Motorola radio frequency changes

[Puffie40]

Hey guys! I'm new here and dead green to the radio hobby.

What I want to do is set up a house unit tuned to the local two-meter ham radio band (I have a Yaesu VX-6, but the reception in my area is scratchy). I happen to have some old Motorola two-way radios from surplus sales that I have been looking at to change the frequencies on. (I am a electronic engineering technology student, and I want the challenge!)

So I have:

• 6 Mocom 35's (Most common model is MD33CFA-1000A)
  Maxar 80(Model MD33TSA1900A)

The Mocom 35's are single-frequency units with what looks like adjustable oscillators. The Maxar 80 has a 4-channel selector range with the classic crystals. The frequency I'm after is 146.800 MHz

The main problem I have is I cannot seem to find any service manuals for these two models. I am really curious about how the channel selector on the Maxar works, and how to tune it. My googling of frequency changes mentions a IF Alignment - What do I need to do that?

Thanks for helping a newbie!

Chris

[Jim202]

Hey guys! I'm new here and dead green to the radio hobby.

What I want to do is set up a house unit tuned to the local two-meter ham radio band (I have a Yaesu VX-6, but the reception in my area is scratchy). I happen to have some old Motorola two-way radios from surplus sales that I have been looking at to change the frequencies on. (I am a electronic engineering technology student, and I want the challenge!)

So I have:

• 6 Mocom 35's (Most common model is MD33CFA-1000A)
  Maxar 80(Model MD33TSA1900A)

The Mocom 35's are single-frequency units with what looks like adjustable oscillators. The Maxar 80 has a 4-channel selector range with the classic crystals. The frequency I'm after is 146.800 MHz

The main problem I have is I cannot seem to find any service manuals for these two models. I am really curious about how the channel selector on the Maxar works, and how to tune it. My googling of frequency changes mentions a IF Alignment - What do I need to do that?

Thanks for helping a newbie!

Chris

I haven't looked myself on the "repeater builder" site, but it is normally a good source of info. Another place is the site www.batlabs.com and go to the model specific selection. Then go to the mobile section and find your radio. If it isn't in either of those 2 sites, your going to have to rely on someone on here coming up with the info.

Jim

[RFguy]

Mocom 35's are crystal units. They pre-date Mocom 70's.

You might be better of picking up some Maxtracs. As they are not narrowband capable, I would think you can pick them up cheap.

[Will]

Both the Mocom35 and Maxar 80 are crystal controlled radios. The crystals will cost more than the price of a used Maxtrac or Radius mobile, which are programmable.

The Mocom 35 were made in the early 70's, the Maxar 80 is the updated Maxar and made in the late 70's, hence the '80' in the model number. These are both mid tier radios.

[WB6NVH]

Service manuals show up on eBay semi-frequently. You will need a pair of crystals for each frequency, one for transmit and one for receive, and they cost about $ 25 per crystal from International Crystal, or slightly less from Bomar crystal.

These are not broadband radios, they have to be aligned to the channel of interest. I don't see why you would need to touch the IF stage of the receivers but you will need to realign the entire transmitter and the RF and OSC stages of the receiver. Some equipment will not pull down to the 2 Meter band without some modifications. I never used either the Mocom 35 or Maxar 80 on 2 Meters so I don't know if these will tune down that far or not. If they do not, you will need to add some capacitance across the tuned circuits in the RF stages of the receiver. The transmitters probably will tune to 2 Meters without difficulty.

At about $ 50 per radio per channel for crystals you could probably find programmable much newer gear for the same expense.

[Puffie40]

Service manuals show up on eBay semi-frequently. You will need a pair of crystals for each frequency, one for transmit and one for receive, and they cost about $ 25 per crystal from International Crystal, or slightly less from Bomar crystal.

These are not broadband radios, they have to be aligned to the channel of interest. I don't see why you would need to touch the IF stage of the receivers but you will need to realign the entire transmitter and the RF and OSC stages of the receiver. Some equipment will not pull down to the 2 Meter band without some modifications. I never used either the Mocom 35 or Maxar 80 on 2 Meters so I don't know if these will tune down that far or not. If they do not, you will need to add some capacitance across the tuned circuits in the RF stages of the receiver. The transmitters probably will tune to 2 Meters without difficulty.

At about $ 50 per radio per channel for crystals you could probably find programmable much newer gear for the same expense.

Thanks for the input on what is needed for this job. That was just the type of info I needed.

ICM just quoted me $23.25 each for both crystals, with a one month manufacturing delay. Considering a MaxTrac equivalent would cost me at least $80 (Both radio and shipping) to get it here (I live in BC Canada), I would agree that it gets cost prohibitive pretty quickly to work on a crystal machine. (I would probably need an oscilloscope or a radio tester just for the alignment - that's close to 3 grand of equipment!)

So I'll keep looking. What I'll do is set the Maxar 80 aside (If I do a freq. change, I'll do it on that - at least I have the hope of an option of channel selection) for a strong moment of insanity and part out the 35's - I might be able to use some of it in some electronic projects

[stay-con]

ICM just quoted me $23.25 each for both crystals, with a one month manufacturing delay.

However, if it's the older gear you want to play with... Considered buying one of the DDS (Direct Digital Synthesis) units. Most have a TR line and a programmable offset so you can switch between the trans and receive crystal frequencies required.

It makes playing with swap meet and eBay "junk" a lot more fun.

Jeff

[train_radio_guy]

If you'd like to 'play' with commercial radio gear, and want something that tunes down to 2 meters (144-148 MHz), you may want to consider some of the frequency agile radios out there, which support front panel programming (FPP).

Portable-wise, the Motorola JT-1000 is a good choice, and has a host of accessories available. Bendix King also has a number of portables, which are equally as versatile.

Mobile-wise, Bendix King made the LMH-3142 (ver.3) which tunes down to 2 meters, with a software mod. Kenwood TK-705D’s will program down to 2 meters, with no re-tuning, just move one jumper inside the radio. It even has a VFO mode, just like a traditional ham radio!

The list goes on, but you get the idea. There are options, if you look… just a matter of price & availability.

- trg