Ron, the Andrew N connectors for LDF5-50 do have captive center pins, they
don't make them any other way. The problem discussed doesn't occur with
Heliax, it occurs with flex cables that use connectors having separate
center pins. You can always use captive pin type Ns on the RG-213/U or
whatever flex cable you'll be using. Just buy them that way. They're
available from many sources including Amphenol, Delta, Kings, Trompeter, et
From: Ron Stordahl [mailto:email@example.com]
Sent: Wednesday, April 19, 2006 1:31 PM
To: Ian White GM3SEK
Subject: Re: [TowerTalk] Power limitation for N-Connectors
The consensus is that N connectors are fine at 1500 watts up to 30 MHz
(and probably beyond but my use is 30 MHz or lower). My problem with
N-connectors in the past, and it's a distant past, is in assembly..maybe
I had some bad ones. And I am from the old school...like to use
solder. But if the compression connection for the shield is good enough
and long lasting..apparently it must be..then fine.
The cable will be LDF5-50A which is foam.
Is there a certain connector which has a 'captive center pin' as you
My plan would be to use female connectors on the heliax, then male
connectors on the more flexible jumpers at the ends, probably short
length of 213.
Am I on the right path?
Ron Stordahl, N5IN
Ian White GM3SEK wrote:
> Steve Katz wrote:
>> I'd say they're wrong.
>> Type Ns flashover at >3000V at STP, and that's a lot of voltage. The
>> pin can handle 6A continuously, probably 12A intermittently. 1500W is
>> in a 50 Ohm system. 1500W is 273.9V in a 50 Ohm system.
>> I don't see the issue. I've used type Ns at 1500W output power on 70cm
>> eme work, and never had one fail...
> There is no problem with correctly assembled N connectors at these power
> levels; but there is a risk of failure if the centre pin is not mated
> This can happen when N connectors with a floating centre pin are used
> with semi-airspaced cables whose centre conductor is free to move
> inside the cable. A hanging length of cable, and/or some flexing in a
> rotator loop, can sometimes pull the centre pin partly out from its
> socket, causing high resistance (especially at UHF where skin depths are
> smaller) and failures at high power.
> The solution is always to use connectors that have a captive centre pin,
> and to take care when installing cables that have a floating centre
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