Motorola Mostar Questions

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Motorola Mostar Questions

Postby Eddie » Mon Sep 20, 2004 2:24 pm

I know that about everyone does not like the Motorola Mostar because of all their problems. I have a legal way to program the Mostars and they are a low cost radio to use on my GMRS system. I have a few questions I hope someone can please can help me with. Question #1 I have programmed several UHF & VHF Mostars with 2, 8, & 16 channels. The problem is they will only TX & RX on only one or half the channels I programmed in. I was told that these radios must have channel jumpers on them that will limit them to how ever many channels have been jumpered reguardless of how many channels the selector shows. Does anyone know where or how I can find information on how to restore all the radios channels? Question #2 Will the UHF Mostar cover the 450-470 MHz spread or will it only cover 450-459 / 460-470? I have problems everytime I try to program one with 453 / 458 and 460 / 465 freqs. together. Question #3 Most of the UFH Mostars I have are real good on transmit but bad on receive unless your right under the repeater! Does the receive have to be realigned each time their re-programmed? I was told something about you had to torque some of the some of screws just right and or use jumpers in the back connector or they would not receive good?? Thanks for any help.
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Postby d119 » Mon Sep 20, 2004 4:46 pm

If I remember correctly, the MOSTAR radio requires the front end to be realigned any time it is reprogrammed, similar to the MCX-1000.

The service manual should cover how to do this. The "rough & tumble" way to do it is to locate the front end tuning screws in the radio, and inject a weak on-channel signal into the radio and then peak the screws in order to clean the signal up, and then reduce the power of the test signal to noise again and go back through and peak again until you can't get any better.

It's ideal to do this on a channel that is in the middle of the spread of frequencies you have programmed in.

Never heard of having to have stuff in the back connector that affected sensitivity though.

Good luck.
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Motorola Mostars

Postby Andy Brinkley » Mon Sep 20, 2004 6:01 pm

The Mostar is not a "program and play" radio. Answers to your questions below:

Question #1 I have programmed several UHF & VHF Mostars with 2, 8, & 16 channels. The problem is they will only TX & RX on only one or half the channels I programmed in.

The channel capacity of the Mostars is limited by the channel selector and the microprocessor / eeprom.
The channel selector options were:

Single channel with no display or channel knob

Two channel model that utilized a pushbutton switch to select ch 1 or 2.

NVR series with a rotary channel select switch, 1 - 8 channels

Display series that utilized an LED readout, 1 - 32 channels

The microprocessors used were

1 - 8 channel microprocessor is 51-97003C11
16 or 32 channel microprocessor is 51-97003C09

The 32 option also requires some jumper changes on the command board and a larger eeprom.

So you will need to determine what is limiting your channel capacity - the microprocessor / eeprom or the channel selection method.

Question #2 Will the UHF Mostar cover the 450-470 MHz spread or will it only cover 450-459 / 460-470?

The Mostar receiver is only rated for a 3 mhz frequency spread. It will be deaf as a can be if you try to stretch it from 453 to 460 mhz freqs.


Question #3 Most of the UHF Mostars I have are real good on transmit but bad on receive unless your right under the repeater!
The Mostar needs a complete realignment unless your new frequencies are very close to the old frequencies. I would recommend purchasing a service manual along with the necessary RF test equipment to tune the receiver and transmitter. There are no external jumpers that affect the sensitivity.
Andy

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Re: Motorola Mostars

Postby Eddie » Tue Sep 21, 2004 5:48 am

Andy Brinkley wrote:The Mostar is not a "program and play" radio. Answers to your questions below:

Question #1 I have programmed several UHF & VHF Mostars with 2, 8, & 16 channels. The problem is they will only TX & RX on only one or half the channels I programmed in.

The channel capacity of the Mostars is limited by the channel selector and the microprocessor / eeprom.
The channel selector options were:

Single channel with no display or channel knob

Two channel model that utilized a pushbutton switch to select ch 1 or 2.

