Ham Radio Digital Modes Including P-25

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Ham Radio Digital Modes Including P-25

Postby TheHam » Thu Nov 10, 2016 5:03 pm

How does it work?

P-25 is a communication system essentially created and utilised by public service agencies in North America, the system allows communication between several agencies such as Fire Fighters and Paramedics and Police Officers. Digital communication systems are available to Ham radio Operators, D-star and Fusion to name but two. Like all other digital modes, the normal analogue signal which we produce when we speak, is sampled, in the case of G.S.M. mobile phone technology 8000 times per second each sample produces an eight bit word.

We have a similar digital system used here in the United Kingdom for our Public Service personnel; it's called TETRA, or Terrestrial Trunk Radio. Many of us started out in Ham radio by listening to the Emergency services although in those days the Emergency services used Amplitude Modulation and Frequency Modulation to communicate between mobile and base stations and there was no encryption in those days. I learned a lot about radio by converting receivers to the Emergency service frequency allocations.

Short wave listening or utility monitoring gave you a great sense and awareness where other services transmitted, utility listening added to this awareness and soon you became knowledgeable about out-of-band transmissions and how to keep harmonics from your transmitters to a minimum. A requirement by law for the active Ham Radio Operator.

Digital communication has the advantage over analogue technology because it allows many operators to use the same channel by splitting up time into bite size portions; these bite size chunks of data are converted into digital streaming packets of data and can be sent around the World via the Internet. By using this method of superimposing speech on to a radio signal, radio bandwidth is used more efficiently. Digital systems have the advantage over analogue in many other ways, once the speech is converted into digital signals they can be mixed up in a particular way that's how encryption is produced, making the transmission secure. Frequency hopping is also employed to make the process of recovering the digital signal more difficult to intercept.

Ham Radio Operators can now send and receive these digital signals from all over the World because devices are placed before and after transmissions to allow these digital streams to be sent over the World-Wide Web.

My Ham Radio days started with building simple crystal set receivers and tuned radio frequency, T.R.F. equipment to listen to Hams on top band, 160 metres. I soon developed an interest in the V.H.F. and U.H.F. spectrum two metres and seventy centimetre bands where I soon discovered transmissions from Aircraft and Ships.

Ham radio is a rich and varied subject and many find themselves experimenting with all of the modes and bands. I have no doubt that P-25 will be on the experimental radio hams experimental agenda.

John Allsopp G4YDM https://www.qrz.com/db/G4YDM

Article Source: http://EzineArticles.com/expert/John_Allsopp/1925417



Article Source: http://EzineArticles.com/9548452
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Re: Ham Radio Digital Modes Including P-25

Postby Metradio » Thu Nov 10, 2016 5:07 pm

Nice speech.. :rolleyes:

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Re: Ham Radio Digital Modes Including P-25

Postby redman99 » Thu Nov 10, 2016 5:30 pm

Metradio wrote:Nice speech.. :rolleyes:

Mike
Pity ham radio has shot it's self in the foot again, with a format war.
Makers/dealers have too many vested interests.
Look at the licenced repeaters, there seems to be a clear leader.
Many repeater keepers said they were advised by the RSGB re Fusion etc
A real mess.
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Re: Ham Radio Digital Modes Including P-25

Postby G4RMT » Thu Nov 10, 2016 8:06 pm

I'm a bit confused now. John seems to have loads of articles on the ezines site - but I don't quite see why they're then copied here? Double bubble.

They're quite informative, but fall into the educational trap that trainee teachers, especially those working in Further and Higher Education sectors. It is extremely difficult to write a generic article that covers technical and concepts based on science and maths. The authors of this kind of material have a big problem. They want to get across a complex technical subject, but have no idea of the level of the recipients. So a guess has to be made as to the 'typical' reader. This often means that a solid scientific principle has to be 'diluted' and simplified - but this process distorts the actual understanding. In essence, they understand the simplification, but will understand it with errors. On this forum we often get into this kind of deep water. The recent conversation on propagation is a good example. It seeks to educate, and is written in friendly terms, but includes sentences such as this one.
Aerials are balance entities, meaning that the current in each leg of your dipole are carrying the same current as the cycle changes, consider using balanced line as opposed to coax.

