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Passive Antenna Repeater - UHF

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Graham G0SCV View Drop Down
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    Posted: 28/October/2010 at 11:21

Hi All.

Leading on from the Talk Through on a Hand Held.

Using a duplexer made me consider the use of a UHF Yagi to increase signal and therefore reduce power.

Some time back I set-up a Passive Repeater for an event, Lakeland 100, so a signal could be repeated along a valley without the need for a remote operator to baby-sit a talk through, 24 to 48 hrs operation would have needed multiple operators and battery replacement.

So a Passive Antenna Repeater for UHF relay what tested by the RAYNET group doing the event. My job was to remote site it for the event. This went OK but the repeater did not do its job.

So I would like to know if any other group have tried this method of relaying and what is needed.

I've got the two UHF yagi's, mast and places to test it.

Does the coax length need to be anything specific, do you get any advantage with the orientation of the antenna, regarding mutual interference at the site, i.e. both vertical or one horizontal?

Still doing interweb searches for the answer.

Regards

Graham

Just trying to take less on the hills, less radio's more food :-)

Graham Belt, G0SCV

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g7gmn View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote g7gmn Quote  Post ReplyReply Direct Link To This Post Posted: 29/October/2010 at 02:57
Hello Graham,
                Similar, but not the same frequency....  John ( M1ENA ) and myself set up a "passive repeater" at a 'user-service building' to enable the two of us to talk to each other, John in the basement and me on the roof.  This was while we were fault-finding / investigating a problem with a mobile phone repeater.
                There were several large bore co-ax's between roof and basement that had been provided for RAYNET use.  We put a small mag-mount aerial on the roof end and a 'rubber-duck' aerial in the basement on one of the feeder's.  I believe the magmount was for 144 MHz but we were actually taking liberties and using it at  433.775 MHz.
True, there was very little distance between either John and the rubber-duck or me and the magmount, but it worked very well even with about 250 mW bothways, in fact I think we tried a dummy load on one end and still had a signal...  leakage I suppose.  There was at least 150 feet of feeder between the two ends.

Anyway, it was usable.  Both aerials need to be the same polarization as the radios using them.  I should think it is only suitable for short distance comms though.

Good luck.  I think I will have a play with this set-up also.

Ian.
Ian, G7GMN.

Controller, NE Hampshire RAYNET.
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G6URM View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 29/October/2010 at 05:04
good lord ,not heard any one talk about these things in years

like passive "reflectors" - they can be a bit hit and miss and seem IME to work best if you use them at an acute angle ( vis want to work round corners ) and there is a school of thought that they work better cross polarised for signal isolation ( vis one vert & the other horizontal )

when you say you worked along a Vally - where the antennas back to back in near enough a straight line ?? - if so then you would have needed a VERY large ( preferably solid ) reflector on each to stop the signal impinging on the other antenna and cancelling out any benefit which is why something like a corner reflector works better than a yogis back to back

as to connecting the two - shorter the better and low loss as possible - rg 58 will not cut it

will be surprised if you get much joy looking on the net for info - as i said not heard anyone talk of these things in oh must be 20 years or more - promote yourself to "grand wizard" status - for here we be dealing with the "black arts " of radio transmission
BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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Post Options Post Options   Thanks (0) Thanks(0)   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 29/October/2010 at 05:31
after thought : - another "way" of doing this if you want to set up a cheap repeater is to use hi gain preamps and 2 sets of antennas - but of course each "set" will only work one "way " ( and of course needs power )and then there are all sorts of "isolation" problems to contend with

- its more useful as a means of getting an RX signal into say a shielded building or other area where there is NO signal

other things to look at for "problem areas " are passive reflectors - although these are not really something you can set up "ad hoc" - or even the vagaries of "knife edge " refraction

we had one site on the moors that for some reason reflected signals from an area that was other wise unreachable direct - and concluded ( though the theory was never confirmed ) that a large metal military mast was doing the job ( in the local firing area on top of a tor ) - as if you pointed a yagi ( not a yogi ) at it 90 degrees off the direct path - good signal -( swing either side by a few degrees - nothing )

strange stuff be radio waves arrrr
BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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Post Options Post Options   Thanks (0) Thanks(0)   Quote g7gmn Quote  Post ReplyReply Direct Link To This Post Posted: 30/October/2010 at 00:47
Hello Brett,

         My instance was only an example, where over a short distance the system worked.  We have not ( as yet ) tried the same set-up over a large distance.  The building that we used this "passive repeater" set-up on was about 4 storeys high plus 2 levels of basement.  We were working between the bottom basement and the roof where all the aircon stuff and tanks were, hidden behind an aluminium screening wall around the roof-space.  We put the small mag-mount on the underside of one of the horizontal steel beams across the top of the roof-space, connected to one of the large feeders to the basement.  At the basement end of things was a rubber UHF aerial on the other end of the feeder.  I was wandering around the roof-space ( with the correct gear on of course ) and John was wandering around the basement ( severe screening from concrete and steelwork, not to mention four storeys of car-park and office space ) and getting a solid signal there-in, so no direct signal from roof.  Signal only by the conducted signal via the two aerials and the interposed feeder.   We were actually investigating a similar ( amplified ) set-up for 900 & 1800 MHz mobile phones.

         I will be checking-out whether this would be of use at any other event that we frequent.  The experiment it's self will be interesting though.

Wish you well.

Ian.
Ian, G7GMN.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 30/October/2010 at 04:22
quoth Ian: "The experiment it's self will be interesting though."

well they do say one experiment is worth a 1000 theories

good luck with that and please post any results as stuff like this is very useful to know - as i bet there re a few readers thinking "that's a good idea " or conversely " never heard of that before "

BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GW4KJW Quote  Post ReplyReply Direct Link To This Post Posted: 03/November/2010 at 20:59
Originally posted by Graham G0SCV Graham G0SCV wrote:

So a Passive Antenna Repeater for UHF relay what tested by the RAYNET group doing the event. My job was to remote site it for the event. This went OK but the repeater did not do its job.

Still doing interweb searches for the answer.

 
If you haven't already done so, try a Google for 'passive TV repeater,' Graham.
 
The technique has been used often in getting tv signals into remote valleys etc.
Gareth - GW4KJW - I don't post on here anymore. 73 to my many Raynet friends, see you on the blog.
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