UHF - Fold Down Base

Submitted: Sunday, Feb 27, 2005 at 19:43
ThreadID: 20830 Views:5969 Replies:9 FollowUps:4
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I've just installed an Icom IC 400 Pro UHF in the chariot. Having decided to opt for the formula ... [ performance with some inconvenience ], I've chosen to mount the antenna in the recommended centre-roof position. Its a ground plane independent 2/6 db set up - with wire screw ons: The snag is that its just too high for the shed - I need a fold down base that can still accomodate the fixed/in-line coax arrangement. Would appreciate any feedback re hardware available - otherwise I'll make one with some stainless sheet etc.Brad has seen one in a mag somewhere - maybe others have too. Onyezorl.
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Reply By: Member - Phil G (SA) - Sunday, Feb 27, 2005 at 20:02

Sunday, Feb 27, 2005 at 20:02
Roof mount is always a good choice for UHF.

I have the same problem as you. I use a ground independant base which is gutter mounted. 95% of the time, all I use is a 6 inch high rubber stubbie aerial on a swing down bracket. Remainder of time I'll put the 6db up there. But being ground plane independant, side to side positioning is not critical (height always is).

Great system as you always get good transmission from the aerial being high up; The stubbie aerials actually work better in sandhills and mountains; and the stubbie aerial is indestructable and not likely to be stolen.

All the its are available at Electric Bug on Torrens road. They will gve you the same blurb :-)))

Cheers
Phil
AnswerID: 100392

Reply By: Nick R - Sunday, Feb 27, 2005 at 21:30

Sunday, Feb 27, 2005 at 21:30
Banjo,
At the Surf Lifesaving Club where I am a member we have a big 5.7m inflatable boat with uhf and 27 meg, both have hinged aerials so we can back it into the shed, therefore I would try someone who does marine radios, the hinges are plastic and have lasted for years in a marine environment. Otherwise try the stubbie while you are close to home and screw on the longer one where height is less of a problem, where we all like to be.
Regards,
NickR
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AnswerID: 100411

Reply By: Member - Jeff M (WA) - Sunday, Feb 27, 2005 at 22:36

Sunday, Feb 27, 2005 at 22:36
If it's gound independant then you should be able to mount it on the gutter, ground place should not be important. You can easily Folding gutter mount bases.
AnswerID: 100425

Reply By: Member - Jeff M (WA) - Sunday, Feb 27, 2005 at 22:36

Sunday, Feb 27, 2005 at 22:36
If it's gound independant then you should be able to mount it on the gutter, ground plane should not be important. You can easily Folding gutter mount bases.
AnswerID: 100426

Reply By: Member - Banjo (SA) - Monday, Feb 28, 2005 at 08:28

Monday, Feb 28, 2005 at 08:28
Team .... should have said - even the little 150mm stubby is too high, when on the elevated feed base. Also - I don't have a roof gutter - only a channel ...... anyway ...... I'll look into the channel mount issue - there might be something ..... point taken re side mounting is the same as centre mounting in the case od GPI's.
AnswerID: 100446

Reply By: MrBitchi - Monday, Feb 28, 2005 at 09:56

Monday, Feb 28, 2005 at 09:56
Mount it on the bullbar. The extra height gained by putting it on the roof (approx 18") is so small that any performance gain is negligible.
Use a 6/9db antenna. Can see absolutely no reason to ever use a 2db model.

Cheers, John.
AnswerID: 100456

Follow Up By: Member - Banjo (SA) - Monday, Feb 28, 2005 at 11:22

Monday, Feb 28, 2005 at 11:22
I thank you for your contribution John - noted your positive view on the bull mount - but it clashes with so called "expert" advice I've received re height being everything. I am quite prepard to accept that there might be neglible difference on performance - hmmmm - more to consider.
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FollowupID: 358614

Follow Up By: MrBitchi - Monday, Feb 28, 2005 at 11:40

Monday, Feb 28, 2005 at 11:40
Banjo, I think you'd suffer more performance loss through using a knockdown mount than by mounting on the bull bar.
Have mounted many UHF systems over the years and have yet to meet anyone who can prove a roof mount is better then the bull bar. Yes under ideal conditions with a calibrated test unit you may be able to measure an increase in gain (range) one position over the other but that doesn't translate to the real world. You'll get far better performance using a 6db antennae on the bull bar than a 2db on the roof, and of course, far better with 9db on bull bar than 6db on roof.
Antennae gain is far more of a factor then mounting location.
The ideal setup is a 6/9db antennae, using 6db configuration in hilly country and 9db in open flat country.

Cheers, John.
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FollowupID: 358617

Follow Up By: Baz (NSW) - Tuesday, Mar 01, 2005 at 10:33

Tuesday, Mar 01, 2005 at 10:33
The only advantage with mounting in the centre of the roof is a broader range in recieving and transmitting unlike on the bullbar which is more directional but the advantage with directional is a greater distance so it can be advantage either way, as said above db gain is more important, higher the gain the better in flat country, that does not mean height either if you get an arial with a high gain and a tighter wind this means you don't have to have an arial that is 50' tall.

Baz.
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FollowupID: 358786

Reply By: Member - Captain (WA) - Monday, Feb 28, 2005 at 12:07

Monday, Feb 28, 2005 at 12:07
Hi Banjo,

I use a bullbar mounted 2.2m ground plane independant 7.0 dBa UHF antenae and it works extremely well. I have been able to converse with others while vehicles with me could not even hear the other side of the conversation.

The 2.2m bullbar mount is, IMHO, much more convienient than a roof mount and at 2.2m tall, is overall much higher than any centre mounted aerial I have seen used. It also doubles as a flag holder for sand dune driving. But it does get a beating on overgrown tracks.

However its a real PITA as I cannot get in in my garage, so for day to day use I have a ~800mm 4.5dBa that also happens to be exactly the same height as my roofline, great for pre-warning about low undercover garages.

Cheers

Captain
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AnswerID: 100473

Reply By: Member - Bradley- Monday, Feb 28, 2005 at 12:56

Monday, Feb 28, 2005 at 12:56
Geez i'm a good bloke (well maybe), had a fick through some old mags and found the ad for the 'dont bend em, fold em' antenna brackets.

contact Phill - phillphy at bigpond dot com - 0429 002 930

Cheers Brad
AnswerID: 100482

Reply By: Eric Experience. - Monday, Feb 28, 2005 at 22:32

Monday, Feb 28, 2005 at 22:32
Banjo.
You have made the correct choice to mount on the roof, the signal to noise ratio is much better, if you want to make an electric folding base you can use the actuator from the seat back of an electricaly adjusted seat, they are very strong and reliable, you will have to make a waterproof boot to protect it and if you want to make a swish job of it you can set up a couple of micro switches to make it stop and park in the desired spot. Eric.
AnswerID: 100602

Follow Up By: Member - Banjo (SA) - Tuesday, Mar 01, 2005 at 08:55

Tuesday, Mar 01, 2005 at 08:55
That sounds interesting Eric - I'm happy to do it manually for the present though - I get too little exercise as it is. Whatever - I can get the electric gizmo you speak of for nix so won't rule it out.
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FollowupID: 358777

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