Rhode Island Amateur FM Repeater Service

146.940 / 146.340 - Repeater Rebuild Summer 2007 - Steve KA1RCI

Cumberland - Rhode Island

 

The initial problem / repeater configuration

After moving the 146.940 repeater from the Lincoln site to the new location in Cumberland, and adding a new power amplifier, the system developed a problem with RF from the transmitter causing interference to the receiver. This problem had been manifesting itself in several different ways, causing unpredictable operation, including a howling feedback that Paul KB1OCU thought sounded like pipes rolling off a truck. The repeater would also randomly get locked into a form of self oscillation, where the transmitter would get into the receiver activating the repeater, locking it into transmit for long periods of time.

These photos show the duplexer, power supply, and Kenwood TKR-740 RF deck as I found them at the Cumberland site in late April 2007 when the "rolling pipes" noise was periodically blasting out of the transmitter.

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After meeting with Denis KD1HA at the Cumberland site, to investigate the awful howling, we quickly identified several issues. There were multiple cables and connectors in poor condition, one connector on the duplexer was damaged and another connector on the phasing harness was falling off the coax. Other cables were poorly shielded, which can be very troublesome in the demanding RF environment of repeater service, so it was easy to see there was not going to be any quick band-aid that could resolve the problems.

It was at this point that our plans to rebuild the repeater hardware was born

Denis helped me load everything into the Big Blue Beast and I brought the repeater back to my QTH in Lincoln to disassemble all the hardware and evaluate what could be reused and what needed to be replaced. These photos were taken just after bringing the repeater into the house. If you look closely in the photos below to the right you can see a small RG-58 jumper of poorly shielded coax that runs from the 2 meter band pass filter up to the top of the cabinet and out to the extra receiver cavity. You should notice that it is not only in close contact with the transmitters (100 Watt PA) output cable but that it is actually wrapped AROUND the coax.

So we have the 100 watts of transmitter RF screaming thru poorly shielded RG-8 coax with the barely shielded RG-58 receiver coax wound around like an inductor.

An inductor is a passive electrical device employed in electrical circuits for its property of inductance.

 Does anyone else see a problem here?

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Let me tell you, Sandy was so very happy that I had dragged yet another repeater in the middle of our living room.

 

The inspection and tear down

It was obvious that all of the RF cables would have to be replaced, there were multiple adaptors, jumpers, and damaged connectors that all could be contributing to the problems with the transmitter getting into the receiver and I also noted some room for improvement in the power cabling as well. More appropriate gauge wire and proper fuse protection was in order. I carefully labeled all the components taking everything apart while still working in the middle of my living room because that was the only space available at the time (with all the other repeater projects scattered around the office/radio room).  I make an inventory of the parts and a shopping list for new items that were needed for the rebuild.

The photos below show several of the issues with poor cables and connectors.

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The first item would be a larger rack cabinet, so I called Pete AA1PL and was able to get a larger cabinet that I could rebuild all the hardware into one complete package instead of having loose components piled up around the small rack. Getting the large duplexer cavities into the new rack cabinet was not easy. When all four cavities are mounted on the duplexer bracket they would not fit thru the opening in the cabinet so I had to take the unit apart and rebuild the duplexer inside the cabinet.

The cavities just barely fit with the external capacitor rods for the reject tuning. Taking the duplexer apart also afforded me the opportunity to change the cavity configuration so that the receive cavities were on the same side as the receiver connector and the transmit cavities were on the same side as the power amplifier connections. This would allow the coax cables to be routed AWAY from each other instead of wrapped AROUND each other.

I also installed a rack mounted shelf just above the duplexer cavities that gave some protection to the tuning rods while providing a support for the heavy Astron power supply.

 

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Power supply repair

While removing the rack mounted Astron power supply I noticed that the positive power post was spinning freely in the back panel so I took off the cover to tighten the stud and found several of the components inside have been torn apart. I inspected for damage and replaced all the broke components. These photos show the damage, parts, and finished repair.

