Interelectrode Capacitance For An 30 Meter Band Receiver

[Honduras]

I have a Ramsey HR-30 that I bought and assembled several years ago. It has a problem that makes it frustrating to use.

The tuning is controlled by a variable resistor, R2, which is 10 kOhm., but the full mechanical range of tuning is about 270 degrees.

I think I would like to use this a lot more if it had a wider mechanical tuning range, to give me more selectivity.

The ideal solution would probably be that I find a 10 kOhm, 10 turn, drop in replacement for the one in there now, but that leaves the problem repeatability.

Another option that seems reasonable is to use a vernier knob, but size becomes an issue. The only suitable vernier I have is three times the height of the HR-30, and would require that I move the other two variable resistors on the front panel.

So, I hope that explains the issue well enough. And we finally get to the interelectrode capacitance.

Most of my electronics experience has been in the VHF or UHF range. For UHF, I was taught that interelectrode capacitance could cause a number of problems that reduced the efficiency of the gear, and were hard to diagnose.

Basically, if I have to start moving components off the circuit board, what kind of problems will I cause myself?

 

[JimB]

I think I would like to use this a lot more if it had a wider mechanical tuning range, to give me more selectivity.

Selectivity is the wrong expression to use in this context. Selectivity is usually a property if the filter on the IF amplifier.
What you are looking for is a lower tuning rate, or in older parlance, greater bandspread.

Most of my electronics experience has been in the VHF or UHF range. For UHF, I was taught that interelectrode capacitance could cause a number of problems

At 10MHz, I dont think that this will be a problem.

if I have to start moving components off the circuit board, what kind of problems will I cause myself?

Depends on which components you move.
If you move the oscillator coil, that will give you problems.
But the variable resistor for the tuning has (or at least should have) only DC voltages on it. Moving that of the board using reasonably short wires should not cause a problem.

JimB

 

[Honduras]

TYVM, JimB. I didn't mention that my training wasmore than 45 years ago, and I haven't worked with radios for 20 years. I've forgotten a lot of the caveats and terminology.

I was only thinking about moving variable resistors. Tuning, volume and Gain. They are all soldered directly to the circuit board, so IEC should be of 0 concern now.

I get paranoid, though. I thought about using very fine coax for a while, for the leads to the new mounting point(s). If I do that, I've heard that, sometimes, grounding the shield on both ends can have a negative effect, but I don't know where or when I heard it.

If that's not worth the effort, and I do have problems with with noisy signals, what would you recommend? ferrite beads, or decoupling capacitors?