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I'm working on converting a Mocom 70 mobile to use in a repeater setup.
I remember reading somewhere that you can convert the radio to work as a duplex radio, only requiring an external controller and duplexer...but I've been unable to find any information in this regard.
Failing that, I'd like to use the radio as the transmitter, as it's got "True FM", so the audio quality is, most likely, very good.
However, all I have is the radio. I can't find the control head anywhere, so I'm at a loss as to how to connect the dang thing.
I've got access to a complete RF bench, so alignment and deviation adjustments aren't a problem.
What might even be better...anyone know of a good source for service manuals for these old things?
Mike, I don't have the time to do it right now, but maybe in the next few days, if someone else doesn't beat me to it, I'll dig into my old Mocom70 Consellete manual and see what I can find for you. Shouldn't be hard at all to do what you want to do with those old rigs.
What I'm specifically looking for is the pinout of the connector on the front of the radio, as well as how to tune/align the thing.
I also need to order a pair of crystals (VHF)...my local source has since gone out of business, so if anyone could suggest a decent place, that'd be excellent.
Niel McKie, AKA "the shoe", did one of if not the first UHF M70 conversion to full duplex while we were working at a Los Angeles MSS in the early 70's. He also duplexed some M70 Consolete stations and made local repeaters for customers. Some of the information in Lightning's, Mike Morris', articles, comes from Niel.
Will is right, Neil is probably a good one to ask. Go to QRZ.com and look under his ham callsign (WA6KLA), and get his email address and contact him.
I've converted many Motorola radios for duplex over the years, but never a Mocom. I've heard that its been done though. IMHO, a better radio for repeater service is the Mitrek - cheap, very rugged, easy to convert & easy to work on.
Good luck, and I'd like to know how it comes out. Happy New Year!!
- Darrell
Aww screw it. I didn't wanna fool with it anymore anyhow.
My two bits worth:
What you REALLY need is the service manual.
Not likely you could tune this one by ear.
You may fry somthing if you don't follow the alignment procedure in the manual.
A test set would be most helpful.
Using the wrong alignment tool will crack the coil cores.
To open a channel element pry the bottom off, exposing the crystal.
The capacitor is for temp compensation.
I may have a spare manual, let me know the Model number.
There were several variations when production was moved from
Schaumburg to Austin.
Be very careful when tuning the power trippler.
The threads can be damaged if forced. there was a tool shipped with each radio for loosning the lock nut. A "channel Lock "pliers will crush the lock nut.
Pay attention to receiver meter 4 readings.
If the idle is too high this indicates a possible IF filter problem, resulting in distorted audio.
No receive audio problems are frequently L314 broken, usuially on new equipment, as well as the audio output emitter resistor. An open resistor does not necessarily mean a transistor shorted, I have seen these fail due to corrosion.
The Mocom 70 came out in 1970.
The electrolytics may be at the end of their service life at this time.
Don't be surprised if you get some smoke if this unit has not been powered up in years.
The Mocom 70 was a very reliable in the '70s and '80s.
The technology dates to the Motrac, which came out in '59 or so.
The design is stright forward, not an IC in a boat load.
Have fun !
....the later mocom 70's did away w/ the varactor tripler and went towards a micor- like pa....think the older ones were actually more reliable, though....(ah the days....tuning the tripler, and hearing it hissing at you, literally.....just like the Mark 12 IMTS phones...) I'd go mitrek, if only for the fact that those "permakay" if filters in the mocom's got semi-bad often, and the replacements were not any better...really bad in the high band radios...caused all sorts of minor but annoying problems...
'whaddya think they would do if we sent one in for replacement ? (besides laughing at us...) think RCA was the reason for that lifetime crap...they did that warranty thing first...they all knew those 80 billion ceramic tombstones stuffed under a can was a disaster...funny, motracs had much fewer problems in that regard ...speaking of RCA, now, that was some real "fine business, O.M." gear....(being facetious)... what crap.....I'm thinking TAC-TEC.....
'm thinking TAC-TEC..... don't you mean "Trash Tec" !!!! then FidelComm!!!
I know, I worked for them, for a while, went back to /\/\.
On the PermaKay filters, RCA/TacTec replacements had Murata cermaic IF filters in them, maybe the same Murata filters used in the Maxtrac, Radius, Maratrac, could be used for Mocom 70's and Motracs.
Accually Motorola had a problem with bad solder joints in the Permakay filters. I may still have some 'good' ones.
I have done some IF "tightning up" on Maxtrac/Radius receivers by replacing the Murata cermaic IF filters. It is hard to find the realy good ones with steep skirts, not Muratas.
Do your self a favor, don't do it.
The Mocom 70, is a fine radio. ( allright, stop laughing.....), but it doesn't duplex very well. Like the others have said, use a Mitrex, or soemthing a lot easier.
Well, I've done some looking and yes, I agree I wouldnt use the 70 for duplex...from what I read online it has superior TX audio, so I think I'd just use it for that.
I've got a UHF Mitrek that I'm hoping to use as the UHF transmitter. It came with a PAC/RT that's only x-tal'd up for RX -I guess it was used as a one-way mobile repeater...so now i just have to get a VHF receiver.
I've got a VHF Moxy that I was thinking of using for the receiver.
I don't necessarily like the idea of using mobiles hacked together to work as a repeater, I'd much prefer an actual repeater...but when I got it all for free/really cheap, I guess beggars can't be choosers But I definatly appreciate all the input!
In the '70s have installed and maintained hundreds of VHF, and UHF Mocom 70s.
I was the Motorola "man in a van", on several islands, so I have worked on these every where from Volcanoes Nat park to the Kauai Police & fire Dept.
I am very well aware of the problems, as well as the construction.
I used to stock at least 3 M70 permakays in the van.
Compaired to a Mocom 30, or an equivalent GE Exec, Accent 450, EF Johnson or an Aerotron, or whatever, was very reliable, performed very well, much better receiver than the compitition, especially in the UHF band.
The Mitrek came out about '77 or so.
The construction, shielding, and about everything else that I can think of is far superior in the Mitrek.
I would presume that all you need is a receive channel element for your receiver and you should be in business.
I am not aware of a "Transmit only" model.
There is information on bat labs on how to build a repeater from a Mitrek.
I have built a few, and have no problems.
I would be glad to give you a receive channel element for the postage.
Incidently, the MSR2000 Base/Repeater is essentially a Mitrek in a different housing.
As long as we are talking about antique radios, there were KAARS, Canadian Marconi, English Marconi, Halacrafters, Dumont, Bendix, Aerotron, Comco, EF Johnson, Harris RF com, Sonar, Repco, LEAA.
Not to mention assorted RCC car telephones
And perhaps the most imfamous of them all, the GE Accident 450, and the Pacer, not to mention the TPL. (I don't mean Tom Liddy's amplifier)
Modern radios are SO much better.
True, they are difficult to impossible to repair to the component level, however they seldom need much maintenance.
But I definatly appreciate all the input!