Portable repeater with no purpose. An exercise in frugality.

[prcguy]

I was trying to clean out the garage for the last few days and thought I would stack some random equipment in a portable rack to save some space. That as usual turned into seeing if the equipment works, which it usually doesn't then trying to fix it before stacking it away. I found an old commercial repeater I built and leased out a good 35yrs ago and when I plugged it in a few days ago it blew a couple of Tantalum caps. I replaced those and it came back to life but on some old 460MHz business freqs I'm no longer licensed for. I found a friend who still had a prom programmer program for the RF modules in the repeater on floppy which he transferred and sent to me and I programmed and aligned the little 2-10w repeater on GMRS. The stupid thing actually works better than most meeting 12dB SINAD at -122dBm or .178uV and has a very clean transmitter.

The repeater had a controller already wired to it and then I uncovered a Henry 200w amp that only needs 2.5w drive which I got it at the Dayton Hamvention for $100 and it was factory tuned in the 462MHz range. Then I uncovered a nice Motorola 526 duplexer I got at Dayton for $150 missing a cable and mounting brackets, so I hand made a new cable and brackets and tuned it for GMRS.

The portable rack came from Dayton also and was used to haul some junk home in the back of a friends pickup all the way from Dayton to So Cal. I didn't have a power supply that was adequate for the 200w amp so I bought a new 15V 66A job for $130 and turned it down to 14V, the most expensive piece in the rack With everything tuned up its doing 150w out of the duplexer with no measurable desense, not bad. Now what to do with it? GMRS rules only allow 50w and the Henry amp is designed to run nearly full power so its not gonna turn down to 50w. There are no tuning adjustments on this amp so retuning for the amateur band would be very time consuming unsoldering parts and moving them around. And we are only allowed 50w for 70cm repeaters in this area due to some military conflict.

So here sits this nice working repeater cobbled together from mostly scrap parts and I can't really use it. The layout is clean and uncluttered using a number of RF cables laying around that were a perfect fit. Not including the 10w repeater I built 35yrs ago from parts the total cost of this 200w repeater system is about $383. At least it was a nice exercise in frugality and it gets the parts off the garage floor and stacked nicely.

 

[prcguy]

Someone asked me what the repeater actually is and here is an inside pic. Its made of Part 90 receiver and transmitter modules made by a local company many years ago. I mounted a transmitter and receiver module in a chassis and remotely located its 14w power brick to the rear panel with my own heatsink. The commercial repeater controller mounted above this repeater takes care of the repeat audio path and PL/DPL tones. All wiring in and out of the modules have feedthrough caps and all wiring is Teflon. I've put together many of these and this one is unusual with a 16ch selector switch on the front. This one is also very dusty and crusty from years of storage.

 

[davidgcet]

we had a few Henry 460 band amps back in the days of paging, i could have sworn they had tunable caps in them. i a pretty sure i had that same one as well as a 100w model, we ran them at about 75% rated output and they were rock solid.

 

[prcguy]

we had a few Henry 460 band amps back in the days of paging, i could have sworn they had tunable caps in them. i a pretty sure i had that same one as well as a 100w model, we ran them at about 75% rated output and they were rock solid.

They might have changed things over the years but this one has no tuning caps anywhere. Its got a single transistor module feeding a single transistor module then split feeding two modules containing a driver and two output transistors in parallel then its combined at the low pass filter. It works well over +/- 5MHz but in the amateur band its about 150w out max. I would not run it there without retuning and I don't want to experiment on a good working amp right now. I'm surprised it sold so cheap but that's the Dayton Hamster fest.

An old friend of mine Gene, now deceased designed many of Henry's amplifiers, probably including this one and I've watched him in his shop tuning them up with a wooden stick that had a ferrite blob on one end to add inductance and a brass blob on the other end to lower inductance when placed near any tuning coils. Then he would either bend the tuning coil or unsolder a cap and slide it back and forth on a trace. I'm too impatient for that these days.

 

[kayn1n32008]

Very nice. Just the repeater and controller, how many watts @14v in standby?

With a signal present at the receiver, and the exciter at 10w TXPO, how many watts?

 

[RFI-EMI-GUY]

Add some more filtering and triple circulator(s) until you get 50 ish watts (we wont tell) out the duplexer. Then donate it to someone living in a tall condo with a balcony. Set up your private tones in the panel and let it fly!

