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Strange UHF Experience on Birdsville Track

Submitted: Wednesday, Nov 21, 2007 at 22:58

Gone Bush (WA)

Article Overview - UHF Radio
If you are considering a trip into Australia’s vast outback, then a UHF Radio is an important communications device to have. View Full Article...
Last August we were travelling south on the Birdsville Track with another vehicle and our two caravans. As we passed south of Mungerannie we noticed that our transmissions were being re-transmitted back to us like it was an echo.

Now I know a reasonable amount about radio propagation and after changing channels we found that this only happened on channel 18.

We drove for what I considered way beyond the range of any vehicle mounted UHF and there aren't any repeaters on 18 but this phenomenon continued. I then called anyone else on channel 18 and actually got an answer. I asked the person what sort of setup he had that re-transmitted our calls and he said it was just a radio.

We passed a couple of road construction camps with their big vans and noticed they had fairly tall antennas so I'm assuming that these transmissions were coming from them.

What I want to know is:

What possible use is a radio that re-transmits incoming calls?

Is it some sort of repeater on a non standard channel and if so what is the paired channel?

Has any one else experienced this in the same location?

"the truth is out there"... I hope.

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A voice in my head said:
"Don't look back,
You can never look back".
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ThreadID: 51866 Replies: 7
Views: 1429 FollowUps: 11
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Thread Summary

AnswerID: 273058   Submitted: Thursday, Nov 22, 2007 at 01:08

disco1942 replied:

Sounds like a repeater where they record the received signal and when you release the PTT your message is re-transmitted to you. These are around. They are easy enough to construct, you just use the same sort of digital recorder that is used in the tape less answer phones.

PeterD
Reply 1 of 7
FollowupID: 536383   Submitted: Thursday, Nov 22, 2007 at 03:49

Gone Bush (WA) posted:

What I can't work out Disco, is what use would it be?

Even if it was set up as a little private network, what use would that feature be? It wold be annoying to everybody.

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A voice in my head said:
"Don't look back,
You can never look back".
FollowUp 1 of 2
FollowupID: 536441   Submitted: Thursday, Nov 22, 2007 at 11:43

disco1942 posted:

It may be slower to pass messages through this system but much cheaper than a two frequency repeater. Last time I priced a duplexer for one of these it was around $6K, add to this you need a well shielded Tx & Rx plus double shielded cables to get it to work. For a delayed repeater you can use the guts from a $60 answer phone and make your own electronics to add to a cheap tranceiver.

PeterD
FollowUp 2 of 2
AnswerID: 273060   Submitted: Thursday, Nov 22, 2007 at 05:06

Peter 2 replied:

As you said it would probably be the road construction mob, it would be an easy way for them to have an emergency/call channel on all their vehicles and equipment. They probably call on that channel and then go to another for private conversation.

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Peter
1988 M1026 Humvee
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Reply 2 of 7
AnswerID: 273061   Submitted: Thursday, Nov 22, 2007 at 05:27

Member - Kiwi Kia replied:

Hi Gone Bush,

This also happened to me on the Birdsville Track a few kms nth of Claytons Bore in early September. Jolly confusing wondering what was going on.
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Reply 3 of 7
AnswerID: 273064   Submitted: Thursday, Nov 22, 2007 at 06:15

stocky replied:

Its called a "simplex repeater"

They where a popular choice for stations many years ago but are now ILLEGAL under the CBRS class license

Simply mounted on a high point like a repeater it picks up and records a signal then rebroadcasts it after the transmission stops. The sending party the hears themselves back and the distant party also hears it (hopefully!)

More modern ones usually allow on.off control via SELCALL so they can be disabled when not needed so they are not annoying

My bet it was on Etadunna Stn.

Reply 4 of 7
FollowupID: 536426   Submitted: Thursday, Nov 22, 2007 at 10:16

Gone Bush (WA) posted:

Stocky that sounds like it to a tee.

Thanks to everybody above and below this entry for helping me solve this "mystery".

See, the truth IS out there.

