Posts Tagged ‘2m FM’

Shack photo

This was me on the 2m FM net in East Cambridgeshire last night. There were only 3 of us on last night. These days I tend to use WSPR quite a bit as my voice is still pretty poor. We meet on 144.575MHz FM at 8pm local time most Mondays. Note, this is in the all-mode section. Newcomers are always welcome to join us. QSOs are never more than 1 hour and frequently much less.

Digital Voice (DV) – the new FM?

Once upon a time FM swept away AM, but DV is taking its time despite some clear advantages.

I’ve had yet another stunning 5W mobile QSO on 2m this morning on my way to work. Several miles of clear, unbroken chat, without mobile flutter. DV mode delivers good quality voice against a noiseless background. It is sometimes claimed that coverage is roughly extended by 20% due to advantages of this mode, even. I doubt this is entirely true, but an excellent quality of communication is doggedly maintained before ‘falling off’ very quickly. It is quite robust and packed with extras. Ideal for V/UHF and it’s been around for several years.

Even the 2m band-plan in the UK lists all the simplex channels as dual FM/DV. I must admit that I and my friends keep traffic to the UK DV calling frequency (144.6125 MHz) to ensure anyone equipped with DV will hear us and join. If the current FM population heard our carriers on normal working channels, they would be quick to complain about the noise the noise as QRM.

This is what DV sounds like on your FM radio:


DV mode is famous for being the common mode that binds the larger DSTAR system (Digital Smart Technology for Amateur Radio), but excels as a simplex mode too. No analogue mode will embed your callsign for display, report your GPS position, over a low speed data link – all during a normal voice QSO, rounded off with an inoffensive little beep at the end of the over. (Because there is absolutely no background noise, it’s difficult to detect when someone has released their PTT). This is why DV is such a superb candidate to network via DSTAR. This is where radio marries the internet and we are its children.

The new Icom IC-7100 even has people quirkily chatting away on 4m with DV mode, which I gather works very well.

So what is DV mode made from? Well, your voice is encoded digitally using a vocoder optimised for voice communications in the same way your mobile phone does. The device that does this is called the AMBE chip (Advance MultiBand Excitation). Some people moan that this is unfair being a proprietary device, not being open source technology. However an AMBE chip can be freely bought for just a few dollars and uses proven, reliable technology. Inmarsat have been using it for years.

The digitised voice at 3600bps combines with an additional 1200bps (which you can do anything you want with! Think file transfer, photos, messaging etc.) before being modulated. The 3600bps voice data also includes 1200bps FEC (Forward Error Correction), which sends a little extra data in case any gets lost over the air. When bits are lost, the receiver uses this extra data the plug in the gaps. The modulation scheme is GMSK (Gaussian Mode Shift Keying), which is basically a form of phase modulation. You’ll also appreciate that all new modes often save bandwidth as well as improving quality and a DV carrier will happily fit into 12.5kHz channelised plans.



So, what are we waiting for? The manufacturers! The market is caught up in adoption stalemate, with Icom having settled for DV whilst others shun compatibility. But there are also homebrew DV options out there, with modulator/codec boards that will plug into your FM radio (via the packet port or tap into the discriminator) turning your analogue radio into a dual-mode digital delight.
My home DSTAR hotspot. Comprising 2m PMR radio (underneath), GMSK modem (top) and Raspberry Pi computer (bottom).
There are other digital modes out there too, all with different strengths and weaknesses – and they are interesting. But for the sake of everyday commonality and general take-up, I think DV has it.

So is it time to catch up with modern telecommunications techniques and move away from analogue FM? Maybe there’s something in the more ‘tactile’ feel of FM: The waxing and waning, the background hiss, the heterodyne-ing. You seem to know exactly what’s happening and what’s about to happen. So many modes – enjoy the hobby!

Mic Clickers: Easy 3-Point Guide.


And I’m not talking about the clicking of computer mice here. I’m talking about the highly vexatious and irritating habit of jamming people, mainly on 2m FM by others. Sometimes this escalates to music-playing and verbal abuse. They are here and here to stay. Thankfully there aren’t many of them, but we’ve nearly all heard one from time to time. What to do?

Don’t worry! I’ve compiled a quick, easy and memorable 3-point guide on what to do if you encounter any wireless abuse. Feel free to print this out and place it above your rig:

1. DO NOT acknowledge any interference
2. DO NOT acknowledge any interference
3. DO NOT acknowledge any interference

Clear enough? Self-evident? One would blooming think so. However, I’ve regularly heard some less-than-fully-brain-QRV amateurs :

1. Acknowledge the interference, repeatedly
2. Provide the abuser with a useful and accurate signal report
3. Articulate ‘entertaining’ anger and frustration to encourage further abuse

Once you can grasp the simple, blinding reality that these abusers only do this to elicit a response – provide them with that response and they will continue, satisfied and emboldened. Deny them that response and they will, eventually, cease and desist. I promise you.

In my beloved country of Wales, we have a legend that the entire army of Owain Glyndŵr, rebel leader and last (Welsh) Prince of Wales (1400 – 1415 AD) lies sleeping in a hidden cave in the mountains, waiting for the call to defend the country once more. I have heard amateurs say on-air ‘that a group of detecting stations’ was out-and-about and would quickly track down the offender with their accurate yagis and Jedi-like triangulation skills. Oh. Would this mythical radio foxhunting elite be the band of 2m septuagenarians who only exit their shacks to eat, make tea and perform vital bodily functions, would it?

Owain Glyndŵr,
detection genius.
It’s equally remarkable and disturbing how some people even enter into one-sided psychological games with their abusers, labouring under the misconception that they are cleverer than the offenders who must be naturally stupid. They are not. Threats of ‘I know who you are’ (when you don’t), reports to government agencies (who don’t care or are too busy), Owain Glyndŵr’s sleeping detection-army – I’ve heard it all. Don’t rely on the fact that you’ve passed a foundation exam that a five year-old girl passed last month will guarantee you intellectual superiority in this case. The same goes for intermediate and advanced licence holders for that matter.

Break any of my 3-point guide rules and you’ve lost before you’ve begun.

In my next blog: How to deal with pesky competition stations…….

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