A Rogues Gallery of Panel Mount UHF Jacks

Discussion in 'Amplitude Modulation' started by K5UJ, Nov 21, 2020.

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  1. K5UJ

    K5UJ Ham Member QRZ Page

    rogues_gallery_UHF_jacks - 1.jpeg
    I was dumping 900 watts of RF into a dummy load, but I wanted to see it on an oscilloscope so I got out my trusty homebrew line section and put it in. It's nothing but an aluminum project box with UHF jacks on the ends, a copper tube inside between them, and a BNC on one side connected to an AWG 14 wire going in and running parallel to the copper tubing. After 10 minutes I killed the RF and pulled out the line section and set it aside. A few days later I saw the line section on a table and noticed one of the UHF jacks looked odd. Upon inspection the dielectric looked carbonized, and the opposite end jack was starting to show signs of heat stress as well. Let's take a look at an assortment of jacks to see what happened. the_bad_guys - 2.jpeg
    the_bad_guys - 1.jpeg
    First are the bad jacks. These were once nice pretty items for sale at some hamfest. They appeared to have silver plating, Teflon dielectric, and pin cups that appeared to be gold plated. They looked great sitting in a bin on a vendor's table at a hamfest. What could go wrong? In reality these were poor off-shore junk.

    the_good_guys - 1.jpeg
    Now the jacks wearing white hats: On the left is a genuine Amphenol jack. You can't go wrong with this one. It's dielectric is PBT polyester, and it's nickel plated zinc and takes solder easily, but it is machined perfectly to mate with a UHF plug, and the pin cup has four fingers that really grip the plug pin. It will handle power indefinitely or at least, indefinitely in ham time. The Teflon dielectric jacks are made off-shore and closely resemble the bad jacks, but look closely and you'll see that the pin cup inner diameter isn't quite as wide, allowing them to also make fairly good pin contact (but I'm throwing them out anyway because fairly good isn't good enough).

    In the case of the bad jacks, what happened is that the machining of the pin cup was so sloppy and inferior that it didn't grip at all. I put a plug in one without screwing on the collar, and held the assembly vertically with the jack facing down and watched the plug fall out and hit the floor. Amphenol jacks provide such a tight grip they easily pass this test. A poor grip of course means resistance, which means heat, and after 10 minutes of continuous RF, that means a carbonized dielectric.

    I learned my lesson and have been going through the irritating process of rooting out the bad jacks in my homebrew gear and replacing them with Amphenols. The next time you are at a hamfest and see the nice pretty and inexpensive jacks, think twice. At least, carry a UHF male with you to check the seating of the pin in the females before purchase.
    the_good_guys - 2.jpeg
    KD1AM, W2VW and AG5CK like this.
  2. K6CLS

    K6CLS Ham Member QRZ Page


    How would I recognize a properly sized male connector?
  3. K5UJ

    K5UJ Ham Member QRZ Page

    I have not encountered one that was out of tolerance. I've slobbered solder down the side and made one too wide but I've never seen one that was too thin. Get a genuine Amphenol (it should say Amphenol on it) and you'll be okay.

    But Amphenol, the UHF connector gold standard has a QC problem also. I put a male on RG213 and discovered the ridge ring that bends inward on the back of the collar so it pulls the body into the female as it is threaded on, was flawed. It didn't bend in far enough. The body of the UHF male has a short threaded ring behind the solder holes, and the collar ridge was threading through this and coming off the connector instead of pulling it into the jack as it's threaded on. I could push the connector body all the way into the jack but tightening the collar didn't force the plug in and stop, it would keep turning until it went past the stop ridge. In that state you could pull out the plug and leave the collar threaded on the jack.

    This really sucks because that cable run is installed, so soldering a new plug on the end will mean bringing all the solder gear to an inconvenient location. I don't like crimp jobs but in this case one would make my life easier.
  4. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Back in the early 80s I took a job at a radio repair shop. The first day the boss threatened to dismiss me because I didn't know how to attach a PL-259 to a piece of coax, without having to look up step-by-step instructions and a pictorial digram. The reason I didn't know was that I had always used open wire transmission lines and had never had any use for coax. The boss changed his mind after I fixed a radio in a an hour or so, that had been sitting in his shop for weeks because none of his other employees could figure out what was wrong with it.
    AG5CK likes this.
  5. G0GSR

    G0GSR Ham Member QRZ Page

    I still don't know how to attach one :)
    I refuse to use them!
    N0IOP likes this.
  6. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    The absolutely most infuriating thing at least for me to attach is a BNC connector to coax. I have never had any success with them, getting all the little rings, washers and rubber O-rings just right, even with a brand new connector and illustrated step-by-step instructions. If I need to attach a male BNC connector to something like a piece of RG-58 or RG-59 in my shack, such as for connecting the VFO to the transmitter, I'll look in my junkbox for a scrap piece of coax with one already attached, cut it about 2" from the connector, then splice that short piece to the end of the one where I want to attach the connector. It doesn't look pretty, but it works, and saves me a lot of frustration.
    K6CLS likes this.
  7. K5UJ

    K5UJ Ham Member QRZ Page

    It took a long time for me to figure out how to put on a UHF plug. I can only do it with RG213 because it has a dielectric that doesn't immediately melt. For every ham, there's a way to do this and threads on this topic usually wind up with hundreds of posts on "here's how I do it" followed by devolving into arguments about which way is better and name calling.
    You must run open wire line everywhere like Don and Cid K8JLY. That's awesome but the job of converting everything over to that topology here would be mind blowing. I'm therefore, a junkie addicted to coass.

    I've put on BNC female panel jacks but never a male on coax. I guess I've always had a lot of BNC jumpers on hand for oscilloscopes that came with equipment and never needed to make one.
  8. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    There isn't a sprig of coax anywhere in my transmitting antenna system, from the tank coil in the transmitter all the way to the radiating element of the antenna.

    I do use a coax transmission line for my Beverage receiving antenna: about 140' of RG-213 and the rest RG-6. The 50Ω to 75Ω splice doesn't hurt anything; a fraction of a dB loss in a receiving antenna doesn't matter, since the receiver has an excess of RF sensitivity anyway.

    I use smaller gauge coax to couple my VFO to the transmitter, as well as to feed the RF sample taken off the feeders to the monitor scope. Those mostly use BNC connectors or RCA plugs. I already explained above how I attach male BNC connectors to the ends of the coax. I need to purchase a crimping tool and some crimp-on connectors. That's one application where I think crimp-on would be better.
  9. W2VW

    W2VW XML Subscriber QRZ Page


    Cheap jacks with cheap insulation.

    The good stuff is PTFE.

    Old plugs can zorch and make it look as if the jack was the source of failure too.

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