> Rich said:
>>But the suppressor isn't a series X and R.<
Peter G3RZP said:
> Made of resistance wire, it is. If it isn't, then the
> measurements Wes did, which show an impedance that
> increases with frequency, are wrong.
It's easy to see the series resistance added by the nichrome
primarily affects low frequency performance, and has a
decreasing effect as frequency is increased. The correct
term for a nichrome suppressor would be a "low HF Q
suppressor", not a "low Q VHF suppressor".
This is why anything we might want to do at VHF can be
accomplished by simply changing resistance and inductance in
a conventional suppressor.
As you say Peter, the resistive loss of the nichrome is in
series with the inductance and only increases the impedance
of the suppressor. It increases the impedance of the
suppressor at all frequencies, even those where we normally
don't want to increase it.
It isn't any magic bullet. If I took a regular suppressor
and added a small series resistor at one end, I'd have the
same electrical characteristics.
If you take a stock AG6K hairpin suppressor kit for 3CX800's
and measure the anode load Q looking into the tank from the
tube and compare it to a stock suppressor in the AL800
amplifier, the nichrome hairpin INCREASES VHF Q of the
system. This is because the inductance is much lower than
the multi-turn stock suppressor coil that is shunted by a
100 ohm resistance, and the added resistance of the nichrome
doesn't make up the difference.
The only time a nichrome suppressor and conventional
suppressor are equal at upper VHF is when the nichrome is
wound in a multi-turn coil about the same size and turns as
the stock suppressor. The two are very much the same. The
only place there is a major difference is at HF and lower,
where the nichrome adds series resistance.
This is all pretty basic stuff. It's easy to see how it
works. If I had an amplifier oscillating at VHF, I'd most
likely use a regular suppressor to fix it. If I had an HF
amplifier oscillating at the operating frequency or near ten
meters, nichrome could be an option. It isn't anything magic
or special at all, and it certainly isn't a universal cure.
It is just something that is lossier at lower frequencies,
and about the same at VHF.
73 Tom
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