Multicoupling Advice - UHF 3 Channels

[mrtor]

Good Afternoon from Sunny Melbourne, Australia
Seeking some advise on the best way to multicouple three (3) UHF frequencies into a single antenna
I need something relatively portable, the transmitters and power supplies will all be in a rack on wheels. Running everything at 5 watts

Freq 1 472.2750 tx 477.4750 rx
Freq 2 473.8750 tx 478.0750 rx
Freq 3 474.4250 tx 479.6250 rx

I have no real idea on this aspect of things... Do I still have duplexers as well or does the multicoupling take care of the whole TX/RX stuff and I just connect my antenna and away I go ?

If anyone can suggest brands/makes/models to pursue that would be helpful and also some indicative idea on approx costs as I understand it is substantially cheaper to get this stuff from the USA and have it shipped than it is to get it built by the very limited number of vendors here in Australia

Any help appreciated
Thanks in advance
Mike

[d119]

A multicoupler does not take care of duplexing, it just allows a single antenna to be properly connected to multiple receivers. On the transmit site, you'd have a combiner that does the same thing for multiple transmitters.

You could then couple the output of the combiner and the input of the multicoupler through a window filter to put everything on one antenna, but there are caveats to this such as frequency spacing, TX/RX splits, etc.

Most systems of this type are purpose built and tuned by the manufacturer for their intended end systems. Retuning these systems in the field for other frequencies, offsets, etc. is a sort of "black magic".

[Bill_G]

Multicouplers are used for receivers. Since you also want to transmit for repeater operation, you need duplexers. Because you are combining three repeaters into to one antenna, the duplexers need to be bandpass, not reject only (low cost mobile type), to keep one transmitter from clobbering another. Because all your channels are within three meg of each other, you need pass reject duplexers with isolators since most duplexers have a min separation of 3Mhz.

Or you need a combiner with min channel spacing around half a meg for the three transmitters, a multicoupler for the receivers, and a weirdly tuned pass reject duplexer to put it all into one antenna.

It will be an interesting project with some moderate insertion losses, but if all you are expecting is 5w at the antenna, you have some headroom to play with. It won't end up being very small, but with some careful planning it could be rolled around by one guy.

[escomm]

Most systems of this type are purpose built and tuned by the manufacturer for their intended end systems. Retuning these systems in the field for other frequencies, offsets, etc. is a sort of "black magic".

Combiners can't be retuned? Who do you work for, Sinclair or something? Sure it ain't like tuning a duplexer but it certainly ain't a black art either

[d119]

Most systems of this type are purpose built and tuned by the manufacturer for their intended end systems. Retuning these systems in the field for other frequencies, offsets, etc. is a sort of "black magic".

Combiners can't be retuned? Who do you work for, Sinclair or something? Sure it ain't like tuning a duplexer but it certainly ain't a black art either

Oh come on Jeff, you know damn well what I meant. You really need a network analyzer and some really good knowledge of RF to make it work... But then again, I'm used to combiners with 10+ channels, if you know what I mean

[Bill_G]

The problem here is three pairs of close freqs into a single antenna. The cavities will not be small fer sure. Or cheap.

[mrtor]

Multicouplers are used for receivers. Since you also want to transmit for repeater operation, you need duplexers. Because you are combining three repeaters into to one antenna, the duplexers need to be bandpass, not reject only (low cost mobile type), to keep one transmitter from clobbering another. Because all your channels are within three meg of each other, you need pass reject duplexers with isolators since most duplexers have a min separation of 3Mhz.

Or you need a combiner with min channel spacing around half a meg for the three transmitters, a multicoupler for the receivers, and a weirdly tuned pass reject duplexer to put it all into one antenna.

It will be an interesting project with some moderate insertion losses, but if all you are expecting is 5w at the antenna, you have some headroom to play with. It won't end up being very small, but with some careful planning it could be rolled around by one guy.

Hi Bill

Thank you for that insight, does my problem get easier &/or cheaper if I go with a TX Antenna and an RX Antenna ?

