Radio Gurus - Help

A couple of us in 4WDs are at Useless Loop (near Sharks Bay WA).
We each have computers and mobile phones connected to Telstra’s Next G Network.
One person has a 9db aerial – the other has a 6db aerial.
We have interchanged the aerials between all the phones and computers.
The 6db has a higher strength signal – why is this?
Regards Dennis
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Reply By: Gossy - Friday, May 07, 2010 at 18:16

Friday, May 07, 2010 at 18:16
put a multi-meter pins on the positive pin (middle) and the outside (screw part). There should be no connectivity between the two. If there is then the earth part of the co-ax cable has not been separated correctly and is touching the inside part (positive) of the antenna when the plug was connected during manufacture.

If there is you will have an antenna that does work but not effectively. If this is OK then not sure.

I had a similar experience with an antenna and when I took it back to Electric Bug in Adelaide they tested it and it was all OK. with a smile I pulled out the multi-meter. They promptly exchanged it :)
The alarm bells rang for me when I was chatting to a truckie going over to Melb. When he was only 200metres behind me when we passed I lost him !

Cheers,
AnswerID: 415755

Reply By: Shaker - Friday, May 07, 2010 at 18:23

Friday, May 07, 2010 at 18:23
Is the terrain flat or undulating? If it is undulating then 6db would work better.
AnswerID: 415756

Reply By: Member - Ian H (NSW) - Friday, May 07, 2010 at 18:35

Friday, May 07, 2010 at 18:35
It may also depend on the mounting of each aerial. Are the mounts similar?
Ian
AnswerID: 415757

Reply By: Steve and Viv - Friday, May 07, 2010 at 18:37

Friday, May 07, 2010 at 18:37
Both good posts and also the length of cable used on the mount also changes the frequency so you think you have 6.5 db but it can be 6 or 7 depending on the cable length. Some installers cut the cable which is wrong which put them off frequency.
AnswerID: 415758

Follow Up By: Robin Miller - Friday, May 07, 2010 at 20:28

Friday, May 07, 2010 at 20:28
Hi Steve

The cable length doesn't change the frequency , and should have also no effect unless the antenna is faulty and badly off tune which creates a high Vswr that the cable may interact with.

Robin Miller

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Follow Up By: get outmore - Saturday, May 08, 2010 at 18:05

Saturday, May 08, 2010 at 18:05
isnt that idea a throwback from the 27mhz radios?
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Follow Up By: Steve and Viv - Saturday, May 08, 2010 at 18:22

Saturday, May 08, 2010 at 18:22
Yep, I read that wrong. I thought we were were talking UHF where the cable length does effect freq.

Sorry to all, I'll read better next time rather than just post away.

With cell the only cable issue is loss caused by a to long cable. Any over ten metres will effect reception. That I can assure you and can post the test result when needed. Also we get a lot of these issues up in communities north of Broome

Again sorry I messed that up
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Reply By: Member - Leave_enough_space - Friday, May 07, 2010 at 19:03

Friday, May 07, 2010 at 19:03
I'm confused!

I thought the 4.5, 6 and 9 db aerials were for UHF communications, and that different aerials are required for mobile comms.

Am I wrong? - hoping to be unconfused by the end of the evening!
LES
AnswerID: 415761

Follow Up By: _gmd_pps - Friday, May 07, 2010 at 19:16

Friday, May 07, 2010 at 19:16
db gain has nothing to do with UHF or VHF or HF for that matter ..
it is purely a measure of ratio of the gain of an antenna over a basis value.
There are different measurements used like dbi etc which normalises the ratio
to a specific type of antenna.

ANY antenna in ANY frequency range may be specified with a certain signal gain in db. Higher gain usually means more directional and requires you to know where the nearest receiver/sender is located roughly and needs more line of sight, although other factors come into play. Not always is a higher gain antenna a better option especially not for receivers unless you can really aim at the source like your TV antennas, which is an example of a directional antenna (yagi). Also of relevance is the polarisation of the signal , vertical or horizontal, this also depends on the source.

good luck
gmd
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Follow Up By: Allan B, Sunshine Coast, - Friday, May 07, 2010 at 19:55

Friday, May 07, 2010 at 19:55
gmd is on the ball LES.

So,....... db's ain't db's Sol.

Cheers
Allan

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Follow Up By: SNAKE No1 - Saturday, May 08, 2010 at 12:55

Saturday, May 08, 2010 at 12:55
gmd pps is spot on,it is a pity some of the stores selling this gear know less than the buyers but that does not stop some of them trying to baffle people with b......t,some of the crap members of the public ,who rely on the correct info get told is criminal.I have seen and heard some fairy tales over the years,my advice is deal with people who make their living out of selling and installing radios and ask these people questions,most will gladly let you know.
(I do not have anything to do with the sale or installation of radio gear but have been an Amateur radio operator since 1993. Cheers Snake.
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Follow Up By: Steve and Viv - Saturday, May 08, 2010 at 18:30

Saturday, May 08, 2010 at 18:30
Yes, agreed, spot on.
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Reply By: Mike DiD - Friday, May 07, 2010 at 19:51

Friday, May 07, 2010 at 19:51
1. The "9dB" is a made-up figure.
2. The coax cable used is crap
3. The antenna/cable was damaged during installation
4. The connectors were installed incorrectly.
5. You're in a valley and the signal comes from a high angle where the 6dB has a stronger signal

etc
AnswerID: 415764

Reply By: disco driver - Friday, May 07, 2010 at 19:57

Friday, May 07, 2010 at 19:57
Dennis,

Just because I'm a pedantic bugger, I would like to point out that there is no S at the end of Shark in Shark Bay.

It is simply just Shark Bay!

As far as your question goes, don't ask me.........as long as the thing works that's all I need to know

Enjoy your trip

Cheers

Disco.
AnswerID: 415766

Follow Up By: get outmore - Saturday, May 08, 2010 at 18:07

Saturday, May 08, 2010 at 18:07
MMM these guys from there disagree

and being 2 of them maes it sharks

if you want to be pedantic it would be Shark's
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Reply By: Dennis Ellery - Friday, May 07, 2010 at 22:33

Friday, May 07, 2010 at 22:33
To gmd – Thanks for the info, it’s good to get technical advice.
To Disco – Yep smarty -Shark Bay’s correct
To all others – Thanks for your advice – much appreciated
Regards Dennis
AnswerID: 415796

Follow Up By: disco driver - Saturday, May 08, 2010 at 00:45

Saturday, May 08, 2010 at 00:45
Hi Dennis,
Remember that today is Friday, I'm not so pedantic during the week.

Cheers

Disco.
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Follow Up By: Member - Stuart K (WA) - Saturday, May 08, 2010 at 01:13

Saturday, May 08, 2010 at 01:13
Hi Dennis
Just a quick off subject one ,if you work at Shark Bay Salt you will probally know the brother and sister inlaw Steve and Tracey.Say g,day if you do.
Cheers Coolup
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Follow Up By: Dennis Ellery - Saturday, May 08, 2010 at 23:55

Saturday, May 08, 2010 at 23:55
I am just visiting the son who works at Shark Bay Salt.
I'll mention Steve and Tracey's to him.
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