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Re: [TowerTalk] Measuring Coax Loss-Dealers - Response DAVIS R

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Measuring Coax Loss-Dealers - Response DAVIS R
From: jimlux <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Wed, 24 Feb 2010 06:38:31 -0800
List-post: <">>
Roger (K8RI) wrote:
> My problem is neither the loss per connector or number of connectors. It 
> is the breakdown voltage when running QRO into a very high SWR at the 
> band edges on 75 and 160.
> I standardized on N connectors, but they don't have the voltage ratings 
> to handle that kind of voltage. I see at much as 8:1 at the band edges 
> on 75 and even higher on 160 so I've had to go back to UHF connectors on 
> the HF bands. IT's not a problem or hasn't been on 40 through 10, or 
> 3ven far.  But I need to have higher voltage ratings for 
> at least 160 and 75 and the only way I can see doing that is with true 
> UHF connectors even on LMR-600 even if I have to resort to "Clamp type 
> connectors"

Have you actually had breakdown occur?  The "databook" ratings for 
connectors are quite a bit less than the actual AC breakdown voltage, 
for a variety of reasons.  For instance, PL-259/SO-239 gets used for 
20kV all the time, although the spacing is wider on that connector, 
particularly across the face.  There's also lots of different kinds of 
N, in terms of the dielectric construction.  Some have air dielectric 
quite a ways back from the connector face, others have the dielectric 
close to the face (with correspondingly different dimensions so the Z 
works out ok).  There's also the difference in the shield connection of 
the N: whether it's a single solid piece or 4 little tabs with slots.

There's also HN connectors, which are a high voltage N (even though the 
databook says 1500V for both), although I suspect that 7/16 DIN might be 
a better choice (cheaper).  An HN can not intermate with an N (3/4 vs 
5/8" thread diameter).

Having used a variety of connectors for purposes they were not specified 
for in the HV world, you need to actually test the connector in your 
application.  A variac and neon sign transformer (or Oil Burner Ignition 
Transformer) makes a good start for a sort of hi-pot tester.
On the other hand, you're looking at high Z applications, so maybe 
something like dual banana jacks would be better.  The impedance 
discontinuity at 2MHz is going to be negligble.

> It adapters you mentioned work fine until I hit the high voltages on 160 
> and 75. Then I lose the N connectors and the adapters. Near as I can 
> figure off the top of my head all connectors between the rig the 6-pack, 
> remote 160 and 75 antenna switches and the outputs to the 160 and 75 
> meter bands from the six-pack. That results in about 9 or 10 UHF 
> connectors between the rig (pig tails from amp to patch panel) bulk head 
> connectors in patch panel, coax from patch panel to six pack at tower, 
> jumper from six pack to bulkhead connector leaving equipment box.  
> Jumper from bulkhead connector to remote antenna switch, and pig tail 
> from remote switch to antenna feed point.
> The jumper from the remote switch to the antenna is RG-8X on 40 (3 
> runs), LMR-400 or Davis Bury Flex on 75 (3 runs) and 160 (currently 1 
> urn to soom be two runs)  All connectors in these lines need to be UHF.
> "I think" I can get buy with N type connectors for 20, 15, 10, 6, and 2 
> meters even running the legal limit.
> Stephen Davis wrote:
>> A brief response to some TT'rs observations herein:
>> What's a dB worth:  
>>     As much as you can afford to spend to achieve your desired result, 
>> without short changing  the rest of the family...a distinct point of 
>> "diminishing (moral?) return".

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