Thanks in advance from the Newbie into this stuff

Michael

[Bill_G]

Hi Michael. A tiny bit, but not much. Using two antennas means you could cut one set of cavities from the total, but then you would have to add a window filter (fancy name for broad bandpass cavity) to your receiver line to keep the transmitters out.

Your problem is the same one we have at hilltops. You want the minimum number of antennas, zero self interference, and complete isolation between the transmitters with the least amount of loss while supporting as many stations as necessary. This is when you run into the limitations of passive cavities. All this work is done with cavities. No matter what name we apply for the purpose - multicoupler, window filter, combiner, duplexer - it's all done with the same basic passive tunable can arranged to pass the frequency of interest while rejecting all others. Multiple stages of cavities will interact with each other, cable lengths become critical, insertion losses pile up, and the whole thing can become a holy mess if done wrong.

Let's look at the Telewave 1031 series 6" four port combiner. You can combine four transmitters into one antenna if the channels are at least 300khz apart. It has approximately 3db insertion loss which means you lose half your power. It's 19" rack mount, 12" high, and 17" deep. 60lbs.

Let's look at the Telewave 2033 series four port multicoupler. You can have up to four receivers to one antenna. It provides up to 18db of gain if needed. Otherwise, expect at least 6db insertion loss. It's 19" rack mount, 5.25" high, and 3" deep. Requires AC or DC power for the amplifier. 4lbs.

Let's look at the Telewave 2023 8 cavity bandpass filters. You need at least one of these for the receivers before the multicoupler panel to reject the transmitters. It's 19" rack mount, 8.75" high, and about 10" deep. 28lbs.

So, you'll use up slightly over two feet of rack space just for the equipment listed above, plus it will weigh just under 100lbs not counting the rack. You can cut down the size a little bit by using a four port splitter instead of the rcvr panel. You'll lose the gain, but you may need to cut gain anyway to reduce desense during final tune up.

You can probably get away with coupling the rcvr bandpass filter input and combiner output ports together through a simple Tee to the antenna. Someone will need to tune the whole array for the freqs of interest. Then they will need to set the xmit power and check desense first through the master antenna port (Tee), and then through the load (antenna).

I have not looked up the pricing yet.

This will work, and it will work well, but it's not going to be small, light, or cheap.

[Bill_G]

I took a peek at the pricing, and doing it this way could easily cost $15K for new equipment.

Which is why move in costs and monthly rentals to sites is so expensive. Multiply that out over all users on all bands, and it turns into a whole lotta money real fast.

[mrtor]

I took a peek at the pricing, and doing it this way could easily cost $15K for new equipment.

Which is why move in costs and monthly rentals to sites is so expensive. Multiply that out over all users on all bands, and it turns into a whole lotta money real fast.

Hello Again Bill

Thank you for that overview that was really helpful. Looks like it may not be that much more to do it here in Australia then because I was told to allow around $6K PER CHANNEL so if I take your estimate and factor in the shipping of something that weighs 100 lbs to Australia we are probably on the mark.

Looks like an expensive project for me

Once again thank you for your through explination to a new comer to the world of cavities

Cheers
Mike

[Bill_G]

Mike - what is your application going to be? Short term rental events, music concerts, sporting events, that sort of thing? Is there a specific reason these repeaters need to use the same antenna? If there is any way to get several hundred feet separation between the repeaters, and there is little or no other competition with other on site repeaters, you can get away with using the low cost mobile duplexers on each repeater.

[mrtor]

Mike - what is your application going to be? Short term rental events, music concerts, sporting events, that sort of thing? Is there a specific reason these repeaters need to use the same antenna? If there is any way to get several hundred feet separation between the repeaters, and there is little or no other competition with other on site repeaters, you can get away with using the low cost mobile duplexers on each repeater.

Bill
Primarily short term events could be event comms could be broadcast as we do a lot of both
Reason why I was going for possibly 1 or 2 antennas was that I have a nice 70ft mast that we could stick up to give good coverage on the top of a mountain for example Single or 2 antennas = easy set up, however the cost at the moment is a tad prohibitive based on estimates above

Does my scenario change anything ?

