DMR vs FM on 70cm simplex

There's been many cynics pick fault with DMR and various digital modes; citing things such as "Murmurmur That's not real radio, that's cheating putting it through internet voice links murmurmurmurmur!" and so on and so forth.

Yeah, that's all very well and good. Personally, I see it as another dimension for amateur radio and a different mode to try that should be exploited - as highlighted in my 'DMR - A love/hate relationship' blog posted earlier.

A friend of mine M6AIF decided to scurry off to my local hill with some VHF and UHF gear, and I had a brainwave:

Why not do a FM vs DMR simplex test?

I asked him to give me a shout on DH2 438.600mhz while I had the MD-380 running in the house, and he came through with a perfectly legible signal. Which is remarkable seeing as it had to fight with getting to the bottom of the hill to GOF towers, and getting through to 2 or 3 walls to my radio.

On SU19 433.475mhz it was a different story. I could barely copy him inside the house!

Intrigued, I decided to walk to a few streets away, find some clear space and perform an A/B comparison. The results can be found in the video below.



I believe DMR simplex can have some serious potential, as S1 of DMR signal is perfectly stable versus S1 of FM.

An FM signal would usually suffer from severe degradation (as seen in this video), while a DMR signal would be perfectly fine until it 'Goes a bit Max Headroom' and s..ssss...suff....suffer from sig....sig...signal...d..ddd.ddrop outs, and meets a steep signal cliff where it would go altogether.

Intriguing and compelling stuff.

DMR – A Love/Hate Relationship

[Disclaimer: This is my experiences of two weeks with a DMR transceiver, quite literally that. This blog may contain some holes and may not be entirely concise, and bits of info as a result may contain inaccuracies. Don't take it overly seriously and as a definitive guide]

I've joined the 'dark side' of radio, as they call it on the UK wide talk groups over there. The latest ham radio craze that seems to have swept across the UK like wildfire; with people getting NoV's all over the place and sticking repeaters up just because they can and want a slice of the digital action – combined with “handie's” that only cost in the region of £90 upwards for something imported from China that you have to program up yourself, or have a local friend send you a code plug.

Yes, I've bitched and moaned about digital telephony methods in the past such as Fusion or D-STAR. Yes, I'm fully aware I've gone totally against my original views – the viewpoint of migrating to another transmission mode on VHF & UHF that's already spreading a thin user base even thinner than ever before.

UNTIL – GB7JL opened in Wigan, and pockets of users threatening to dump 2 meters as they're sick of morons, numpties, and pirating dickheads. Which left me with the worrying prospect of 'radio tumbleweed' whistling through 2 meters and 70 cm.

At the time of this particular blog – it's week 2 of owning a Tytera MD-380, the handie that's sparked a veritable DMR revolution in the UK.

First impressions:

What do I make of it so far?

Well, first of all I quite like the Tytera rig. One of the things you'll notice if you've ever had a go of one is that they're far better screwed together than a Baofeng UV 5R, or similar VHF/UHF Chinese import. The Tytera MD-380 isn't just digital only, it also covers 70cm FM – which I suspect from a business user's perspective aids the transition of going from analogue to a digital format and to have a 'fall back' mode if DMR goes down, as DMR is originally a digital PMR system that has been cannibalised by ham radio operators (so far, DMR is 70cm only).

However, there are some quibbles with the transceiver. Off the top of my head, the worst one is that the signal meter half the time appears to have a mind of its own, while programming receive only banks doesn't appear to knock the transceiver down to 'receive only' if you knew a local DMR frequency that you wanted to monitor and use as a form of digital scanner. There's more odd little bugs out there, but they're gradually getting resolved with firmware updates which aren't too problematic to do. Recently, (at the time of this blog) there has been some enterprising ham radio ops that have made some experimental firmware that in effect turns the Tytera MD-380 into a digital scanner. and to instantly QSY when it finds a station transmitting without having to change channel. Although, I've not tried it for fear of bricking it.

DMR annoyances:

The biggest problem with DMR as a format is that it's originally for business users, and not for ham radio purposes, and it shows.

Repeaters are programmed as 'zones', and inside those 'zones' are the 'talk groups' which are in effect your channels to QSY to. For example, if you were on TG230 which is a UK wide group, the general convention is to keep the contact brief and ensuring you QSY to another talk group which would be something like TG80 or TG81. On some repeaters, you also have a 'parrot mode' where you are able to check the legibility of your transmitted audio into the repeater which is TG9900 (if I recall correctly).

