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G0FTD > TECHNI 05.06.06 23:48l 25 Lines 1107 Bytes #999 (0) @ WW
BID : B74767G0FTD
Read: DL1LCA GUEST
Subj: Re: Skin depth in copper
Path: DB0FHN<DB0FOR<DB0SIF<HB9EAS<DB0FSG<I4UKI<IW5CWB<IR0UCI<I0TVL<CX2SA<
GB7YFS<GB7LGS<GB7ESX<GB7NNA
Sent: 060605/1741z 08248@GB7NNA.#31.GBR.EU $:B74767G0FTD [Witham, Esx]NNA V3.1
GM0CSZ wrote:-
> Some time ago I tried to convert an italian made (valve) CB amplifier for
> operation on 70 MHz , to assist a fellow radio amateur ,having received
> reports that others had been successful. After reducing the number of
> turns of the output PI (tank) filter I checked output impedance with an
> MFJ antenna analyser
> However ,although I got a resistive 50 Ohms value on both in- and output
> ,the unit produced 'zilch' output power.
> Upon reflection I think I should have changed the PI output filter
> inductor ,by replacing the 1.5 mm OD wire by say 4 or 6 mm OD copper
> tubing .
> This because of the increased skin effect changing from 27 to 70 MHz.
> Perhaps you can confirm this.
You did check that the valve/tube in the amp was *capable* of being used
at 70MHz didn't you ? These 27MHz amps usually run PL519/EL519 line output
valves *hard* just to get something useful out of them.
My set of "Andy's Tool Box" spreadsheets has links to valve/semiconductor
databases for such tasks, as well as two skin effect calculators.
Or do you live in a 7+ deprived area ?
- Andy -
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