w8cbc
06-05-2006, 04:46 AM
I got one of these at Dayton. The guy wanted $200. I had $151 in my wallet and offered it. Sold.
It is a high-pass T (motor-tuned Cs, switched L) rated for 500 watts carrier, 1000 watts PEP, and meant as a companion to a 500-watt ICOM linear amplifier.
Power supply is built-in. It can also run off an external DC supply.
I have it hooked between the IC-751A and T/R switch box (i.e. it's only for the 751A).
I parallelled the thing's antenna connectors as my antenna switch is outside. I use it to tune the 90-ft wire and the zigzag.
Results:
It tunes the wire just fine, to within 1.2:1 at the 751A, in all but 80 and 30 metres. In those two bands I have an extremely high feed point impedance that it just cannot handle. The manual tuning contraption takes care of those.
I read somewhere that it needs 50 watts of input to tune. It'll usually rough-tune with 5 watts however, and fine-tune as I raise the carrier. I've noticed it bumping the tune a bit when I QSY a fair ways within a band and transmit SSB. That's nice.
There are times it cannot find a match unless it's been set to the default, which I adjusted for each bandswitch setting. Going from 12 to 15 metres in the 24-28 setting (it tunes 15 better there than on the 18-21 setting) is an example. I reset it by flipping the bandswitch down one and back up. Once it's settled down, it'll tune 15 okay.
It takes awhile to settle down to its defaults before being ready to tune. That's not a big deal. It takes me longer to tune up with the manual homebuilt contraption after all. Once it's ready, it'll tune up within a few seconds.
The AT500 adds a bit of capacitance parallel to the line when bypassed. I noticed that both my wires' resonant frequencies (1800 kc for the 90-footer, 18100 kc for the zigzag) dropped below their respective band edges. I can use it to self-compensate in those bands of course but prefer to run straight into the wire when possible.
I don't know how much loss there is on my transmitted signal but I'm getting out just fine through the thing so I guess there isn't much. It's not built as heavily as my homebrew manual contraption though. Since I can make the latter arc and heat up (input cap and rotary coil respectively) with 100 watts in a tough-match situation, I'd be a little hesitant to run rated power into the AT500. That may not be relevant though as those situations that strain the ATC3 are in 80 metres, which I mentioned the AT500 won't match here.
Conclusion:
I consider it a good buy. I'm already getting spoiled lazy by not having to manually tune the bands that the AT500 can match.
It is a high-pass T (motor-tuned Cs, switched L) rated for 500 watts carrier, 1000 watts PEP, and meant as a companion to a 500-watt ICOM linear amplifier.
Power supply is built-in. It can also run off an external DC supply.
I have it hooked between the IC-751A and T/R switch box (i.e. it's only for the 751A).
I parallelled the thing's antenna connectors as my antenna switch is outside. I use it to tune the 90-ft wire and the zigzag.
Results:
It tunes the wire just fine, to within 1.2:1 at the 751A, in all but 80 and 30 metres. In those two bands I have an extremely high feed point impedance that it just cannot handle. The manual tuning contraption takes care of those.
I read somewhere that it needs 50 watts of input to tune. It'll usually rough-tune with 5 watts however, and fine-tune as I raise the carrier. I've noticed it bumping the tune a bit when I QSY a fair ways within a band and transmit SSB. That's nice.
There are times it cannot find a match unless it's been set to the default, which I adjusted for each bandswitch setting. Going from 12 to 15 metres in the 24-28 setting (it tunes 15 better there than on the 18-21 setting) is an example. I reset it by flipping the bandswitch down one and back up. Once it's settled down, it'll tune 15 okay.
It takes awhile to settle down to its defaults before being ready to tune. That's not a big deal. It takes me longer to tune up with the manual homebuilt contraption after all. Once it's ready, it'll tune up within a few seconds.
The AT500 adds a bit of capacitance parallel to the line when bypassed. I noticed that both my wires' resonant frequencies (1800 kc for the 90-footer, 18100 kc for the zigzag) dropped below their respective band edges. I can use it to self-compensate in those bands of course but prefer to run straight into the wire when possible.
I don't know how much loss there is on my transmitted signal but I'm getting out just fine through the thing so I guess there isn't much. It's not built as heavily as my homebrew manual contraption though. Since I can make the latter arc and heat up (input cap and rotary coil respectively) with 100 watts in a tough-match situation, I'd be a little hesitant to run rated power into the AT500. That may not be relevant though as those situations that strain the ATC3 are in 80 metres, which I mentioned the AT500 won't match here.
Conclusion:
I consider it a good buy. I'm already getting spoiled lazy by not having to manually tune the bands that the AT500 can match.