2 Repeaters 1 Hardline/antenna

[busted_knuckle]

You all are a funny bunch.

All you need is 2 sets of BpBr duplexers. 6 cans each is great but can be done with 4 can sets if the have the proper isolation. No need to interlock transmitter PTT as it will work simultanious. The length of the jumpers from the T from the duplexers to a new T going to the antenna are going to be important. It appears you have a VNA and can measure the return losses to make sure your cables are correct lengths. Some of this will be a little trial error building cables. So be patient. Double shielded coax or heliax is a must.

 

[buddrousa]

This goes against everything that is done by 2way radio shops.
This is why they make combiners. I am glad that Myself or my crew does not have to put our lives on the line for something this hair brain as it will put lives in danger. almost as hair brain as the 110 volt 100 watt VHF repeater running on a generator hooked up a mobile antenna on a fire truck. Sorry but my old school ways were taught to me by Henry Lesh from West Tn in the early 80's.

 

[mikewazowski]

We mix amateur and public safety on the same antenna all the time.

Of course, the amateurs are using properly installed commercial equipment so the only difference is frequency and we tend to put them at the end of the chain so they can easily be disconnected.

 

[buddrousa]

Our system here is VHF uhf 800 on a rx tx combiner broke out at the top to a bogner 800 db420 and db224 on 1 7/8 line but everything is done correctly

 

[prcguy]

Not at all, if the existing duplexers are capable of providing enough isolation and you have the knowledge and equipment to do it there is nothing wrong at all with the idea. If you don't have all of the above in place then don't attempt it.

This goes against everything that is done by 2way radio shops.
This is why they make combiners. I am glad that Myself or my crew does not have to put our lives on the line for something this hair brain as it will put lives in danger. almost as hair brain as the 110 volt 100 watt VHF repeater running on a generator hooked up a mobile antenna on a fire truck. Sorry but my old school ways were taught to me by Henry Lesh from West Tn in the early 80's.

 

[Project25_MASTR]

I'm going to agree with @buddrousa @mikewazowski and @mmckenna. The proper way to do this would be with a combiner/multi-coupler setup. Due to the frequency separation, there is no practical way to do this with a single antenna (home brewed or commercial solution such as RFI's mini-combiner). Stacking multiple band-pass/band-reject duplexer together will not work as you would have to reject the other three frequencies which are frankly spaced too far apart.

You could take your two individual duplexer systems and then combine them with a notchplexer (such as a mobile duplexer) set up to pass everything above 460 MHz on one side and everything below 450 MHz on the otherside. You run into two issues doing this. One is you create excessive loss (looking at almost 5 dB through the system) and the other is you are really going to have to search to find a notchplexer that is stable enough that far away from the notches.

As for your repeater switching system, sure you could throw a T/R relay in front of the duplexers to select which repeater gets to use the antenna but you'd have no way to signal the receiver of the repeater not in use because it would be disconnected. You would also need to have circulators on the TX side of each repeater so if the repeater were to key up while disconnected from the antenna, the load would absorb the power without killing the repeater's transmitter with high reflections.

The only way to get it done is to have a RX antenna up that is full time to one of the repeaters or that is shared between the two repeaters (receive multi-coupler).

My suggestion, find another UHF system at the site and approach the owner to justify a receive multi-coupler/transmit combiner setup without the added cost of an additional tower climb to hang the new antenna and line.

 

[12dbsinad]

For the record, nationwide for 80yrs or more amateurs have installed repeaters on PS towers and buildings sharing sites and site resources. Amateur radio is officially a part of our county and state Emergency Management resource plan. Amateur radios are installed at the State EOC and most county EOC's. In NC and SC amateur sites are not only on State towers but connected by Dept of Public safety microwave networks. Auxcomm is a DHS creation for bringing amateur radio into the EOC and operate BOTH as hams and PS. Many of us are COML's and COMT's. So what is the problem here??? How can the setup be weird since at this point the technology has not been decided or I would not have posted my original question? My intended project will either work or it will not, but if it works it will continue to work reliably. What is your definition of mission critical? In the last 7 years the county trunk has gone down countless times from minutes to hours while the amateur DMR at this site has NEVER gone down even when the public safety repeaters at this site did because generator failed to start (Amateur DMR had robust UPS and lasted till mains restored), so which is more mission critical? Everyone including auxcomm amateurs when activated have immediate access to 2 trunk systems, 4 8TACs, backup conventional repeaters for fire, police, ems and sheriff as well as a simplex plan which is tested weekly by the fire dept anyway. We don't degrade comms we improve them and are a valued part of the responder community.