Click Image to Enlarge
A voice in my head said:
"Don't look back,
You can never look back".
FollowUp 1 of 1
AnswerID: 273078   Submitted: Thursday, Nov 22, 2007 at 07:19

Member - Uncle Phil (TAS) replied:

Hi Gone Bush
We experence the same thing in September and we thought it was the people from the nearby station. Someone was talking and it sounded like a Farmer talking to his wife.

We just change channel for a hour or so and didn't hear them again.

It was strange how the tranmissions we coming through.

Cheers Uncle Phil
uncle Phil
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Reply 5 of 7
AnswerID: 273086   Submitted: Thursday, Nov 22, 2007 at 08:10

Member - Mike DID replied:

Conventional repeaters that operate on Channels 1 to 8 are complex and costly to set up because they immediately retransmit all signals they receive - BUT you need big expensive filters to stop the trasmitted signal interfering with the received signal.

A Simplex Repeater may cost as little as adding a $50 box to a standard UHF CB radio.
Mike R
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Reply 6 of 7
FollowupID: 536431   Submitted: Thursday, Nov 22, 2007 at 11:08

stocky posted:

but they are illegal now..................
FollowUp 1 of 8
FollowupID: 536442   Submitted: Thursday, Nov 22, 2007 at 11:49

disco1942 posted:

See my FollowUp to Reply 1. I should have also added that for portable use they do not need a trained tech with $30K of spectrum analyser to retune the duplexer when you have to change channel.

PeterD
FollowUp 2 of 8
FollowupID: 536451   Submitted: Thursday, Nov 22, 2007 at 12:14

stocky posted:

$3k for a duplexer........
doesnt get around the fact they are still illegal - and so are telephone interconnects to UHF CBRS devices for that matter! :-)
FollowUp 3 of 8
FollowupID: 536452   Submitted: Thursday, Nov 22, 2007 at 12:15

stocky posted:

Ignore the telephone interconnect comment - I misread the post - sorry PeterD! :-(
FollowUp 4 of 8
FollowupID: 536466   Submitted: Thursday, Nov 22, 2007 at 13:03

disco1942 posted:

Stocky

Are you going to report these illegal repeaters? No one has argued that they are not. You are so insistent about them you should be doing something about them.

PeterD
FollowUp 5 of 8
FollowupID: 536471   Submitted: Thursday, Nov 22, 2007 at 13:32

Member - Mike DID posted:

. . . and about the people using threatening and foul language on the legal repeaters.
Mike R
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FollowUp 6 of 8
FollowupID: 536472   Submitted: Thursday, Nov 22, 2007 at 13:34

stocky posted:

Where I am aware if them, I do make an effort to educate the owners - and have previously done so to the owners of the unit in question - *just in case* they want to reconsider their usage of the device. It only takes one curious & uneducated traveller to pose a query to ACMA about "weird radio stuff" and the unsuspecting owner gets a visit.....and a potentially a fine!

I was more making sure that anybody who thinks "wow - what a good idea - i think i'll make heaps and sell them" realises that they are stricly forbidden under the current CBRS class licence...the same as most people are not aware it is now ILLEGAL to use UHF Ch 22 & 23 for VOICE traffic!!

Stocky :-)
FollowUp 7 of 8
FollowupID: 536475   Submitted: Thursday, Nov 22, 2007 at 13:38

stocky posted:

Mike,

Its the old problem i guess

Their is an idiot in every crowd - a small minority of RED NECK MORONS ruin the whole UHF CBRS experieince for many users.

Some that say "its OUR repeater - GET OFF" - WRONG if you are the holder of a CBRS repeater station license it is clearly stated that it must be avaialble 24/7 for FREE PUBLIC ACCESS - ie you cannot control who accesses it when.

We have a local repeater (that works TOO well) - picks up from Whyalla - Broken Hill - half way to Adelaide. Most commonly heard word starts with F!

I understand your plight!

Stocky
FollowUp 8 of 8
AnswerID: 273245   Submitted: Friday, Nov 23, 2007 at 00:06

Barry 2 replied:

Hey, all you guy's there's a simple answer to the UHF problem ??
"UFO's" !!!!!!


He,He,He,
Cheers all
Bazza

Ps The Bundy Bear made me do it !!!!

Reply 7 of 7