Strange UHF Experience on Birdsville Track
Submitted: Wednesday, Nov 21, 2007 at 23:58
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51866
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Gone Bush (WA)
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.
Reply By: disco1942 - Thursday, Nov 22, 2007 at 02:08
Thursday, Nov 22, 2007 at 02:08
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
AnswerID:
273058
Follow Up By: Gone Bush (WA) - Thursday, Nov 22, 2007 at 04:49
Thursday, Nov 22, 2007 at 04:49
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.
FollowupID:
536383
Follow Up By: disco1942 - Thursday, Nov 22, 2007 at 12:43
Thursday, Nov 22, 2007 at 12:43
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
FollowupID:
536441
Reply By: Peter 2 - Thursday, Nov 22, 2007 at 06:06
Thursday, Nov 22, 2007 at 06:06
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.
AnswerID:
273060
Reply By: Member - Kiwi Kia - Thursday, Nov 22, 2007 at 06:27
Thursday, Nov 22, 2007 at 06:27
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.
AnswerID:
273061
Reply By: stocky - Thursday, Nov 22, 2007 at 07:15
Thursday, Nov 22, 2007 at 07:15
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.
AnswerID:
273064
Follow Up By: Gone Bush (WA) - Thursday, Nov 22, 2007 at 11:16
Thursday, Nov 22, 2007 at 11:16
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.
FollowupID:
536426
Reply By: Member - Uncle Phil (TAS) - Thursday, Nov 22, 2007 at 08:19
Thursday, Nov 22, 2007 at 08:19
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
AnswerID:
273078
Reply By: Member - Mike DID - Thursday, Nov 22, 2007 at 09:10
Thursday, Nov 22, 2007 at 09:10
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.
AnswerID:
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Follow Up By: stocky - Thursday, Nov 22, 2007 at 12:08
Thursday, Nov 22, 2007 at 12:08
but they are illegal now..................
FollowupID:
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Follow Up By: disco1942 - Thursday, Nov 22, 2007 at 12:49
Thursday, Nov 22, 2007 at 12:49
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
FollowupID:
536442
Follow Up By: stocky - Thursday, Nov 22, 2007 at 13:14
Thursday, Nov 22, 2007 at 13:14
$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! :-)
FollowupID:
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Follow Up By: stocky - Thursday, Nov 22, 2007 at 13:15
Thursday, Nov 22, 2007 at 13:15
Ignore the telephone interconnect comment - I misread the post - sorry PeterD! :-(
FollowupID:
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Follow Up By: disco1942 - Thursday, Nov 22, 2007 at 14:03
Thursday, Nov 22, 2007 at 14:03
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
FollowupID:
536466
Follow Up By: Member - Mike DID - Thursday, Nov 22, 2007 at 14:32
Thursday, Nov 22, 2007 at 14:32
. . . and about the people using threatening and foul language on the legal repeaters.
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536471
Follow Up By: stocky - Thursday, Nov 22, 2007 at 14:34
Thursday, Nov 22, 2007 at 14:34
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 :-)
FollowupID:
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Follow Up By: stocky - Thursday, Nov 22, 2007 at 14:38
Thursday, Nov 22, 2007 at 14:38
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
FollowupID:
536475
Reply By: Barry 2 - Friday, Nov 23, 2007 at 01:06
Friday, Nov 23, 2007 at 01:06
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 !!!!
AnswerID:
273245