UHF aerial tip replacement not working

Our UHF aerial snapped off going over some corrugations in the West Macdonnell Ranges the other day (I know this is apparently common - the bullbar on our Colorado shakes a fair bit). It snapped just at the base of the black (fibreglass?) tip (which is about 2 foot long) and just above a stainless steel section you can screw off.

After screwing off this 1 inch long stainless steel section it looks like there was a bit of solder sitting on top of the internal thread that was holding the core of the tip on.

The base of the antenna has a Uniden AT-870 sticker on it.

We went to a communications joint in Alice Springs and we were given a near identical replacement tip (different brand but similar gain at 6.6dB vs 6.5dB) that came with the same looking 1 inch screw base.

After screwing it on I am certain we have poor reception with our unit (maybe 2km range) and when transmitting to small hand held units only a few metres away the sound is full of static.

Even though the replacement antenna tip screwed on nicely my concern is that there is no contact internally between the remaining solder tip on the internal thread and the inside of the new aerial. Is this correct? Should I be able to simply screw on a replacement as I have done and have it work?

Currently at Mataranka heading up towards Darwin via Katherine and Litchfield - should I go to a comms joint there to get it checked out?
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Reply By: PJR (NSW) - Monday, Jul 23, 2012 at 08:48

Monday, Jul 23, 2012 at 08:48
Skip to the last sentence if you do not have a good clean and small soldering iron. And the "reliable and clean environment" skills to use it. And my advice.

That "bit of solder" was connecting the antenna cable (coax) that enters the bottom of the whole antenna to the "active" section of the antenna (the tip). When you undid the screw you broke the connection inside the "silver" 1 inch long bit. The cable has to be extracted from the antenna and stripped back and tinned and the braid prepared for a new fitting. Then all solder and left over wire has to be removed from the short section. You then screw it back on the antenna "base" and feed the prepared wire up the center of the base so that the tinned end sticks out the top. Depending on the design of the base the braid has also got to be folded back and connected to the base. Then the wire is soldered to the 1" bit and the rest of the natenna put back on.

I may have missed something there as it's years since I have done it.

The easy and best way: Get the communications mob to do it.
AnswerID: 491465

Reply By: Bob Y. - Qld - Monday, Jul 23, 2012 at 08:49

Monday, Jul 23, 2012 at 08:49
In 30 years of using UHF equipment, I've never seen a fibreglass aerial break, except when colliding with a gidgea tree, at speed. Those are serious vibrations on your bull bar, mate!

Seriously, if the fibreglass has broken, I'd be a bit concerned about the soldered joint, underneath, where the co-ax is soldered on. It may have fatigued, and broken, causing your apparent loss of signal.

Don't know if Katherine has any techs in town, but there should be some in Darwin. May only need the aerial to be dismantled and re-soldered.

Bob.

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Follow Up By: Member - GregK5202 Qld - Monday, Jul 23, 2012 at 13:55

Monday, Jul 23, 2012 at 13:55
Hi Bob.

I had a Cruiser like yours, the bar is solidly mounted. I now have a Prado 120 which have air bags. The bars are rubber mounted and vibrate a lot, subjecting the aerial to much more trauma. My first stainless spring mast lasted a few hundred km on dirt, the replacement fibre glass mast lasted from The Alice to Caloundra plus a few hundred km more.
I now have the heaviest spring base, which is stiffened with wrappings of tape, plus I have reinforced the bottom 150 mm of the mast with electrical conduit. This has lasted years so far.

Greg.
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Follow Up By: Bob Y. - Qld - Monday, Jul 23, 2012 at 20:46

Monday, Jul 23, 2012 at 20:46
Greg,

I've got a heavy spring base too, with one of Sandman's wanker poles (sic) fitted to it. Doesn't move about much, and though I don't always notice, it doesn't vibrate very much either. Think that aerial in my profile photo would be 8 - 9 years old.

Yeah, was surprised just how much those Prado bars move. Mkes you wonder what would happen with a major strike?

Rapt in that profile photo of yours Greg. Looks really grouse when it's enlarged.

