How can I tell if an RF realignment is needed?

[medge799]

Hey gezza (post #15), thanks fo posting the diagrams and notes; I may give that a go...

I've had a lifetime of electronics, starting with radio but now too many years in software. Repairing/restoring old valve stuff is still a bit alien, so 'budding Radio Engineer' may fit well. I'm fine with the radio theory, but its the practice that I lack, and I can't think of a better bunch of people to consult than those who walk these virtual streets....

I remember using something like the magic wand described in post #18 when at Racal in the 80s but I'd completely forgotten this - thanks for the reminder! To tell the truth RF always appears to be a bit of a black art - software can be a lot more predictable. Still, nothing beats getting a bit of code working or hearing music from a radio that died 10s of years ago.

[Ian - G4JQT]

Just a word of warning about stations not appearing in the "right place".

A number of UK stations (Radio Five Live, Classic Gold, Absolute, etc.) use more than one frequency. Just because Absolute Radio advertises its 1215 kHz (247m) channel as national, you may live in an area where one of 1197, 1233, 1242 or 1260 are strongest. So tweaking one of them to read 247m will be wrong - although in practice, the difference in metres between 1197 and 1260 kHz is probably only a few needles' widths on many sets!

The easiest way to check what medium-wave channels the strong ones are operating on in your area is to tune them in on a radio with a digital frequency readout, and for most people that's probably a car radio. They all have digital readout these days - unless you have a vintage one of course!

Then convert the frequency to metres thus:

300/frequency (kHz) = wavelength in metres

e.g. 1) Radio Five Live 693 kHz 300/693 = 433m (ok, 432.9m!)
e.g. 2) Radio Five Live 909 kHz 300/909 = 330 m

You can look up the frequencies on the web for any station, but you'll have to calculate to convert to the wavelength for the old dials.

Regards,

Ian

[ms660]

Originally Posted by Leon Crampin

The wand will shift the resonant point of an L-C circuit in just the same way if the L is air cored.

Leon.

Hello Leon, I was thinking primarily about capacitor tuned IF transformers, the access hole to these types usually exposes the rotor of such tuning capacitors, invariably the rotor on the primary side will be live (HT) HT being the earthy end of the tuned circuit.
The magic wand is very usefull on slug and air cored inductors, had them when we used to do tellys. Also good for helping to track birdies in wiring.

Lawrence.