Thanks again
Michael

[Bill_G]

Sounds like you want short term, wide area coverage if you are putting the antennas on a hilltop rather than down at the event. ie: 50k run rather than circle track car racing. And you need three channels to support the basic services. ie: security, concession, & admin, or craft, production 1, & production 2. How much traffic is on the air when it gets busy? Could a single MotoTrbo repeater in digital mode work? It will let you have two simultaneous conversations at once, and it can be set up in talk groups so that one group does not hear another until they change to that "channel". I wouldn't use it if you are trying to produce live television because the digital mode is almost a quarter second behind real time. But, for everything else it would be fine. One Trbo repeater, one duplexer, one antenna, no combining necessary.

[mrtor]

Sounds like you want short term, wide area coverage if you are putting the antennas on a hilltop rather than down at the event. ie: 50k run rather than circle track car racing. And you need three channels to support the basic services. ie: security, concession, & admin, or craft, production 1, & production 2. How much traffic is on the air when it gets busy? Could a single MotoTrbo repeater in digital mode work? It will let you have two simultaneous conversations at once, and it can be set up in talk groups so that one group does not hear another until they change to that "channel". I wouldn't use it if you are trying to produce live television because the digital mode is almost a quarter second behind real time. But, for everything else it would be fine. One Trbo repeater, one duplexer, one antenna, no combining necessary.

Have to stay in the analogue domain for exactly the reason you said... Time lag when we do broadcast on air, wouldn't be an issue for the event comms except I have 200 portables and 300 mobiles all analogue already

Potentially all 3 channels going at once and hammered hard doing event comms

So looks like I need to invest in some serious additional infrastructure as you originally suggested

Do it right, is going to cost me

[Bill_G]

Indeed, it will cost. But, it will last forever. It is a one time investment. Assembled by the right constructors in the right case, it will take the abuse of travel albeit be the size of a Marshall speaker. These systems typically support multiples of four repeaters. So, you have an opportunity to add another channel if necessary. It is worthwhile to pursue.

Cheers, Bill

[escomm]

There's a lot of 4 channel combiners on the 'bay right now for about 3 grand. FWIW.

[mrtor]

There's a lot of 4 channel combiners on the 'bay right now for about 3 grand. FWIW.

Thanks escomm I'll take a look at what is there, I may need to come back here to ask if something will be suitable... I assume that is OK with the rules on Ebay stuff here ?

[RFguy]

Multi-coupler are not just for receivers, check out the Sinclair C3034 RezLoc series. One for every RX and TX frequency. It would be optional, but add a single or dual stage isolator on each TX for added isolation.

They run about $1200 CDN per unit, so about $7,200 for the 3 required for 3 repeaters. The spec sheet shows 1 MHz minimum, but I have seen them in use down to 500 KHz.

http://www.sinctech.com/catalog/resourc ... 3.1-DI.pdf

[mrtor]

Multi-coupler are not just for receivers, check out the Sinclair C3034 RezLoc series. One for every RX and TX frequency. It would be optional, but add a single or dual stage isolator on each TX for added isolation.

They run about $1200 CDN per unit, so about $7,200 for the 3 required for 3 repeaters. The spec sheet shows 1 MHz minimum, but I have seen them in use down to 500 KHz.

http://www.sinctech.com/catalog/resourc ... 3.1-DI.pdf

Thanks for that, need more money

But I guess, if I am going to do it, I have to do it right !

[Pump3]

Guess you can get anything on ebay lol
http://www.ebay.com/itm/Complete-Sincla ... 415ab98492

This setup is for seperate Tx and Rx antennas however....

[mrtor]

Guess you can get anything on ebay lol
http://www.ebay.com/itm/Complete-Sincla ... 415ab98492

This setup is for seperate Tx and Rx antennas however....