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The first mockup for hardware placement and cable planning

The existing configuration using the Kenwood TKR-740 and it's internal repeater function did not have any method for remote control or linking so I donated a S-Com 7K controller and Kenwood TK-830 commercial UHF radio for use as a remote control / link. My brother-in-law (Sandy's younger brother) is a professional medal worker and welder. He fabricated a custom mount for me, using some spare aluminum blank plates, so that I could mount the UHF link radio in the rack.

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With the addition of the link radio and S-Com controller the hardware just fit perfectly in the space available with no room to spare. I sat on my couch in the living room staring at the new configuration and that PA for quite some time... In the larger photo below you can see the new Henry PA sitting on top of the cabinet.

"Where the hell am I going to put that new power amplifier?"

 

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New hard-line phasing harness for the duplexer

The original coax phasing hardness was falling apart, the PL-259 connectors were all corroded, and as I removed the cables one PL-259 connector fell right off! There was nothing worth salvaging from the phasing harness and I had already planned on making all new cables using Andrew FSJ-2 hard-line. I also replaced the PL-259 connectors with Type-N where ever possible and made sure that all of the RF cables had the correct Andrew connector installed so that NO adaptors of any kind would be needed.

These photos show the new duplexer phasing harness construction

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Testing... One, Two, Three.

Once the power supply had been repaired, and I had finished making the new FSJ-2 hard-line phasing harness cables, I was anxious to put the repeater back on the air to see if all those nasty rolling pipes had been properly strapped down. Running with just the 5 watt TKR-740 in this configuration we already could see a noticeable improvement.

Lee KB1OVM was full quieting from the parking lot at Raytheon out in Portsmouth!

These photos show the configuration during the first testing with new FSJ-2 hard-line phasing harness

 

(click on images to enlarge)

 

Fitting 10 pounds of hardware into a 5 pound cabinet

Even with the larger rack cabinet from Peter AA1PL there were still space issues. Once the hardware was bolted into the rack there was no place to mount the new Henry PA or the extra receiver cavity. Since the extra cavity had been bolted to the side of the original smaller rack cabinet I decided that was my only option for mounting it on the new larger rack cabinet. I mounted the cavity so that the RF cables could be kept as short as possible and made holes in appropriate locations to keep the bends in the FSJ-2 hard-line to a minimum.

This group of photos show the extra receiver cavity installation

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 We need more power captain!

Ok we knew that testing running 5 watts was good but this whole mess started because Peter AA1PL stopped by my house and saw me building the new 147.390 repeater for the Westerly site and liked the 100 watt PA that I was using. Now that I was rebuilding the 146.940 repeater in the new cabinet I had to find a place to mount the new PA. The only place there was any space available for the power amplifier was in the back of the cabinet behind the link radio and S-Com controller however there were no mounting rails in the back.

So once again I asked my brother-in-law for help making custom brackets to hang the PA from the top of the rack. This was a tricky step and required some planning to make sure the controller cables, DC power cables, and RF cables would have room behind all the equipment and still have the PA far enough inside the cabinet so the back door would fit properly. As an added (un-planned) bonus the two cooling fans on the PA lined up right were the vents in the back door are located.

These photos show the "measurement" phase

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These photos show the finished brackets and the PA mounted

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Cables, Cables, Cables...

Now that I had the final placement of the duplexer, TKR-740 RF deck, and power amplifier, I could turn my attention to the rest of the cables. These two photos show the main repeater hardware mounted in the rack so I could measure and start fabricating all of the other RF coax cables.

(click on images to enlarge)

 I wanted to use Andrew hard-line where ever possible to minimize any chance of "rolling pipes" and also always use the correct connectors so that no adaptors would be needed.

This of course would mean that each cable had to be custom made to fix each specific location.

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In these photos you can see all the RF cables coming together

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NONE SHALL PASS!!!

Roland N1JOY had installed a 2 meter band pass filter in line with the receiver, I (my brother-in-law) had planned on fabricating a bracket that that the filter would mount on, and would support the filter, allowing it to be bolted into the rack however there was just no room left.

