Help, Need Diagnosis

[cassidy1190]

Today I had the highly acclaimed Diamond D130J discone installed 10 ft above my roof (about 40 ft above ground). Everything was excellent; a contractor that normally installs HDTV antennas properly mounted the apparatus on my chimney with a 10 ft mast, grounded it and ran 75 ft rg8x coax to my radio setup. He used solder on pl259 connectors and on the receiver end I put a bnc adapter.

Like I said all was well...that is until I actually turned on the radio. With high hopes of pulling in local approach control and some nearby rcags (all VHF air), I found to my disappointment I couldn’t even hear the AWOS at the local airport which comes in belting loud and clear through a stock telescoping antenna.

So I ask, what gives? All the right pieces are in place it seems. Is 75 ft too long for rg8 and should I think about a preamp? Could I really be losing that much signal with my BNC adapter? I can’t imagine anything on the antenna end that is causing me trouble. I assembled it to spec and all components are tight as can be. The only thing that seemed off to me is that the coax doesn’t say rg8x exactly, but mini 8/u. From what I can seem to conjure online there is not a difference.

I am at my wits end. This project cost me over $500 total. How can I make this work?

 

[mass-man]

Hmmm, from the beginning! Have you put a continuity tester to the center pin and shell of the coax connector? could tell you if the thing is really assembled correctly. Was the coax new? Have you checked the BNC adapter? Is the center pin there? I know, sound goofy, but they have been known to fall out. Have you tried the antenna on any other frequencies...something like the NOAA broadcasts make an excellent test broadcast.

Did you check the antenna before it was installed on the roof? Could be a bad connector there...how about the coax connector up top. Is it plugged in and seated totally?

75ft. is not too long for VHF freq...the BNC adapte would not attenuate that much...and the coax is the same.

It sounds like instructions from the grade school teacher, but start at the beginning and go over every possibility. Not sure if you can get to the roof and check there...it may take the install guy coming back. And if the thing does not work, he should.

 

[cassidy1190]

Thanks for the fast reply! And please don't hesitate to sound like a grade school teacher; this is the kind of thinking that works. I did think to try the NOAA channels, but they are no better, if not worse, than with the stock. Here is something interesting though...An 800 MHz trunked system in my area is coming in at around 66-70%, way more than with the stock antenna, and almost as much as an 800 MHz Yagi which is aimed at this particular tower. Unfortunately I don't have a continuity tester, but could this stand alone reception of 800 MHz be a hint that I am having continuity issues?

My guy is actually coming back this week, free of charge of course. I'll definitely have him take down the antenna so we can get a good peek at it. Unfortunately, being a TV person, he doesn’t know too much about radios. I just needed someone who could properly ground an antenna and go up on the roof for me. I really didn’t know who else to go with.

EDIT: Hey found a continuity tester! just need to learn how to use it properly now haha...

 

[mass-man]

The continuity tester should have two probes, red and black. Turn the thing on, touch the probes together and a LED will glow, a tone will start something to tell you have continuity between the two probes. Now touch the center pin of the PL259 and the outer shell. If you get continuity, then the connection is bad. Often just a tiny piece of the outer braid will touch the center pin and it won't work right. If you find a problem at the connector you can save the hassle of taking the antenna down!!!

As for it hearing a 800mhz system OK, that is a head scratcher...

 

[cassidy1190]

well how about that...I toched the probes to the center conductor and outer shell and wham, up went that needle! looks like the guy doesnt know how to solder haha. now mind you I do have the coax connected to the antenna while I ran the test. There is no continuity in the antenna is there? From what I have learned from basic home brews that shield never comes into contact with the center conductor.

 

[LtDoc]

There is no 'continuity' with a discone antenna. All that test showed you was that there is a short somewhere, but it doesn't tell you where. Next step would be to disconnect the coax from the antenna and repeat the test. If there's still continuity at the connector then one of the connectors is shorted. If no continuity, then the antenna is shorted.
- 'Doc

 

[K9WG]

... snip ... He used solder on pl259 connectors and on the receiver end I put a bnc adapter. ... snip ...

I would bet that there is a small hair of the shield shorting out the PL259. If I had a dollar for every time I saw that I could afford another new scanner....

 

[prcguy]

RG-8X is very hard to solder without melting the innards due to the foam dialectic and close spacing of the conductors. I've been soldering PL-259s for over 40yrs and last night I F'd one up and shorted the braid to center using RG-8X.