Repeaters in the UK usually use one or two different servers that enable UK wide, Europe wide, or Worldwide communication – which come in the form of Phoenix, or Brandmeister. So far, Phoenix based repeaters are easier to work out as you just turn the dial to the appropriate call group. However, Brandmeister requires you to type in the appropriate reflector on the keypad to QSY – supposedly like Echolink somehow, Christ knows. Don't quote me, as I've not fully got my head around it. The repeaters I can access are GB7PN (Prestatyn), GB7HM (Hope Mountain, Wales), GB7LP (Liverpool), GB7MR (Manchester), and lastly GB7JL (Wigan) – just about, as it has a hell of a job getting into my home location of West Lancs as it scrapes over Billinge Hill. The rest I can navigate around, but GB7JL uses Brandmeister and I've no bloody idea how it works – I can't get a straight answer out of anybody about it and ended up with two people bickering over the air on how it should be done. Which resulted in me getting pissed off with the thing, switching off, and making a brew.

[predicted UK coverage, taken from UK Repeaters site, Feb 2016]

You may hear talk of 'code plugs'. This in effect has your unique DMR ID and callsign, which is ALWAYS transmitted with you – nothing escapes the the 'Big Brother' aspect of DMR, and your repeater transmission information which can be checked online. The transceiver has to be registered, and a PDF copy of your licence (downloadable from Offcom) has to be uploaded as proof of who you are to the DMR-MARC website. The DMR system allows the option of remote shut down, remote kill, and even to to force the rig to transmit automatically if the user is in distress or danger. I've no problem with a uniquely transmitted ID, as it in theory should keep pirates and arseholes off the air, however – who's to say the local repeater keeper might turn nasty on you, have a fall out and boot you off their repeater over some totally frivolous reason? Or worse, be one digit out on an ID and disable your transceiver in error? What makes it a nightmare is that not all code plugs you get from sources are entirely accurate, and may be missing information – such as incorrect talk group information or in my case the wrong CTCSS tone for GB3PZ. Which can leave a user not knowing where the hell to QSY to as it isn't in your code plug or theirs, or worse still – a rogue bit of corrupted information that can crash a DMR repeater (this supposedly happened with GB7JL that really pissed people off).

[Current Google map showing DMR repeaters that are active, Feb 2016]

What needs to happen is some form of complete standardisation instead of rogue code plugs flying around that could be missing pieces of information, perhaps complied by Offcom themselves would be a good idea. Right now, the continuous fighting over how it should be done could result in the death of the format if it's not kept in check. Also, it'd help if certain repeater's internet pages were clearer about how they operate as most are clear as mud.

How about making your own code plug then? Nope, all of the nope. If you struggled with programming something like a Baofeng or Yaesu FT897D via a computer then you will find setting up a DMR transceiver 50 times more complicated and very easy to bugger up. I got around this by buying a pre-programmed Tytera MD-380, but even then it had a couple of bits of wonky info that I had to correct (although the Brough Telecom 'v2' code plug I was sent appears to be okay – so far). If you buy a 'blank' one, ensure you get a reliable code plug from someone who already has DMR first and put your user ID and call sign into it. Programming by hand? Forget it.

DMR advantages:

I believe that once the dust settles with the DMR format, it may conquer the other digital telephony methods that are out there – D-STAR by Icom, and Fusion by Yaesu.

The DMR 'codec' is something that Motorola made, called MotoTRBO that has some very clever tricks up its sleeve. The best part is that repeater activity can allow two sets of traffic, taking up 6.25khz of bandwidth versus 12.5khz used for FM. So, it can carry two separate conversations in the same channel which allows for very effective usage of 70cm. People complain of the compressed nature of DMR transmissions, which to be honest remind me a a loud and punchy sideband transmission with a curious vocoder quality – and not as terrible as you'd be lead to believe. Also, an S1 DMR signal is significantly more robust than S1 of FM signal – which at that point will become very scratchy and hard to make sense of. A DMR signal has error correction to a certain point, before it turns a bit 'Norman Collier' and drop outs happen – which reminds me of a corrupted mp3 file. Essentially, it suffers from a steep 'signal cliff' where it would lose everything.

What really interest me as a ham radio op, is to see how it performs under lift conditions such as Sporadic E or Tropospheric Ducting. After all, TV-DX is still possible and often quite legible using DVB-T versus analogue PAL or SECAM – and people already use PSK31 and JT65 where normal telephony may fail. I dare say I'm tempted to make a 70cm band beam just to see what the hell it would do for a laugh!

One of the things I like about DMR (even though the purists say it's against the spirit of ham radio) is the linked repeater capability so that people can speak to UK Wide, World Wide, or Europe Wide – and (so far, don't quote me precisely) experimental 'roaming repeater' options for mobile operators. Yes, it's 'cheating' – but you are still using a form of radio, and let's face it – due to coming out of sunspot peak years has made HF bloody awful for days on end unless you're running a 60 ft tower, Cushcraft beam, and a kilowatt. Another important aspect for me is that under terrible band conditions, you can still 'play radio'. Also, it has advantages for people who are living in sheltered accommodation who can't put up overly elaborate antenna systems. It'd certainly keep old Bert happy who had to move into a home, who used to enjoy going on 40 meters and 80 metres nattering to the boys – as long as he had a Grandson to keep his Tytera up to date, that is.

