Batboard

Hi gang. Well, it turns out I can use my MSF5000 in our repeater project. This leaves me with the question of tuning.

It's a UHF machine, the Digital station version. It's presently on 451/455 and I need to tune to 442/447. I've got the metering panel. I'm going to be getting my hands on the manual to tune it. I also have access to a full suite of test gear (including a comm. service monitor).

Anyways, aside from the test set, metering panel and manual...what do I need to tune this thing, and can anyone provide any tips/quirks?

Thanks very much!

I believe that you are also going to need that little tuning coax probe to tune the station.

The part # for the quantro station is TRN7799A, It may be the same for the MSF...

Good Luck, Rob

Bellersley,
There are several good points of interest within the domain here. I am mainly in reference to the filtering sections of the station. MSF repeaters have a nasty habit of growing whiskers. Its up to you but I usually disassemble the filters and clean them before I start tune-up procedures. (I have found it makes life easier for me )
The alignment procedures on the MSF are pretty straight forward. Follow the manual step by step and life will be good. FMROB mentioned a coax tunning probe, we differ in part numbers I show it to be a TRN7794A.
Doug

Doug,

You most likely right with your part#. The one I have is for use with the quantro station, However it looks the same as the one for the MSF, which mine doesn't have a part # on it..


Rob

Okay! Sorry to bring a dead thread back to life. My repeater project recently got new wind, so to speak. Our MSF5000 has been sitting in storage for a few months now. I'm still in need of tuning. Unfortunatly, I don't have the manual anymore, and don't think I can get my hands on it anytime soon.

Is there any way to tune this sucker without the manual, or would I be better off paying a shop an hour or two of labor to do it? Thanks!

Copies of the alignment instructions can be scanned and gotten to you. That's the easy part.

If your station is a UHF repeater with the internal filter/duplexer, a full alignment "by the book" requires an RF millivoltmeter, a signal generator, a metering panel for the MSF, the afore-mentioned tuning probe cable, a screwdriver or two, and a 5mm Allen wrench.

If the station is just a base, or has an external duplexer, then you can get by with a tuning probe cable, a 5mm Allen wrench, a screwdriver or two, a metering panel, and a signal generator.

The RF millivoltmeter is the critical part. Some people have this in a service monitor; others have used a spectrum analyzer instead. You use this to measure the signal coming out of the tuning probe cable, and an RF millivoltmeter would probably be a high-impedance device, whereas a spectrum analyzer, and maybe a service monitor, would be 50 ohm, and that might load down the signal level too much. I used an HP 3406A wideband sampling RF voltmeter and the results are excellent.

As far as quirks and tips, since you're moving the operating frequencies about 8 MHz, you'll find the mixer coil adjustment hard to do, initially. Very little signal squeaks past those coils, and you have to tweak all of them a little at a time until you see the slightest movement on the meter, like 1/4 of a microamp (it's that small). Eventually you'll get the meter up to 20-30 where it should be. The rest is quite straightforward - adjust the two VCOs, tune the front end, and the station is done (except for the internal filter/duplexer, if present). Follow the procedure exactly for the internal F/D - adjust the coils once, like it says. Don't go back and tweak them again, because you'll detune everything and end up chasing your tail.

Bob M.

Excellent! If a scanned copy of the instructions could find their way to [email protected] I would be VERY thankful! We have access to a full suite of test equipment as would be found in a broadcast shop, so I imagine we can get an RF millivoltmeter.

bellersley: I scanned about 30 pages into a PDF file. I sent you a PM telling you where to go get it, rather than e-mailing the file.

Did you get the message?

Did you retrieve the PDF file?

Bob M.

Sorry its taken me awhile to get back to you, things have been pretty hectic here lately. I did get your email but haven't had a chance to print off the PDF. Thank you very much though! We do have an RF millivoltmeter available so that shouldn't be a problem.

All we need now is a UHF duplexer of sorts. I read somewhere that because the MSF has such a good prefilter that a duplexer isn't necessarily required. In terms of RF noise, our location isn't too bad. Using a Radius mobile directly into the antenna, we can easily hear portables well within the coverage area we desire, with little desense from nearby transmitters.

