Aligning Keychain Remotes
 

Hello,

I own a 52-unit apartment complex. About a year and a half ago, I
installed power gates. The power gates use a Multicode 300MHz
receiver, and I issue keychain remotes to all the tenants. I am having
a problem with the remotes dying. At thirteen bucks a remote, it
adds up fast.

These are very simple units, and I suspect they're mostly just
going out of alignment. Without going to the trouble of tracing the
circuit, they have:

* A one-transistor RF oscillator
* A ten-place DIP switch
* A single DIP IC - presumably a shift register to serialize the
DIP switches
* A variable capacitor - one would suppose, to tweek the freq.
* A potentiometer - to adjust the low frequency pulse oscillator?

When you press the switch, the remote emits a single squirt of
pulsed 300MHz RF.

The problem is: how to measure it? You can't just stick a counter
on it, because it's pulsed. I'm thinking to use an RF oscillator and
a mixer going to an audio amp - when the oscillator is close enough to
the remote, I'll hear it heterodyne. I don't think it needs to be
super accurate. Or maybe a scope with an XY input for lissajous
figures?

- Jerry Kaidor ( )

For 600 mhz approx. units, I used a Yaesu FRG-4900
Communications receiver! Rono.

Unfortunately, I don't have a receiver that covers 300MHz.
Essentially, that's what my oscillator+mixer+amp setup would be -
an ad-hoc receiver.

I just had a couple new ideas: Wonder where my old grid dip
meter got off to? Think it's in the garage. Would it be accurate
enough? Probably not....

Might be the excuse I've been looking for to buy an old HP
spectrum analyzer :).

I just traced the thing's circuit. I think I've identified a node
that
can be grounded to the battery to make the thing emit continuous
wave RF. Then just belly it up to the frequency counter....

wrote in message
oups.com...

The problem is: how to measure it? You can't just stick a counter
on it, because it's pulsed. I'm thinking to use an RF oscillator and
a mixer going to an audio amp - when the oscillator is close enough to
the remote, I'll hear it heterodyne. I don't think it needs to be
super accurate. Or maybe a scope with an XY input for lissajous
figures?

Use a receiver connected to a scope? How much is an extra gate receiver?
I've seen items like this offered in "Ciarcia's Circuit Cellar".

N

The receivers cost $45 plus shipping. Not excessive. Might be a way
to go. A spare receiver
would be a sure go/nogo test for the alignment too.

- Jerry Kaidor

wrote in message
ups.com...
The receivers cost $45 plus shipping. Not excessive. Might be a way
to go. A spare receiver
would be a sure go/nogo test for the alignment too.

And a useful backup!

N