View Single Post
Old 8th Dec 2017, 12:58 am   #11
Skywave's Avatar
Join Date: Jun 2006
Location: Chard, south Somerset, UK.
Posts: 6,190
Arrow Re: 'Kalmus' wideband RFPA: info.?

Originally Posted by G0HZU_JMR View Post
One thing to bear in mind is that you need to be careful what test gear you use to measure the RF power level from some of these amplifiers if you run them close to full power.
Ah yes! Of that - and things related - I am well aware. In the past, I spent several years working as a technician for a firm who designed, sold and serviced VHF FM radio transmission equipment. Amongst all manner of other items, typically transmitters up to 10 kW O/P. Permanently, on my bench, was an AR wide-band RFPA (lots of orange on the front panel!): that one had an O/P power control and, IIRC, also had ALC.

Anyway, back on topic. I tested this Kalmus amp. at an O/P power level of approx. 25-W. Two methods:
(1) O/P to a 50 Ω, 50-W. dummy load, with a BNC 'T' to feed a 10 'scope probe (flat to 100 MHz), then to a Tek. 2465 'scope.
(2) O/P direct to a Marconi R.F. power meter, model TF2512. That has a max. FSD of 30-W and claims a 'flat' response to 500 MHz. I have no reasons to disbelieve its indications.
The coax cable for these measurements was 'thick, 50 Ω' coax with N-type connectors. IIRC, that cable was RG-215. The test freqs. were between 5 and 50 MHz. Drive source was an HP 8640B.

"Your idea is crazy! But the question is this: is it crazy enough . . . . to be true?" (Niels Bohr)
Skywave is offline