It is ridiculous that this still needs to be explained. Again I'm asking for help with how to do something from a technical point of view only. Why does it have to be political---this is why in my original post I DID NOT give the back story because I didn't want to waste my and other's time on politics, philosophy or sexual orientation. -----OK, I feel better now... I'm going to inventory my toilet paper, Scotch er I mean hand santitizer and go to bed. And again any help would be great. I think the consensus is that what I want CAN be done, now it's down to how expensive or elegant a solution to use.

With all due respect, you're coming to radio reference asking if you can "tee" 2 repeaters together and set them so only 1 transmits at a time, and 1 repeater is PS. My phone just rang, and it was Mickey Mouse.

Both services absolutely can co-locate, but it needs to be done correctly with the correct engineering and testing, with the right test equipment. I don't know how many times our shop goes out on a PM or a service call to a site (because we can't talk as far as we used too) to find some cobbled together ham or gmrs repeater causing havic on the PS system(s). Some of those sites no longer allow ham repeaters on them, and some still do but they have to be engineered and installed by a professional radio shop.

My philosophy is if you have to come to this site to ask questions, especially something as strange as the initial question, you should not be touching ANY PS repeaters or systems of any type. I understand this is a "secondary" system, but what if that changes, as you mention other systems going down. Good luck.

 

[MTS2000des]

With all due respect, you're coming to radio reference asking if you can "tee" 2 repeaters together and set them so only 1 transmits at a time, and 1 repeater is PS. My phone just rang, and it was Mickey Mouse.

My philosophy is if you have to come to this site to ask questions, especially something as strange as the initial question, you should not be touching ANY PS repeaters or systems of any type. I understand this is a "secondary" system, but what if that changes, as you mention other systems going down. Good luck.

It never ceases to amaze me how anyone would consult a hobbyist forum regarding life safety/IDLH/public safety radios then get all butt hurt when advised "you really should be seeking PROFESSIONAL guidance from a PROFESSIONAL firm".

It's one thing if a ham wants to do something for HAM purposes. No one is going to die (despite the ARRL whacker mantra about ham radio saving lives). Public safety radio, OTOH, isn't a game and needs to be done right to industry standard best practices or not at all.

 

[rescuecomm]

I must be the only one who read the post that indicated the public safety user access was secondary (non-critical). Their communications are carried on other systems. Okay, l get the gist of the matter is that secondary public safety use doesn't compute. Maybe the OP should put his repeater on an IB frequency. Then the guys here can reset and answer without prejudice.

Bob

 

[mikewazowski]

The other thing to consider is multicoupling one repeater and hanging the duplexor off the end.

 

[otobmark]

Due to the frequency separation, there is no practical way to do this with a single antenna (home brewed or commercial solution such as RFI's mini-combiner). Stacking multiple band-pass/band-reject duplexer together will not work as you would have to reject the other three frequencies which are frankly spaced too far apart.

This I will check out. As per my previous post the antenna works fine on the frequencies to be used. May be a fluke but the 441 freq is in a sweet spot (I don't remember how wide that spot is or where the falloff begins)

My suggestion, find another UHF system at the site and approach the owner to justify a receive multi-coupler/transmit combiner setup without the added cost of an additional tower climb to hang the new antenna and line.

This idea is not necessarily off the table but I wanted to avoid the negotiations if possible. The 2nd UHF antenna is slightly above the first and on a different leg of the tower so would obviously not be in a physical null. Would that still be OK?

My philosophy is

I didn't ask a philosophical question. Your philosophy is not irrelevant if it is informed by experience but would be far more interesting and useful to me if you had shared your expertise on the engineering first, and then your opinion on how good an idea it is. Can you design a 2 repeater 1 antenna setup that will work? If you can tell me how you specifically would do it and the advantages/disadvantages of it I will be closer to an informed opinion.

All you need is 2 sets of BpBr duplexers. 6 cans each is great but can be done with 4 can sets if the have the proper isolation. No need to interlock transmitter PTT as it will work simultanious.

Thank you very much! I have a starting point. I didn't want to interlock the repeaters but thought it "might" get around circulator.

We mix amateur and public safety on the same antenna all the time.

