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959 VFO windup question...
- Thread starter Hawkeye351
- Start date
Ok, maybe the added inductance from long wires is making it go up. Maybe try just the cap without the switch?
Pretty sure inductance makes it go down, besides, there is another electrolytic and ceramic cap and voltage divider near the varactor isolating that long wire..
You're right, but still can't figure out what's making it go up.
Ok,
My conclusion:
Either the spst switch is throwing it up 500hz off frequency (27.2055) upon settling, or the type/length of wire in using is causing it to settle at 27.2055 instead of 27.2050.
Removed wires for switch all together, switch no longer in circuit. Took another brand new 1000uf 25v cap (this one is rated at 85°, the other was 105°) and soldered it directly to the flapper of VR7 and the negative lead to ground side of R197. Settles dead on frequency (27.2050), perfect.
Removed everything from the spst switch and soldered on just the positive lead of the 85° 1000uf 25v cap to the center leg of the spst, and then a wire to the other leg of the spst that goes to the flapper of VR7. I then ran a separate wire from the negative lead of the cap to the ground side of R197. Settles at 500 hz (27.2055), with switch on, issue.
I even tried the added variable resistor. I tried a 1k ohm first, very little change. Tried a 50k ohm, no change. Tried a 500 ohm, very little change.
Guess I need to figure out whether it's the switch itself, wire type or wire length.
My conclusion:
Either the spst switch is throwing it up 500hz off frequency (27.2055) upon settling, or the type/length of wire in using is causing it to settle at 27.2055 instead of 27.2050.
Removed wires for switch all together, switch no longer in circuit. Took another brand new 1000uf 25v cap (this one is rated at 85°, the other was 105°) and soldered it directly to the flapper of VR7 and the negative lead to ground side of R197. Settles dead on frequency (27.2050), perfect.
Removed everything from the spst switch and soldered on just the positive lead of the 85° 1000uf 25v cap to the center leg of the spst, and then a wire to the other leg of the spst that goes to the flapper of VR7. I then ran a separate wire from the negative lead of the cap to the ground side of R197. Settles at 500 hz (27.2055), with switch on, issue.
I even tried the added variable resistor. I tried a 1k ohm first, very little change. Tried a 50k ohm, no change. Tried a 500 ohm, very little change.
Guess I need to figure out whether it's the switch itself, wire type or wire length.
Might not help, but could you twist the wires going to the switch? Like, leave the cap at vr7 and extend wires from ground to the switch, then back to the cap, twisted wire between?
Was just thinking about that.
I was also thinking of how I can determine if it's the wire or switch that's causing it. I figured I could just tie the flapper wire and positive lead of cap together at the switch end of the radio and see how far it goes before setting. If it settles on frequency then it's the switch, if it settles at the same 500 hz up then it has to be the wires.
I was also thinking of how I can determine if it's the wire or switch that's causing it. I figured I could just tie the flapper wire and positive lead of cap together at the switch end of the radio and see how far it goes before setting. If it settles on frequency then it's the switch, if it settles at the same 500 hz up then it has to be the wires.
If it is the wire thing, I wonder if extending them toward the rf power section isn't picking up some rf, possibly getting rectified by d68 and changing the voltage potential. Probably something stupid, but sometimes when it seems these things don't play by the rules, it's due to our own ignorance.
Well, tied the positive lead of the cap directly to VR7 flapper. Ran a wire from negative lead of cap to switch in the rear, ran another wire from switch to ground. Settles on frequency on AM with switch on and is dead on frequency with switch off in AM and SSB.
SSB seems odd with the switch on though, receive and xmit both are affected either way it's wired, not by much but enough for others to tune you in slightly and you to tune them in slightly. SSB works perfect with switch off though.
He's probably just gonna use it on AM anyway, and since it's settling dead on frequency with the switch on as it is on frequency with the switch off, then I guess it's fine.
SSB seems odd with the switch on though, receive and xmit both are affected either way it's wired, not by much but enough for others to tune you in slightly and you to tune them in slightly. SSB works perfect with switch off though.
He's probably just gonna use it on AM anyway, and since it's settling dead on frequency with the switch on as it is on frequency with the switch off, then I guess it's fine.
Since there is no carrier on ssb, no reason to turn it on. No, I've never heard of vfo wind-up on ssb, I imagine it gets wonky. Sounds like you got it beat now.
Hawk, where did you get the term flapper? I've never heard it called that, but it's growing on me haha. I chuckle every time I read it, I guess because that's what I call the thing in the toilet reservoir.
After some research (first Google result) I think it's a carryover term from way back, from industrial potentiometers and rheostats and such. It will now forever be called the flapper in my vocabulary. Flapper or wiper, still toilet related.
What about using a small mosfet like a 2N7002 to switch in the cap?
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