Grundig G5, the best way to
describe it would be like the capital letter "V". The loudest audio from
the transmitter is on the ends or fringes of the carrier. If you tune
"right on" the frequency, audio is almost dead. Tune + or - from center
and the audio comes back. As well, I would expect this thing to modulate
much more than what I'm getting. I have to turn the volume up a fair bit
to"<<
You built it, now take it apart.
You need to start with a stable core oscillator section. It has to be
capable of putting out a good spur-free CW RF signal at the proper
frequency. A simple tunable LC tank will work but if you are expecting
modern synthesized tuned BCB receivers to pick your signal up you will
need to either use a frequency counter to set it or build a crystal
controlled oscillator with the frequency you need.
You then need a power amplifier that will take that frequency stable
signal and amplify and buffer it and feed an antenna. The oscillator will
need to be able to feed a varying impedance source well (without shifting
frequency or spurring) if you use a Class C PA, so a buffer might be in
order.
Finally you want to amplitude modulate the output section. The best way
is the classic modulation transformer. A simple single ended tube amp OPT
will make a fine mod transformer for a tube transmitter of up to a few
watts.
Yes you can modulate other ways, but you still need the isolated starting
point. This is called the MOPA-master oscillator power amplifier- design
and is the only one you are likely to get working well without a lot of
test gear and engineering expertise to produce AM or FM with any kind of
quality.
You will need some basic test gear but nothing very expensive. You will
need a grid dip meter and a receiver with a BFO, though jackleg methods
will get you started.
Read the tube era ham radio books, ARRL or RSGB, carefully before you
start.
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- References:
- Yep. I built it.
- From: Ty Unes
- Yep. I built it.
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