I was able to place it in the small space above the duplexer cavities just below the power supply.

(click on images to enlarge)

 

 Damn it.. what the hell is causing all that "crackling"?

Now that I had most of the work done I put the basic repeater back on the air with the PA in line and right away we started hearing a lot of crackling on the signal. It was not always present but was too bad to over look. I could also induce the snap, crackle, and popping by touching the cabinet with one finger. It was clear that something was loose somewhere in the works that was arcing now that I was running with the higher power. As it turned out there were multiple issues causing crackling...

One was the polyphaser that had been hanging out in free space in the original configuration, whenever I touched the polyphaser the crackling would start or get much worse.

(Peter AA1PL provided me with two new polyphasers that I installed later in the project)

The next big source of those nasty snap, crackle, pops turned out to be the duplexer cavities touching the bottom of the rack cabinet. With the polyphaser issue eliminated I found that touching the duplexers was causing bad crackling. Normally I would have used the mounting bracket on the duplexer to bolt the cavities to the cabinet, so they would be hanging in free space without touching anything, however the brackets on this duplexer appear to have been cut off and that was not possible without making extensive modifications.

After a few hours of staring at that the problem I came up with the idea to install a rubber mat on the bottom of the rack so the cavities would not touch the metal bottom.

These photos show how I suspended the duplexer so that I could install the rubber mat, there was no easy way to get the cavities back out of the cabinet so hanging them with a strap was the only way I could work on the bottom of the cabinet and cut the mat to the correct size.

 

(click on images to enlarge)

Finding the last source of the mystery crackling was a little harder to locate. Each previous step had reduced the problem noticeably and now I could no longer cause the snap, crackle, and pop to happen on command. The crackling would come and go while folks were talking and it was very unpredictable. I had to keep asking Denis KD1HA and Paul KB1OCU to have long QSO's on the repeater while I poked, prodded, smacked, and then eventually started KICKING the cabinet.

I found myself jumping out of bed and running to the radio room at all hours whenever the crackling would start.

Then I recalled that extra cavity on the receiver had a loose nut on the tuning rod and I focused my attention on that nut. Although I knew it had been loose when I had picked up the repeater and when I asked Peter about the issue he said that the cavity had always been like that and it should be fine, I started to think it could be causing the problems. After some testing I did determine that it was however the last crackle source, I could touch the tuning rod with one finger and instantly cause the receiver sensitivity to change dramatically and the crackling to start.

In the photos below you can see how the loose nut would allow the tuning rod to move almost a 1/4 inch up and down.

 

(click on images to enlarge)

Now I am not expert when is comes to building repeaters, but that little that I have learned (which is just barely enough to be dangerous), I do know that any tuned cavity that uses this type of fine adjustment (where just moving the rod a 1/8 of a turn) can move the band pass notch right off the desired frequency, should not have more than a 1/4 inch of play. The entire rod was moving around in the cavity and not only causing the crackling but also making the receiver deaf.

When I removed the extra receiver cavity all of the crackling finally stopped and the receiver sensitivity came back to an acceptable level.

Peter was able to stop by my house one evening after work and we were able to confirm with his service monitor that the receiver was going deft with the extra receiver cavity in line. We decided to remove this extra cavity and after a few hours of fine tuning we were able to get the duplexer re-tuned with all the new FSJ-2 hard-line cabling.

 

 Link Me Baby... (You now have Control)

Not having the ability to remotely control your repeater can be a nuisance, especially when it get stuck in a howling transmit loop for sixteen hours, and you should really have at least two control points available (I prefer three) so that a control operator can shutdown the repeater when problems arise. The addition of the S-Com 7K controller and UHF link radio provide just that. Remote control with two input frequencies and the bonus of being able to link the newly rebuilt 146.940 Cumberland repeater to the 447.425 Scituate repeater.

I have been using the S-Com controller for 20 years and have a good comfort level configuring and programming them. I made the necessary modification to the S-Com 7K to tailor the audio for the Kenwood TKR-740 and TK-830 and then I had to make several modifications to the link radio. John WA1ABI had developed several handy modifications during out project to build the 147.075 Portsmouth repeater for receiver COS control to the 7K and one for grabbing the receiver audio for the 7K.

