[TowerTalk] Selecting Coax connectors

[Roger (K8RI) on TT]

I see a lot of preferences from UHF, To :N: type, to DIN, but for the 
average ham, does it make a difference?

Take UHF, essentially the design is crude and they are cheap! The loss 
figures are high, but those figures are for frequencies few hams ever 
approach and the connector specs say up to 300 MHz and 500 volts.. On HF 
the loss is minuscule. The arguments are those figures add up and they 
do, but it's still a very small value. With SO2R and remote antenna 
switches, plus the rotator loops and pigtails to the antennas I've 
counted as many as ten connectors between the rig and antennas, but the 
loss was barely detectable. Impedance bumps? Yes, they are there, but 
what do the mean? Added up for the 160 through 10 meter bands, they are 
insignificant. I can see where the reflections "might" make a difference 
with digital modes, but it's still very small.  The only down side I can 
see is the learning curve for the solder types.  "Probably" the average 
ham does a miserable job of soldering them, over heating the connector 
and coax when soldering the braid, turning the coax dielectric into a 
mass of goo, while getting solder on the exterior of the center 
conductor pin.

Off brand UHF connectors: Many adherents say Amphenol 
http://www.amphenolrf.com/connectors/uhf.html  is the only way to go and 
they do have reasonably good quality control.  As I said at the 
beginning, the original connector design is crude, but it was designed 
long ago.  They are easy to make, so there are many off brand connectors 
of various qualities. Amphenol lists both Nickel and silver finish as 
well as a whole slew of dielectrics from Phenolic and Styrene, to Teflon 
and more.  The off brand stuff varies, but a good inspection by the Ham 
who knows what to look for, there are good ones out there.  The typical 
Ham would do better sticking with known brands, but with the UHF design, 
the important point is whether the particular connector will pass the 
test of time.  OTOH even top-of-the-line connectors are inexpensive and 
if you purchase very many, the discount makes them about the price of 
the stuff you see at the swaps..

Installed according to the directions (braid on the inside and properly 
soldered), the connector will provide reasonable strength.       NOTE 
UHF connectors are not weatherproof!

N-Type. Not for those running "high power". By high power, I'm nor 
referring to 1500 watts. 
http://www.amphenolrf.com/connectors/n-type.html  OK, so they represent 
less insertion loss with less impedance, but what do they gain us at 160 
through 10?.  Amphenol lists them "These connectors are used in all 
systems where excellent RF and mechanical performance is critical."  I'm 
not sure by what they mean when they refer to mechanical performance, 
but I've never found the typical N-type connector I couldn't pull off 
the coax with my hands (crimp type excepted) In my experience, They have 
two limitations.  Mechanical strength and center pin migration are the 
problems I've seen.

Mechanical strength is pretty much self explanatory. Center Pin 
Migration? On vertical runs, the center conductor in many, if not most 
coax cables will slowly move downward  This tends to pull the center 
pin, in on the top connector, and push the center pin out on the bottom 
connector. This doesn't happen with connectors where the center pin is 
captive.

DIN (7-16) connectors. https://en.wikipedia.org/wiki/7/16_DIN_connector 
Is kinda like an N-connectors on steroids. The 7-16, or 7/16 is the size 
of the center pin (7 mm) and the ID of the outer connector (16 mm) They 
are still a bit on the expensive side and not for the ham who purchases 
connectors at swaps to save a buck, but " It is among the most widely 
used high power RF connectors in cellular network 
<https://en.wikipedia.org/wiki/Cellular_network> antenna systems." and 
"The 7-16 DIN connector out performs other non-flange options, such as N 
connectors <https://en.wikipedia.org/wiki/N_connector> or BNC connectors 
<https://en.wikipedia.org/wiki/BNC_connector>, when it comes to 
interference and intermodulation rejection or higher power handling at 
RF frequencies.^[1] 
<https://en.wikipedia.org/wiki/7/16_DIN_connector#cite_note-UTC-1>" 
(Quoted from the above Link)

Adapters: Amphenol lists 689 adapters. Pages from  
http://www.amphenolrf.com/adapters.html However, other than the most 
common it's likely the distributor would need to special order them.

Crimp, Vs solder. Other than requiring a specialized crimp tool, crimp 
connectors tend to be more uniform, faster to install, and mechanically 
stronger than the solder type.  Properly adjusted cable prep tools 
(strippers) really speed things up and present identical cable ends to 
the connectors with the proper dimensions. Nearly identical crimp tools 
can be found with widely varying prices.  One crimp tool with two sets 
of inserts can cover cables from RG-58 through RG-8 (LMR-400) sizes.  
Depending on the vendor, nearly all connectors for these cables are 
available in solder or crimp versions.

NOTE The RG designation has not been a specification for many years. It 
simply refers to cable sizes. Nothing more.

So the question is, why would the average, or typical ham need anything 
other than the crimp, or solder, UHF connector?

A SIDE NOTE: on weather proofing: There are several approaches to 
weatherproofing. One uses vinyl electrical tape wound sticky side out 
over the connectors, to keep the weatherproofing material (coax seal, 
various self vulcanizing tapes, and  "flooded" heat shrink tubing) from 
sticking to the connector Flooded heat shrink tubing has a layer of hot 
melt glue on the inside. If you don't want the glue to stick to the 
connector, a film of Silicone grease or mold release agent, will allow 
for a seal without the glue sticking to the connector. Just don't get 
any on the coax jacket.  Me?  I make sure it's all clean and bond to the 
whole works.

By bonding to the coax jackets and the connectors, the flooded heat 
shrink tubing makes for a very strong mechanical connection.

One other comment: In over 55 years as a ham, I've only seen two bad 
connectors from Amphenol. I can't say that  for the few "brand unknown", 
I've purchased from swaps.

73

Roger (K8RI)


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