Peter Chadwick wrote:
> Rich said:
>
>>But the suppressor isn't a series X and R.<
>
> 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.
The point is that the suppressor can be viewed as a series L and R, with
different values at each frequency. To my mind this is a much better way
of looking at it.
What we want from the suppressor is low resistance between the anode and
blocking cap/tune C at hf, and high resistance at vhf. Given that
there's a series circuit from the anode through the suppressor, blocking
cap and tune C to ground, looking at the series resistance the
suppressor introduces is the useful way to view it. Unfortunately, in
Wes' data, this value (which he calls ESR) is not given for the AL80
suppressor.
Taking what Wes calls the 'NiCh 60+100R', at 30MHz it behaves the same
as 100nH and 4.3R in series (I'm rounding the figures). At 100MHz it
behaves like 76nH in series with 36R - lots more resistance, just what
we want it to do, the resistance between anode and blocking cap is 8.4x
higher at 100MHz.
Looking at the 'Pure NiCh +100R', at 30MHz it behaves like 88nH in
series with 3.3R and at 100MHz, 71nH in series with 26R - 23% lower R at
30MHz, 28% lower at 100MHz. The ratio from 30 to 100MHz is 7.9x
For the AL80 unit, the figures calculate at 111nH in series with 2.7R at
30MHz, and at 100MHz 102nH in series with 29R, a ratio of 10.7 between
the 30 and 100MHz values - slightly lower absolute values, but a higher
ratio than these particular nichrome versions.
For further comparison, here's values I've measured:
Suppressor from a Dentron MLA2500
30MHz looks like 145nH in series with 2.7R, 100MHz looks like 133nH in
series with 27R
TL922
30MHz 85nH in series with 1.7R, 100MHz 74nH in series with 8.9R
Henry 2KD5
30MHz 104nH in series with 1.3R, 100MHz 102nH in series with 15R
Compared with any of the others, the TL922 compares poorly in the vhf/hf
resistance ratio.
Different suppressors introduce different amounts of inductance in the
path from anode to ground - whether that's significant will depend on
the construction of the amplifier and how much inductance is added
elsewhere in the wiring.
Steve
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