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[TowerTalk] Connectors--Weak Fingers

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Subject: [TowerTalk] Connectors--Weak Fingers
From: (
Date: Thu, 5 Apr 2001 06:14:55 EDT
In a message dated 4/4/01 6:52:41 AM Pacific Daylight Time, writes:
 Hi Ian - -
 The silver plated PL-259's are DEFINITELY easier to solder.  Texas
 Towers ( used to carry the good Amphenol
 PL-259 connectors, and I assume they still do.  In short, they're
 definitely worth the extra money.   
The regular brass PL-259's are very easy to solder if you drill the holes one 
drill size larger and then beveling the hole.  It exposes clean brass also.  
Adding soldering paste makes it even easier.  It's faster, takes less heat 
and the solder grabs more shield and an idea procedure for pollyfoam coax.  
Tinning the shield as has been suggested is a good idea.  To keep the overall 
diameter small enough to get into the connector after soldering, wrap the 
shield with #30 or smaller bare wire.  If you get too much solder on it, use 
a file.   I had an article on all this and other related topics in CQ about 
35 years ago.

Type N connectors have a problem outside.  I used one on RG-14 coax with a 
solid center wire.  In cold weather the center solid wire contracted to the 
point of disconnecting the pin.  If there is only .01" contraction of the pin 
after initial shoulder to shoulder contact, the larger diameter shoulders 
aren't touching and only the small pin and 4 fingers make contact--potential 
trouble at high power.

Another problem with soild wire,  just gravity on a vertical run can pull the 
center wire down enough to brake the critical shoulder to shoulder contact.  
If the 4 fingers pressure contact only carry the RF, higher powers can heat 
them up to a point were they tend to lose their pressure and that creates 
more heat.  I make sure the 4 fingers are flexed tight when first used.  I've 
inspected them later after a slight pin separation and power level tests to 
satisfy me what was going on and they lost their tension to the center.  They 
will take 5 KW and 10A with pin shoulder contact.  I use fine steel wool on 
the pin, the pin shoulders, inside the fingers and the shield contact area 
inside the connector before use--in all connectors.  I even lightly buff the 
copper shield that is pressed against this area.  In time the rubber 
compression ring over the pressure ring begins to dent the coax dialectric 
and reduces the pressure on the shield.  The compression ring on top can be 
retightened.  They should be dissasembled from time to time, checked and 
cleaned.  Look for dents in the coax dialectric, reduced 4 finger pressure 
and carbon paths.  For this reason type N's don't work well with air 
dielectric or polly foam coax.  

Henry uses the Type N female output on their 8K rig.  Inside the shack there 
should be no trouble if the male connector is properly prepared.  Just do the 
heat test with the fingers on 10M regularly.  

PL-259's have a full time and much longer, larger diameter 4 finger contact 
area (at least 5 or more times) and the center wire is soldered to a "secured 
pin."  Cold weather can't move it in and out of the female pin.  The shield 
is soldered also whereas a type N has a pressure contact for the shield which 
lessons in time.  I alway clean the pin, inside the female fingers and 
retension the fingers if necessary before use.  I've never read of anyone 
suggestsing this.  I started coating the pin and fingers with silicone greese 
and it stays clean outside.  At legal power levels it works just fine--year 
after year.  I coat the PL-259 and SO-239 threads with Silicone grease also.  
Years later and or in cold weather it comes apart easily, they are both still 
clean and show no evidence of heat. 

If you run more than 1 KW into Type N's outside use PL-259's.  If you use 
more than 5 KW into PL-259's in or outside or can have high SWR's, use the 
next bigger connector  or eliminate the connector with a direct connection 
with bolts, soldering lugs and weather proffing   It's mandatory to keep the 
water out of the PL-259s and I spray acrylic spray around the center pin 
insulator a couple of times, let it dry and then RTV silicone rubber.  I use 
removable shrouds over any exposed coax connections also.  On vertical 
antennas where the SO-239 is on the bottom pointing down, I remove it and add 
a shroud made from an aluminum cat food can 1 1/2" high or 1/2 an aluminum 
pop can with the edges bent over to prevent cutting your hand.   It keeps the 
water from running down the threads into the connector.  I also epoxy a 6 
inch length of .875 aluminum tubing that I knurled to the PL-259 shell that 
allows one to really tighten or remove it with ease in particular in tight 
places.  No plyers needed.  

A very smart Mfg should make a longer knurled outter shell for the Pl-259's.  
Any mfg that installs a SO-239 without blown rain protection is guilty of 
ruining a lot of coax--after the first rain.  Many find water in a lot of 
connectors and sometimes in the shack after just one rain and changes of SWR. 
 With my procedures I don't and I have some good coax 40 years old that has 
the same loss year after year when I do my yearly loss tests.  One version of 
RG-8AU coax has a "non migrating plasticizing" agent in the outer covering 
that prevents cracking and water entry claimed for 20 years.  I have some 
older that this that is still good coax.  With regular RG-8 the plasticizing 
agent migrates to the center dialectric changing the VP, the color of it, the 
loss and allowing cracks in the outside covering.   Buy the good stuff, 
install connectors properly and protect the connection outside from blown 
rain and it will last a long time.  My coax investments have been very very 
minimal over some 50 years.  I started with open wire line and still use one 
length of open wire line 60 years later.  I never have to check it for loss.  
The rain keeps the insulators clean.  With the proper tuners like the Johnson 
Match Box properly used (and without only opinions of it's capabilities),  it 
transfers more RF to and from the antenna than coax ever will and at the 
least cost.  You just have to learn how to use it.  

NOTE!  With link coupled finals, a link of the right number of turns with a 
series Xc, it  will match any balanced or unbalanced load from 30-1000 ohms 
at the end of any feedline--WITHOUT A TUNER.  I still have my old Pr-813's 
rig I'll be using with open wire line in the rain and snow with the least 
loss.  There are simple matching techniques to 450-600 ohms at the antenna 
that also allow a flat open wire line (1:1 SWR) and eliminate the need for 
certain 1/4 or 1/2 multiples.   I do use insulated open wire line now.  I got 
some great wire from Boeing Surplus.  

Over 35 years ago I purchased 4000' of a special 50 ohm Teflon coax for 11 
cents a foot from Boeing Surplus.  It cost $1.75 then.  It is silver plated 
and 2 shields.  It's thin Teflon tape wrapped, then the 2 shields, some more 
thin tape wrap and then a Teflon outer coating--Absolutly Awsome Coax.  It 
has a .7 VP and about the same loss as pollyfoam.  It could take a lot of 
over power heat without any damage.  I have given some away and still have 
2000'.  I found at a flea market 250' of $3.75/ft solid Teflon center 
dialectric and dual shield new coax I couldn't resist at $1/ft.  That's the 
first RG8 coax I've purchased in 35 years.  I found a large prop pitch motor 
in great shape for $50.  I've enjoyed thoroughly converting it for higher 
speed as I did my first one some 50 years ago I still use without all the 
problems and needed Band-Aids many have with rotators today on TT.  Ham radio 
has a lot of constant maintenance and expenses if you don't select your toys 
properly.  k7gco

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