Thank you for that, for a moment I thought I'd drifted into an alternate universe. A few months ago I met some amateur radio guys in KY who were doing that. I didn't see their sites. Also, not so much in my county but in the coastal areas the repeater groups contain people who have or work in radio shops and some are dealers for Moto, Kenwood, and others. Amateur radio does not mean that the people are amateurs, many are professional engineers, as well as doctors, lawyers and maybe indian chiefs.

Not at all, if the existing duplexers are capable of providing enough isolation and you have the knowledge and equipment to do it there is nothing wrong at all with the idea. If you don't have all of the above in place then don't attempt it.

I have no interest in putting up anything that "doesn't work". I guess I thought that was a given. All of the actual ideas stated here are in effect "splitter combiners" no matter what we decide to call them.

It never ceases to amaze me how anyone would consult a hobbyist forum regarding life safety/IDLH/public safety radios then get all butt hurt when advised "you really should be seeking PROFESSIONAL guidance from a PROFESSIONAL firm".

So, everyone on this forum is a hobbyist, including you? I was under the impression that many of the members here are in fact working professionals and would provide far more diverse, collaborative, and comprehensive information than a given single "radio shop", which in my area are NOT engineers--they are technicians and they make plenty of mistakes. The more information I get the better result I will get even if the result is to not do it. From the start I worried about performance degradation. Reliability is an entirely separate issue in that even a poor design can be reliable and an excellent design not. My issue is not the "quality" of components but the type of components. I'm not building filters out of tennis ball cans and rusted out fire extinguishers!

It's one thing if a ham wants to do something for HAM purposes. No one is going to die (despite the ARRL whacker mantra about ham radio saving lives). Public safety radio, OTOH, isn't a game and needs to be done right to industry standard best practices or not at all.

So by definition Ham purposes are always inferior and never to industry standards? Public Safety comms ARE a game--one of money, bribes, kickbacks and politics in general. Our statewide trunk system has ongoing problems and is ridiculously complex. While there is supposed to be redundant paths to each site there are not. If certain sites were damaged they would bring down almost half the state backbone (still sitetrunk though). One of our hurricanes took out the outer 1/3 of our system due to damage and inability to refuel generators with nothing but amateur repeaters on the air for several days (The one in particular that I remember had a solar backup). We did learn to put all tower houses well above flood plane (duh) and provide better flood resistant access for service/fuel after our epic fail.
My ultimate point is judge the technology and implimentation not judge the motives or intelligence of people putting it forth--called stereotyping. Smart people sometimes have dumb ideas and dumb people sometimes have smart ideas so lets stick with the actual idea.

 

[otobmark]

The other thing to consider is multicoupling one repeater and hanging the duplexor off the end.

I think the frequencies are too far apart if I'm understanding correctly. 1 repeater is listening 446 and the other 465. The 460 tx of the second repeater would fall between the 2 receive frequencies instead of outside of them. Dang, I'm going to have to draw some diagrams to get this straight in my head---
I keep thinking about what Project25 said :
"Stacking multiple band-pass/band-reject duplexer together will not work as you would have to reject the other three frequencies which are frankly spaced too far aparts"

Our 800mhz splitter/combiners have ridiculous losses coming and going. Have to use preamps at the top of the tower on the receive arrays and put in auxiliary fans on top of AC to keep the combiners from overheating. That image is so ingrained in my mind that the term splitter/combiner gives me a Pavlovian response....

Not to give too much ammunition to the nay-sayers but there is a fundamental difference typically between commercial radio and amateur radio in that hams are always looking for range and ability to work weak signals. Commercial (or PS) is usually based on much stronger more mature RF environment. Signals go below -90db or so and it is time to put up fill in sites or go back to the drawing board. So for the commercial crowd losses are not as critical. I have never been a fan of single high sites and even in amateur prefer multiple lower sites linked for more reliable coverage as well as redundancy. At this particular site I don't want to lose range/performance on the amateur side while the PS side is not nearly as concerned.

 

[prcguy]

What make/model duplexers do you you have now? See what the band pass characteristics are and how they look 10-20MHz out of band. If they are 50-60dB or more down looking at the 460 transmit to the 440 receive and so on, then you probably have more than enough isolation to T them together with critical lengths of cable. If the 460 transmit filter is 50dB down at the 440 receive frequency and the 440 receive filter is 50dB down from the 460 transmit, you have 100dB of isolation right there. The transmit to transmit isolation is not as critical and you would need an isolator on each transmitter which will add another 25-35dB isolation.

If your current duplexers are notch only, then all bets are off.

