Feasibility of a portable repeater

[K7NOP]

I have been investigating the feasibility of a temporary, portable repeater. So far my research has basically showed that both cost, performance and reliability points toward UHF as the better contender as there is the availability of mobile-sized duplexers that are designed to be moved around and are generally much cheaper. 100 dollars (chinese) to 3-400 (american-made).

The intended use case is vehicle mounted, with the ability to operate in-motion from a vehicle mounted antenna.

So far I have not looked into the radios or repeater controller. These are not an issue until I solve or clarify my concerns of the antenna network.

Regulatory:
My local repeater coordinators provide a temporary repeater pair, so that would be my target frequency, and I'd use a non-standard PL tone to avoid interference (enc/dec). Am I missing any other regulatory issues? Do I just have the repeater identify as my callsign?

Duplexer:
Should I plan on obtaining the lab equipment to (re)tune the duplexer given it will exist in a mobile environment? I haven't found much info on the ebay/chinese 100 dollar duplexers, namely the coating on the inside of the cavitys. Is there a big difference between these duplexers and something like bridgecom's offering?

Antenna feed line:
My option for antenna feed line is thin RG316 coax. I could probably go up to 1/8-1/4 inch coax, i'm basically closing a door or trunk on this. This could literally be the dealbreaker of the vehicle-mounted repeater.

Antenna:
I don't own a dedicated UHF antenna but my options are the somewhat cheap diamond/comet/etc mobile whips. I don't mind obtaining a special antenna. Whats a good solution for this?

Is there anything I'm missing so far? I tried to ask a question in each category and propose the solutions that given cost/space constraints would work best for me.

I'm slowly getting through the repeater-builder.com reference material, and have studied a few of these topics.

Thanks for your time,
Jordan
K7NOP

 

[lmrtek]

Yes a uhf mobile repeater is pretty easy and cheap.
You should avoid the Chinese mobile duplexers as they are junk.
Buy a celwave 633-6A and it needs to be professionally tuned using a
service monitor with a tracking generator.

A 1\4 wave uhf whip works fine for the antenna and the 12ft of rg58
that comes on mobile mounts will be just fine.

 

[K7NOP]

Where might I find one of these celwave duplexers? I my target frequency is 440.2750 and I'm really only finding their 450-470mhz model for sale.

Any suggestions on how to find someone willing to tune the duplexer with their service monitor? Local ham club?

Any thoughts on the bridgecom systems duplexer?

https://www.bridgecomsystems.com/co...cts/uhf-6-cavity-duplexer?variant=23459696071

Thanks,
Jordan
K7NOP

 

[Project25_MASTR]

Another option for duplexers are Epcom’s duplexers. They spec out as advertised (actually a little better) and are $215 or so shipped from El Paso, TX (Made in Mexico).

Celwave got bought out by RFS a while back and nothing really changed about the duplexers. Still a mainstay but in my opinion, getting silver plated connectors and good tuning slugs for less put the Epcom offering in my favor.

As far as the repeater goes, I’d try to find a LPI Motorola R1225. Easy to use, capable of stripping PL from ID, and the size of a GM300.


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[K7NOP]

I'm seeing R1225s that look quite different. One appears to be just a radio and one looks like a desktop cabinet. Also, I'm only seeing one RF connector on the back of the "just a radio" and possibly one on the front?

 

[kayn1n32008]

You should avoid the Chinese mobile duplexers as they are junk.

For the price they are about the only Chinese RF components I would buy. Every one I have used have tuned up at or better than the Sinclair duplexer they are a copy of.

There is nothing wrong with them, besides being a PITA to tune due to the tuning rod/screw/nut design.

Do not rely on the factory tuning. Do it yourself or get someone who has the gear to do it.

... and the 12ft of rg58
that comes on mobile mounts will be just fine.

Huh??? RG-58??? That’s like 75% shield??? For a repeater???

Wow, just wow.



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[mmckenna]

I have been investigating the feasibility of a temporary, portable repeater. So far my research has basically showed that both cost, performance and reliability points toward UHF as the better contender as there is the availability of mobile-sized duplexers that are designed to be moved around and are generally much cheaper. 100 dollars (chinese) to 3-400 (american-made).

If you can, find one that has locking nuts on the rods. Some of the cheap ones do not. Vibration from being used in a mobile environment can detune them.

Duplexer:
Should I plan on obtaining the lab equipment to (re)tune the duplexer given it will exist in a mobile environment?

