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Transmission
Category: EME Equipment,
Created: 2001-10-21 15:02:20
The market offers many species of tubes to generate RF power. Some principles, however, might help to avoid costly and time consuming exercises:
- Do not trust those who promise you RFout of more than 150% the dissipation power of the tube. Expect the efficiency you might get not better than 50%. On 23cm good efficiency is 40%.
- There is an ideal plate voltage Ua. Efficiency matters when you decide on which level you allocate Ua.
- Thermal stability of an amplifier rewards with two benefits: a) you tune in spring and still enjoy stable conditions in autum. b) you have both hands free for qso-ing, which is particularly helpful during contests.
- If you have the choice between a single tube per stage and a multi tube concept, go for one tube per stage.
It is easier to control and feed a single tube and trouble shooting and repair is obviously less challenging - Take a tube (for big power) and let the solid state devices do the small power job.
- Be aware of the dangerous nature of high voltage in tube amplifiers. Avoid early Silent Key listing in Ham magazines.
Here are pictures of my favourite tubes:
  
Here you see the amplifiers for the TH308 and the cavity and power supply for a TH327:
   The Output 
And this is the result of all the hours spent with power amplifiers:HB9BBD recorded by ON7UN
with 6m dish and one of my preamplifiers.
P43L was an expedition to ARUBA by K2UYH in November 2007. Here is an extract of his interesting report, related to solid power in EME:Dish is up. Should be on tomorrow. Got to go, Write more later.
73, Al K2UYH
HOT news 24th of November 2007
Hi Zdenek,
It was very close time wise. When we tried to mount the dish on Thursday, we discovered the back plate of the dish had totally rotted away. It was like paper. We had to design a different mounting arrangement and re-build the back of the dish. This took a lot of time and made operation on moonrise on Thursday/Friday not possible. I had business meetings in the morning on Friday, and could not be at P43L until the afternoon to do the final feed mounting and equipment setup. When I arrived we had rain for the first time since I have been here. We had to work between showers, but everything was completed before sked time. Our only problem was we had no moon to reference our readouts. Fortunately I was able to find HB9BBD's big signal on our first sked. It was close hi, but once we found him, we were in business.) Things worked very well from then on. Later the moon became visible, which made operation easier. We did have another rain show that should us down for a while, but this was in a no skeds period - between end of Eur/NA skeds and beginning of JA/VK skeds.
WE QSO'd HB9BBD on sked, K1JT tailend (TE), OK1DFC (your signal was FB, but weaker than I expected - was something wrong?), K5JT TE, K9SLQ TE, PA3CSG, OE9ERC early, DF3RU TE, G4CCH early, OZ4MM TE, OK1KIR TE, DJ9YW TE, OK1CA TE, HB9Q TE, RW1AW TE, K2UYH TE, DL1YMK, W5LUA TE, DL4MEA TE, LA9NEA (called just before on low end, but did not respond), 0430 VE6TA Ran, G4CCH on JT, K1JT JT, nil WW2R, K2DH, called JA8ERE at low end, but did not respond, K5SO ran, nil JR4ZZH, nil JH1KRC, some QRZs, nil VK3UM. We have some trees on the western horizon, but continued until 5 degrees. I hope for similar luck tonight, although some rain showers are again predicted.
I do not use this tube anymore:
I got a R+S cavity resonator lately which will go to Al, K2UYH to warm up his shack, hopefully:
   
Transmission lines are to be well matched and low loss. The total loss of RF in the transmission line from the final amplifier to the antenna is l.2 dB.
 
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