I think the frequencies are too far apart if I'm understanding correctly. 1 repeater is listening 446 and the other 465. The 460 tx of the second repeater would fall between the 2 receive frequencies instead of outside of them. Dang, I'm going to have to draw some diagrams to get this straight in my head---
I keep thinking about what Project25 said :
"Stacking multiple band-pass/band-reject duplexer together will not work as you would have to reject the other three frequencies which are frankly spaced too far aparts"

Our 800mhz splitter/combiners have ridiculous losses coming and going. Have to use preamps at the top of the tower on the receive arrays and put in auxiliary fans on top of AC to keep the combiners from overheating. That image is so ingrained in my mind that the term splitter/combiner gives me a Pavlovian response....

Not to give too much ammunition to the nay-sayers but there is a fundamental difference typically between commercial radio and amateur radio in that hams are always looking for range and ability to work weak signals. Commercial (or PS) is usually based on much stronger more mature RF environment. Signals go below -90db or so and it is time to put up fill in sites or go back to the drawing board. So for the commercial crowd losses are not as critical. I have never been a fan of single high sites and even in amateur prefer multiple lower sites linked for more reliable coverage as well as redundancy. At this particular site I don't want to lose range/performance on the amateur side while the PS side is not nearly as concerned.

 

[otobmark]

What make/model duplexers do you you have now? See what the band pass characteristics are and how they look 10-20MHz out of band.

If your current duplexers are notch only, then all bets are off.

The amateur repeater in place has high grade cans (Sinclair Q3220E 406-512mhz) & X265UM narrow preselector 435-470.
Sinclair was kind enough to provide correct jumpers which was nice.

As to specs I will have to look it up.

The 460 machine is yet to be assembled. I have a spare xpr8400 that I was planning on using.

 

[prcguy]

The specs don't show out of band performance but I think the Sinclair Q3220E will have at least 50dB isolation between the 440 and 460 range. If the other repeater duplexer has similar specs you should have a very simple solution to combine them, although a knowledgeable person with test equipment would have to test and verify isolation and operation with the right length cables to a common T adapter. If it were me I would go for it because I have the means and equipment to pull it off.

What make/model duplexers do you you have now? See what the band pass characteristics are and how they look 10-20MHz out of band. If they are 50-60dB or more down looking at the 460 transmit to the 440 receive and so on, then you probably have more than enough isolation to T them together with critical lengths of cable. If the 460 transmit filter is 50dB down at the 440 receive frequency and the 440 receive filter is 50dB down from the 460 transmit, you have 100dB of isolation right there. The transmit to transmit isolation is not as critical and you would need an isolator on each transmitter which will add another 25-35dB isolation.

If your current duplexers are notch only, then all bets are off.

As to specs I will have to look it up.

The 460 machine is yet to be assembled. I have a spare xpr8400 that I was planning on using.

 

[otobmark]

a knowledgeable person with test equipment would have to test and verify isolation and operation with the right length cables to a common T adapter. If it were me I would go for it because I have the means and equipment to pull it off.

For tweaking I have resources in people and equipment. Thank you so much for cutting to the chase.
Thanks also to all who offered constructive suggestions. Glad to not be shooting in the dark, I just needed a starting point.

 

[Project25_MASTR]

If you are seeing insane losses on 800 MHz systems, something is not right. Cavity combiners (a band pass cavity and circulator) have an insertion loss of roughly 2 dB. 100W in gets you 60W out. Now using a hybrid combiner you'll see something more along the lines of 8 dB of loss (45 W in will get you 8 W out) but there aren't a ton of reasons to do that for a fixed site. As far as receive multicouplers go, they are basic division circuits. Simple conservation of energy, 1 W into a 2 receiver split gets you 1/2 W out (3 dB loss), 4 receiver would see a 6 dB loss and a 10 would have a 10 dB loss. That's part of why pre-amps are used, to fight the loss through the receive system. Preselectors will induce some additional loss but again, pre-amps.

In a UHF receive coupler, you'd typically see two preselectors. One with a pass band (window) of ~455-460 MHz and one with a pass band of ~465-470 MHz tee'd together. The rejection outside of the passbands will determine how far the antenna needs to be.

 

[prcguy]

Its just a little more complex than that. Lossy Hybrid combiners must be used when all the transmitter frequencies to be combined are too close together for lower loss cavity filter types to give adequate isolation due to filter skirts. If you want to combine several transmit frequencies all within a MHz then you must go 3dB Hybrid type and dual isolators. If you have 10" cans on a filter type combiner you can maybe get within a MHz for each transmit frequency but with a single 4" or 5" can, no.