NVR series with a rotary channel select switch, 1 - 8 channels

Display series that utilized an LED readout, 1 - 32 channels

The microprocessors used were

1 - 8 channel microprocessor is 51-97003C11
16 or 32 channel microprocessor is 51-97003C09

The 32 option also requires some jumper changes on the command board and a larger eeprom.

So you will need to determine what is limiting your channel capacity - the microprocessor / eeprom or the channel selection method.

Question #2 Will the UHF Mostar cover the 450-470 MHz spread or will it only cover 450-459 / 460-470?

The Mostar receiver is only rated for a 3 mhz frequency spread. It will be deaf as a can be if you try to stretch it from 453 to 460 mhz freqs.


Question #3 Most of the UHF Mostars I have are real good on transmit but bad on receive unless your right under the repeater!
The Mostar needs a complete realignment unless your new frequencies are very close to the old frequencies. I would recommend purchasing a service manual along with the necessary RF test equipment to tune the receiver and transmitter. There are no external jumpers that affect the sensitivity.


First of all thank you both for your responce on the Mostar. Where are the RX adjustment tuning slugs located on the UHF Mostar? I have a VHF service manual ordered but would the RX slugs be located in the same place on the VHF models as on the UHF radios? I dont have a service monitor so I'm going to try to use another radio transmitting on the receive frequencie I need and a meter to adjust the RX. Do you think this will work?
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Re: Motorola Mostars

Postby kc7gr » Tue Sep 21, 2004 7:18 am

<bigsnip>

Eddie wrote:First of all thank you both for your responce on the Mostar. Where are the RX adjustment tuning slugs located on the UHF Mostar? I have a VHF service manual ordered but would the RX slugs be located in the same place on the VHF models as on the UHF radios? I dont have a service monitor so I'm going to try to use another radio transmitting on the receive frequencie I need and a meter to adjust the RX. Do you think this will work?


Excuse me for butting in. Speaking from a position of 20+ years in the field -- Yes, your idea of using another radio will work, in the same manner that using an antiaircraft gun to kill mosquitoes will work.

My position with questions like this has always been that if you do not have the correct test equipment, and the skill to use it, you should not attempt the task.

Permit me to expand on this. First, you need to use a dummy antenna to load the second radio while you're transmitting (trust me, you do NOT want to be making test transmissions into an antenna for as long as it will take to tune the target radio). This is a problem, because the dummy load will soak up so much of the RF that you may not have enough to properly nudge the receiver you're trying to align.

Second, you have no accurate way to determine how much signal strength you're putting into the target radio (some alignment procedures call for a specific level to be injected).

Third, you have no idea how accurate (or not) the source radio is unless it has been aligned recently. Even then, you have no way to know if the thing's drifting with temperature.

If you expect optimal performance from your target radio, you need to use the right test gear, test bench setup, and the specified alignment procedure. Anything else is just going to be guesswork.
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Postby Mike_K8LG » Fri Sep 24, 2004 6:54 pm

Hello again Eddie,

As we talked about on the telephone the Mostar needs to have the receiver retuned when it is moved more that a few MHz. If you would like I could send you the section of the UHF service manual that shows the tune-up procedure. You will need a GOOD signal generator (I use a Fluke 6060 here) and a voltmeter to do the job.

As I said I have moved them into the Ham band without any problems and with good receiver performance. I change the injection side when I put them in Ham service as we talked about.

All the advice you received above is correct. There are so many button options you must get a manual with good diagrams to know what is going on. The 8 channel radios have a switch (with a stop at 8) that has 16 channels number on it. The PROM is still only able to hold 8 channels (small PROM models).

I like these radios for what they can do for the low cost. A buddy of mine bought two at a hamfest for $5 (Yes, two for five dollars) and we set them up in about 45 minutes (including programming and tuneup). He is happy!

Good luck with the tun-up..
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