>
>Last week I made a posting requesting sources of commercial
>plate chokes, since my homemade choke had arced. I ended up
>ordering a unit from RF Parts. In the process of removing the
>old choke and installing the new one, I made some dip
>measurements over the range 9.5 to 51 Mhz. Both chokes were
>measured, using an AN/PRM-10 GDO under three conditions:
>
>1. On a wooden bench, with a copper strap shorting the two
>terminals. The strap was positioned two choke diameters away
>from the windings, with two right-angle bends to connect to
>the terminals.
>
>2. In the amplifier, with the same copper strap in place, no
>HV or RF wires connected to the choke.
>
>3. In the amplifier, with no strap, and all circuits connected.
>The output pi-net was set to approximately its normal 80 meter
>settings.
>
>Old choke results:
>bench 25, 34, 43
>amp/strap 25, 43, 49
>amp/connected 22, 42, 49
>
>New choke results:
>bench 12, 15.2, 34
>amp/strap 10.9, 14.9, 26.9
>amp/connected 10.5, 14.8, 26.8
>
>A few observations:
>
>1. With the choke in the amp, all circuits connected, the resonances
>could be moved all over the place if the plate tune capacitor
>was unmeshed.
>
>2. The old choke arced on 15 meters.
? hardly surprising since the 22MHz resonance is not that far from 15m.
Removing a enough turns to move the resonance up to c. 23 MHz would have
made a significant difference.
>Perhaps the measurement
>with all circuits connected was the best indicator of this
>potential problem?
>
>3. I am concerned with the 14.8/14.9 resonance of the new
>choke,
? 15.1MHz might be a safer parking place.
>but so far no problems in two days of heavy use, with
>a lot of band-hopping, retuning and 20M transmitting.
>
? It likely won't combust without a contest.
- cheers, Dave
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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