446 Repeater - Offset?

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stageofhistory
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446 Repeater - Offset?

Post by stageofhistory »

I'm now seriously considering setting up a duplex repeater to take advantage of programable import HTs, for use by myself and our neighbourhood group, on PMR446 CHNs with tones. I'm deciding whether this will done using a repeater box off eBay hooked to HTs, or through a base unit like the one nicely covered by Bogget in the Wouxung 920 review. Probably the latter.

What would be considered a minimum offset between freqs, and can this be done with the allocation on 446? Could I e.g. repeater Rx 446.00625 (PMR1) and Tx 446.01875 (PMR2) - I suspect these freqs are too close together?

What would you guys suggest? I've been brief, but what problems (other than legal!) can I expect in trying to set up a system like this...

Cheers for any help! SoH
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Re: 446 Repeater - Offset?

Post by RadioPixie »

Sorry SoH but that's not a viable system. I think you need to do some research into how repeaters actually work. There are many technical problems, for example: receiver desensitisation, filtering RX/TX signals, logic control, shared antenna system and so forth....

Radios like the Wouxun 920 may have duplex facilities, but wouldn't be able to be used as a repeater on purely 446 MHz.

At less than 0.1 MHz, 446 MHz band is too narrow to have a duplex repeater. Have a look at an UHF/70cm amateur or commercial duplex repeater. They have a split frequency difference of several MHz!!

This is why many people have installed simplex "parrot" repeaters, as it can use the same frequency on both RX and TX, but have to put up with the repeated message. Like this: http://radiopixie.blogspot.co.uk/2012/1 ... eater.html
73 from Dave the Pixie - 26CT052 - G7OPC - CB & Ham Radioaficionado
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Re: 446 Repeater - Offset?

Post by stageofhistory »

Thanks RP... I've seen the Parrot systems and they should work, but was just hoping for more. Oh well...

Desensitisation is a concern I've read about, and my example was extreme worst case, but it's obviously even worse than I thought then! What I haven't read is whether this is a problem which would be exacerbated through increased power? 446 is too narrow a band- accepted, but talking in general does lower power allow for a narrower offsets in repeater systems? Just curious.
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Re: 446 Repeater - Offset?

Post by Classic »

Ignore people that say it can't be done you need a split site for what you want to do,i know someone who sells all the bits needed to get your repeater going.


Here is a example of what is needed.

2 pmr446 sets and 2 other sets they could be cb radios for example.

Site a will be the rx for the pmr446 and there you will have a cb that retransmits the signal to another cb radio at site b where the pmr446 tx is and that is that you have a real pmr446 repeater not some parrot crap lol

It's whether you can be asked to do it all and spend all the money making it happen,to me it's only worth it if you have users in the area that use pmr446
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Re: 446 Repeater - Offset?

Post by RadioPixie »

stageofhistory wrote:Thanks RP... I've seen the Parrot systems and they should work, but was just hoping for more. Oh well...

Desensitisation is a concern I've read about, and my example was extreme worst case, but it's obviously even worse than I thought then! What I haven't read is whether this is a problem which would be exacerbated through increased power? 446 is too narrow a band- accepted, but talking in general does lower power allow for a narrower offsets in repeater systems? Just curious.
In theory yes! But you would have to transmit at a very low power level with poor range. Also transmitters will emit low level spuri (unwanted emission) either side of the carrier which can cause interference to the receiver therefore reducing range. As you may gather there are many issues. So a wider difference between the RX and TX frequencies is better practice (and hopefully with no spuri, which would have to be filtered from the TX side). The filtering used on a typical amateur repeater on both RX and TX is 90dB to prevent receiver overload and reduce unwanted transmitted interference.

As for Classic's proposal, there's many problems. For a start that's a great deal of expense, and to find usable sites and power sources. CB 27MHz would be a crap link between the two sites due to other CB'ers locally and abroad causing interference (yeah man that's key out the CB link and f***'em up, he he he). That could be reduced with CTCSS, but then you have to get two CTCSS enabled CB rigs. Then you have to consider that two sites will have two different RF footprints especially on 446. Then a suitable controller for the CB's and UHF repeater radios. Is this really viable just to talk to a few friends??
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Re: 446 Repeater - Offset?

Post by Classic »

RadioPixie wrote:
stageofhistory wrote: As for Classic's proposal, there's many problems. For a start that's a great deal of expense, and to find usable sites and power sources. CB 27MHz would be a crap link between the two sites due to other CB'ers locally and abroad causing interference (yeah man that's key out the CB link and f***'em up, he he he). That could be reduced with CTCSS, but then you have to get two CTCSS enabled CB rigs. Then you have to consider that two sites will have two different RF footprints especially on 446. Then a suitable controller for the CB's and UHF repeater radios. Is this really viable just to talk to a few friends??
What is to stop anyone doing the same to the rx freq on UHF ? If he can find a site or someones house who would be willing to have the rx and don't live too far away from the tx then it's worth it,that way he could lower the tx power from the cb tx to limit people knowing about it
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Re: 446 Repeater - Offset?