If you took your amateur radio exam in the 80s, this makes sense - but probably means nothing at all to somebody without the physics background.

John has posted a number of educational topics - but sadly, even when simplifying the content for beginners, it's necessary to slip in a few more complex concepts and these I think may just go whoosh over many reader's heads.

When you become a teacher, especially for these kinds of subjects, you usually set a lower limit for your level, and stick to it, then coach the strugglers to understand each section. dropping the level is a common beginners solution, but unless you understand the basics, talking about current, cycles and entities is meaningless - to understand current in this concept requires the knowledge to deal with resistance, impedance, transmission lines, balanced and unbalanced deliver systems and Ohms law, capacitance and inductance. If these terms are understood, along with the links between them - then understanding results when the subject is discussed. I wrote some of the BTEC Nationals and Higher Nationals for 15 years, and we always had this problem. Do you word it for the Distinction level older students or for those just scraping a Pass? No space for both versions, and lots of stuff many of us wanted in the qualification just couldn't go in, because you cannot set things for students to do that a proportion simply cannot do. Level, writing style and vocabulary all fight with each other.

The stuff John is producing is useful information that deserves a home somewhere on the forum, but perhaps it needs an educational section.

The problem is that it would be simple to punch loads of holes through it - but I can see he's attempted to short cut a few tricky things, and perhaps some over simplification has crept in (which I do understand) but this could actually confuse. There's always going to be the folk who are green taking it in as 100% accurate, while others will be tempted to correct the slight 'bends' that have crept in.

Any chance we could have a beginners basics section (with a more catchy title?) where this stuff could be housed - perhaps as read only once posted?
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Re: Ham Radio Digital Modes Including P-25

Postby Alfie » Thu Nov 10, 2016 8:54 pm

Different digital modes for business is understandable but i agree totally that the dmr ham radio scene is a mess and as we all know its down to greed on the part of yaesu, icom and motorola each wanting to own and market their own incompatible products that are in fact using the same open standard. The digi standard for ham should always have been a standard one yet instead to have full access a ham is expected to buy three different radios covering each digi mode. and when you bear in mind the lack of dual band digi radios then that means they will need 6 different radios not including the analogue ones and this is only to cover 2 bands (vhf/uhf). pretty ridiculous!
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Re: Ham Radio Digital Modes Including P-25

Postby m0lsx » Thu Nov 10, 2016 9:39 pm

The VHF/UHF digi market is wide open for anyone who produces a simple SDR radio that can work with open source software.
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via http://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
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Re: Ham Radio Digital Modes Including P-25

Postby TheHam » Thu Nov 10, 2016 9:46 pm

Thank you for taking the time and trouble to reply. Most of my articles are written from questions, questions asking if I can enlighten the new Ham. I was asked by others to post here and on a new blog website, eventually all will see, however I decided to copy them to this website.

Best wishes to all.

John Allsopp G4YDM
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Re: Ham Radio Digital Modes Including P-25

Postby redman99 » Thu Nov 10, 2016 10:22 pm

m0lsx wrote:The VHF/UHF digi market is wide open for anyone who produces a simple SDR radio that can work with open source software.
The biggest problem is the repeater keepers have gone down the path of no return.They are now stuck with what they've got.We have got open source radio's of a kind in the cheap DMR products, not far from SDR's.
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Re: Ham Radio Digital Modes Including P-25

Postby m0lsx » Fri Nov 11, 2016 10:13 am

redman99 wrote: The biggest problem is the repeater keepers have gone down the path of no return.They are now stuck with what they've got.We have got open source radio's of a kind in the cheap DMR products, not far from SDR's.


But with SDR's using open source software, the variety of systems being used could all be used from one radio. Icom & Yaesu for example may not like the fact that radio amateurs are using open source software to decode or transmit their systems. But it would be what we should expect of radio amateurs.
And personally I blame the people who have spent stupid amounts of money on black box radios when Echolink would do much the same job, but without the "Digital" label. Rather than the repeater keepers. This whole Death Star etc thing, was all about that label, Digital, not what the systems actually do.
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