HT220 Crystals

[mfn002]

I am working on resurrecting an old HT220 from the dead, and I recently acquired a large box of crystals for it. I was told they are UHF, but there is no frequency stamped on them, instead there is some sort of number--such as 8624.074 or 49888.88. Is there any way to tell the frequency from this number? I also can't tell which are TX and which are RX.

 

[davidgcet]

i believe for RX you multipy by 6 and add the IF, but i don't remember what tx was. it should have a different KXN( or whatever prefix they used on those) number though.

 

[W2NJS]

The 8600 is a transmit crystal; multiply it by 18 to get the transmit frequency.
The 49888 is a receive crystal; multiply it by 3 and then add the IF frequency to get the receive frequency.
The IF might be 10.7 mHz but it might be somewhat different; it's been so long since I worked on a 220 that I have forgotten what the IF frequency is.

 

[davidgcet]

dang, i was way off on the multiplication! i know some of the older radios were 6 but don't remember which ones.

 

[mfn002]

Thanks for the help. Also, some of the crystals were packaged with some sort of thing that looked like a ceramic-disc capacitor or something. These were either solid red or orange with stripes on the top. What do these do, and are they important? I'll try to get a picture of one later (I'm at school right now).

I did the math, and I'm still confused. When I did the equation for the RX crystal I mentioned, I got 149674.7. Is this supposed to be something like 149.675 MHz?

 

[davidgcet]

HT220 Page has some good links with info. i think for UHF it is multiply by 6, VHF was 3. then add the IF to either. you also must know which IF crystal your radio has. and remember to move your decimal after multiplying, the xtal will come out to 4xxxxx.xx and the IF is 1x.x so you convert the crystal to 4xx.xxx and then add 1x.x

clear as mud yet?

 

[fineshot1]

If your gonna order crystals for it give bomar a try - i use them whenever i need them
and have never had a problem. You could also give ICM a call.

About Bomar Crystal Company | Clock Oscillators, TCXO, VCXO, OCXO, Crystals

Crystals, oscillators, filters, precision crystals, TCXOs and more from International Crystal

 

[jackj]

It has been over 30 years since I worked on one of those but I think they are dual conversion with a 1st IF of around 40 Mhz. The crystals with what looks like a ceramic capacitor are temperature compensated. The capacitor's temperature curve offsets or compensates for the crystal's curve. The numbers on the crystal are, I think, the fundamental frequency of the crystal in Khz.

The model number of the HT will tell you what frequency band it worked in. H34xxx would be Hi Band. I think H64xxx would be UHF. Motorola encoded their model numbers to show what options were factory installed.

 

[mfn002]

The numbers on the crystal are, I think, the fundamental frequency of the crystal in Khz.

Then how do you tell what frequency the crystals are for? I tried to look for some sort of part number on the crystals, but couldn't find any (Except for KXN, but nothing following it).

I found the radio model number on the eBay listing: H34FFN3170E-SP5. It's NYPD surplus.

 

[davidgcet]

what he means(and said) is that they are in kilohertz and not yet multiplied up to the operating frequency of the radio. once multiplied it is still in khz, so you have to move the decimal to make it mhz, then add the IF. once you figure out the first one, it is really simple. the problem is no one has fooled with those things in years so memory gets fuzzy abotu the details without one in front of us(at least in my case).

sorry but i have to ask, do you even have the proper equiment to tune a crystal radio? it is not like just plugging a rock in a scanner, you have to peak various pots and dip others. it requires a service monitor and a few other test tools. read the link i gave above and they give the procedure.

if you are doing this to learn or just for the fun of it, that is good. but remember that these units are useless for anything other than GMRS(iffy on that) or HAM in a couple years. so if the plan is to use it, it ain't worth spending money.

 

[jackj]

Ht-220

Then how do you tell what frequency the crystals are for? I tried to look for some sort of part number on the crystals, but couldn't find any (Except for KXN, but nothing following it).

I found the radio model number on the eBay listing: H34FFN3170E-SP5. It's NYPD surplus.

I was wrong about the model numbers. The first number is the power of the transmitter, the second is the frequency band, yours is a UHF unit. In your case the unit is a handheld or portable radio (the H). Power out is, I think, 5 watts. I don't remember what the three letters FFN stand for but it has PL and it's a special build.

In order to figure out the carrier frequency of the receive crystal you will need to know the 1st IF frequency. Then you will need to know what multiplication is applied to the fundamental crystal frequency. Figuring out the transmit frequency is a little easier. You need to know the multiplication and then multiply the crystal's fundamental frequency times the multiplication.

As I said, the number stamped on the crystal is its fundamental frequency in Khz. So if you have a crystal that is stamped 14253.125 and the radios operating frequency is 456.1 Mhz, then the radio multiplies the crystal frequency by 32. 14.253125 Mhz X 32 = 456.1 Mhz.

As others have said, this radio will be unusable in commercial land mobile service shortly. So, unless you are going to do a band change on it for ham use, don't waste your time and money. Parts are not available for it from Motorola anymore. You might be able to find crystals to put in in the ham band but I wouldn't know where to tell you to look for a band change kit.

 

[mfn002]

I was thinking of using it as a monitor (receive-only) for some UHF channels around here. I have well over 100 crystals now, so I have to dig through them to find what I'm looking for. Also, there were a bunch marked either KXN6206 or KXN6207, and had various color dots stuck to them.

 

[upndn]

Ht 220

MY dad is retired from nypd,i remember the ht 220 he used was VHF on 151.xxx.When they went to UHF they used the MX series.Hope this helps

 

[blaze]

MY dad is retired from nypd,i remember the ht 220 he used was VHF on 151.xxx.When they went to UHF they used the MX series.Hope this helps

NYPD used HT-220s when the division (precinct) dispatch radios went to UHF in the 70's; the switch to MXs was much later. The citywide channels (SOD, Traffic, etc) switched later, and may have gone directly to MXs, but I'm not sure.

In any case, most (all?) of the NYPD surplus HT-220s on ebay are UHF T-band (~476MHz). I bought a couple for old time's sake, though I don't have any hope of restoring them.