Steve Thompson wrote:
>
> Firstly, the gain spec. is usually checked using a single frequency tuned
> amplifier circuit - the tuning might well be tweaked for each individual
> transistor to ensure maximum yield in production. It's unusual to get the
> same gain in a broadband circuit, where there are compromises.
The spec sheet says 15 db typical, 13 db minimum at 28 MHz. I would expect the
gain to be greater at 14 MHz. And I have a 2 x 2SC2879 amplifier, as well as my
TS850S which uses 2SC2879s; both of these put out a full 100 watts (or more)
through 28 MHz.
> It's entirely normal for the gain to drop as the output increases. This is
> affected by both the device and the circuit. For neighbour friendly SSB
> operation, don't go beyond where the output is 10% below what you would
> expect out if the gain didn't drop off.
This would make the situation even worse, then.
> In a SS amp. like this, there's no tuning adjustment available - the
> collector load is fixed by the matching circuits and whatever you hang on
> the output connector, and your output power figures could easily arise from
> the load line being wrong (knowing the supply current figures would help
> check this).
I will rerun the test and post the results with the current readings.
> Try running it through an ATU and see if you can coax more power out, then
> look again at the linearity.
Interestingly, I do get a lot more output indicated on my wattmeter (RF
Applications VFD) when feeding my antenna, which is a quad whose SWR is about
1.5:1 on 20 meters. However, I assumed the wattmeter was misled due to the
non-50 ohm impedance it was seeing. I will rerun the power test with the
antenna and see what happens.
73,
Vic, K2VCO
Fresno CA
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|