Analogue and P25 digital transmission, a comparison

[Rob_Brookes]

I'm still having difficulties with the website keeping the file available unfortunately so it's now in my Dropbox. The link is
http://dl.dropbox.com/u/45733427/LDSAMR ... arison.mp3
Apologies for the broken link previously.

As some of you will know, I've recently been loaned a couple of P25 enabled portables by Team Simoco. These are the new model of SRP9180 and as supplied to me were capable of both standard analogue and digital P25 modes. I was testing the transmission modes primarily and not the radios themselves however with the exception of a couple of firmware glitches, they appear to be fine and are now fully waterproof which is appreciated by several Lakes MRTs!

Rather than go into great length about the tests we carried out, I thought a recording of one of the final tests would be more informative and so it's attached to this posting.

A very brief (for me) summary of the results was that initially I didn't like the rather 'electronic' sound of the P25 audio but once you've been using it for a while, the fact that you actually can still hear any audio when compared to an analogue signal over the same range and conditions soon has your ear trained to ignore the slightly strange element of the sound. In fact there's little strain involved in listening to digital audio where initially I thought there would be. The first time I used these radios under deliberately harsh conditions was something of an epiphany and I'm now of the opinion that digital at some time in the future, is the way for us to go.

The test:-

Sue, my better half was coincidentally going for a walk up Farleton Knott, a fairly small escarpment that's 7.4 miles (12km) from our house line of sight. She had with her the SRP9180 programmed for both P25 and analogue on the same frequency. This was a private VHF channel and not one of the UKSAR ones I hasten to add. It was however, very close in frequency to the UKSAR channels. The SRP was fitted with a standard helical aerial and was hand-held throughout.

The final location for the test, north of the summit and slightly down out of the wind, was deliberately chosen as being poor as far as analogue was concerned. When I began the tests and the recording, I hadn't tried P25 mode and so knew only that analogue was beginning to struggle. This location was maintained throughout the test. There was a very high wind and it was snowing heavily. Those of you who know Sue will hear her opinion of all this in the tone of her voice.

My own radio was identical to Sues and was inside the house at all times. In all respects the radios were 'standard issue'.

The recording was carried out using an Olympus WS-210S Digital Voice Recorder which was held in one hand with the radio being used in the other. I can multi-task!

Because I had the recorder running all the time, I've edited out the silences and fumbling noises where we changed modes. In all other respects the recording has not been edited in any way and no levels between modes were adjusted. The original recording was in .wma format and here I've converted it to .mp3 to allow me to remove the silences. Apart from that this is exactly what I heard.