 

[buddrousa]

I had a 25 Watt UHF Repeater with duplexers and the same CSI32 in a NEMA Box 400 foot at the top of a tower 10 foot 1/2 inch Andrews to a DB420 antenna setting on 500 foot ground elevation. Run AC and Phoneline up the tower in PVC. This setup had a range of 60 miles to a 35 watt mobile I used this setup for Phone before cellphones came along.

 

[prcguy]

Very nice. Just the repeater and controller, how many watts @14v in standby?

With a signal present at the receiver, and the exciter at 10w TXPO, how many watts?

The repeater does about 11 watts out full tilt and can turn down to about 2 watts. I'm running it at 10-11 watts into a 6dB attenuator to give me 2.5 watts into the big amp. That gives a nice load on the transmitter and a really good match on the amp input. With the 2.5w drive into the amp it does about 210 watts at keyup then drifts down to about 200w as it heats up. With duplexer loss its 150w out of the duplexer.

When I got the amp it was wired for the two heatsink fans to run full speed all the time and the fan over the circuit board was on a thermal switch. The fans are really loud so I bridged the thermal switch with a 15 ohm 25w resistor and put all fans on the thermal switch which runs them about half speed and after 3 1/2 minutes of keydown the fans ramp to full speed.

 

[prcguy]

Add some more filtering and triple circulator(s) until you get 50 ish watts (we wont tell) out the duplexer. Then donate it to someone living in a tall condo with a balcony. Set up your private tones in the panel and let it fly!

I would normally have an isolator on this but I don't have one that will handle 200 watts. Most of mine will do 100 to 150w max. If I run across a 10w in 60w out amp I'll swap it and then this will become a more legal GMRS repeater. Plus the front cover will finally fit the case.

 

[prcguy]

I had a 25 Watt UHF Repeater with duplexers and the same CSI32 in a NEMA Box 400 foot at the top of a tower 10 foot 1/2 inch Andrews to a DB420 antenna setting on 500 foot ground elevation. Run AC and Phoneline up the tower in PVC. This setup had a range of 60 miles to a 35 watt mobile I used this setup for Phone before cellphones came along.

In the late 80s I built a similar repeater using the same rx/tx modules with autopatch licensed on a 460MHz 2w business freq on a 1,000ft hilltop and it was my mobile phone way before cell phones were affordable. I still have that repeater buried in the garage somewhere. I should dig it out and see if it still works, maybe take some pics and post here.

 

[prcguy]

Very nice. Just the repeater and controller, how many watts @14v in standby?

With a signal present at the receiver, and the exciter at 10w TXPO, how many watts?

You asked in standby, I think about 1 amp for the rx/tx modules and the controller. 3.5A on transmit @ 10 watts.

 

[RFI-EMI-GUY]

In the late 80s I built a similar repeater using the same rx/tx modules with autopatch licensed on a 460MHz 2w business freq on a 1,000ft hilltop and it was my mobile phone way before cell phones were affordable. I still have that repeater buried in the garage somewhere. I should dig it out and see if it still works, maybe take some pics and post here.

What are the modules?

 

[prcguy]

What are the modules?

Modules were made by Telemobile, an obscure little radio company that was a continuation of Pace/Pathcom of CB fame. The receiver and transmitter were designed by a guy that designed the Pace land mobile radios and also many Henry amplifiers.

I used to run 12.5KHz split repeater channels in the 80s and 90s and there were narrow IF filters available for these radios which I installed and I had many mountain top repeaters using these modules that worked really well, better than some Motorola repeaters I had at the time. And they never failed during the 10yrs or so they were on mountain tops. Both the receiver and transmitter are prom programmed and not wideband, you tune the entire board for the specific frequency and they have really good rejection at 5MHz away for repeater use. These modules were used in their 2-way radios, repeaters and rural telephone interconnect systems.

Its interesting that the guy I rented several mountain top repeater sites from in So Cal was the one responsible for petitioning the FCC for 12.5KHz splinter channels on UHF and he got it passed. He was amused I was doing business with 2 watt repeaters on splinter channels from his sites.

 

[kayn1n32008]

Modules were made by Telemobile, an obscure little radio company that was a continuation of Pace/Pathcom of CB fame. The receiver and transmitter were designed by a guy that designed the Pace land mobile radios and also many Henry amplifiers.

