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SO-239 Concerns -- Another Perspective

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Joel R. Hallas

SO-239 Concerns -- Another Perspective

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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alsopb

Re: SO-239 Concerns -- Another Perspective

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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>

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P.B. Christensen

Re: SO-239 Concerns -- Another Perspective

In reply to this post by Joel R. Hallas

> 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...

I have nothing against the SO-239s used in the K3, although during assembly,
I decided to use Amphenol connectors as a substitute. I also like using
Amphenol-branded SO-239s on custom projects. The added expense for the name
is usually a small percentage of the total project cost.

> 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.

And that's my objection to the UHF connector combination. For example, I
gained 0.75 dB in the shack on 10m simply by re-tightening a series of
connectors that seemed hand-tight. After installing some new equipment, I
decided to conduct a loss budget analysis from the transceivers to the shack
antenna output ports and all points in between. I was seeing too much loss
through the system.

When I used slip-joint pliers and ensured that the teeth of all '259s mated
with the '239s, measured shack losses were minimized. I have a lot of
switching here and with switching, there are many UHF connectors.
Electrically, the sole conduction mechanism of the PL-259 is the inner
surface of the threaded shell and to Joel's point, the threaded shell is
only press-fitted against the connector body. A low-loss connection path is
wholly dependant on the force of the shell to the body and the shell against
the 239 threads. It's a miracle the UHF connector works at all.

Paul, W9AC

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n7ws

Re: SO-239 Concerns -- Another Perspective

In reply to this post by Joel R. Hallas

I'm not Joel, but I'm going to respond.

Although I've previously argued that UHF connectors are fine for HF applications and type N isn't necessary, that doesn't mean that type N is unsuitable.

If type N is suitable for high power (I've used them at 1.5KW on 2M) on VHF-UHF, then why would they not be suitable at HF?

As a matter of fact I do use them on HF on my 1/2" Heliax feedline and will use them again when I get around to replacing the lines with 7/8" Heliax. I have also used N-connector Transco relays for antenna selection. The only downside to them is that they are 28V (and expensive unless you find them surplus)

Of course they have to be assembled and mated correctly, but that is true of any connector.

Wes N7WS

Joel,

How do you respond to this blurb from a
"DX Engineering" guru?

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Eric Scace K3NA

Re: SO-239 Concerns -- Another Perspective

In reply to this post by Joel R. Hallas

The "turn of the screw" method for tightening (used for many nut and
bolt fasteners) is appropriate with UHF connectors: firm finger tight,
and then use a tool (pliers) to tighten an additional quarter-turn.

If you can remove the shell without using a tool, it's too loose.

-- Eric K3NA

on 2010 Jul 23 09:23 Joel R. Hallas said the following:

W8JI

Re: SO-239 Concerns -- Another Perspective

In reply to this post by Joel R. Hallas

> 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.

Nearly all problems I've seen with female contact flaring were caused by
males that have solder on the outside of the pin, increasing pin diameter.
I've seen a few really cheap females, too.

I've got many dozens of connectors in my system, and N's are just as much or
more problem overall. So are BNC's, especially when subjected to high
humidity.

The only nearly perfect connectors are DIN, type-C, or EIA flange
connectors.

> 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.

Actually the shell provides a backup for continuity in the N, and while I
have fewer shell tightness problems I have a whole lot more center pin
issues or pin arc-outs from lightning or wrong antenna selection.

The thing I like best about type N's is I can chuck them up in my lathe, cut
the female a little on the end, bore out the center, press the guts from a
Teflon SO-239/PL259 in the middle, and convert them to UHF type connectors.
I convert all my surplus heliax connectors to UHF style. :-)

I avoid shell tightness problems by LIGHTLY using pliers, and snugging,
backing off, and resnugging two or three times. That way I make sure the
locating bump on the male is in the female notch and everything is flat, and
there is some distortion on the shell to keep it locked. Anyone who works on
cars understands that something has to slightly stretch or distort to lock a
threaded connection. Finger tight or wrist tight will never hold under
temperature or vibration, but a slight snug with piers will.

I probably have a few hundred connectors in the system. I can't recall the
last time I had a tightness or water issue with a UHF, although I sure have
had pin problems in N's. Mostly due to someone picking the wrong antenna at
full power....or lightning. Most of the N's left in my system are being
replaced as they fail.

73 Tom

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Eugene Balinski

Re: SO-239 Concerns -- Another Perspective

In reply to this post by alsopb

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 <[hidden email]> 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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> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list:
> http://www.qsl.net/donate.html
> >
>
>

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