Also, we have a 45W PA and a 110W PA. I was thinking we might be better to run the 110 at half power rather than the 45 at full. Does it really make a difference, effiency wise, or would there be no problems running the PA at full power all the time? If that's the case, we would just run the 110W "full tilt".

Thanks again!

If you haven't already read it, there's a photo tour of the MSF5000 over on http://www.repeater-builder.com in the Motorola/MSF section. That article details the various power levels and duplexer options you can get with the station.

The cable used with the internal filter/duplexer is cut specifically to work with the MSF5000. The receiver is good, but it can still be desensed. If you can find a good base station duplexer, and your station is already a base station, I'd recommend going that route. Two antennas might also work if there was sufficient attenuation between them.

An external duplexer will give excellent performance on an MSF5000. The power amps are rated for continuous duty at full power, but since it's hard to measure the power feeding the internal filter/duplexer, they derate the stations by almost 50% when you measure the power at the output of the station.

FCC rules mention using the minimum power required to get the job done. If 45 watts is enough use it. 110 watts is only about 4dB more, and after you put in a duplexer, it's even less.

As long as you downloaded the PDF file, I can remove it from my server and give back some space.

Bob M.

Well, I would really like to use a decent set of casns, such as the Sinclabs ResLok series. I've used them on VHF before and was extremly impressed!

Unfortunatly, two antennas at our location isn't an option. We have been given access to an exsisting antenna and cannot change it. Fortunatly, its in very good shape and gives very low SWR at our frequency (with a 35 watt mobile forward power, less than 2 come back.).

If you would be able to leave the PDF up just tonight, it would be appreciated. I saved it to the office computer but would like to print it here at home. If you've already taken it down, no sweat, I can get it tomorrow.

Thank you again for your input!

I'll leave it up until you've gotten it wherever you need it. Printing can be done whenever you see fit.

2w reflected out of 35w forward isn't terribly good. 0.2w reflected out of 55 forward is what I have on my repeater, and even that's double what it was when I first put it up. But I can live with that !

I've had very good luck with Celwave 6-cavity Bp/Br base station duplexers. They're pricey but they provide over 100dB of rejection. The only downside to them is that they notch really well, but the bandpass is not what you'd get with a separate bandpass cavity, i.e. there's very little rejection 10 MHz away.

Bob M.

Hey Bob, I've downloaded and printed off the PDF, thanks!

One question for the group though. The manual talks of using a metering panel to plug into the RJ jacks on the front. My metering panel has an IDE style connector to plug into the top of the repeater "brain". Is this one and the same or do I need something different?

Same DMP.

There is an RJ45 type 8 pin jack on the edge of the DMP to the left of the control ribbon jack. Just use a computer network type jumper to hook from there to the metering jacks on the station.

You can use either the TLN2518 or TLN2519 meter. There should be three connectors on the bottom edge: the 40-pin IDC-type for picking up power, ground, audio, and the digital signals, an RJ45-style connector for TX, RX, and PA metering, and a pair of pin jacks for the red/black test probes that are active when the meter switch is set to the 10V or 25V position.

Three cables should have come with the meter: a 40-pin flat cable with IDC connectors at each end, an 8-conductor cable with RJ45 connectors at each end, and a red/black test probe pair with pin plugs at one end and longer probes at the other. These last cables are the ones most often missing from any used metering set.

Bob M.

Hmm, I'll have to check, but I'm pretty sure our panel only has the IDC and the two pin connectors.

A friend of mine who says he knows his stuff told me you only need to use the IDC connector, when I mentioned that the manual says to use the RJ-45 plugs, he thought I was full of it.

Also, I was offered a nice ResLok duplexer for a really decent price, but the guy said its corroded inside. Is this something I can somewhat easily clean up?

If your meter is the 2518 or 2519, and it has a meter, a speaker, and some switches on the front, then it has to have the RJ45 jack along the bottom edge.

I guess it depends on where the corrosion is. If it's inside, and you can take it all apart and get rid of it, or it's not in the area where the insides have to make contact, then you should be OK. If it's badly pitted, it might take a lot more work to get it running nicely.

If the price is right and you can take it all apart, do a real nice job cleaning it all without removing any silver (try a commercial metal cleaner such as Tarn-X first), and all the moving parts work, then it's probably worth spending some time on it.

Bob M.