Depends if you can find the right gear at a decent price. However, you might be better off finding a case with some way to provide some shock absorption to reduce vibration. Check around, you may find a local ham that can tune them for you.

I haven't found much info on the ebay/chinese 100 dollar duplexers, namely the coating on the inside of the cavitys. Is there a big difference between these duplexers and something like bridgecom's offering?

I'm not really much help on the differences between them. I did recently have to tune a couple of Bridgecom repeaters, including their duplexers. Not horribly impressed with them, but they'll do the job.

Antenna:
I don't own a dedicated UHF antenna but my options are the somewhat cheap diamond/comet/etc mobile whips. I don't mind obtaining a special antenna. Whats a good solution for this?

Skip the hobby antennas. Get a decent commercial mobile antenna. Larsen antennas are my personal favorite. Go with the NMO mounts, that way you have the flexibility to change them out easily. A much wider selection of antennas with the NMO mounts. I've not found that Diamond, Comet or the other amateur brands are any cheaper. On the contrary, the name brand commercial stuff (Larsen, Laird, Maxrad, etc) are often cheaper and better quality. I've got 30 year old Larsen antennas I'm running. Skip the Chinese stuff, Tram, Browning, etc. It might save you a dollar or two, but you'll pay in the long run.

I'd start with a simple 1/4 wave. In a mobile environment higher gain might lead to more issues, picket fencing, radiation angles, etc. You can get those for less than $10.00. Add an NMO mount and that'll run you another $15.00.

Is there anything I'm missing so far? I tried to ask a question in each category and propose the solutions that given cost/space constraints would work best for me.

Use a separate battery for the repeater. That way you won't have issues with starting/stopping the engine or the repeater dragging down your starting battery. Should be pretty easy to figure out your current draw based on expected use, power levels, etc. Use a battery isolator so it'll charge off the car.

 

[kayn1n32008]

Still a mainstay but in my opinion, getting silver plated connectors and good tuning slugs for less put the Epcom offering in my favor.

I will look them up. I have not heard of them before. Good point on the silver.



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[K7NOP]

Huh??? RG-58??? That’s like 75% shield??? For a repeater???

Wow, just wow.

How am I supposed to interpret this. Which coax grade should be used for a portable repeater?

Depends if you can find the right gear at a decent price. However, you might be better off finding a case with some way to provide some shock absorption to reduce vibration. Check around, you may find a local ham that can tune them for you.

Good suggestion. I have been leaning toward mounting everything in an upright pelican case. That may have to be revised.

I'm not really much help on the differences between them. I did recently have to tune a couple of Bridgecom repeaters, including their duplexers. Not horribly impressed with them, but they'll do the job.

What do you suggest? Price-performance? I have no issues underdriving the duplexer. I'm more than happy running 25 watts through a 50 watt duplexer. Also, whats a cheap way for me to get into "good enough" test equipment to tune a duplexer? I've been eyeing the miniVNA tiny, but that is a bit of an investment in and of itself.

Skip the hobby antennas. Get a decent commercial mobile antenna. Larsen antennas are my personal favorite. Go with the NMO mounts, that way you have the flexibility to change them out easily. A much wider selection of antennas with the NMO mounts. I've not found that Diamond, Comet or the other amateur brands are any cheaper. On the contrary, the name brand commercial stuff (Larsen, Laird, Maxrad, etc) are often cheaper and better quality. I've got 30 year old Larsen antennas I'm running. Skip the Chinese stuff, Tram, Browning, etc. It might save you a dollar or two, but you'll pay in the long run.

I'd start with a simple 1/4 wave. In a mobile environment higher gain might lead to more issues, picket fencing, radiation angles, etc. You can get those for less than $10.00. Add an NMO mount and that'll run you another $15.00.

Does the coax quality matter here? How about what type of mount? I have a mag mount that I usually use, or I can clamp mount to a roof rack. Both are NMO. This may be a good time for me to get a uhf capable antenna analyzer to determine the performance of the mount and make sure im targeting 50 ohms.

Use a separate battery for the repeater. That way you won't have issues with starting/stopping the engine or the repeater dragging down your starting battery. Should be pretty easy to figure out your current draw based on expected use, power levels, etc. Use a battery isolator so it'll charge off the car.

I was already expecting to do this. I usually use a deep cycle that I place in my trunk when I volunteer at dirt rally events, though I should get a battery isolator.

 

[Project25_MASTR]

I will look them up. I have not heard of them before. Good point on the silver.



