Posted by
Don Wilhelm-4 on
Dec 13, 2007; 3:53pm
URL: http://elecraft.85.s1.nabble.com/KPA-100-QRP-except-on-80m-tp456874p456875.html
Bob,
What have you finished of the Testing and Alignment. If you have not
yet done the PA bias adjustment, your KPA100 will have little or no
output as you describe.
Actually I had some trouble understanding your exact problem.
Do you mean that you have no KPA100 output on 80 meters, but it is OK on
other bands? Or do you have no hi power output on any band? Or, do you
mean that you have about 11 watts of power anytime the power request is
set above 11 watts?
It is not 'T sense' - that only controls when the fan comes on.
If QRP transmit is OK, then likely your Low Pass Filters are good -
check on all bands.
If you receive properly when set to 11 watts or higher, then at least
part of the T/R switch is working properly.
Calibrate your wattmeter initially at 9 or 10 watts (you can re-do it at
higher power later), but the wattmeter must work to control the power of
the K2 (and the KPA100).
If your problem is that you have some power output when the power
request is set above 11 watts, but not the proper amount, then check the
Scaling function of the wattmeter - RP1, R24 and R25 and Q10 and Q11.
During hi power transmit, the drain of Q10 and Q11 should be near 0
volts and you should have 4 to 6 volts on the gates.
73,
Don W3FPR
Bob Towers wrote:
> I've just completed building the kit (bought 3 months ago from
> Elecraft) and all went well until I got to Page 50 of the manual, the
> QRO transmit tests. I could only get any power above 11 watts on 80m
> (I don't have the 160m module). On all the other bands the output
> power to the dummy load, measured on my power/SWR meter, got to 10-11
> watts when K1/K2 tripped and then dropped to a few watts and would not
> increase at all. On all bands the SWR into the dummy load was 1.1:1 or
> better.
>
> I thought at first it might be the LPFs, but now I think it isn't
>
> a) receive performance was the same across all bands
> b) QRP maximum output was 9-12 watts on all bands
> c) the KPA-100 relays tripped at the appropriate band changes eg 17/2
> -> 10/12/15 -> 80.
> d) the toroids in the LPFs were all soldered in right
> e) the physical layout of the LPFs (toroids, capacitor values) is right.
>
> I did a few voltage measurements:
>
> Bands QRP (<11W) QRO
> (>=11W)
>
> T sense (pin 5 of U1) 80 0.00V
> 0.62V
> all other 0.00V 0.00V
>
>
> For some reason, the power amp isn't switching on, on all bands except
> 80m. Presumably T sense is the trigger...
>
> Any help would be much appreciated.
>
> Many thanks
>
> Bob Towers
> MM0RKT
>
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