Post by Windy_Miller »

Theres always the LPD channels, 12-13 MHz below..... ;)
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Re: 446 Repeater - Offset?

Post by stageofhistory »

Windy_Miller wrote:Theres always the LPD channels, 12-13 MHz below..... ;)
That was what I was thinking, although I was looking at 443, or maybe forget RF altogether and go wired! Reading up on Split Site set-ups; I'm seeing a lot variation on what would be required in separation distance of the of antennas... What would you be recommend as a ball park distance with dual band white sticks and 5w? What I've read would makes me think I couldn't simply put them at each end of my house... Continued thanks for your help!
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Re: 446 Repeater - Offset?

Post by Classic »

stageofhistory wrote:
Windy_Miller wrote:Theres always the LPD channels, 12-13 MHz below..... ;)
That was what I was thinking, although I was looking at 443, or maybe forget RF altogether and go wired! Reading up on Split Site set-ups; I'm seeing a lot variation on what would be required in separation distance of the of antennas... What would you be recommend as a ball park distance with dual band white sticks and 5w? What I've read would makes me think I couldn't simply put them at each end of my house... Continued thanks for your help!

Give us some more info and i'll help you,i need to know what you are working with and what you plan
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Re: 446 Repeater - Offset?

Post by radiosification »

Just for an idea, on the 2M amateur band, they use 600KHz offsets, and they have to have quite large duplexers for that kind of separation. Anything less than that would be even more difficult, and within the 446 frequencies would be downright impossible. (without considering split site)

Split site probably could work but then you have the problem where some people will hear the repeater and not be able to get in, and others may be getting in but not hearing the repeater. And you also need a reliable radio link between the two.
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Re: 446 Repeater - Offset?

Post by stageofhistory »

Thanks gentleman for your input...

Classic: I didn't really have a plan or equipment at this stage; just a very early idea to try and gathering info, sharing my design on the forum as I went... I think clarification on the issues from just my first question has made this a none starter- No room or desire to invest the amounts needed to do it right!

I may start a new thread in the Commercial board, though, as now I'm considering a cross-band solution using SUK VHF/UHF for occasional use... Drifting further and further from the line of legality!
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Re: 446 Repeater - Offset?

Post by ChrisUK »

It must be possible as the french do it.....
There are a couple of french repeaters on 446 that i hear when conditions are up and i spoke to one of the repeater keepers and his one had the input on Ch 4 and output on Ch 8.
When conditions are right then i can access it with the right ctcss tone and i do hear people use it, but it is not that busy.
We also used to have a 446 echolink station around here a few years ago which was good to listen to....i used it a few times while out mobile, but because of lack of use that shut down.
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Re: 446 Repeater - Offset?

Post by RadioPixie »

Hi SoH

All food for thought. You could use 433 MHz LPD for connection between sites but I think some amateurs won't like it whether it's within the law or not, as they have to share that frequency range on the 70cm amateur band. At least avoid 70cm repeater input frequencies and simplex frequencies like 433.500, 433.550 etc to prevent hassles.

Radioification quote:
Split site probably could work but then you have the problem where some people will hear the repeater and not be able to get in, and others may be getting in but not hearing the repeater. And you also need a reliable radio link between the two.
That's what I meant by RF footprint. 100 metres distance for example can potentially be very different especially for a fringe station.

SoH quote:
What would you be recommend as a ball park distance with dual band white sticks and 5w? What I've read would makes me think I couldn't simply put them at each end of my house...
Can't give you a distance as different handsets will have different receiver overload performance. 5 watts and white sticks is quite a large signal, so the distance would be considerable. Certainly would be greater than a typical house and garden. Also don't forget what I said about low levels of spurious emissions either side of the main carrier TX frequency could cause interference to the receiver if the distance of the two handsets is too close.

I realise that simplex "parrot" repeater isn't everyone's cup of tea, but for costs vs performance vs simplicity it's an instant solution to a locally useful repeater system. To go beyond this means complexity, higher costs and increased unreliability.
73 from Dave the Pixie - 26CT052 - G7OPC - CB & Ham Radioaficionado
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Re: 446 Repeater - Offset?

Post by Windy_Miller »

With LPD channels, you wouldnt need to be multisite. Depending what radios you are using, LPD and PMR might be within their range of ofsetting. So you would only need a single site setup.
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Re: 446 Repeater - Offset?

Post by superdave »

Input on 446 output on 433 simples. With a 13mhz split you wouldn't need any cavities either and you could have the radios right next to each other
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