Need Help Find 121.775Mhz Crystal

[nes_ds]

For all you electronic buffs out there, I have a 121.5MHz transmitter, and for those of you who don't know 121.5MHz is an emergency frequency, used in ELT's. ELT, is an Emergency Locating Transmitter, they are used in planes, boats, and sometimes hiker's use them, when ever a plane takes a few G's, it turns on, as with a boat, it sinks and the ELT floats to the surface and activates, of course they can all be activated manually.

Being in the Civil Air Patrol (US Air Force Auxiliary) I take part in the search for these devices, most are false alarms, battery going bad, or some bloke activates it accidentally. When ever we find ELTs in a boat, we usually confiscate them, so we currently have a hand full of them at our disposal.

I have taken apart an ELT and removed the 121.5MHz crystal, I'm looking to put in a 121.775MHz crystal, but I have only been able to find one vendor who supplies them, I Email him, but no word back yet.

One more thing to add is that the ELT I'm working with transmits on both 121.5, and 406.0, but there is only one crystal, so I'm assuming the 121.5 is doubled (terminology?) to 406.0, and if my calculations are correct the 121.77 replacement crystal would be doubled to 406.92MHz, do you think that it will bleed over to 406.0? If it does it will be useless, because 406.0MHz is also an emergency only frequency.

I have attached a picture of the crystal, does anyone know where I can buy another?

 

[SenKat]

Have you checked at soem hobby stores ? I recall in the way backs that they used to sell crystals for different tranmitters - radio shack USED to - but it is a crap shoot any more What are you going to be using this crystal for ? I read your post, but am a little bit confused Are you jsut simply attempting to create a better transmitter ? Also - you can check some old electronic surplus shops - I know there is an AWESOME one in Orlando ! I cannot recall the name of it, but it is right off of I-4, and the sign looks like a rocket

G !

 

[nes_ds]

I should have mentioned it, but 121.775MHz is a practice ELT frequency.

I'm trying to covert the ELT to the practice frequency so I can use it for training.

 

[SenKat]

GOTCHA ! Okay, now I understand ! (DUH !!!) LOL

You may want to check Usenet - there has got to be some radio newsgroups that may be able to point you in the right direction perhaps ? I really cannot be of too much help with this - my ideas are exhausted OOOOOOO ! One more ! Google the frequency - see what Google has to say ? There may be some links that are useful !

G !

 

[Hemlock_Mike]

That's one HUGE picture !!!

Transmitters in this VHF spectrum typically employ an oscillator followed by a trippler and a doubler or some similar arrangement. In the process, a "harmonic" is generated at UHF frequencies. Doubled, trippled ??

To order a Xtal, you will need to know what the oscillator/ driver string is made to do. Sometimes the xtal is also stamped with the fundamental frequency. The capacitive loading, series or parallel will be needed to order a xtal.
Perhaps your friends in CAP already have this info for your ELT unit. If you change the xtal to get a 250 Khz increase, the 406 should also increase because it is based on the same xtal.

Mike

 

[nes_ds]

Perhaps your friends in CAP already have this info for your ELT unit.

I checked today when I first opened the unit up, they knew nothing about the electronics, except that I would need a new crystal. :-?

@ SenKat, I tried googling earlier today, and I found almost nothing.

I went to the manufacture site of most of our equipment is made by, and I found a crystal, but I have to oder at least three units and it can take up to three months to arrive So I would still like to find another place to buy them.