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Micor channel element and crystal formula information.

Repeater Info - N7KP Articles

Micor channel element and crystal formula information.

Verify that the formulas are correct for your radio.

Not responsible for errors, or loss due to use of this information.

Compare the formula with the elements removed from your RX and TX strips before you modify the strips to the ham bands or order your new crystals.

Be aware that you most often will be changing from Low Side injection to High Side injection on VHF High receivers being moved to the two meter band.

Some may not know what a “Channel Element” really is.

In older radios the crystals were just that, a crystal in a small metal or plastic casing that plugged directly into a socket or sockets in the radio.

Then came crystal heaters where the crystal was installed in the heater to make the frequency more stable, then the heater plugged into a socket in the radio.

In newer crystal controlled radios the crystal is installed in an enclosed channel element that is then plugged into a socket in the radio.

There are variations in what channel elements do based on Tx or Rx and frequency stability (accuracy), Frequency modulation vs. Phase modulation, and other factors.

On the Micor line of radios the channel element is not only an oscillator, but in most cases also a multiplier.

Depending on band and band split, they can be doublers, or triplers.

This is why it is important to have the correct element. It is NOT just a crystal holder.

An example is the VHF High band RX element actually outputs three times the crystal freq.

Another example is the VHF High band TX element which also puts out three times the crystal frequency, and it is the TX channel element where the modulation is actually done.

Let that above paragraph sink in. The element is where the modulation is done, meaning either true Frequency Modulation or Phase Modulation. A PM element won’t have any audio if installed in a FM exciter, and a FM element won’t have any audio if installed in a PM exciter because the pin out and operation of the element is different.

You CAN get the exciter to put out RF just for testing with the wrong element, but you can’t test for audio deviation or PL.

 

Six meter Micor:

Reportedly, the station exciter uses a six times multiplication of the crystal, and the mobile uses a three times multiplication.

I have found station manuals (not mobile manuals) that list both the times six, and the times three multiplication. So, it appears that the discrepancy may be an issue of older vs. newer versions of the exciter.

All of the ones I have use the times six multiplication, so that is the only one I have some experience with.

Note that this is for the 50 MHz range, the 25 thru 30 “something” MHz versions are also different multiplications.

TX formula:

Oscillator (crystal) freq times 6 equals the carrier freq.

Example, 52.8 MHz carrier freq is a crystal of 8.8 MHz times 6.

Channel element is K1004 for the Phase Modulated, 5 PPM version.

RX formula:

Oscillator (crystal) freq times three, plus the IF of 5.26 MHz equals the carrier freq.

Example, a crystal of 15.68 MHz times three plus 5.26 MHz equals the carrier freq. 52.3 MHz.

The element is K1003 for the 5 PPM.

 

Two meters:

According to Motorola manuals, for the Two meter range you should use “High Side Injection”.

A quick explanation is that receivers use an Intermediate Frequency ( IF ) that is mixed with the oscillator and its multiplier stages to derive the desired operating frequency.

In many (most) receiver designs, there is the desired signal, and the “image” that is at the opposite “side” of the Intermediate Frequency.

The way the Micor “selects” the correct of these two signals is the VERY selective mechanical receiver front end preselector.  That is the metal casting with the five tune able screws that allow only about a 3 MHz bandwidth to pass from the antenna to the IF stages.

If the Micor did not have the preselector, the receiver would actually hear both the desired signal, and the “image” that is 23.4 MHz from the desired signal equally well, in addition to being overloaded by nearby strong signals of any sort.

The 23.4 MHz is twice the IF of 11.7 MHz.

For two meters your desired signal is 11.7 MHz DOWN from the crystal/multiplier/ IF and the unwanted “image” is 11.7 MHz UP from crystal/multiplier/IF stages.

So, in fact, crystals for the two meter band are the same frequency as crystals for 23.4 MHz up, in the 168 & 169 MHz range. For example the crystal for 146.52 is the SAME as the crystal for 169.92, only the preselector would be different.

And that is why you need the receiver preselector to be tuned (modified & tuned) for use on two meters. The coils in the preselector are pretty band specific. A preselector made for 155 MHz won’t work at 146 MHz without new low split coils or modification of the 155 MHz coils.

Also, the manuals specify that the crystal frequency (oscillator in the element) should be between 15.455 MHz and 18.055 MHz.

I sometimes see where people have stayed with the Low Side Injection that is appropriate for 150.8 MHz and up.

So, they use crystals that are below that 15.455 range to get the receiver down into two meters. If you do that, then you are much more likely to have to change components in the multiplier stages and channel element to get the receiver to work, because Motorola designed the oscillator / multiplier stages to run in the 15 to 18 MHz range.

I figure the designers knew what they were doing. As long as you are not using the AFC, sticking with a Low Side Injection crystal freq works better.

There are excellent descriptions of this on the Repeater-Builder website so I won’t duplicate it here.

 

RX formula for the Two meter band:

Oscillator times nine minus 11.7 MHz equals the carrier freq.

Example, 17.37667 times nine minus 11.7 equals 144.69 MHz.

Channel element is K1005 for 5 PPM.

RX formula for the 150.8 MHz and up commercial band:

Oscillator times nine PLUS 11.7 equals the carrier freq.

TX formula:

Oscillator times 12 equals carrier freq.

Example, 12.1075 MHz times twelve equals 145.29

Channel element is K1007 for Phase modulation exciter, and 5 PPM.

220 MHz ham band

Rx is low side injection, and the modification most of us use is crystal times 12.

The modification changes the tripler in the multiplier stages to a “quadrupler”.

The channel element output is triple the crystal freq, then in the normal High Band receivers is tripled again, then added or subtracted by the 11.7 IF to get the carrier freq.

The popular modification (Find it at RepeaterBuilder.com) changes the multiplier to “times 4” instead of three.

The transmit multiplier is also changed, normally it is “times 12” in the 220 MHz modification it is now “times 18”.

The “first doubler” in the multiplier chain is changed from double to triple, see the formula below.

220 MHz RX formula:

Oscillator times twelve plus 11.7 equals the carrier frequency.

Example, 17.606666 times 12 equals 211.27999 plus 11.7 equals 222.98 MHz.

Channel element type is K1005 and 5 PPM.

220 MHz TX formula:

Oscillator times 18 equals the carrier frequency.

Example, 12.476666 MHz  times 18 equals 224.58 mhz

Channel element type is K1007 for PM 5 PPM.

KXN1019 is FM, and 5 PPM.

The above two formulas can be compared to the next set above for the Two meter band.

If you think about it, you may notice that crystals for the Two meter band can also be used for the 220 band for testing. May not be exactly on a frequency you need, but may be close enough for testing.

440 MHz Ham band

 

440 RX formula:

Oscillator times 24 plus 11.7 equals the carrier frequency.

Example, 18.2125 MHz times 24 equals 437.1 MHz plus 11.7 MHz equals 448.8  MHz carrier frequency.

Channel element type is KXN1024 for 5 PPM.

440 TX formula

Oscillator times 36 equals carrier frequency.

Example, 12.327777 MHz times 36 equals 443.8 MHz

Channel element type is KXN1052 for FM and 2 PPM.