Thread: 4NEC2?
View Single Post
  #11   Report Post  
Old October 14th 18, 08:38 AM posted to uk.radio.amateur,rec.radio.amateur.antenna
Jim GM4DHJ ...[_3_] Jim GM4DHJ ...[_3_] is offline
external usenet poster
 
First recorded activity by RadioBanter: May 2017
Posts: 28
Default 4NEC2?


"Jeff Liebermann" wrote in message
...
On 13 Oct 2018 20:53:13 GMT, Stephen Thomas Cole
wrote:

Gareth once complained about a mobile CB set-up he installed in a 4x4
couldn't reach further than a quarter mile. That's all you need to know
about Gareth and radio.


He probably didn't need any antenna at 1/4 mile (400 meters).

About two months ago, one of my friends was complaining that the range
of his VHF/UHF mobile was severely limited. He decided that he must
have blown up his radio. I did a bench test of the radio and it was
fine. That left the vehicle power system, power cord, coax cable, and
antenna as the remaining potential suspects.

I inspected the electrical system and found that fuse on the negative
lead had blown. Why manufacturers persist in providing a negative
wire fuse will remain a mystery as there are very few positive ground
vehicles still in service and even marine radios with floating grounds
are scarce. I have no idea where the radio was getting its ground
return for reasons that will soon be obvious. I replaced the fuse and
continued looking for problems.

Next came the coax and antenna system. I have a nifty little gadget I
built that has been very handy for troubleshooting mobile installs.
It's an NMO antenna "connector" to UHF adapter.
https://www.americanradiosupply.com/opek-nmo-8-nmo-antenna-connector-to-uhf-female-so-239-adapter/
I remove the NMO antenna, screw this adapter onto the NMO mount, and
check for RF power. In this case, no RF as in zero, zilch, none, no
RF. However, at the radio end, there was 45 watts of VHF RF. So, the
coax must be the problem.

Fast forward an hour of fruitless testing and I'm still not seeing any
RF. Eventually, I run a simple ohmmeter continuity test between the
ends of the coax cable and find that it's open circuit. Huh? Unless
something has cut the cable (we have a local mouse problem), even a
defective coax cable will show end to end continuity.

I trace out the coax cable only to find two identical cables running
in parallel. That wasted another hour because all the multiple radio
cables were behind a workbench and a pile of junk in the van. One
coax cable had the RF connector at the radio end and nothing at the
other end. The other cable had the NMO connector on one end, and
nothing on the other end. I should have guessed but I had assumed
that the owner had done a VSWR test during the initial coax cable
installation. Apparently, it had been like that for several weeks
before the owner noticed that his VHF/UHF coverage was lacking. Since
he lives just below the local repeaters, that's somewhat
understandable.

So, if anyone asks if they really need an antenna, tell them no.



no idea why but that reminds me of a car I had that lost the engine earth
and it earthed through the accelerator cable which overheated and caused a
lot of smoke...just thought I would throw that in ....no idea why