Thanks for all the varied advice on this topic.
Summarising earlier comment, it appears that making a properly
matched set of J-310s requires testing several under the same
conditions, for example with the same 100 ohm resistor. But if thats
the correct approach then its also necessary to check the
individual equalising resistors in the rig itself .... because if they
are not also pretty close to 100 ohms then its not a lot of use
matching the J-310s in the first place. The moral would seem to be
that you only swap the 310s if there is a good, measurable reason.
Suspicion is not good enough !
I'm still going to get some as spares, but they are not going into my
Omni-V unless there is good reason.
Shorting the antenna connector makes good sense, especially in a
climate prone to high static levels. I have a low pass filter and 253
ATU between the Omni-V and the coax to the Centaur balun hung outside
the house. But with an antenna 55 ft up on a hilltop, the possibility
of static build up is obvious. I have a switch to connect a dummy
load or to swap antennas. I leave it in a blank position which
grounds all the other outlets, including the feed to/from the Omni,
when the rig is off, or when I want to use the backup TR-7 instead.
The TR-7 generates quite enough RF to damage a solid state front end.
(Maybe you only make that mistake once; thunderstorms are less
predictable).
John G3JAG
On 26-Jan-99 rohre wrote:
>
> Normally, there should be no degradation of an active device with
> aging.
>
> Contamination of semiconductors was solved long ago, and the
> processes are
> pretty reliable now; look at all the successes of long duration
> space missions
> to Mars, Jupiter, etc.
>
> Barring a plastic problem allowing some abnormal condition, in
> spite of
> passivating layers, etc., my belief is most likely any change of
> operating
> character of the active devices comes from either operation on the
> limits of
> thermal rating, or from static build up on antennas left connected
> to a
> receiver when not in use. It never hurts to reduce the operating
> temperature
> within reason, inside the radio, for longer life of all components.
>
> My concern is that everyone have a positive disconnect, and maybe
> with more
> spacing than an antenna switch, to avoid static arc over from wind
> or nearby
> thunderstorms. These could affect the antenna and then cause rig
> problems
> later on. One way around the static build up is to bridge the feed
> with a
> high value carbon resistor such as 100,000 ohms which will take
> almost no
> power while transmitting but will equalize the voltage gradients
> due to static
> on the halves of the antenna. A way we used in the tube days, was
> to shunt a
> bare 65 volt arc over NE-2 neon lamp across the receiver end of
> dipole
> feedlines. It would flash when thunderstorms were still 5 miles
> away!
> However 65 volt rating would not protect most semiconductors used
> today.
> Zener diodes or silicon diodes used in shunt to ground might act as
> AM
> detectors I fear, so I have not used them. Positive disconnection,
> and moving
> the coax away from the operating table is my SOP in between on the
> air
> sessions.
>
> Same is done with AC power, unplugging power supplies to the rigs.
>
> ---Stuart K5KVH
> rohre@arlut.utexas.edu
>
> --
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----------------------------------
E-Mail: patents@dx0man.prestel.co.uk
To: <tentec@contesting.com>
Date: 26-Jan-99
Time: 09:58:54
John Crux
Consultant in product forgery - Asia and
Africa
----------------------------------
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