Wireless Set No. 52 Canadian - Project

[Chris Suslowicz]

Originally Posted by Mike Kelly

I noticed the same issue. Those old capacitors will not be reliable, they need to be replaced. I also don't like the exposed high voltage terminals on the power supply , over 500 Volts

The Wattmeter is not to be believed - it will be adding up and displaying all of the harmonic and spurious content of the transmitter, giving a false reading. The load impedance needs to be matched to the output impedance of the set otherwise there will be a false indication of the actual power output.

It's a very nice power supply, just missing the perspex/plexiglas sheet over the terminal strips and suitable DANGER - HIGH VOLTAGE labels.

As for the output power measurement, the EMERs specify a dummy load of (I think) 10 ohms and 30pF (plus a thermal ammeter) connected to the variometer output terminal in order to simulate an 8-foot whip aerial. Even that will include any harmonics, and you'd need modern test gear (spectrum analyser) to get any idea of the actual useful signal output - especially if using wire aerials or a different length of whip.

Chris. (I've got the "Dummy Aerial Set", but not the original Valve Voltmeter used with it (which is a little on the bulky side). Might try it with a later one at some point.)

[Mike K]

This is a good article by Dave Lawrence. From what I have read about variometers, they are not ideal in a electrical sense , the rotary inductor or roller tuner is a better method of electrically adding length to the antenna.

https://www.qsl.net/ve3bdb/antmeas.html

These days, you can buy a nanoNVA device for hobby use. The VNA has the ability to analyze the complex impedance of the 19 set variometer and antenna and give a direct result in various forms. The nanoVNA are easy to buy on most of the popular retail platforms . And small spectrum analyzers are available for hobby use as well.

https://www.aliexpress.com/item/1005...d=gkAQdhUhNQmF

https://www.aliexpress.com/item/1005...170019037756_1