Will I be ditching it all for DMR?

No way!

For me, it's just another transmission mode to doodle about with – that if it wasn't for GB7JL opening up I wouldn't have originally cared less about it. I often use a handie while going to the girlfriends gaff,or cycling where I've had a repeater signal and no phone signal. DMR has added another dimension to portable radio operating that would not have otherwise been possible with my Baofeng UV 5R on 2 metres and 70 cm FM.

Lastly, will it kill off D-STAR or Fusion and should you buy one?

The biggest problem with Icom and Yaesu is the huge expense of the transceivers for something just to talk locally on with 2 metres and 70 cm (excluding that Icom rig that can do HF D-STAR). Icom and Yaesu are too possessive with the codecs, and won't let anybody make a transceiver using them (as far as I'm aware). However, DMR – or to be more precise MotoTRBO is designed by Motorola and there's quite a few transceivers that use it and they're not that possessive over the rights. Currently, various radios exist made by Hytera, variations of the Hytera brand (Tytera, Retevis, etc), Connect Systems, and Motorola themselves (the Motorola transceivers are the absolute kings of the DMR game, sound amazing, cost an arm and a leg but are totally worth it).

DMR can be obtained for as little as £90 upwards, while D-STAR and Fusion is at least £350 to start with – which has made DMR very attractive and very affordable, which is why it appears to be a runaway success in the UK.

D-STAR and Fusion to me are Betamax (a good system that's badly marketed), while DMR is VHS (a not entirely perfect solution, but one that will be hugely successful due to cheap cost and the TDMA system that allows for twice the radio traffic in the space of one channel).

To conclude, if you don't have a DMR transceiver and you have repeaters that cover it near to you that you can access – then give it a whirl. It's a particularly cheap and interesting gateway into the realms of digital telephony methods, that won't break the bank. The quibbles will be ironed out and improve over time.

Captain Potherb and the 100w Chicken Box

It was an autumn day on my local hill, and I had cycled up there to clear my head and to be alone with my thoughts; as the 'black dog' had decided to pay a visit and I needed some much needed distraction.

There was a nice blue sky, while I sat there on a park bench; people were walking their dogs and generally just frolicking around with frisbees, kites, or jogging. However, my attention was turned more towards a late 90s registered Volvo V40 whose engine fans kept firing up when the driver was speaking to someone loudly via some form of radio, followed by the typical 'Skkkrrrrt!' noise caused by the break in squelch after transmission. This continued on for some time, as he was drawing a lot of attention to himself due to the engine fans kicking off and the car left on tick-over.

This became a source of mild annoyance, and my curiousity got the better of me while I walked over to investigate.

I was greeted by a guy who looked like a genetic experiment between Father Jack, Jack Harper and Bruce Forsyth sat in the drivers seat. Perched on the dashboard was a Maycom EM27, that covers UK FM and PR 27 GB (CEPT block) channels. Sat on the top, was a spiky red cooling finned RM linear amplifier, which look like a KL203.

Me: “Afternoon. Sorry to bother you, but is that CB or Amateur Radio?”

Guy: “CB”

Me: “Ah, cool, I'm into Amateur Radio and CB radio but I'm having too fun with amateur radio and got nothing set up for that side of it. Good to see someone else that's into it all, any decent contacts?”

Guy: “I got all the way into the Midlands and had Cornwall stations, I was getting stations down south”

Me: “Nice one. It's good when the skip is running Inter UK and you hear other stations; I lug all my stuff over here and run portable, one night got into New York on 20m. Do you know that you can use AM and SSB on mid block now? I'd be having a go of that if I were you, that's where it all came from in the first place.”

He looked at me a bit blank.

Guy: “Err, no. I just have this rig at the moment. There's a couple of radio amateurs that always come up here as well as me, seen them a few times up to now.”

Me: “Fair enough. I'll let you go back to it then, catch you later”

Guy: “See you, mate” and he sort of sneered as he picked up a cigarette, with teeth that had clearly seen better days.

He continued chatting to his friends on the rig, and I sat there quite amused as the cars fans fired up again as he continued conversing. Not that I'm being a radio snob of any form, as radio snobbery is one of my major pet hates; especially as an British M6 call sign holder who has on a couple of occasions being accused of getting my licence from a cornflakes packet.

