Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
4NEC2?
Jeff Liebermann wrote:
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. LOL! That’s a great story, cheers! :-D -- STC / M0TEY / http://twitter.com/ukradioamateur |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
a little 4nec2 help? | Antenna | |||
Anybody tried 4nec2 on Vista ? | Antenna | |||
New 4nec2 version | Antenna | |||
4nec2 and linux ?? | Antenna | |||
4nec2 question | Antenna |