Saturday, August 29, 2015

Building the Coax Cables for the 6-M Station

W5SWL Connectors
Trying to keep the total feedline loss to a minimum, I decided to use LMR-600 to connect the radio to the amp, LDF4-50A (1/2-inch) Heliax and AVA7-50 (1-5/8-inch) Heliax to connect the amplifier to the top of the tower and FSJ4-50B (1/2-inch) SuperFlex as the rotor loop to connect to the antenna.  The LMR-600 has a loss of 0.5 dB per 100 feet, the LDF4-50A is 0.463 dB per 100 feet, the AVA7-50 is 0.137 dB per 100 feet and the FSJ4-50B is 0.724 dB per 100 feet.  My calculations indicate that I should have a TOTAL feedline loss of 0.821 dB between the transceiver and the connection to the balun at the antenna.   This includes an approximate 0.0025 dB of insertion loss for each connector at 50.1 MHz.

The first cable I built was using the LMR-600.  It is the cable to go between the UHF antenna connector of the K-3 transceiver and the "N" INPUT connector of the amplifier.  I purchased the connectors (one UHF male and one "N" male) from W5SWL on eBay.  You can see a photo of the two connectors on the right.  They were really inexpensive ($6.95 each) and look to be VERY well made.  The Times Microwave TC-600-UMC UHF male connector for LMR-600 costs $64.95 at The Antenna Farm so these W5SWL connectors saved me a LOT of money!

Center Pin Soldered on UHF Connector
The first step was to convert the dimensions given by W5SWL for the connector installation from decimal inches to fractional inches (as I did not have a decimal ruler - Hi!)  Once that was done, I proceeded to cut the end of the LMR-600 cable to the proper length.  This cable is much stiffer than RG-213 with a solid center conductor (copper-clad aluminum) nearly 3/16" in diameter.  Cutting it was a little more difficult than usual but not bad.  Combing back the braid was routine but when I tried to tin the center conductor, I ran into a problem.  I apparently applied too much heat (although I thought I was being careful) and the center conductor melted right through the foam dielectric.  On my second attempt, I only soldered one side of the center conductor at a time and let it cool in between heat applications.  I then tinned the inside of the center pin to make it even easier to attach the two together.  This method seemed to work well as I just heated the center pin with the soldering iron (holding it with needle nose pliers) and pushed it onto the center conductor.  A little more heat and a touch of solder was applied to the pin and it was securely attached.  Screwing the connector body together was a snap.  It worked just like a normal clamp-on "N" connector.  Then I added some heat shrink and a label to finish the installation.

Finished UHF Male Connector
I proceeded to install the "N" male connector on the other end of the cable.  As I always seem to have trouble installing "N" connectors, this one did not disappoint!  It took two tries to get the dimensions correct to allow the center pin to extend the proper distance inside the connector.  But, I got it done.  Click on any of the photos to see a larger image.

The next cable to be constructed was the FSJ4-50B (1/2-inch) SuperFlex jumper from the amplifier to the LDF4-50A (1/2-inch) Heliax that runs from the shack to where it can connect to the 1-5/8-inch Heliax.  I purchased a pair of Andrew F4PNMV2-HC N Male connectors on eBay that were NIB (New in Box) for $27.10 delivered. 

Prepped End of SuperFlex
Here Mr. Murphy reared his ugly head!  Years ago while assembling a 4-bay array of 432 yagis for EME (Moonbounce), I purchased the Andrew prep tool for the LDF4-50A 1/2-inch Heliax.   Unfortunately, that tool will NOT work on SuperFlex which has different dimensions.  BUMMER!  It took me about 3 hours to put on the first connector and I was really stressed doing it.  I tried to find someone who had the right tool to no avail so I had to claw my way through the second connector installation without the proper tools.  Since I had learned some things in my first few failed attempts, this time it only took about 1-1/2 hours (along with Evelyn's help) to install the second connector.  On the left below you can see the cable prepped and ready for the connector to be installed.  On the right is the finished connector with heat shrink installed.  It makes for a nice finished connector.
Installed "N" Male on SuperFlex

Later, in setting up my antenna on a temporary basis, I needed to install a couple of "N" male connectors on a length of LDF4-50A and - HEY, I had the proper tool.  It only took about 2-1/2 hours to install BOTH connectors and I'm proud to say they are done right!  Running 1,500-watts through that cable has been flawless.

UPDATE - When I went to install the beautiful LMR-600 cable I made above, I became truly depressed!  As I tried to screw the male "N" connector onto the amplifier, it seized up and would not turn.  I could force it to turn with a wrench but it was effectively no longer a working connector!  I am really sure I did nothing to screw up the installation of the connector, it is just that the money I saved with the W5SWL connectors turned out to be a false savings.  Now I'll have to purchase a REAL Times Microwave "N" male connector and cut the bad one off then install the one I should have put on to begin with.  Live and learn!

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