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I had a friend turn me on to them when I was doing some tactically deployable P25/Interop repeater builds. Oddly enough they were the only manufacturer who said they could handle the wide (in terms of how the duplexer was banded) of all of the core VTAC pairs (VTAC33/34/35) so I ended up building one that was for those core pairs and one for VTAC17. They didn't have it spec'd as such but they kept me on the phone while they tried it out (re-verified with a R8000 upon delivery) to see if it would work.

K7NOP, this is what I'm talking about by R1225 (GR1225 is a desktop housing for it, RKR1225 is a rack mount, R1225 is just the module).

 

[kayn1n32008]

I had a friend turn me on to them when I was doing some tactically deployable P25/Interop repeater builds. Oddly enough they were the only manufacturer who said they could handle the wide (in terms of how the duplexer was banded) of all of the core VTAC pairs (VTAC33/34/35) so I ended up building one that was for those core pairs and one for VTAC17. They didn't have it spec'd as such but they kept me on the phone while they tried it out (re-verified with a R8000 upon delivery) to see if it would work.

I built a couple of portable repeaters using the Sinclair VHF mobile duplexers years ago. managed to be able to get the notches wide enough to pass 13 VHF pairs. Repeater transmits were 153.xxxxMHz and repeater receive were 5.260MHz above (roughly 158.xxxxMHz)

They were in a pelican case. We used Icom mobiles(Was working for an Icom dealer) with a Zetron tone panel. Radios were tuned for 5w out of the duplexer. NMO mount in the top of the case and a Larsen NMO-WB antenna. Worked pretty decently.

 

[zz0468]

Huh??? RG-58??? That’s like 75% shield??? For a repeater???

Actually, the shielding requirements for the antenna cable are not as stiff as the intercavity cabling. Consider that it's leading straight to a radiating element that is completely unshielded. In that part of the network, past the filters, the need for isolation between transmitter and receiver is non-existent. A second shield is buying you very little.

 

[crazyboy]

I have a GR1225 UHF complete with radio and internal duplexer, PM me if you are interested.

 

[jim202]

Just because you have a duplexer, that doesn't mean you have enough isolation between the TX and RX frequencies You also require to have good isolation built into the radio or radios that you are using. A good sharp front end on the receiver, good intermod rejection, good clean transmitter signal with no spurs. The list goes on, but don't forget good shielding in the receiver and transmitter.

I have seen some people try to use a couple of portable radios to try making a repeater. When they have all sorts of desense, they can't understand the problems. Their repeater has a problem hearing and may even have crazy audio sounds coming out of it. In many cases, the repeater will lock up on itself or pump on and off with the problem.

The use of double shielded coax between the radio TX and RX ports to the duplexer are a must to limit the problem of the TX signal leaking into the RX input. This is where good shielding of both the RX and TX potions of your repeater help reduce the issues. Good coax going from the duplexer to the antenna won't hurt.

Being that your talking low power in the order of around 5 watts, you should be good to go with many of the radios designed for repeater use. But let me stress one BIG IMPORTANT FACT HERE. Don't turn down a TX power output more than 50%. Going beyond this point on most transmitters will cause them to start generating all sorts of birdies. The output amps were not designed to operate that low of power and will start to oscillate and become unstable.

The other big point to keep in mind is heat generated by the repeater transmitter. Unless the transmitter has a large heat sink and is rated for repeater operation, the transmitter power amp will get very hot and probably self destruct. Heat is a major problem in repeater service for any transmitter. Even some of the big commercial, constant duty rated repeaters will have fans installed to keep them happy. This generally is not a problem for 5 watt operation, but you need to keep the heat issue in mind when building and using any repeater.

Make sure the transmitter has a built in time out timer in the control circuit. This way if a signal becomes locked up on the input, you won't destroy your transmitter. Set the time for say 2 minutes. Most transmissions on a portable repeater will not be of the rag chew type conversations. But your better off making sure you have your equipment protected.

Use of a 1/4 wave antenna will not cause you any problems that the fixed repeater antennas with gain can develop over time So your good to go on this.

Good RF bypassing on any wire leaving or going into the repeater and control circuitry is a must. This keeps any RF from getting into the radio and control board that can cause problems. Most new comers to repeaters don't even take this into consideration when building a repeater.

If you need any guidance on installing the diode isolator for 2 battery operation in your vehicle, just ask. The big thing to remember is to lift the output wire on your alternator and move it to one of the battery position terminals on the isolator. Then run a new wire from the common of the isolator back to your alternator. this will allow for voltage correction due to the voltage drop the isolator will cause. Then connect your second battery to the other battery terminal on the isolator. Any time your engine is running, it will charge both batteries.

