Rich Measures wrote:
>>Despite the fact that the change in VHF Q is very minor, and
>>Measures original suppressors actually have higher Q when in
>>circuit than many conventional suppressors!
>>
>? Not according to N7WS' measurements. Nichrome has over 50x the
>resistance of copper. Add R and ''actually have higher Q''? Behold, the
>world according to Tom.
>
N7WS made a direct comparison between two nichrome/resistor suppressors
supplied by Rich, and a conventional copper-coil/resistor supplied by
Tom. He used a vector impedance meter to measure equivalent series or
parallel resistances and reactances, and hence Q, from 10MHz to 200MHz.
The Qs at 100MHz were similar (about 30% different in one case) and the
Q vs frequency curves were almost parallel through the VHF region. Both
Qs became higher at lower frequencies, as you'd expect, but the Q of the
nichrome suppressor did not rise as fast as the Q of the conventional
suppressor, so the Q vs frequency curves diverged at lower frequencies.
What W8JI probably meant to say (and I *did* say, at that time) was that
the use of nichrome in the suppressors made more difference to the Q at
HF than it did at VHF. From N7WS's measurements, that was totally beyond
dispute.
This would mean that for the same degree of effectiveness in suppressing
parasitics at VHF, the losses in the nichrome suppressor at HF would be
higher.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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