[Elecraft] SO-239 Concerns -- Another Perspective

Fri Jul 23 14:20:28 EDT 2010

I have also been bitten by the non-captive center pin on
Type "N" connectors.  In my particular case, I had 100 feet
of RG-213 runing outside from the shack to a roof mounted
antenna.  Type N connectors on both ends.  

Then came the cold weather.  One day, no receive signal,
and funky SWR.  Hmmm.  After a brief investigation, and a
trip to the roof, it was determined that the non-captive
center pin had been pulled out of its N connector and
therefore, the mating N connector, by the apparent
contraction of the coax copper center conductor in the cold
weather.  What a pain.

Therefore, whenever I use Type N connectors for
professional or amateur use, I specify captive center pins.
 Failing that, I use another type of connector.   

All usual disclaimers apply.  Your milege may vary.  Void
where prohibited, taxed, or otherwise snarled at...

73,
K1NR 

On Fri, 23 Jul 2010 14:32:11 +0000
 Brian Alsop <alsopb at nc.rr.com> wrote:
> Joel,
> 
> How do you respond to this blurb from a "DX Engineering"
> guru?
> 
> I have been bitten by the non-captive center pin
> migration problem 
> (almost impossible to find) and won't use N connectors
> again for any 
> non-UHF high power application.  This migration if enough
> creates an 
> open circuit.  It is hard for me to tell the difference
> in captive pin 
> and non captive pin N connectors.  Also I prefer the
> larger center 
> conductor surface area of the UHF center pin connectors.
>  They are 
> proven to have very little heat generation beyond UHF.
> 
> 73 de Brian/K3KO
> ----------------------------
> For example, DX Engineering does not offer the RR-8
> series switches with 
> N connectors. Using UHF type connectors, this system of
> remote relays 
> offers superior port-to-port isolation and power handling
> from 1.8 
> through 54 Mhz at low loss and low SWR. Only due to
> superior engineering 
> is this series of Remote Switches usable at 144 Mhz with
> slightly 
> elevated SWR and reasonable loss of only 0.25 dB.
> However, these units 
> are not intended and cannot be used on UHF, so N
> connectors are 
> intentionally not available.
> 
> There is no question that the constant impedance
> characteristic of the N 
> connector make it a superior choice for low loss VHF and
> UHF applications.
> 
> However, it is a fact that on HF frequencies, very high
> power at high 
> duty cycle modes will heat the small diameter center pin
> of the N 
> connector. Heating can cause the center pin to migrate,
> ruining the 
> impedance characteristics of the connector and, at
> continuous high 
> power, potentially cause a short circuit. If this problem
> were to happen 
> during testing or operations, one might mistake high SWR
> or high loss as 
> a defective of the switch, rather than a problem with the
> connector. 
> This cannot happen with PL-259 and SO-239 connectors that
> are properly 
> installed. At low SWR they can handle several kilowatts
> of HF RF.
> 
> This is not to say that you cannot use N connectors on
> HF. Rather, the 
> question becomes "What are the benefits derived versus
> the cost of 
> changing to N connectors for HF, where constant impedance
> is 
> unnecessary?". The answer
> 
> This is not a concern if you already have N connectors,
> though. You may 
> use adapters or short coaxial jumper assemblies with
> differing 
> connectors at each end, as offered by DX Engineering,
> with custom 
> lengths available by telephone. These would cause
> negligible losses on 
> HF, and would allow you to experience the superior
> port-to-port 
> isolation of a DX Engineering RR-8 series Remote Antenna
> Switch immediately.
> 
> Let us know if you need any additional information. We
> look forward to 
> hearing from you.
> 
> Thank you and 73,
> 
> Rod Ehrhart - WN8R
> DX Engineering Customer Support
> 
>
----------------------------------------------------------
> 
> Joel R. Hallas wrote:
> > I agree with most of what has been said in support of
> UHF connectors for HF
> > and low VHF -- with two reservations.
> > 
> > 1. Many SO-239s provided as part of radio equipment are
> not up to the
> > quality of Amphenol units. In particular, the spring
> fingers of the socket
> > for the male pin loosen over time to the point that the
> connection becomes
> > less than solid. This is particularly a problem if the
> connector is used
> > repeatedly. I usually replace with Amphenol units, if I
> can get to them.
> > Another great option is the Oak Hills BNC kit, designed
> to fit the hole
> > pattern of the SO-239.
> > 
> > 2. The other potential problem with UHF connectors, in
> my opinion, is the
> > integrity of the shield connectivity through the
> connected pair. If the
> > backshell loosens, there is no longer a solid
> connection either at the
> > toothed parallel portion, nor through the backshell.
> This can be an issue in
> > mobile or other high vibration environments and has
> caught me many times.
> > Note that a type N, C or BNC pair makes it's shield
> connection through the
> > inner spring tension sleeve, maintaining contact almost
> until the pair
> > separates. The backshell is just used for mechanical,
> not electrical,
> > purposes.
> > 
> > FWIW
> > 
> > Regards, Joel
> > Joel R. Hallas, W1ZR
> > 
> >
>
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