Another word of caution here is the alternator in your vehicle. You need to consider how much of a load you will put on the alternator trying to charge up a second battery that has been pulled way down with the repeater operation and not starting your engine now and then depending on repeater use.

The reason I even mention this is I have burned out a couple of alternators in my vehicles over the years with a 2 battery operation. So it is wise to have an alternator in the range of like 100 to 120 amps. The larger the second battery, the more this issue is a concern. Don't forget that the alternator must maintain the vehicle electrical load and charge the vehicle battery as well as try to charge the second battery.

Let the group on here know how you make out. There are some very knowledgeable people here that can lend a hand if you run into a problem.

 

[mmckenna]

How am I supposed to interpret this. Which coax grade should be used for a portable repeater?

There are 100% shield cables out there. There are also "dual shield" RG-58. Probably won't do much for you. Just use good coax. You can buy NMO mounts with various cable types. You can also buy NMO mounts with no cable and solder in your own.

Good suggestion. I have been leaning toward mounting everything in an upright pelican case. That may have to be revised.

There's some companies that make cases with built in shock absorption. Take a look at one of those, especially if it's going to get beat up/moved around a lot. If it's going to be in a passenger vehicle and you don't beat the crap out of it off road, you probably will be OK. The mobile duplexers are just that, designed for mobile use for in-band repeaters/extenders.

What do you suggest? Price-performance? I have no issues underdriving the duplexer. I'm more than happy running 25 watts through a 50 watt duplexer. Also, whats a cheap way for me to get into "good enough" test equipment to tune a duplexer? I've been eyeing the miniVNA tiny, but that is a bit of an investment in and of itself.

Name brand stuff. Sinclair, as stated above, Celwave, Telewave, etc.
Or, if you have room, they make compact duplexers that are bigger, but not "full size", that will give you a bit better performance.
As always, avoid the cheap crap out of China. Sounds like you are really doing your homework on this. No reason to cripple it with a shoddy duplexer.

Does the coax quality matter here? How about what type of mount? I have a mag mount that I usually use, or I can clamp mount to a roof rack. Both are NMO. This may be a good time for me to get a uhf capable antenna analyzer to determine the performance of the mount and make sure im targeting 50 ohms.

Quality always matters. Go with the best you can. If you really must use a mag mount, then you are going to be limited by your cable routing. Stiff cable is going to be problematic. If you do it right and drill the hole, you have a bit more leeway. Larger/stiffer cables will work.

I wouldn't use anything but NMO. There's no benefit to anything else.

As for tuning the antenna, if you go with the lower gain/no gain antennas, the useable bandwidth is wider. With a quarter wave, they are very broad and have a nice smooth radiation pattern that would work well in a moving environment.

I was already expecting to do this. I usually use a deep cycle that I place in my trunk when I volunteer at dirt rally events, though I should get a battery isolator.

Our police cars are set up the same way. Battery in the trunk fed through an isolator from the starting battery. When the engine is off, the rear battery gets isolated. That way if they get stuck on scene for a while and/or the timers don't kick it off or the officer keeps resetting it, they can still start the vehicle.

 

[K7NOP]

I've been very impressed with the knowledge and suggestions I've received from this group. I chose radioreference because in my research I largely run into information on people building GMRS repeaters. My intended application is slightly lower in frequency and uses a slightly different specced duplexer, but all of the rest is generally the same.

Thanks for clarifying the R1225 radio MCore25! I was assuming as much to be true, but its good to know that the R1225 is just the core of all the other housings.

To be completely honest I'm having trouble finding a retail outlet for epcom, sinclair or other recommended duplexer brands. I'm waiting for a reply from epcom to find a distributor to end users.


jim202: the R1225 motorola has been reccomended. I started this adventure figuring I'd use a couple portables I had with my "end game" high quality antenna network and work my way up, but it seems like I should go straight to a repeater radio. I intend to affix temperature controlled fans with a sensor mounted in an acceptable location on the heatsink.

The issue with the battery isolator is I'm not looking to modify my vehicle in any huge way. I will be running 12v from the battery into my passenger compartment in the long run but for now the repeater will just draw off a completely isolated deep cycle. Given a reasonable duty cycle its probably not unreasonable for a large deep cycle to run a repeater for a few hours? I'll do the math before I put that into practice.

