How to determine crystal frequency?

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How to determine crystal frequency?

Postby 601 » Sat Mar 01, 2003 8:00 am

Would anyone be able to show me how to "decode" a stamped frequency on Motorola crystals. I have one out of a mobile that i'm trying to detemine what frequency it on. All the nfo that's on the crystal is: 17097.22. On the side it says KXN6121 and R8947.

Anyone know what this means?
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Postby ExKa|iBuR » Sat Mar 01, 2003 8:18 am

Crystals are usually never made for the actual frequency you want to operate on. Instead, they work on an overtone frequency. For example, you would take the operating frequency and divide by 12, or some other value set by the manufacturer.

The 170whatever number is the actual frequency of the crystal (fundamental frequency), but the actuall frequency of the radio is different than that. I'm not sure what the formula for Motorola radios is, but I'm sure somebody else would.

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Postby Monty » Sat Mar 01, 2003 9:02 am

HI:

17097.22. On the side it says KXN6121 and R8947.


The KXN6121 is a Xtal Type is for the Motorola Maxar Series
Boith VHF & UHF

For UHF it would be:

the 17097.22 ( X ) 27 = 461.62494 Mhzwhich when tuned on the
proper freq will be'

461.625 Mhz ( Transmitt )
MS

For VHF see below:
Last edited by Monty on Sat Mar 01, 2003 10:59 am, edited 2 times in total.
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Postby LACityFD » Sat Mar 01, 2003 9:21 am

Just to be a smart ass:

I guess you would says it is:

17097.22 (x) 0.027 = 461.62494 becuase if you just did (x) 27 you would get = 461624.94 :D
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Postby wa2zdy » Sat Mar 01, 2003 10:33 am

LACityFD wrote:Just to be a smart ass:

I guess you would says it is:

17097.22 (x) 0.027 = 461.62494 becuase if you just did (x) 27 you would get = 461624.94 :D


Actually 461624.94 is correct. It is the answer in kilohertz, which is how the crystal is marked. 17097.22 KHz x 27 does in fact equal 461624.94 KHz. The crystal could have been marked 17.09722 and that would have been megahertz. This is why you have to keep the unit of measurement consistent from start to finish in any equation, or be prepared to move the decimal point appropriately. And why you have to be familar with the convention used by the manufacturer of a particular crystal.
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Postby 601 » Sat Mar 01, 2003 10:46 am

Ok, Now I'm really confused.

This is a Motorola Maxar. It's model # D33TRA30000CK. Doesn't 33 mean VHF? I picked up a set of 4 of these on ebay, one was UHF, and the rest were VHF (at least that's what the auction said)

The UHF radio (Model # D24TRA3000CK) Has 3 buttons on the front of it instead of monitor and channel selectors. It has [Lts] [Hrn] and [QC In]. It also came with a box connected to a cord that looks simmilar to a rib box (minus the connections).


And one more thing!..... Is there such a thing as a "digital" PL tone encoder for this radio. No, not a DPL board, but a board that generated a PL tone without a reed? I was going to change the PL code in the radio but was stumped when I found this in it.

Are there any Maxar fans out there that know about this stuff?


Help! :lol:
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Postby Monty » Sat Mar 01, 2003 10:58 am

Hi:

Sorry you got confuzzed.


Manytimes the [ Formula ] for the multiplier stages, are similar
for VHF and UHF are the same and rest assured, the Crystal you have is used in BOTH types of radios, and since you did not indicate it was from a VHF Radio:

For UHF one uses X27; for VHF one uses X9

The Freq for VHF is:

153.875 ( 17097.22 Khz ( X ) 9 = 153.87498 Mhz ( and gets tuned
to 153.875 Mhz )

Indeed the Crystal Type for the Maxar is KXN6121AA for Receive
and the Crystal Type for Receive is KNX6122AA
==========================================

Your radio sounds like one of the old type VHF Phone style
radios, and Yes they did make a Muli-PL Tone Encoder/Decoder
that used a Chip which was programmed for 4 PL Tones.

Not a worth while project to persue.

You would be better off using one of the Com Spec Boards and
then you can select any of the 32 PL tones and they work very
well as I have installed a number of them in the UHF Models
so that GMRS users can easily select many repeaters on the
same freq.

Monty
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Postby RKG » Sat Mar 01, 2003 3:04 pm

Wouldn't a receive crystal be offset by plus or minus (depending on injection side) the 1st IF freq?
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Crystals etc...

Postby Tom in D.C. » Sat Mar 01, 2003 7:27 pm

RKG:

Yes, the receive formula includes using the IF frequency, so if you had a 45 mHz crystal and a 10.7 mHz IF you would multiply the 45 by 3 (usually) and then ADD the 10.7 to the answer, in which case it would be a 145.700 receive channel. Going the other direction you would subtract the 10.7 and then divide by 3.

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Postby 601 » Sat Mar 01, 2003 7:30 pm

Why do they make it so complicated, instead of just stamping the real frequency on it, instead of having to do all this? What is the reasoning behind it?
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Postby Monty » Sat Mar 01, 2003 10:30 pm

HI:

The main reason Motorolal does not " Stamp " the operating
Freq is simple.

The Same Crystal can be used in both VHF & UHF as explained
above....( Low band too )

Also, the formulas are pretty universal.....

Xtals in the VHF Operating range one divides by 9, xtals in the UHF
Operating range you divide by 27.

There are some variations, but most use the same formulas.

The Receiver Crystals are somewhat the same, BUT there
is a IF Freq to consider, but even the IF Freq is constant
in " Most " cases, 10.7 & 11.245 Mhz

In the Maxar, like the one you have you take the 47~48 Mhz Rx
Crystal, Multiply ( X 3 ) and Add 10.7 Mhz, and that will give
you your Operating Freq,

In the Case of UHF Maxars, one uses ( X9 ) and use the same
formula..

Once you have been around Crystal controlled radios for awhile,
you get use to it....

Even seasoned techs sometimes have to " review " the Model
Numbers if they do not use them all the time.

Monty
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Postby 601 » Sun Mar 02, 2003 5:34 am

Ok, thanks Monty, now I finally understand it! :D

I was always under the impression that crystals were cut to the exact frequency. I thought that if you took a VHF crystal and put it in a UHF radio that it wouldn't work..... You learn something new every day!

So has anyone ever heard of the Maxar (UHF one) that I had explained above?
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Postby DAL-COM » Sun Mar 02, 2003 5:48 pm

If it had no markings at all, you could use a spectrum analyzer/tracking generator to display the resonance curve. See "Introduction to RF Design" by Wes Hayward.
Many modern service monitors are capable of this.
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Postby 601 » Mon Mar 03, 2003 6:08 pm

Well, I just took a closer look at this box, and this is the info on it:

A small sticker that says HLN4720A

Under it is a larger decal that says the following:

GROUP NO: ____01_____
FLEET NO: _____01_____
UNIT NO. ______16______

(The numbers that are underlined were written in with marker)
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Postby hfitzgerald » Mon Mar 03, 2003 8:10 pm

Hmmm... That sounds like a UHF trunking radio. Time to do some research, -unless someone else already knows the front panel that he described in his earlier post.
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Postby 601 » Mon Mar 03, 2003 8:28 pm

Trunking on an old maxar? Never seen one of these before..... Hmmm... I tried just taking the cover off and found a large silver plate with a lot of what appears to be tuning screws on it... I'll have to do a little more digging into it to see what I can find :D
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