HF or Digital equipment

Lifeboat1721
21st June 2008, 20:45
I had a polite argument with one guy who said that in his opinion Digital was the way to go and that HF should be scrapped(MAD) (MAD)

That made me MAD and I pointed out that if we ever go to WW3 the first thing that will happen is that the enemy will fire a laser at your comm satelites and you will lose most of your communication network,

You would loose VHF and UHF at the blink of an eye but HF will still be running(Thumb)

Ian

charles henry
21st June 2008, 22:07
I had a polite argument with one guy who said that in his opinion Digital was the way to go and that HF should be scrapped(MAD) (MAD)

That made me MAD and I pointed out that if we ever go to WW3 the first thing that will happen is that the enemy will fire a laser at your comm satelites and you will lose most of your communication network,

You would loose VHF and UHF at the blink of an eye but HF will still be running(Thumb)

Ian


I find it strange that whenever the word digital is used everyone thinks of satellites. The last company I was with were in what we called the low density microwave radio business. 800mhz to 50 Ghz. By low density we meant the ability of sending up to 300 channels of people speaking at once.

We used standard analog multiplexing and initially most of our business was making transmitters in the 2ghz range using one or two watts output.

Then "digital" techniques became acceptable (By the users) and we entered the field with a 45Mhz capacity digital radio. The modulation and multiplexing techniques allowed us in many instances to design systems with longer reaching paths sometimes with a savings on repeaters (About a million bucks). The 45mhz stream also was a neat package for delivering television channels across the country.

Ditgitisation (If there is such a word) allowed this, it allowed the internet and
changed the communications of the world.

HF will no doubt continue to be usefull, probably in some way that we cannot even imagine at the moment but the concept of passing messages using morse on HF is sadly to be compared with paying an R/O huge amounts of money to put in eight hours of reading paperbacks (That should stir the pot!!)

regards Chas Henry(Pint)

Ron Stringer
21st June 2008, 23:58
You would loose VHF and UHF at the blink of an eye but HF will still be running(Thumb)

Ian

I do understand how satellites could be disabled to prevent them from relaying radio signals. However it isn't obvious to me what techniques are available to an enemy that could prevent you from using terrestrial, maritime and airborne VHF and UHF radios without also affecting HF communications.

As CharlesHenry indicates, the terms analogue and digital refer to methods of modulating (and demdulating) radio signals and does not refer to any particular part of the radio spectrum, or any specific means of propagating or delivering radio messages.

The Oceanlink EMX, the last emergency transmitter designed and manufactured by MIMCo, operated in the 405-525 kHz MF (morse) telegraphy band. On 500 kHz it produced type A2 (MCW) signals which were derived using digital modulation. This allowed us to 'tailor' the keyed waveform to exactly fit the permitted 'envelope' for the transmitted spectrum. In earlier designs it had always been a struggle to optimise the various compromises needed to produce a good signal without exceeding the permitted bandwidth. If you got it right at 25C then it would go out of spec at -10C or +55C.

Once we generated the signal digitally, meeting the requirements at any temperature or humidity was a doddle. Unfortunately that was only a handful of years before MF and morse was put to rest. Isn't it always the way? Just when you find out a great way to do it right every time, someone moves the bloody goalposts.

rwincer
22nd June 2008, 05:14
Don't worry Ian the GMDSS radio system still retains HF in the form of Radio Telex and Radio Telephone augmented by the Digital Selective Calling system (DSC) whch is a ship radio paging system using HF. Satellites are only half of the story. VHF would not be affected surely.
Cheers Roger

unsteadyken
22nd June 2008, 05:37
Surely Morse is a very low bit rate digital transmission?

hawkey01
22nd June 2008, 12:50
Regarding HF morse etc. Before I retired in 98 we had suffered years of very bad QRM on the HF bands from the Woodpecker signal. This was attributed to the Russians using over the horizon radar (true or false I don't know) but all the stations which monitored it said so. It certainly caused us a lot of headaches. I am sure RO's who were still at sea then will have experienced it. So you can blot HF too if you have the right equipment and Tx strength.

Hawkey01

Jan the lightship man
22nd June 2008, 12:53
Surely Morse is a very low bit rate digital transmission?