Many years ago I was sent to connector school to be certified to install various microwave connectors to 40GHz but they didn't cover how to install connectors on crap coax like 8X. I suppose if you quickly solder the center conductor first it might keep it from migrating when the entire connector is heated to solder the braid through the peek holes in a standard PL-259 and reducer.

It might be possible to tin the area of the reducer where the braid will rest then solder the braid to just the reducer so you could inspect and measure for shorts before screwing it into the connector. Tinning the reducer first should cut the amount of time needed to tack the braid down.
prcguy

 

[smason]

Agree with PRCGuy. I actually like RG8X as it's lower loss than 58, but not as bulky and hard to work with as RG8 or 9913 etc. That said, it's a mother to solder PL259s without screwing up.
Like PRC I've been doing 259s since 1976, and still mess up 8x on occasion.

Being your antenna guy is a tv guy, if it were me, I'd use good low loss RG6. he probably has tons of it. Yes it's 75ohm (and this has been beaten to death on the forums) but it's low loss, cheap, and connectors are plentiful and easy to install, and it works well for scanning. You'll need a F to PL259 at the antenna (somewhat hard to find, but available) and an F to bnc for the radio, much easier to find.. That said, you've already paid for everything, so may as well try to make it work.

 

[cassidy1190]

I suppose RG-6 would be the way to go then. I just hope he doesn’t charge me to run a new cable down. He screwed up with the connectors, not with installing the cable that I told him to install…

Is there an existence of a crimp or compression connector for rg8x? I couldn’t imagine it with the braided center...

 

[smason]

There are PL-259 crimp connectors for 8x (Google found quite a few) 6 UHF Male Silver Plated Crimp PL-259 for RG8X - Coax Connectors - 6 UHF Male Silver Plated Crimp PL-259 for RG8X - NewHamStore.com
but I imagine you'd need the proper tool, which wouldn't be economical for 2 connectors.

 

[cassidy1190]

Yeah for a crimping tool I would only use 2 or 3 times its not worth it on my budget. I picked up a few more solder connectors. I really think I can do a better job than this guy, I have tons more experience soldering than I do with radios. Also upon closer inspection I noticed the center conductor was way more flooded than it needed to be and the solder to the shield was not fully absorbed into the connector...of course in his line of work he probably is used to compression type connectors.

This guy has a good video on the proper technique...
YouTube - PL-259 Installation Made Easy for RG8X

 

[mass-man]

As the 8X is run, I wouldn't substitute RG6 unless the connectors are REALLY messed up on both ends. If you want go ahead and replace the connector there in the house. That maybe all it is!!!!

 

[cassidy1190]

I did, but its still shorted. Must be on the antenna end...or the antenna itself...yikes!

 

[mass-man]

Until your antenna guy gets there plug the PL259 into the BNC adapter, but DO NOT screw down the outer shell. It won't fix anything, but might give you the reception of the AirBand signals you are looking for!!!! Then again, I have not used a discone in decades, so I may be telling you all wrong!!!!

 

[majoco]

I try not to use PL259's that need the braid soldered - get the right ones and they have a screw thread that the cable braid goes into - you still need to solder the centre conductor but that requires so little heat that it doesn't melt the insulation.

Here's another cunning tip - if you are installing an antenna that is supposed to be open circuit such as your discone, solder or fit a high value (say 47kohms) resistor across the elements where the last bit of coax is connected. The 47k is far to high to affect any signal strength. Then your ohmeter will see the 47k if all is well, if it sees open or short, you're in trouble.:roll:

 

[cassidy1190]

I try not to use PL259's that need the braid soldered

Is there a specific name or brand of these types? I can only find the solder types.

 

[majoco]

The one I have in my hand definitely has a coarse screw thread down the braid hole and no provision for soldering. No manufacturer's name or part number. Jaycar Australia catalogue part number PP0860 and PP0862.

 

[talkpair]

Before deciding on whether to use a compression or solder type connector, you need to know the makeup of the cable shield.

If it's aluminum, you can't solder it.........If it's copper or tinned copper, you can use either.

 

[cassidy1190]

Oh yeah I know, it is copper. In fact I already re-did the pl259 connector on the radio room end. There was still a short even with the connector off and the braid folded back, but I decided to solder the new connector anyway. I feel like I did a good job, and will find that I won't need to redo it after I fix the topside connector.

Now I am just waiting on my contractor to come and take down the antenna for me…will have to wait until Thursday now. Otherwise I have a nice decoration on the roof until then. I am also happy to say that the Diamond D130J has lived up to its structural claims, surviving two thunderstorms and wind gusts over 40 MPH in just the week it’s been up haha!

I'll have to take a look at my radio shack pl259s and see if they have threads in the holes.