Carl Clawson wrote:
>MHV are suggested in some ARRL designs, but I don't find current
>information on them which makes me wonder if they're going obsolete. SHV
>appear to still be made but are more expensive. Both of these are coaxial,
>which is unnecessary although it does provide a convenient geometry for the
>recessed contacts. So what do you like?
IMO a coaxial connection *is* necessary, for safety reasons.
The "nightmare scenario" that you're trying to avoid is where the two
chassis are at different potentials because they're interconnected only
by a live B+ wire. The single-wire Millen connectors can do that rather
easily, and it can be lethal!
A coaxial HV connector automatically bonds the metalwork of the two
cabinets together - you can't get a HV connection without a safety
ground connection too. Also the coax shield provides some "armoring" for
the high voltage conductor, and an automatic short to ground if the
cable is accidentally cut.
SHV connectors are much better than MHV because *both* pins are deeply
recessed, and it reliably connects the ground before the HV. Also there
is no possibility of forcing on any other type of connector. (Contrary
to what the manufacturers say, a BNC plug *can* be forced into an MHV
jack. And when that happens, the center pins connect before the safety
ground!)
If you are connecting HV between two cabinets, the B+ is not the whole
story. You presumably want a B- return as well, separate from chassis
ground. I use a good-quality 3-pole connector for this, carrying:
1. B-
2. Chassis ground
3. 24V DC for the HV mains contactor, coming *from* the PA.
The 24V DC line gives the PA circuitry full control over the HV supply.
There will be no mains to the HV transformer unless the power supply is
plugged into the PA, and this also makes a chassis ground and a B-
return. It's a good and *safe* way to use the same HV supply with a
range of different RF/control decks.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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