The thing that amused me, was the absolute poor research of the set-up the guy was using. While on a hill and with flat conditions with CB radio, you will get around 50 miles versus the usual 15-30 of a base station set up in your average street, taking into account terrain obstacles. Assuming your antenna is at a decent enough height of at least one wavelength from the floor (which on 11m band is around 30ft excluding the base of the antenna on a bit of scaffolding pipe bolted to the house by 2 T and K brackets). Oh, and I almost forgot – using 4 watts AM/FM, and 12 watts of SSB which is legal in the UK from last year between 26.965-27.405mhz as well as the original UK 40 block between 27.601.25 - 27.991.25mhz FM only.

So, he was using needless power for no reason, causing adjacent channel splatter due to a cheap linear with power levels that would be of far better use on the 20m band for contacts outside of Europe, not forgetting using needless petrol keeping his car running on tickover, and slowly murdering his car. I also doubt the reliably and SWR of the antenna; if it was me I'd have checked it was low as possible before using that level of power and kept an SWR/ATU in line to measure power levels, reflected power, and ensured a 50 ohm match. Personally (even though it's still illegal and somewhat dubious), I'd have understood if he was on 'the channels between the channels' on SSB and working DX, rather than using ludicrous amounts of power for local FM chat. In fact, he may have clawed back some credibility if he did – after all the allure of 11m SSB has often brought more radio amateurs into the hobby that wanted more bands to play with, and to learn more about radio. With the CB boom in the early 1980s, you can't ignore that they're closely linked and brought a load of radio amateurs into the hobby – especially the Class B G7's that were originally on VHF/UHF who bought Yaesu FT290R's like hot cakes.

We discussed this character on 2 metres one night with a few radio hams I befriended while on my local hill, two of which were found by happy accident one summer afternoon last year and kept in touch with since. Our CB'er friend earned the name 'Captain Potherb', who turns out to be a frequent visitor along with other CB and ham radio ops that visit my local hill who have been doing so ever since I was a small kid and probably before I was born. In fact, I vividly remember a local 11m group once made a 2 element delta beam and used to 'shoot skip' during 1988-1992 sunspot peaks who were not interested in becoming radio amateurs; as there was the Class A morse requirement to use HF.

Turns out that Captain Potherb isn't very popular with some of the lads over here, due to an amusing altercation that occurred one afternoon.

A couple of the local lads that I know often work DX from the hill, as well as me and another guy; their preferred weapon of choice being a late 1980s Kenwood HF rig, Yaesu ATU, and a modified 10m plus long Prowhip end fed vertical into a 9:1 balun and a couple of radials spread across the grass, all powered by a petrol generator. Captain Potherb was there one day, and were duly noticed by the intrepid DX-ing duo.

Captain Potherb was noticed in the rear view mirror by one of the duo, and he felt it was good practice to warn him and find out if he was a radio amateur or not. As the 10m band was in particularly great shape due to high sunspot activity caused by the recent 11 year sunspot cycle peaks.

He walks over to Captain Potherb, and taps on the window.

Ham: “Hello?”

Capt P: “What?”

Ham: “Is that CB radio, or ham radio?”

Capt P; “CB radio, why?”

* Captain Potherb studiously attempts to ignore him, due to the linear and CB setup knowing that he's obviously in the wrong *

Ham: Do you know of the 10m band?

Capt P: “No, errm....Don't know what you're on about”

Ham: “Well, it's 1 mhz up the dial from CB and we're going to be wiping the front end of your rig out seeing as we're in the same 50 square yards of each other. We're going to be on there, so we're just warning you that it's going to blitz it”

Capt P: * Mumbles under breath, powers window back up*

The ham thought “Oh well, I warned him” and went back to the car. They went to 10m, and found horrendous splatter caused by our CB-ing chum. Curiousity got the better of them, and they decided to tune further down the dial to 27mhz. It didn't take long to find him, as he was on the 'UK Muppet band' where the last 20 or show channels range from 27.801.25mhz to 27.991.25mhz FM. Suddenly, they find him as the signal meter bolts hard to the right hand side, end-stopping.

Over modulated FM audio rattles through the rigs speaker.,

“Yeah, fuckin' radio amateurs here again telling me what to do. Fuckin' snobs, who do they think they are picking on us CB-ers, break break!”

The hams co-pilot is a little less patient than the fellow who gave him fair warning, and had to be stopped from shoving the radio and antenna up Captain Potherb's arse.

“Right then, bollocks to him. We're turning the wick up and going on 10 metres. I was polite enough to warn him, and if he wants to play like that then....”

He tunes up on 10m, and alters his power level to max and calls CQ. Soon enough gets a gaggle of stations answering back to the call.

Captain Potherb starts his car up, and aggressively drives away defeated....