I used to run 12.5KHz split repeater channels in the 80s and 90s and there were narrow IF filters available for these radios which I installed and I had many mountain top repeaters using these modules that worked really well, better than some Motorola repeaters I had at the time. And they never failed during the 10yrs or so they were on mountain tops. Both the receiver and transmitter are prom programmed and not wideband, you tune the entire board for the specific frequency and they have really good rejection at 5MHz away for repeater use. These modules were used in their 2-way radios, repeaters and rural telephone interconnect systems.

Its interesting that the guy I rented several mountain top repeater sites from in So Cal was the one responsible for petitioning the FCC for 12.5KHz splinter channels on UHF and he got it passed. He was amused I was doing business with 2 watt repeaters on splinter channels from his sites.

Nice. Playing with some MT-4 gear right now, the VHF and UHF exciters are 7w or 8w max output. Daniels/Codan MT-4e gear is quite interesting stuff. A friend has a 7/800MHz MT-4e and @3w and a signal present on the receiver, no PA, it draws 24w @13.8v in P25 mode.

 

[prcguy]

Nice. Playing with some MT-4 gear right now, the VHF and UHF exciters are 7w or 8w max output. Daniels/Codan MT-4e gear is quite interesting stuff. A friend has a 7/800MHz MT-4e and @3w and a signal present on the receiver, no PA, it draws 24w @13.8v in P25 mode.

My boards have little ovens snapped over the ref crystals, if I remove those it will draw less. But I like not having to tweak them back on freq except every few years.

 

[serial14]

@prcguy I always enjoy seeing your misc builds like this. Thank you.

I've always read that duplexers are fragile things and commonly see "advice" that they should be checked/tuned on site and after shipping. I assumed this meant that vibration & jarring from shipping would knock something out of alignment physically inside the duplexer. Is that true?

Seeing your repeater build and other portable repeater builds from fire crews, I've noticed they are built into hard cases with no vibration isolation, as opposed to being mounted in a hardigg rack case with isolation. Why? Does this imply that the duplexers aren't as fragile as I'm thinking? I know from personal experience that gear being transported by truck or even helo to a remote site experiences plenty of vibration even if the pilot/driver is being kind.

 

[prcguy]

@prcguy I always enjoy seeing your misc builds like this. Thank you.

I've always read that duplexers are fragile things and commonly see "advice" that they should be checked/tuned on site and after shipping. I assumed this meant that vibration & jarring from shipping would knock something out of alignment physically inside the duplexer. Is that true?

Seeing your repeater build and other portable repeater builds from fire crews, I've noticed they are built into hard cases with no vibration isolation, as opposed to being mounted in a hardigg rack case with isolation. Why? Does this imply that the duplexers aren't as fragile as I'm thinking? I know from personal experience that gear being transported by truck or even helo to a remote site experiences plenty of vibration even if the pilot/driver is being kind.

Every make and model duplexer is different with some being more prone to detuning than others. When I tune flatpack mobile duplexers on the bench I usually bang them with a screwdriver handle or rubber mallet while tuning to see if the tuning will change. Sometimes retuning and rocking the adjustments a little before locking down makes them less prone to detuning, sometimes not. I treat my portable repeaters like they are made of glass and avoid any shock to the enclosure.

I've installed countless repeaters where the repeater system worked perfect on the bench and when installed on a mountain top its got desense and I need to revisit the duplexer tuning, which usually fixes the problem. So from lots of past experience I've seen a trip up winding dirt roads detune things even though they were sitting on a cushioned seat and strapped in during the ride. If you do mountain top repeater work you carry whatever is needed to retune a duplexer on the spot. Otherwise you will be driving back down the mountain or off the air.

 

[kayn1n32008]

My boards have little ovens snapped over the ref crystals, if I remove those it will draw less. But I like not having to tweak them back on freq except every few years.

I don't miss Crystal based radios. Thankfully MT-4e is all synthesized. I'll have to see what the actual VHF/UHF stations draw for standby and transmit with out a PA.

 

[prcguy]

I don't miss Crystal based radios. Thankfully MT-4e is all synthesized. I'll have to see what the actual VHF/UHF stations draw for standby and transmit with out a PA.

My boards are synthesized, its the PLL reference crystal that has a snap on heater. When used in mobile radios they leave the oven off and they are reasonably stable.