Good call on the alternator. My alternator upgrade path honestly sucks. I've looked into upgrading it to handle audio system upgrades and onboard air my vehicle is equipped with. Thankfully my stock alternator is 90A. I throw my vehicle on a battery charger once a month and have a multipurpose starting/deepcycle battery to handle the strain.

Mmckenna: Its going in my 2014 Subaru WRX STI. Perhaps a different type of being beat up than off road, but as long as I secure it in my trunk and don't take any "sweet jumps" I should be fine xD

Do you have suggestions on where to purchase these name brand mobile/compact duplexers? I'm having a hell of a time finding a retailer that sells those brands. Right after this post I'm gonna go dig back into google.

Thanks for all the info. This repeater build is going to be a longer term project than I thought, which is fine. I want to make sure I do it right the first time.

Jordan
K7NOP

 

[WA0CBW]

Try looking up Tesco. They have about everything.
BB

 

[PACNWDude]

Portable repeaters can be very useful. Have used GR300 and GR1225 version often. Ones I made used CDM-1250 mobile radios, Celwave duplexor from Tessco, and Astron power supplies. They could be made as AC/DC powered units, with deep cycle marine batteries.

Also made some briefcase versions with various Motorola handheld radios. You can probably buy surplus ones from online auction sites, as I have done this for the core components in the past as well.

UHF works well for short distance use. Used these for a company that responded to oil spills, floods, and hurricanes.

 

[vagrant]

A Yaesu DR1X repeater has a $600 club purchase price. The controller is built in. It is ready to go for either UHF or VHF. You can use it for analog only and avoid any of the digital/C4FM stuff if you want. Again, the built-in controller will handle the ID etc. The main issue with it is do not use the "high" setting for TX at 50 watts. Just use medium and it will kick out around 17-20 watts. You program everything right from the front touch panel....Easy. (This repeater works from AC or DC power. They provide the power cables with it.)

A Chinese mobile UHF duplexer, more like notch filter, can be had for around $100. They will typically tune it, just give them the high/low. I threw one on an analyzer to test and it was within spec to what I told them. They claim to handle 50 watts, so the 20 watts from the Yaesu will work fine. I tested and it does work fine.

As for coax on the UHF frequencies, well your run is typically short for mobile. You could get away with something rather thin at 20 watts. Bigger is better if it works for your environment.

You are correct that a monoband UHF mobile antenna would be the best choice. An existing VHF/UHF in your arsenal will also work.

Are there better solutions out there, you bet. This inexpensive suggestion will probably get clobbered by those whom have never actually used the components I suggested. If you really need 50 watts you could use an amp, but you should look at the actual db gain from 20 to 50 watts first.

 

[Project25_MASTR]

A Yaesu DR1X repeater has a $600 club purchase price. The controller is built in. It is ready to go for either UHF or VHF. You can use it for analog only and avoid any of the digital/C4FM stuff if you want. Again, the built-in controller will handle the ID etc. The main issue with it is do not use the "high" setting for TX at 50 watts. Just use medium and it will kick out around 17-20 watts. You program everything right from the front touch panel....Easy. (This repeater works from AC or DC power. They provide the power cables with it.)



A Chinese mobile UHF duplexer, more like notch filter, can be had for around $100. They will typically tune it, just give them the high/low. I threw one on an analyzer to test and it was within spec to what I told them. They claim to handle 50 watts, so the 20 watts from the Yaesu will work fine. I tested and it does work fine.



As for coax on the UHF frequencies, well your run is typically short for mobile. You could get away with something rather thin at 20 watts. Bigger is better if it works for your environment.



You are correct that a monoband UHF mobile antenna would be the best choice. An existing VHF/UHF in your arsenal will also work.



Are there better solutions out there, you bet. This inexpensive suggestion will probably get clobbered by those whom have never actually used the components I suggested. If you really need 50 watts you could use an amp, but you should look at the actual db gain from 20 to 50 watts first.

Eh. The only thing is there are alternatives which can be found for similar pricing in a much smaller form factor. Icom used to have a repeat module for about $650 that was the size of one of their mobiles (I want to say FR-6000) and would do 50W, not continuously obviously.

Also, if you can find them, R1225 modules are typically under $200 granted you’ll likely have to find someone who can program it, use a GR/RKR control head or rob a head from a GM300.

I’ve found, even with factory tuning, you’ll be lucky to get 38W out before you encounter desense on those notchplexers (even from RFS). Typically, I’ll run 10W or less on Field deployable repeaters. The ones I built that got sent to the Texas coast for hurricane relief this year put out 5W…but had more than enough coverage for the area they were deployed in.


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