Heres a tough one POCSAG 512 Simulcast help

[smittyj77]

Im new here everyone.

I am decoding 154.430 mhz in Ontario Canada , its a county wide fire paging system POcSAG 512. We are paged from a central location Fire Dispatch and we are using Swissphone DE925 pagers.

On the inside of my pager it says  Freq 154.430 MHz Space 20/25kHz PLL 154.430 MHz +/- 0.5 MHz

To decode the POCSAG I am using a radioshack pro 2055 with a discriminator tap and a 2 level data slicer from rene.  It works perfect on 149.770 and 931.5875, which are commercial telephone paging companies one being POCSAG and the other uses FLEX I can sit and decode these all day long.

My problem is i cannot decode 154.430 PDW picks it up and i can here it coming through the speaker in my scanner. I think I have it narrowed down to it being a simulcast system and when the page starts it gets walked over by another page from the next simulcast tower in line. I have tried a couple different antennas, I've tried the stock antenna retracted all the way and it still seems to be to strong, i tried no antenna but then its to weak, i tried a paperclip as a antenna and still nothing.

I have attached a link to the system and the tower locations - https://mapsengine.google.com/map/edit?mid=z3dT6q4v4pYA.klPqU3VH_9EY I am located in Athens which is closest to the Lyndhurst tower.

I have other people in the county decoding succesfully but one is located by the Gananoque Tower and the other is located between the Toledo Tower and Millars corners tower.

Does anyone have any advice for me , im open to options.

[Cagier]

Hi there Smitty,

I'm a Radio Ham and I have a couple of suggestions for you.

Firstly, although other people are successfulyl decoding thsi frequency in your area there may be something else in your set-up that you are not aware of.  A bit of frequency deviation, a harmonic in your data slicer, whatever.  It is unlikly but you need to be sure you are fixing the right problem.  If it is possible, I would recommend moving the kit to somewhere that should work and then proving that everything else is OK and it is purely down to your location.

After that, if you are sure that your theory is correct then you want to make one station much stronger than the other at your location.  The paperclip idea sounds good but you didn't say if you were receiving a signal or not.  Getting an antenna set up where it is just strong enough to pull in one signal and the other one is weaker is one approach.

I'm not sure what way the simulcast works there.  You mentioned another page coming in from another tower.  If both stations are transmitting the same signal at exactly the same time then you could think of it like two stones dropping in a pond and waves spreading out from both of them.  Where the high waves meet low waves they cancel each other out and in other places they just interfere with each other.  At these frequencies the wave lenght is about 2 meters so moving the set around a few inches at a time might find you somewhere that works better (as you mention you are using the built-in antenna).

If that doesn't work then you need a directional antenna.  Ideally this will be some sort of yagi beam and you may have some external antenna already.  However the easiest way to do this is to move the receiver so that the built-in antenna is horizontal.  In Athens, if you point the antenna so that it is parallel to the Lyndhurst tower (and roughly pointing towards the Toledo Tower) then it wil have a much bigger surface area of the antenna for the Lyndhurst Tower to hit whilst the Toledo one will only see the tip of the antenna.

That might work but unfortunately you are surrounded so this mehod will also give a good target for Brookville and Chemical Road.  However, moving it around so that you reduce the signal from thsoe two may still give you enough of the Lyndhurst one to work.  I hope that all makes sense but basically put it on its side and start turning until it works!

If that basic method deoesn't work then a proper directional antenna which will give more gain at the front than the back might do the trick.  You can buy them reasonably cheaply but it can be a fun project and worth a google!

I'd love to hear how you get on!  Good luck...

Cheers,

Keith