Adjusting the BFO frequency using an RF probe

[golden optimist]

If you have the bfo set too low in frequency, it would give you low power out as part of the audio modulation would be down the crystal filter slope.

You can use this method for adjusting the bfo frequency.

Bandpass filter waveform

crystal filter bandpass.gif (10.11 KiB) Viewed 4922 times

Try monitoring the rf output at the dummy load with your RF probe and no modulation. Adjust R66, carrier balance to one end. This will insert carrier. Now adjust C72, the bfo frequency slowly until you get no more increase in voltage on the RF probe. If you start drawing more than maybe an amp, turn down the drive with R83. What we are looking for is the lower corner maximum point. Once you have found the maximum, you want to turn the cap the oposite way to reduce the voltage until the RF probe voltage reads 1/5th to 1/10th of that voltage. That should set the carrier down the slope 10-20db and should be about right. If you reduced the rf drive with R83, increase it now and then adjust R66 and C65 for minimum voltage out. That is adjusting the carrier back out. Now try modulating the transmitter and see if you get more current out. You probably won't get 2 amp peaks watching the power supply while talking.

If you still don't get enough drive, try adjusting for a -6db reduction. That would be 1/2 voltage.

Leonard

[COArgonaut]

The scary part is I understand it.

ed

[JAW]

Howdy there Edderd. When you say you understand it, does it mean the upper or lower skirt or the voltage?

Sure hope to see the whites of your eyes this summer as we will be there.

JAW

[COArgonaut]

Yea, I'll be there.

Ol' Leonard got me, just like he gets Corky.

Corky: "Hey, the fire is getting a little low."
Leonard: "I'll bet ya can't split that piece of wood!"
Corky: "Just watch this!".

Except, what he did to me:

Ed: "That ham radio sure looks like a lot of fun".
Leonard: "I'll bet you can't pass the General test".
Ed: "Oh, yea? Just watch this!".

CCC Com Team
KD0IRT

[golden optimist]

Actually what I think got Ed was when I talked to K9SUB, the USS Silverfish submarine up in Michigan. I have to give him credit. He came back from field day and started studying right away and it didn't take him long to get his General.
Leonard

[russau]

yep ole Ed slipped into this like a ole pair of slippers next to a campfire! i got 1/2 way through my lessons of this license about 35 years ago and never got back to them. it seems a divorce got in the way!