Equipment Details
PMR446 Handsets
I currently have three types of PMR446 handset, pictured above from left to right they are:
Oregon Scientific TP326PMR
Telcom TE-200
Audiovox PMRS838
The Oregon Scientific TP326PMR sets were specifically purchased to create the gateway after reading reviews that mentioned there sensitivity and good preformance, also there seems to be quite a few modifications that can be made to them (however at present they are completely unmodified)
Gateway
Loft Location
The Gateway uses a TP326PMR handset
which is mounted in the loft on a wooden platform. In an attempt to try
to increase preformance the platform has four metal poles set into it
to form a ground plane. I haven't used any weird scientific formulae to
work out angles or lengths etc, I just found four metal poles (50cm long)
in my garage and drilled some holes into the wooden block sloping downward
at about 30degrees!
Two cables run from the handset down and out the loft space through the ceiling into my computer room. The first is a screen two-core audio cable, the other is twisted pair to supply power to the handset. (the other cables you can see in the picture below are for my DAB aerial and my scanner antenna)
Computer and eQSO Interface
The handset has a 2.5mm 'stereo' jack
on the top which is designed for using a headset, microphone and a PPT
switch. This is the how the handset is connected to the gateway PC using
the audio cable. The handset is designed to be powered from 4 AAA batteries,
obviously this is impractical when sited up in a loft, so it is powered
from a 6V regulated power supply and the connecting wires are soldered
directly to the battery terminals. (Okay so you could class this as a
modification but I don't!).
The next important part of the Gateway is the PC, currently I am using a PentiumII-450MHz machine, which is a bit of an overkill but it was available and has an excellent Aureal Vortex I soundcard in it.
I have several PCs, all of which are networked using 100Base-T ethernet to a Belkin Router and Teradyne Cable Modem. This NTL 600K broadband connection allows me to set up a 24 hour, 7 days a week gateway.
To connect the handset to the PC, I constructed an isolating eQSO/Echolink interface as detailed here the interface in mounted in a little box which also contains the regulator for the 6V supply. There are three connectors to the PC, the audio in/out (seperate) and the Com-Port Keying connection to the serial port. and two connectors to the Walkie Talkie, the audio in/out (combined) and the power.
The knob on the interface controls the audio level from the PC going to the handset, the switch switches the PTT control off/on (for times I might want to switch to VOX operation).
Other Radio Equipment
Scanner
This PMR446 Gateway has rekindled my interest in radio, when I was younger I wanted to become a Radio HAM and used to spend a lot of time as a SWL (Short Wave Listener) using various radios and long-wire antenna stung down the garden. Then after going to university and getting a degree in electronics I got a proper job and in 1989 was able to buy myself a scanner a Realistic PRO2022, and spent many an evening listening to HAM radio, the police and the early analogue cellular telephones!
I fully intended to buy a proper full band receiver and even get a HAM licence, but for one reason or another I sort of never got around to it and lost the interest!
Well I have dug out the set, and put an old multiband mag-mount antenna in the loft, on a makeshift groundplane and have started listening again, and will soon start to try and decode all that digital chatter that now seems to fill the airwaves!
More details Coming Soon!
