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I just got a couple of Micors (remote, unified chassis, qrp(10w) lo-UHF).
Since the channel elements are not very versatile to me, I consider replacing them with a couple of synthesizers.
Well, you Micor experts, do you recomend just replacing the elements (synthesizers working on element's freq) or set-up the synth to produce the final useful freq (over-passing the multiplier stages)?
Is the pre-amp a 'must'?
The circulator is the same for all power levels, or in case I upgrade the PA I also have to replace the circulator assy?
Paul:
Modifiying the Micor for a synthesizer probably is not worth the time and effort.
The 13V power suply is very reliable.
I would use a 10W Maxtrac for an exciter.
Circulator:
Circulators are somewhat frequency sensative.
The same circulator will work with all Motorola amplifiers to 70W.
(The 120/250W used a tube PA.)
I presume that you are refering to the output assembly on the unified chassis.
The power amp is not likely to operate out side of its band split.
I know that a 450-470 amp will not have any output on 444 mhz.
Preamp:
You can not receive a signal lower than the noise floor of your site.
This requires "Effective Sensativity Measurement".
I can send you document with the instructions.
Normally a preamp is used to overcome losses from cables, filters, and splitters. I would expect a 12DB SINAD @ .25uv at the antenna port
of the site multicoupler, duplexer, etc.
I performed some experimentation with the stations, they needs some restoration since they were modified for who-knows what application.
I discovered that they have seperate squelch operation for audio and retransmit functions; Wouldn't be more convenient to share the same trigger source? Or there's a secret behind it? and how "matched" the two adjustment can be?
It will be very helpful to read the document you mentioned. Please forward to [email protected]
My two bits worth:
As far as operating out side of the specified limits, it seems that this is by individual case, determined by the tolerances of the parts involved.
In my case it would only output 1 watt at 444, but 70W ar 462.
Squelch gates:
The basic concept of your station controls dates back to the late 60's when the Motrac with plug in boards was designed. The Micor station controls are very similar, but not interchangeable with Motrac cards.
Squelch operation of repeater versus Motorola's squelch gate.
There is a signal originating on the Audio/Squelch card that is "Carrier indicate"
This signal operates with very little time delay, and is active any time the receiver is un squelched.
(May require "PL" decode)
Motorola receivers usuially are optioned for "Or Squelch" That is the receiver will open on the presence of "PL" regardless of signal strength.
This feature is not very beneficial for repeater control.
To avoid random nusiance keying you want to specify a certain amount of time for a signal to be present, as well as a minimum signal level to allow repeat.
We also need "Drop out delay" to eliminate having the repeater un-key, and re-key repetedly on very weak fluttering signals.
Then there are certain applications where a carrier indicate to external equipment is required, so we need a relay
We need a repeat audio path.
The Squelch gate also has the transmit channel element switch.
This ciricutry is present on the squelch gate card.
In the Micor station the required cards to operate the station are:
Station control plus one or more cards to key the transmitter:
Squelch gate, DC transfer, Gard Tone decoder.
If this is a wire line station a line driver board is also required.
There is also an encoder card if this is a voteing station.
You must have the "Control and Application" manual to make any sense of the card cage.
The possibilities for options is endless, so be careful.
Years ago I looked into the possibility of building a DDS-type synthesizer to replace the channel elements in the Micor. I don't remember all of the design issues, but the one that sticks out in my mind was the output of the (I believe) transmit local oscillator was somewhat of a wierd shape, like a sine wave with a lot of distortion. (As opposed to a pure, smooth sine wave.) IIRC, this was to pre-shape the LO to compensate for some non-linearity introduced by the modulation process. I decided that trying to modify the output of the DDS would be too much work.
I would say if you really want to run these machines as repeaters, you should just buy the crystals and use them that way. You won't be changing the frequencies very often, so the financial hit of buying crystals won't be too bad compared to trying modify them to be synthesized.
If you were planning on using these machines as remote bases on multiple channels, I like the idea of using a low power maxtrac/gm300 as an exciter for Micor 75 W PA.
One nice thing about the Micor squelch gate was the "dual action" based on the receive signal level. For strong signals, the Micor squelch is fast-acting, and will close quickly when the signal drops. For weak signals though, the squelch stays open for a second or two in case the signal is just breifly falling into the noise. Kind of a neat design.
My two bits worth:
The first Micor mobile that I saw really impressed me.
I thought that the squelch circuit was really special.
This was 33 years ago, and I was lead tech at Niles Radio in Tucson, Arizona. (GE shop) Gary Fell was the Shop manager at the Motorola shop, and wanted to hire me, so he demonstrated Motorola's finest.
The squelch operation has long been one of the major fine points in perfecting radio receivers.
All of this on 1 IC!
GE was experimenting with "hysterisis" squelch, which rerquired a greater signal to keep the receiver open, than to hold. The result was squelch chopping on fluttering signals. (Many factory revisions on this board)
The Motrac had a long squelch tail, but didn't chop.
Private Line cured these problems, but was rather rare over 30 years ago. GE CTCSS system was not very reliable nor stable at the time.
Here "Squelch Gate" refers to a circuit card in the repeater.
