Power output decreases as a function of frequency? #bitx40

 

John,

Just a thought.

Desolder one end of L1,L2 and L3 and unwind ONE turn but do not cut the extra wire. Solder the ends and then try.
You can put that one turn back if it does not work..
The filter should move northwards and power graph may be more to your liking!

Happy new year!
Raj, vu2zap

At 31-12-2017, you wrote:
Raj,

Could you suggest a method for bypassing L1-L3? I'm not sure how I would do that with any temporary change, any approach I can think of would be permanent and then attempting to reverse the damage later.

And where is the output filter on the board?

Something is definitely off center, I set the Raduino to transmit out of band and the power tails off in a rather symmetrical pattern centered on 7000khz, with another attachment showing the output power vs frequency.

Thanks!

John


On 12/29/2017 11:20 PM, Raj vu2zap wrote:
Could be something with L1-3. Temporarily bypass the filter and try another test.
I have one board with the filter centered a bit and gives less power higher up the band
but we work only till 7.2MHz.

It could be the output filter also.

Raj


At 30-12-2017, you wrote:
Bottom line up front:

I am having a problem with my Bitx40 where the power output decreases as I increase my frequency across the 40m band.


I completed all of Allard's 1.27.3 mods, plus RX/TX lights, and the spurious emissions capacitor, with it transmitting through a SWR meter into a 50W/3.5ghz dummy load. Power is from a variable power supply set to 12.0V, which includes powering the PA.

I'm receiving the following readings from the SWR's forward power gauge and the power supply's current meter as a function of the tuned frequency when using my straight key for ~1 second:

Frequency, SWR meter forward power, power supply current;

7005khz, 4.5W, 1.15A;

7050, 3.8, 1.06;

7100, 3.0, 0.98;

7150, 2.5, 0.91;

7195, 1.9, 0.82;

7250, 1.3, 0.72;




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