I have done some more testing and with my crummy little scope.
I have only run the radio on a 9 volt battery. I did some poking around. Touching the antenna center pin produces loud scratching in the audio. Attaching the ground of the scope probe increases the buzzing. Not really 60 cycle hum, but kind of like that. Sorta like the buzz you get when first plugging a guitar into the amp.
I know it is oscillating right, I can hear it on my FT817.
If I touch the scope probe to the side tone, I see a clean signal. If I touch the scope probe to the amplifier output on pin 8, I get in increase in buzz and the sound changes. Same thing on the input pin 4.
If I transmit with my FT817 into a dummy load, I can hear it LOUDLY in the Cricket. I hear no hiss or band noise on receive connected to an external antenna. Nothing but the buzz. It sounds like a path to ground killing the input sensitivity? But getting loud scratching in the audio touching various point in the audio and RF chain? You would think that would not be the case.
Thoughts?
Jess AE0CW
On Apr 30, 2018, at 2:21 PM, Jess Gypin <
ontarget1911@...> wrote:
I’ll do some more testing. I have several other QRP radios that I run on the same antennas as well as the BJ and none of the others exhibit this symptoms.
On Apr 30, 2018, at 12:38 PM, WA0ITP <
wa0itp@...> wrote:
Jess, Sri I came late to
the conversation.
Does the humm/buzz occur when running on a
battery?
That 60 cycle stuff could be riding in on your antenna too. If so it's a
neighborhood problem.
In any event, it sounds like
you might be a candidate for the BuzzKill
http://www.4sqrp.com/buzzkill.php
72 WAØITP
I love this radio stuff.
Back to the bench, Winter is too valuable to waste.
www.wa0itp.com
www.4sqrp.com
On 4/30/2018 1:06 PM, Jess None via
Groups.Io wrote:
Gotcha will try
On Apr 30, 2018, at 11:06 AM, Don Pitchford <
donw9ebk@...>
wrote:
Jess,
I would start by looking at the output of
the audio stage with your scope and see if an identifiable
pattern shows up. Then move your hand around the board to
see if shielding a certain point on the board affects the
buzz. I have a LCD TV near the shack that generates a
12kHz pulse that can mess with receivers all the up
through 10 meters. I have some Crickets and Pixies that
suffer issues similar to what you describe if that TV is
plugged in. A well shielded and grounded case fixed part
of the problem, and unplugging the TV fixed the rest.
Well,
I verified all components and placement on the board
confirmed that all solder joints are good and no solder
bridges or shorts.
I have confirmed that when the unit is powered up the
oscillator is running. I get .9 or so Watts out. Transmit
tone is clean. So having said all that, where do you all
think I should start looking? I have not verified
operation of the audio chain. A lot of the radios that I
have built with a similar problem was a bad ground
somewhere. I have a 25 KHz scope (yeah I know not enough
band width) and a couple of good DVMs.
Jess AE0CW