Even with a single 10" cavity filter at UHF you only get about 12dB down 1MHz away using 0.5dB filter insertion loss and that would only give you about 24dB isolation between two transmitters each running a 10" can. A dual isolator will cut that down an additional 70dB or more so there is little chance two transmitters could ever mix and create IMD products.

Yes the preamp in a master receive system makes up for divider loss but you have to be careful about the necessary preselector in front of it. Every fraction of a dB loss in the preselector directly adds to the system noise figure. At most busy radio sites its not a big issue because the noise floor at the site is already much higher than a similar location with no radios and I've seen the noise floor 20dB higher than normal at some So Cal repeater sites. For a lonely hilltop with only one or two repeaters you want to make the most of the quiet noise floor and keep your system noise figure to a minimum to enjoy handhelds being able to access the repeaters at much greater distances.

Fortunately the OP is running two systems about 20MHz apart and that paves the way for easier and cheaper methods of combining.

If you are seeing insane losses on 800 MHz systems, something is not right. Cavity combiners (a band pass cavity and circulator) have an insertion loss of roughly 2 dB. 100W in gets you 60W out. Now using a hybrid combiner you'll see something more along the lines of 8 dB of loss (45 W in will get you 8 W out) but there aren't a ton of reasons to do that for a fixed site. As far as receive multicouplers go, they are basic division circuits. Simple conservation of energy, 1 W into a 2 receiver split gets you 1/2 W out (3 dB loss), 4 receiver would see a 6 dB loss and a 10 would have a 10 dB loss. That's part of why pre-amps are used, to fight the loss through the receive system. Preselectors will induce some additional loss but again, pre-amps.

In a UHF receive coupler, you'd typically see two preselectors. One with a pass band (window) of ~455-460 MHz and one with a pass band of ~465-470 MHz tee'd together. The rejection outside of the passbands will determine how far the antenna needs to be.

 

[Project25_MASTR]

Its just a little more complex than that. Lossy Hybrid combiners must be used when all the transmitter frequencies to be combined are too close together for lower loss cavity filter types to give adequate isolation due to filter skirts. If you want to combine several transmit frequencies all within a MHz then you must go 3dB Hybrid type and dual isolators. If you have 10" cans on a filter type combiner you can maybe get within a MHz for each transmit frequency but with a single 4" or 5" can, no.

Even with a single 10" cavity filter at UHF you only get about 12dB down 1MHz away using 0.5dB filter insertion loss and that would only give you about 24dB isolation between two transmitters each running a 10" can. A dual isolator will cut that down an additional 70dB or more so there is little chance two transmitters could ever mix and create IMD products.

Yes the preamp in a master receive system makes up for divider loss but you have to be careful about the necessary preselector in front of it. Every fraction of a dB loss in the preselector directly adds to the system noise figure. At most busy radio sites its not a big issue because the noise floor at the site is already much higher than a similar location with no radios and I've seen the noise floor 20dB higher than normal at some So Cal repeater sites. For a lonely hilltop with only one or two repeaters you want to make the most of the quiet noise floor and keep your system noise figure to a minimum to enjoy handhelds being able to access the repeaters at much greater distances.

Fortunately the OP is running two systems about 20MHz apart and that paves the way for easier and cheaper methods of combining.

There is actually another way around using closely spaced channels with cavity combiners. Multiple transmit combiners. It does require multiple transmit antennas (additional isolation comes from antenna separation) but it isn't an uncommon setup for anyone familiar with the GTR8000 ESS. Also has some additional benefits such as reduced capacity outages versus entire outages due to an antenna system issue.

 

[prcguy]

I've combined high power C band and Ku band uplinks using 3dB hybrid combiners to put eight 2.4kW transmitters onto one waveguide at Ku band a 3.5kW transmitters at C band.. We actually had 16 2.4kW transmitters and had to use two uplink antennas because the filter skirts in the hybrid combiners were not sharp enough to combine consecutive transponders so we had to put every other one on a second antenna. But yes, with two or more antennas you can combine a boat load of transmitters with just about any frequency spacing.

There is actually another way around using closely spaced channels with cavity combiners. Multiple transmit combiners. It does require multiple transmit antennas (additional isolation comes from antenna separation) but it isn't an uncommon setup for anyone familiar with the GTR8000 ESS. Also has some additional benefits such as reduced capacity outages versus entire outages due to an antenna system issue.