HAHA!! Never thought about it that way, but UR right! Love it.. (Thumb)

Shipbuilder
22nd June 2008, 15:22
I must reply to Chas about the myth of paying R/Os vast amounts of money to read paperbacks for eight hours. Many years ago, maybe they did have the time, but they were paid peanuts then! By the time I left in late 1992, I was working harder than in any of the preeceding 31 years. 8 hours in radio room typing & sending literally thousands of words a day (telex, fax & morse) & a large amount of off duty time elsewhere in ship repairing, or trying to repair, computers, tv sets, videos, fire alarm equipment, public address systems, radars & navigational equipment, telephones ad infinitum. When we were all (everybody from captain downwards) made redundant & paid off in late 1992 in order to re-emply us on "new conditions," (& you know what that meant). I took the money & left with an immense feeling of relief. I still occasionally have what are almost "nightmares" of me being back abaord again. Had one last night although it was the ridiculous recurring one of realising on the last day of the trip, I hadn't kept a battery log!

Visiting the ship some time later, I was delighted to see that the work "that R/Os didn't do" had been shared out amongst deck, engine, electricians & pursers (& they didn't like it!)

you may ask what I was doing visiting if I disliked it so much. Main reason was delivering a couple of model ships I had built for friends of management. Secondary reason, still had a number of old friends aboard & it was good to see them again.

Anyway, nothing further to say as I have been quite happily self-employed since late 1992. Never regretted my time as an R/O because everything of any value or importance to me was learned in that job.

You are welcome to modern electronics, but they can manage without me.

Bob
PS
Look what I just designed & built (valve radio), completed it yesterday just for fun. No big deal, but we were not all layabouts.

charles henry
22nd June 2008, 16:04
[QUOTE=Shipbuilder;225677]I must reply to Chas about the myth of paying R/Os vast amounts of money to read paperbacks for eight hours.

Whoops Bob, sorry about that, from now on I will keep my tongue out of my cheek de chas (Pint)

Shipbuilder
22nd June 2008, 17:23
Hi Chas,
I didn't take offence, just grew weary over the years of being told regularly by a minority of shipmates that I was in a dead end job & had no particular skills anyway. I had the last laugh anyway and for the past sixteen years have worked (in the "nostalgia" business) for the finest employer one could hope for (me)!
Best wishes
Bob

R651400
22nd June 2008, 17:44
I had a polite argument with one guy who said that in his opinion Digital was the way to go and that HF should be scrapped

Just tell this "one guy" to nip down to his local library and ask for a copy of Neville Shute's "On the beach" before he considers HF to be scrapped.

andysk
25th June 2008, 12:03
About 25 years ago I worked for a small company supplying a real time HF propagation conditions equipment called 'Chirpsounder' into the UK MoD from the USA. They were at the time about the only company in the USA keeping faith in HF, so when the Pentagon (and later UK MoD) woke up to the vulnerability (and SPF) of satellites, well they were ideally placed.

In my couple of years there it started out as large 19" rack mounted kit, later reduced in size to fit in aircraft and land vehicles.

HF will always have a part to play in comms.

Just found their website :http://www.tcibr.com/ionosphere-propogation-chirpsounder.html

Takes away all the mystique of sunspot cycles and propagation predicting though !

charles henry
25th June 2008, 15:18
(Pint) (Pint) (Pint) IYou would loose VHF and UHF at the blink of an eye but HF will still be running(Thumb)

Ian

1. I seem to remember in the fifties that several thousand tiny dipoles were dropped into space for some experiment or other. In Canda we had complete blackout on HF frequencies for a few days.

2. At one period when the DEW line was being built Canadian Marconi was supplying temporary communications for the project. I was sector super for the Fox sector with 15 out stations sending LOADS of traffic to us by morse which then went by HF radio teletype to Coral Harbor and thence to Churchill where it was put on landline to Montreal.
Once for a period of about ten days we experienced the arctic phenomena of a Black Out on the HF bands. There was not a signal to be heard from 2 to 30 mhz during that period.

Nothing is perfect de chas henry

steve Coombs
25th June 2008, 20:35
On a slightly different note-(but related) has anyone listened to any DRM transmissions). That is digital broadcasts on shortwave/HF.

These transmissions sound near to FM quality. I recently bought a DRM receiver and was amazed at how good it sounded

So hopefully (as far as international broadcasters are concerned anyway) HF will live on and it will be digital as well