Being a newbie at this combiner stuff, from what I understand Sinclair gear is actually very good

Is this thing worth the money ? It certainly is a cheaper option, shipping will be A LOT I guess

Any thoughts from those who know much more than me appreciated

Mike

[Pump3]

Sinclair is top of the line, you don't get any better then Sinclair, those folks really know RF and make great products

JagRF, http://jagrf.com/ in Ontario, Canada are also great people, very smart, and do a lot of interesting work, we've bought their antennas and filtering products and have been very happy, they do an excellent job and stand behind their products, if there's anyone out there I would order this stuff from besides Sinclair directly, it would be these folks, to buy this stuff used these are the only folks besides the factory I would trust 110% to do it right...

Even if you don't get this particular product, which would probably work great for you, I highly recommend contacting Jag and see what they have in stock...

[Astro Spectra]

Since you're in Oz why don't you simply call RFI :

RF Industries Ltd
46 Corporate Boulevard
PO Box 265
Bayswater, VIC, 3153, Australia

Phone: +61 3 9751 7500
Fax: +61 3 9751 7588

They manufacture antennas, cavities, trasmit combiners, and receiver multicouplers. Their customer service is excellent. And they’ll be aware of any ACMA rules that you need to be complying with.

You should count on running two antennas and your freqs look fine for TX combining but if necessary RFI can supply 3/4 wave high Q cavites for extra selectivity.

[mrtor]

Since you're in Oz why don't you simply call RFI :

RF Industries Ltd
46 Corporate Boulevard
PO Box 265
Bayswater, VIC, 3153, Australia

Phone: +61 3 9751 7500
Fax: +61 3 9751 7588

They manufacture cavities and multicouplers. Their customer service is excellent. And they’ll be aware of any ACMA rules that you need to be complying with.

Hi Astro Spectra

The discussion started as I had a copy of a quote from RFI for a similar spec system that was around $20K but I was told I could get it much cheaper from the USA. Prior to me starting this thread, I didn't know much about this at all.

I have since read some great stuff on Repeater-Builder.com and have a slightly better (albeit it none technical) understanding on exactly what I need together with what info has been very helpful from here.

I have sent the Ebay seller in the USA a message to get some details on shipping and see what I am up for.. Looks like it will still be buckets of cash cheaper than getting it from RFI, but we will see

Cheers
Mike

[Bill_G]

That Sinclair on eBay is a nice package. It is a two antenna option, but it would work if you put enough space between the rx and tx antennas - on the order of 100ft horizontal, or 25-40ft vertical. You probably don't need the power monitor, but you might like it. And. like some of the other choices we've discussed, it comes in a four pack meaning you can add another repeater if you want. You should negotiate a cabinet with them, have them tune it up, put it in a wooden coffin (+$200ca), and have it shipped by air freight (DHL, Cameron, counter to counter international flight). You'll get a complete turn key system for around $10K. Not bad.

[escomm]

Sinclair is top of the line, you don't get any better then Sinclair, those folks really know RF and make great products

Let's not get carried away here. They are good. They are not the best.

[RFguy]

That Sinclair on eBay is a nice package. It is a two antenna option, but it would work if you put enough space between the rx and tx antennas - on the order of 100ft horizontal, or 25-40ft vertical.

You probably don't need that much isolation. If it was a Sinclair designed unit, it would probably be configured for the Sinclair 310C2-2 antenna. It has about 30 dB of antenna to antenna isolation. About 3 feet separation.

http://www.sinctech.com/catalog/product.aspx?id=2709
http://www.sinctech.com/catalog/resourc ... BK)-DI.pdf

[Bill_G]

That Sinclair on eBay is a nice package. It is a two antenna option, but it would work if you put enough space between the rx and tx antennas - on the order of 100ft horizontal, or 25-40ft vertical.

You probably don't need that much isolation. If it was a Sinclair designed unit, it would probably be configured for the Sinclair 310C2-2 antenna. It has about 30 dB of antenna to antenna isolation. About 3 feet separation.

http://www.sinctech.com/catalog/product.aspx?id=2709
http://www.sinctech.com/catalog/resourc ... BK)-DI.pdf

Nice! That would do it. It would make an easy deployment for mrtor. And they are available form Tessco for about $1600usd.