TheRadioBoard

Hi all,

Something I've noticed with my latest one-tuber is that the tuning shifts from day to day. Typically in the range of about 5KHz.

I notice because this set tunes very sharply and I have a precisely calibrated dial. One day its on the money, next day the entire band may move by 3-5 KHz on the dial.

I can only attribute this to changes in the antenna impedance due to changes in humidity, temperature, etc. BTW, my antenna is a 125' L at 25' height.

I think any set with an untuned rf amp to buffer the antenna would be immune, not so with a one tube regen/reflex.

Any thoughts on this?

Tim

I believe most of the problems are due to humidity effects on the insulators, including the feedline where it enters your shack. I could see temperature changes effecting the resonant frequency as the antenna wire stretches when it gets warm, but you would have to have some drastic temperature swings.

One of the things that haunted hams back in the self-excited oscillator transmitter days was the wind on the antenna. As the antenna would swing in the wind, it would shift the frequency of the transmitter a bit, so the note was constantly changing. Most hams strung their antennas as tight as possible to minimize this swinging.

Trees near the antenna can also affect its resonant point to a bit by their swinging in the wind changing the antenna to ground capacitance of the antenna.

But what you have observed is nothing new. It has been around since the early days of radio.
Curt

_________________
Curt, N7AH
CW forever
Connoisseur of the cold 807