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[KA3QOT]

Hello All,


I have a new (less than three months old) ICOM IC-706 MK IIG. When I attach a new Radio Shack PL-259 cable (with crimped connectors) from my SWR meter to the SO-239 on the back of the rig, as soon as I insert the center piece and start screwing on the shield, the signal drops appreciably and I can barely hear anything at all. As soon as I loosen the shield and barely have it connected to the rig, the signal reappears at the proper volume. The cable has no shorts.


When I tried an older cable with soldered-on connectors, the signal stays loud until the very last turn of the shield when the signal drops similarly to the new cable which has crimped connectors. It has no shorts as well.


Any ideas on what may be causing this?  One guess is that the center pin of the connectors may not be thick enough when making the connection. Could the SO-239 be bad? Is it safe to operate with the shield not fully connected? I have a low SWR with it < 1.25:1.


73,

Dennis KA3QOT

[KM5WX]

Sounds like a defective coax cable! Take an ohm meter if you have one or can borrow one and check for continuity between the center pin of the cable and the outside. You know the part that's got the shield connected to it. If your meter shows continuity the cable is shorted and needs to be returned to the store. I generally make up my own jumper cables but I've run into this problem several times lately with commercially made cables. Not Radio Shack but another brand. Personal opinion (and yes I know we all have those! For the smart aleks out there just waiting to make some kind of comment about it, rather than ELMER thefella) I don't ever rely on a crimped on coax cable for my Ham gear!! Take Care & 73 Rich KM5WX

[RobertKoernerExAE7G]

What happens when you connect the antenna directly to your rig?

[KB0NLY]

Just my guess and two cents worth, the radio shack cables i have deealt with before seem to have a big problem with mating with the SO-239 connectors more than they would want to admit.  The radio shack crimped on PL-259's have a tapered center pin which doesn't leave a whole lot of contact area to the insides of the SO-239.  I have had similar experiences with radio shack's scanner antennas that include the coax, and usually ended up chopping off the connector and soldering on a good ol' silver plated PL-259 to get the contact back where it should be.  You could also try taking a small flat screwdriver or something similar and carefully bending the four tabs of the SO-239 back in till they all meet on the sides to tighten it back up, a common problem i have seen with radios that have been connected up a few times is that somewhere along the line a PL-259 with to much solder on the pin was forced in and loosened up the SO-239 so other connectors don't make good contact.  I can't really comment on whether or not leaving the shield disconnected on that particular radio will hurt anything, but it may cause the antenna performance to suffer if the outer shield at the antenna is isolated from ground at the feedpoint.  Another thing to consider would be feeding a dipole or yagi, ie. balanced antennas etc.

Scott,  KBØNLY

[KB0NLY]

Reading your post once again makes me also suspect the SWR meter, have you tried connecting the antenna directly to the radio instead?  Also what about the connectors going in and out of the SWR meter are they also the crimped on type?  Check all the connections and tighten up the SO-239's and see what happens.

Scott,  KBØNLY

[WA9SVD]

Check with an ohmmeter that the "New R-S" cable has continuity of "shileld to shield" and "center pin to center pin" at both ends of the cable, as wll as no continuity from shield to center conductor.  It could be a bad crimp, broken shield, or broken center conductor.  (Never did like those crimp connectors... LOL)