Batboard

Ok I have this wireless weather data receiver that uses a 900mhz flex pager board to receive data, and displays the weather on a large LCD screen. My guess is that the board is the same radio board as used in some current alpha pager, but not having much experience with newer pagers, I don't recognize it.

My question is, can I wire on an external antenna for increased range? At work it receives fine (there's a signal strength meter and it's 3 out of 3 bars) but at home, just 25 mi away, there's no signal at all.

At home, I punched the receive frequency into my scanner and was able to hear some Flex and POCSAG traffic.
Attaching a small Yagi got almost full quieting on the scanner when pointed in the direction of the city I work in! So I know I could get this box to work correctly if only I could feed it with my Yagi or some other external antenna.

The board looks like it has two metal strips. Could I just wire some coax to them (is one a ground plane??) and attach the Yagi to it? Is the receiver looking for a 50 ohm impedance?

The board is made by Unication. Some numbers off it are:
NF10X09A04

21.400
NP100FX 9RF
Jan 21, 2K
Ver 0.03 Unication

Maybe these numbers will jog someone's memory who can ID this board. If not I cna take digital pictures
Thanks for any help you can provide.

If you take some good quality pics of both sides of the board, it should be pretty easy to figure out where you can connect an antenna.

Ok will do!

There's a very obvious strip of metal coming up off the board which is the internal antenna. There's another smaller one on the other side.
Can I just solder the center of a small piece of co-ax to this, solder the shield from some coax to ground, and attach the antenna this way?

I'll take a picture asap

Can I just solder the center of a small piece of co-ax to this, solder the shield from some coax to ground, and attach the antenna this way?

While this isn't the "technically correct" way to do it, there's a very good chance it will be "good enough" for what you need. If you think about it, what you're suggesting is kind of like running coax to a yagi antenna, and then soldering another piece of coax to the ends of the elements and running that to yet another yagi antenna. As far as antenna and transmission line theory goes it's all messed up, but practically, it might be good enough. I wouldn't ever try doing that with something that transmits, though!

The "correct" way to do it would be to remove the existing antenna and attach the coax to the point there the antenna used to connect. Even then, there might be components on the board used for antenna matching (capacitors, etc.) that ideally you'd want to get rid of. Again, though, it'll probably be good enough to work for you.

Andy

OK here's pictures of the front and back:





There's some things I recognize; the 'strip' antenna, a 455khz filter, 21.400 IF xtal, test points.. on the back are 3 spots labelled TX, RX, GND- is this the programming port or output data?

The board connects via the 2 row X 7 pos mini header on the front.

Note the antenna I referred to; it's two strips, one over the other. Is one a pseudo ground plane?

Does anyone recongize this board as being from an existing pager?

Thanks!

Anyone ever try this?

What I would do is this: Connect a small loop of wire to end of the coaxial cable that goes to your yagi antenna. One end to center conductor, the other to the shield ground. Make it roughly the same size as the loop in the pager. Then you can put this loop outside of the pager case (pager fully assembled and working) and couple signal into the pager that way. Remember where inside the pager case its loop antenna is, and try to put the external loop as close to it as possible.

This is essentially a passive antenna system.

You might get even better results by tuning the external "antenna loop", i.e. putting a small variable capacitor in series with the loop. And you could build a small wooden fixture with the coupling loop permanently attached, so that you could just slip the pager in and out

This would keep the pager a pager and also allow you to listen in at home.

Or, if you REALLY want to hook coax to the actual circuit board, find the ground end of the loop antenna - where it connects to the ground foil on the RF board. Solder the shield of your (small diameter) coax to the point where the loop connects to the ground foil. Then solder the center conductor about 1/4 inch up from this point, on the loop itself. It may not be a true 50 ohm point but it should work pretty well.


Joe

I have a similar situation and was wondering if you were ever able to get an external antenna connected and working. If so could you send along pictures of the working setup? I'd love to try it myself. Thanks.

|Andrew|

Embarrassingly I ended up just finding a very odd location in the house that picked up a very weak signal, but just enough to get it to work. I still may eventually add an antenna (I actually have a Yagi ready to go) but for now it's working so I don't want to hack it up.