Batboard

I want to modify a 30-36 (non-Extender) Micor to receive 29.600 mHz.
Has anyone on the board done this and other than recrystalling the channel
element, are there any component changes required?

It should tune right down with very little trouble.

Watch out for the crystal formula. The 25-30 MHz radio injects on the other side, so you need a 29 MHz crystal cut using the 30-36 MHz formula. If you leave it up to the crystal house it'll probably be wrong. I didn't have to modify any of the three recievers I did, but one of the exciters wouldn't quite make it without a couple of capacitor changes.

Jeff

W6JK wrote:Watch out for the crystal formula. The 25-30 MHz radio injects on the other side,
so you need a 29 MHz crystal cut using the 30-36 MHz formula. If you leave it up to the crystal
house it'll probably be wrong. I didn't have to modify any of the three recievers I did, but one of
the exciters wouldn't quite make it without a couple of capacitor changes.
Jeff

Thanks for the reminder, Jeff. I forgot that there were Micors manufactured for the 25-30 range
and the crystal formula would be different. The current element is on 35.160 mHz. with a crystal
frequency of 13473.333 kHz.

What you should really do with this receiver is go through the manual and replace the caps they call out as different. I have done several conversions and they always have turned out fine.

If you want to do it the cheap and cheesy way, leave the front end alone but change all the multiplier chain caps. It's pretty easy and will ensure your injection will be there for the mixer to work with.

Just go through the manual and change every value that has a m to a L.

If I remember correctly, some parts may not change...but you can figure out this part.

George

Thanks George. Caps don't bother me, but coils sure do !!
Looks like 16 caps if I change all those pertaining to RF and IF components.
C121, 123 and 129 are the same value.

Since you've done this before, any surprises waiting for me when I tackle the exciter?

I don't understand why you would want to do this. A 30-36 receiver has enough manufacturing tolerance to tune to 29.6 without changing the caps. At least every one I did this on did. If you want to tune it to 25 MHz, that's a different story...

WB6NVH wrote:I don't understand why you would want to do this. A 30-36 receiver has enough manufacturing
tolerance to tune to 29.6 without changing the caps. At least every one I did this on did. If you want to tune it to
25 MHz, that's a different story...

Once I verify that everything meets specs on the current frequency, I'll send the element to ICM
for recrystalling. When it comes back, I'll see where it lands after alignment and if any caps need
changing. I would think that dropping 400 kHz. shouldn't be too big of a deal, but I've found that
Motorola Micors aren't as repeater-owner friendly as the Mastr II when converting to two meters
or 70 cm. Past experience and having never modified a 30-36 Micor before, I thought it might be
a good idea to ask. Thanks !!

If I was going to change the caps in the receiver, I'd use intermediate values, looking for a 2 MHz shift rather than the full 5 mHz. A 28-33 radio seems more useful than a 25-30, and I wonder why one'd want to keep 29.6 near the end of his range, just swapping ends.

On the exciters, I found that a lot of the slugs ended up at the end of the form, perhaps even in danger of falling out in mobile serivce, and there was one that wouldn't quite make it in a couple of stages. I do recommend changing those caps, and again, I wouldn't go for the full 5 MHz.

Jeff