These photos show the COS and audio modification and the controller / link radio setup for testing and audio adjustments

(click on images to enlarge)

 

 You are protected! Thor's hammer be Dammed...

I finally installed the two new Polyphasers that Peter had provided and made the last FSJ-2 hard-line cable that connected the duplexer to the Polyphaser.

In these photos you can see the Polyphasers, finished power cables, and FSJ-2 hard-line cables

(click on images to enlarge)

 

 Wow it really sounds good now, "what did you do?"

With the audio levels set as best as I possibly could and all the control, power, and coax cables completed, I could finally break down the repeater and mount all the hardware in the end state configuration. I even painted the custom bracket for the link radio in preparation for assembling all the components. I know that next to no one will ever see the repeater sitting in a dark basement closet but when that rare visitor does open the rack cabinet and peek inside it will look somewhat presentable.

The fancy flat black paint is what made it sound so good...

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 This is it, everything had better be working now...

Time to start final assembly, the last few components have to be carefully shoe-horned into place, in a delicate ballet to get all the control, power, and RF cables nestled into the correct locations.

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Microphone clip madness!

 

Fun with the BIG STICK at Cumberland PD

Hopefully by the time anyone is looking at this webpage the repeater will have already been moved back to the site in Cumberland.

(click on images to enlarge)

 

Monday October 8th 2007

After coordinating with Denis KD1HA my Dad (KA1VKD) and my brother-in-law from Philadelphia who was in town visiting for the holiday weekend helped me load the newly rebuild 146.940 into the Big Blue Beast so we could return it to the Cumberland PD site. We arrived shortly after 10:00 am and carefully unloaded the repeater and all the necessary test equipment.

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Cumberland PD Setup and Testing

Once the repeater was back at the CPD site we completed the initial testing with the rack cabinet on the floor of the repeater vault just incase there was something wrong and I would have to bring the repeater back home for additional work. (Although I am not sure Denis would have let that happen)

I setup my Bird meters to checkout the SWR and power on both the VHF Repeater and UHF Link while Denis worked on grounding both of the polyphasers. My brother-in-law Keith also helped Denis with the grounding setup.

(click on images to enlarge)

Job's Done (Steve's final thoughts)

I took one last photo of the new 146.940 repeater now perched up on the bench inside the repeater vault as I was packing up all my test equipment and tools. With all the tools and test gear packed up in the Big Blue Beast it was time to leave her in the dark vault all alone, the only thing on my mind right at that moment was...

"Dam thing is to high off the floor for me to KICK it now!"

 

(click on images to enlarge)

This project took longer than I had expected, and I apologize to the group for that, but that was largely due to other events in my work and personal life that kept pulling me away from playing radio. Now that the repeater is on the air and playing so very well, I hope that everyone can appreciate how much effort I poured into this project and just how much it meant to me personally. I have been using the 146.940 repeater for almost half my life, ever since I moved to Rhode Island as a teenager in 1984. My wife Sandy KA1RXB and I have also been the primary users on the 223.760 repeater for the past ten years.

For me to be in a position that I am able to give something BACK to the group that has been providing a service that I have been using for 20 years was something that I felt very strongly about. I know what is involved to building, maintaining, and supporting a repeater, Hell I am running fifteen of them here in Rhode Island so for me it was an obligation to support this group and this repeater.

I hope that it will run another 20 years and that I will still be around to hear her "Beep" Oh wait a minute... Steve WA1POX had me delete the beep.

The Evil Doers!

That's wrap... Here are the Evil Doers - Denis KD1HA, Bill KA1VKD, and Steve KA1RCI at the Cumberland PD site taken on delivery day after the successfully repeater deployment

 

Ok the 146.940 rebuild is finally finished, what's next?

We can rebuild her, make her better, stronger, and louder that before...

223.760 - Next RCI Rebuild?