[R-390] RF Coaxial Cables

[n4buq at knology.net]

On Thu, 13 Jul 2006 14:43:11 -0600, DW Holtman <future212 at comcast.net> 
wrote :

> Barry,
> 
> Do you have new connectors, or you going to re-use the old ones? I'm a 
> little nervous about re-using the old connectors. If I screw one up, I 
> don't think I would ever find a replacement. The R-391 that I'm working 
> on now, like the R-390 uses standard BNC connectors I wish they had 
> stuck to the BNC's. I guess if push came to shove, I could put BNC 
> female connectors in, but it would have to be a dire situation for me to 
> modify the sheet metal in the the RF amp and If Amps.
> 
> Any information on how you are going to do the connectors would be 
> greatly appreciated.
> 
> best,
> DW Holtman
> WB7SSN
> 
> 
> n4buq at knology.net wrote:
> 
> >A few months ago, I started looking for some suitable cable to replace 
the 
> >output coax from my PTO as well as the other RF connections to the IF 
deck 
> >and crystal deck.  These have gotten rather worn in my radios and worry 
me 
> >every time I start fooling with them.  They may be electrically okay for 
> >now, but with the jacket being broken in a few places, it makes the 
cable 
> >kind of weak in those areas and I'm constantly worried about the inner 
> >jacket failing at those same weak points.
> >
> >I finally found something that looks to be a perfect fit.  Some have 
> >suggested using RG178, but its OD is typically 0.072" or smaller and, as 
> >such, the clamp in the PTO won't grab on the jacket of the coax.  I made 
it 
> >work with a little shrink tubing, but wasn't really satisfied with it.  
> >Besides, RG178 is a bit small looking to be a replacement for the 
original 
> >cable.
> >
> >Some have suggested RG174 but with an OD of 0.100" or greater, it won't 
fit 
> >in the various connectors.
> >
> >The original cable's OD is about 0.084" and the coax I have is about 
0.083" 
> >so it should work just fine.  It is PTFE (Teflon(r)) inside and out with 
> >silver-plated braid and inner conductor so it should be a very nice 
> >replacement cable.
> >
> >I stumbled across this on eBay and the fellow is selling another lot of 
it 
> >so if you're interested I can point you to the auction.  I don't know 
how 
> >much of it he has in stock, but I've emailed him to see.
> >
> >Also, if anyone's interested, I may sell some of mine.  I had to buy 25' 
> >and don't plan using all of it, but I don't know if/how much I'll have 
left.
> >
> >I'm just happy to finally have a good cable and hope I can get all of 
them 
> >replaced.  The ones in my Motorola are quite ratty.
> >
> >Regards,
> >
> >Barry - N4BUQ

The connectors aren't a big deal.  I resoldered one on my first radio and 
will resolder this one.  The hardest part is opening the back of the 90-
degree connectors.  Some of them don't like to come apart.  You can 
sometimes heat them up with a larger soldering iron and tap them on the 
workbench (wear protective eyewear when doing thas as the solder can and 
will splatter).  This one was stubborn and a rather tight fit without the 
solder.  I had to resort to a broken dental pick and heat to get it out.

Once you have it apart, the shield is a mechanical connection with a little 
compression thingee and the center conductor solders to either a pin (in 
the case of the 90-deg connector) or (and I'm assuming this) the center of 
the male connector much like a standard BNC connector.

If you do tear one up, though, I believe Fair Radio still sells them.

Good luck,

Barry - N4BUQ