Incidently, the GE MASTR-PRO at the time used the receiver squelch to key the repeater, DOD by a little card in the remote chassis.
As I mentioned the various reasons why you don't want to use receiver squelch for repeater control. The G.E.Mastr-Pro was very touchy to set the squelch so that the repeater worked satisfactorily.
This is one reason that the MICOR became so popular.
I finally got hired by Motorola 33 years ago, so I have been able to play with these over the years.
Channel elements:
The mobile uses a channel element that outputs a series of pulses, which are processed in an IC called the "Serrasoid" modulator. The IC changes the spaceing of the pulses generating Phase Modulation.
The Base uses Direct FM, the channel element is similar to the receive element, with the exception of the modulator circuit.
Keep in mind that the receive element is the same as the mobile, the transmit elements are not interchangeable between base and mobile.
Paul:
I need a valid E mail address your address apparently has something missing.
bernie wrote:My two bits worth:
The first Micor mobile that I saw really impressed me.
I thought that the squelch circuit was really special.
The Base uses Direct FM, the channel element is similar to the receive element, with the exception of the modulator circuit.
The Micor is a real solid piece of equipment. It was one of the better radios that Motorola came out with. Draw back is that it is only a narrow RF band spread.
The max freq spread is something like 2 Mhz at low band and 4 or so at VHF. They were never made to swing full specs over much of a range. Looked quickly through the manual and couldn't find anything listed. Single freq they work just fine.
If you do a search on Micor, you should find a couple of dial a frequency boxes. Just remember keep the spread down. Back about the early 80's, one of my ham friends made one for the Micor he had. Blew peoples mind when he told the he had a dial a frequency 100 watt mobile. It was just unheard of back in those days. The only thing everyone was use to was 25 watt mobiles.
I remember a GLB sysntesizer for the Micor (1975), a friend had it on his Micor, was neat, just dialed the channel with rotating knobs and select + or - or no offset.
I also had one of the GLB synthesizers on a 120w mobile Micor. I replaced all the parts in the exciter and receiver to bring it from the 152-174 MHz band down to the 135-154 MHz band. Took me hours to get any signal through the front end - it was THAT tight. Eventually I borrowed an HT-220 and used that as the signal source - once I got a little less noise in the audio, I was able to revert to an ordinary sig gen to complet the alignment.
Modulation was always a problem with that combination. The synthesizer was extremely vulnerable to cold temperatures and any vibration at all. Apparently it wasn't happy with 120 watts of RF floating around 5 feet away either. Eventually I broke the modulation chain in the exciter and fed the transmitter audio (including PL) up the receive coax and used that to modulate the VCO directly. Choosing the proper coupling cap made the job even more difficult, but eventually I got it to function nicely. I also tore out the reverse burst circuit and made the PL just go away while the transmitter stayed on the air for about 1/4 second. This made the unit compatible with all of the solid-state PL decoders out there that ignored the reverse burst. I think I saved all the parts on the PL board by keeping one lead soldered in. I still have the radio. I also bought the Micor preamp for it which brought the sensitivity down from .5 uV to .25 uV, or so they claimed.
As others have said, the bandwidth was not what you'd call wide band. I believe the receiver was good to +/- 2 MHz so it just about covered the entire 2 meter band. The transmitter was probably less wide, but the power amp control board made up for any losses at the band edge. I do recall once when the pot on the power control board got dirty and let the transmitter go to wide-open-throttle for several days. I pegged the needle on my 150w Bird meter, and that was with the engine off ! I pulled the board, cleaned and rotated the pot, and reset it to 120w and all was working well again.
I bought another GLB synthesizer for a 6 meter Motrac, built it, probably tested it, but never interfaced it, as the vehicle situation changed. I should look into completing that and making it into a base station, but again the mobile units just don't lend themselves to full-band operation.
I understand that Gil Boelke (GLB) died in the last few years. I probably kept his phone warm during the mid 1970s when I'd call and describe a problem that no one else ever had. It seemed that ALL their problems were first-time occurances - something I just could never believe.
....serrasoids were only used at low band, I believe, due to the fact that at low band, you don't have the luxury of having your modulated L.O. being multiplied that many times (and hence your modulation)....
I started in the business June 1969 and saw the first Micor in August. (Didn't know enough to be suitably impressed) Our first one was LB and came back the next day because the office only got the first word. When checked, it was putting out 180 watts and the temperature sensor would shut it down: power control was all or nothing in LB.
The next batch for the power company got numerous complaints of noise, until they realized that the mobile was opening the squelch at a substation 50 miles away. Great, reliable, radio,
My two bits worth:
I really am not sure why they decided to use the serrisoid modulator in the first place, since the direct FM version used in the base exciter works flawlessly. I do know that the serrasoid modulator in LB will do 15KC deviation, the base exciter won't. I had to build a low band wide band base for the military. I wound up with a LB Micor base with a Motrac receiver. 150HZ PL
This base communicated with AN/PRC44 Military radios.
The UHF Micor mobile has a unique exciter which uses an offset oscillator to generate the transmit frequency. This board used direct FM modulation of the offset oscillators.
All other Micor mobiles had a serrasoid modulator which was in 1 chip.
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