Bob.

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Reply By: MEMBER - Darian, SA - Monday, Jul 23, 2012 at 08:54

Monday, Jul 23, 2012 at 08:54
Sounds like the same base as my UHF antenna - if so, the design is more complex than it appears at first glance - some rings on the body insulate parts from others etc. -you'll may find that the inner wire in the coax cable was soldered into the item that you screwed off. Once a new part is just screwed on, you run the risk of cooking* the radio with shorted coax wires. I suggest dis-assembly of the whole antenna body - study the design and once understood, carefully reassemble, with the coax installed as required. Following that, the integrity of the coax's inner and outer circuits have to be checked with a test light or meter to make sure there are no shorts (vital). From you description, there is a fair chance that after fixing the antenna you may find that the radio is cooked* (transmitting with no proper antenna circuit for the energy to go to - here's hoping its ok but).
*bush radio tinkerers' term for "a thingamy inside the radio is probably buggered".
AnswerID: 491467

Reply By: PJR (NSW) - Monday, Jul 23, 2012 at 09:05

Monday, Jul 23, 2012 at 09:05
I forgot this bit.

Do not use the radio until it is fixed. You may blow the finals. Unlikely but expensive. In bush terms. It may blow a poofer valve.

Okay!!!!
AnswerID: 491469

Follow Up By: Nomadic Navara - Monday, Jul 23, 2012 at 11:42

Monday, Jul 23, 2012 at 11:42
That applied to the first generation of transistorised transmitters (60s and early 70s.) Transistorised circuitry has developed a lot since then. If OzNjB's transmitter was going to be damaged by the crook aerial it would be terminally damaged by now.


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Follow Up By: PJR (NSW) - Monday, Jul 23, 2012 at 12:06

Monday, Jul 23, 2012 at 12:06
Very helpful

Thats why I said "You may blow the finals."

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Follow Up By: PJR (NSW) - Monday, Jul 23, 2012 at 12:13

Monday, Jul 23, 2012 at 12:13
Isn't it amazing. You try to help and there is always someone who hops in and has a go at you.

So you are quite happy not to tell him to turn it off and let him continue trying to use it and possibly damaging the radio more then a simple antenna problem. . Are you 100 % confident that his attempts will not damage it. I would dare tell him to keep trying which is what you are doing.
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Follow Up By: Nomadic Navara - Tuesday, Jul 24, 2012 at 00:50

Tuesday, Jul 24, 2012 at 00:50
PJR, can't you accept you have given incorrect advice? I have been in the radio industry for 55 years, or in other words in the days before transistors were commercially available. I went through the days when all transistor two way radios were introduced. There were a lot of problems with operators playing with antennas like bending them over so they would not strike tree branches. This resulted in many cases of transmitter output transistors blowing (same with audio output transistors when speakers were disconnected.) However from the early 70s we had no problems caused by broken aerials.

Can't you take advice from people who have worked in the industry?


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Follow Up By: PJR (NSW) - Tuesday, Jul 24, 2012 at 08:56

Tuesday, Jul 24, 2012 at 08:56
You have worked in the industry for 55 years. Well bully for you. That is very helpful to the PO. Will that help him get the radio fixed. Nope. Would he know what you are taling about. Nope.

Whenever I gave a lesson or lecture I was told to never forget the audiences knowledge base and their "need to know". Keep the content at a level that they need. Talking to the engineers we could talk at atomic levels but with management we could not.

I would be a total ignoramus not to take advice when applicable. But at the expense of the topic and PO it was irrelevant. I was talking to the PO not you and you pop in and lecture me about something that could only confuse him.

I will put it another way. You are at the doctors and he just told you that you had something wrong with you. Not terminal - just an illness that can be cured. A collegue of his walks into the surgery and they drift off into a highly detailed discussion about your illness. Would that help you? I know it wouldn't help me. You would feel ignored and even feel that you were just an inaminate object.

