On Tue, 9 Sep 1997 09:32:08 +0100 Peter Chadwick
<Peter.Chadwick@gpsemi.com> writes:
>What value of shunt resistance is used in the W8JI type suppressor?
It should vary depending on the tube used in a conventional single
resistor suppressor with n turns of copper wire.
>Why
>can't you get the same lowering of impedance by dropping the value of
>the shunt resistor? My (possibly faulty) understanding of the way the
>suppressor works is that the inductance is added to increase the
>amount
>of inductance in the circuit so that the shunt resistor is then
>damping
>a higher proportion of the parasitic circuit, thus reducing its gain.
>The higher the stray inductance in the parasitic circuit ( bad layout
>etc), the bigger the suppressor choke has to be. The bigger the
>suppressor choke, the more volts of fundamental appear across it, and
>the more fundamental power gets dissipated in the resistors. If the
>value of the resistors is too small compared to the reactance of the
>choke at the parasitic frequency, then the effective impedance that
>the
>suppressor offers drops too far, and the assembly looks like a lossy
>bit
>of wire. So there's an optimum value for the impedance of the assembly
>at the parasitic frequency, and too low is just as bad as too high.
Absolutely....in a conventional suppressor Peter. In Rich's and my
approach the resistor value appears to be less critical with the L
material playing a bigger role.
My approach is somewhere between Rich and Tom and appears to be very
tolerant.
>After doing a few sums, I'm not convinced that the nichrome approach
>doesn't have advantages in some circumstances - at least you aren't
>searching for high power (5-10watt) low capacitance, low inductance
>resistors.
Maybe not available in the UK Peter. A good 5W is $.50 in single qty in
the Colonies.
73.....Carl KM1H
>73
>
>
>Peter G3RZP
>
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