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  #1 (permalink)  
Old 12-08-2018, 10:56 AM
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Default Motorola MX300-R Frequency Test

I was able to find an old Motorola MX300-R radio for sale, the seller sent me the following data from the frequency test he performed. Can someone confirm everything is within spec?

433.200 MHz
Receiver 20 dB quieting is @.35 uV -116.0 dBM.
Transmitter output 5.01 watts, frequency error -60 Hz. Deviation analog 4.88 Khz Secure 4.0 Khz.

434.100 MHz
Receiver 20 dB quieting is @.39 uV -115.0 dBM.
Transmitter output 4.67 watts, frequency error -10 Hz. Deviation analog 4.89 Khz Secure 4.0 Khz.
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Old 12-08-2018, 11:16 AM
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That's pretty close to being in spec. Close enough that any variation could be even a test equipment calibration error. Those are the specs of a healthy radio.

Internally there's really not any component in there that's going to fail due to age. But that urethane housing...different story. However, the flex circuits are susceptible to damage if you flex them much. Even when new this was an issue.

If you're lucky it has the later D version PROM that can be reprogrammed and you have access to a means of getting it reprogrammed.

They were cool radios in their day but it's like having a suitcase on your belt.


In the past I spent far more time learning the MX series than any other. And I remember most of it.


I once had a VHF 48 channel non-ruggedized version that had an extraordinarily good VCO system in it. It'd lock up and work across a 24 MHz span of frequencies. That's several times greater than the spec for them indicated.

But, my freuency list was a bit wider in span than that. So I drilled a hole in the back cover and would field tune the VCO on the fly. I had alignment marks on the back cover so there was no guesswork. "Tune to this mark for 2 meter operation. Tune to that mark to listen to the base security police at 171.xxx MHz."

The MX was the most hackable Motorola radio of all time.
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Old 12-08-2018, 3:05 PM
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Glad to hear its A-OK; the radio is a UHF 48 channel with C version EEPROM, he also has the hardware/software to reprogram it so that's convenient.
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Old 12-08-2018, 5:23 PM
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Quote:
Originally Posted by udiver View Post
Glad to hear its A-OK; the radio is a UHF 48 channel with C version EEPROM, he also has the hardware/software to reprogram it so that's convenient.
If you are intending to use this radio in the 440-470 MHz band, be aware that you will need to change a bunch of modules, possibly an offset oscillator (hard to find) Maybe the VCO coil, and some capacitors.

It is not impossible to do, I have done it. but it is not a simple programming job. The C version EEPROM alone might be worth the price.
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Old Yesterday, 7:00 AM
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As an owner of an MX300-R, I'd advise against using it for anything other than a display item. The rubber and plastic coating on the radio will turn to dust or crack at the slightest bump.

Mine lives happily in a glass display case in my office.
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Old Yesterday, 7:52 AM
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The specs are as good as you can expect from a 40+ year old radio. Your main problem is going to be batteries. The cases do deteriorate, but I have found some do some don't. The best ones were the last generation that had a green circuit board. I have a 48 channel UHF with scan from DEA, that I converted to T-band for NYC EMS and PD. I also used the DES encryption in them, it wasn't the best audio but passable for close range.
Having had numerous MX-R radios and having converted many to 450 and even T-Band they are by far my most favorite radio. What is said is true about modules to get the radio up to 450 for ham use, but the VCO will go, as far as I can remember there were only 2 VCO coils for the UHF band a RED one for upper UHF and a GREY one for Government splits. I too have the programmer for the different modules A,C,D. I actually had contemplated trying to shift one down to the 380 Squad channels. I converted many VHF (over 50) ones to my son's Civil Air Patrol channels years back. They were great, you didn't have to worry about breakage or loss since they were so inexpensive (about $25 ea.)
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Old Yesterday, 6:19 PM
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Quote:
Originally Posted by radioman2001 View Post
The specs are as good as you can expect from a 40+ year old radio. Your main problem is going to be batteries. The cases do deteriorate, but I have found some do some don't. The best ones were the last generation that had a green circuit board. I have a 48 channel UHF with scan from DEA, that I converted to T-band for NYC EMS and PD. I also used the DES encryption in them, it wasn't the best audio but passable for close range.
Having had numerous MX-R radios and having converted many to 450 and even T-Band they are by far my most favorite radio. What is said is true about modules to get the radio up to 450 for ham use, but the VCO will go, as far as I can remember there were only 2 VCO coils for the UHF band a RED one for upper UHF and a GREY one for Government splits. I too have the programmer for the different modules A,C,D. I actually had contemplated trying to shift one down to the 380 Squad channels. I converted many VHF (over 50) ones to my son's Civil Air Patrol channels years back. They were great, you didn't have to worry about breakage or loss since they were so inexpensive (about $25 ea.)
Hoo boy what I would do to add scan to my VHF MX360-S! That sucker receives everything
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Old Yesterday, 8:45 PM
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They did have a pretty hot receiver. Especially so if they have the kinda rare RF preamp module instead of the usual filter module.

I continue to hope that I will find a very rare MX310 at some point. I've had just about every other variant including a super rare SP version that offered 14 channels (and low power) of channel elements in a 360 frame size. I've even had an MX360T. And DTMF cover versions.
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Old Today, 1:32 PM
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Thanks to all for the replies.

Quote:
Originally Posted by radioman2001 View Post
Your main problem is going to be batteries.
Yes that's gonna be tough. If anyone has one they'd be willing to sell please let me know (even if its dead), I'd be willing to pay a good amount.
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