He was the one we should be thinking of. Not you nor me.
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Reply By: Nomadic Navara - Monday, Jul 23, 2012 at 12:12

Monday, Jul 23, 2012 at 12:12
Quote - "Even though the replacement antenna tip screwed on nicely my concern is that there is no contact internally between the remaining solder tip on the internal thread and the inside of the new aerial. Is this correct? Should I be able to simply screw on a replacement as I have done and have it work?"

Yes it should work OK. The male thread at the top of the base is the sole electrical connection to the whip. It sounds like you have a problem with the lower assembly. The lower piece that is left when you screw the upper whip piece off is half of a co-axial dipole. The male screw thread at the top is connected to the inner wire on the co-ax cable. The outer braid of the co-ax is connected to the metal outer sleeve (which forms the lower half of the dipole.)

Checking the lower section is very simple. You will have to extend one lead of your meter with a bit of extra wire. Disconnect the plug from back or your transceiver. Set the meter to its lowest ohms range. Check the continuity between the male thread on the base and the pin of the plug. Then check the continuity between the metal sleeve on the base and the body of the plug. The reading on both of of these tests should be zero ohms or very close to that. Then set your meter to its highest ohms range and check between the pin and the body of the plug. It should be open circuit.

If you don't get the results described above, you have a fault in the base (in your case you will know where the fault is.) You can have a shot at repairing it as described above. If that fails then you will need a new base. If you are still within range of the supplier of the whip he may agree to refund you for that and supply a whole new antenna.



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Reply By: Sand Man (SA) - Monday, Jul 23, 2012 at 17:04

Monday, Jul 23, 2012 at 17:04
Why do you need the UHF Aerial on the Bull Bar?

I was advised by a Communications Retailer in Adelaide that a "mudguard" mounted stainless steel arial is as good for reception as a "wanker pole" on the bullbar.
They sell all types to cater for all customer requirements.

Mine is 900mm in length and vibrates a fair bit I have never had a problem.

I had a similar aerial on the Jackaroo and also have one on my Colorado.

The main thing as I was advised, is that the top of the aerial should be higher than the roof and anything else mounted to it and reception will be as good as the big fibreglass poles mounted on a bullbar.

Another thing I like is the top of the aerial acts like a "gauge" for multi-story, or underground car parks. If the aerial is just touching the lowest obstructions then I know I have sufficient clearance:-)

Bill


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Follow Up By: Sand Man (SA) - Monday, Jul 23, 2012 at 17:08

Monday, Jul 23, 2012 at 17:08
If you click on the picture in my profile, you will get an enlarged image that shows the aerial and how it just sits above the roof mounted rack.

I have not had any problems with range for my GME transceiver.

Bill


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Follow Up By: PJR (NSW) - Monday, Jul 23, 2012 at 19:02

Monday, Jul 23, 2012 at 19:02
I put a mount on both guards about half way to the windscreen. No shaking or anything. No breaks either. Sure you have to watch the shrubs. So what. Take it easy through very close country and you wont break them.

In 40 years since CB first came out I have never broken an antenna ther. On the roof is fine but if you have a rall car you may want to think twice about shopping centres.


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Reply By: OzNjB - Monday, Jul 23, 2012 at 17:30

Monday, Jul 23, 2012 at 17:30
Thanks for the advice everyone - my knowledge of UHF is limited so I will get it checked out in Darwin by a comms mob
AnswerID: 491502

Follow Up By: OzNjB - Monday, Jul 23, 2012 at 17:38

Monday, Jul 23, 2012 at 17:38
Forgot to mention that the unit is a Uniden UH7760NB
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Follow Up By: OzNjB - Monday, Jul 23, 2012 at 17:42

Monday, Jul 23, 2012 at 17:42
Also forgot to mention that the replacement whip is a GME
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Reply By: Member - Bucky - Tuesday, Jul 24, 2012 at 03:52

Tuesday, Jul 24, 2012 at 03:52
OzNjB

Forget those wanker aerials
get one of these

Click here

Nothing much worries them, and I can guarantee them not to be effected by corrugations

They just last !

Cheers
Bucky
AnswerID: 491535

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