Post by anon on Feb 17, 2007 15:38:55 GMT
From: B0ssies Sent: 10/10/2005
Can someone please explain how the frequency settings work on PMR's. Are they an industry standard eg If my Cobra is on setting 3, will it be the same frequency as a Kenwood setting three.
Also sub-settings...what's that all about?
etc etc etc
From: Tigger Sent: 10/10/2005
Hi Bossies
I think that the Kenwood is the only one that the frequencies are different on. Sub-channels are just a division of a particular channel. e.g the runs use Channel 7, Sub-channel 30. I'm no expert but thats how I understand it.
Matt
From: Poo4_Boy Sent: 10/10/2005
Also there appears to be more than one standard for "PMR"
I've seen PMR446 and PMRsomething else, advertised (can't remember the other number but it wasn't 446)
So presumably these work on different sets of frequencies but I'm not sure
No doubt an expert will be along shortly to put us both out of our misery
Roger
From: Biff Sent: 10/10/2005
Hey Bossies,
as I understand it the base frequencies are the same to comply with the free licence issue but the 'sidebands' or CTCSS or the group codes (all the same thing just called differently by different manufactures) can be slightly different for different sets.....
e.g. on a Kenwood Ch 3 group code 25 might be the same as a Cobra Ch3 subcode 30.....
If you have a manual for the Cobra it should say what the frequency is for the different subcodes for your radio....
Because the 446 frequancy is free to use it can get very congested...Try using a base channel whilst riding around an estate and you will pick up baby alarms etc. anything that uses that frequency.... Sidebands (or group codes or CTCSS) means that more than one group can use the same channel but not interfere with anyone else......
HTH
Biff
From: ianboydsnr Sent: 10/11/2005
CTSS (continuous tone squelch system) is incorporated in most radio sets as a means to prevent interference with only 8 channels available - the radio ignores all incoming signals except those that are also transmitting this sub-audible tone, which is why some manufactures, use different numbering for these tones, lots of interesting information here www.446user.co.uk , but if you search for pmr 446, someone will have already figured out the conversion.
From: NicosiaNomad Sent: 10/11/2005
BOssies
There are 8 PMR 446 basic frequencies (channels) in the range 446.00625MHz - 446.09375MHz - predetermined by international agreement, with channel spacing of 12.5KHz. That's it - so if a manufacturer makes a Tx/Rx with all eight channels they will be numbered 1 to 8. If another manufacturer makes a Tx/Rx with only 3 channels they may not pick the first three channels, thus their channel 2 will not necessarily match channel 2 of a unit with all eight chanels.
To reduce the effect of interference between users of the same basic channel there are two systems of coding to suppress reception of undesireable transmissions. The systems are CTCSS and DCS. CTCSS uses 38 continuous sub audible tone codes and DCS uses 83 digital codes. They both work in a similar way: ie, two (or more) users agree which CTSS code or DCS code to use, so that any other users not using the same code will not be received. However, not all Tx/Rx have either or both systems.
Our rides out usually use Channel 7 and CTSS sub code 30. Anyone else outside our group transmitting, for example, on Channel 7 sub code 32 will not be heard because our receivers will not lift the squelch and allow the signal to be processed.
Does that make sense (I've had a few glasses of red wine and it still makes sense to me!!)? If not fire away with a question.
Steve
From: B0ssies Sent: 10/12/2005
Thanks steve...you not a teacher/lecturer by any chance?
Using your example:
Say I have the 3 channel radio and channel 2 is the same as your channel 7. Will my sub setting 30 be the same as your's then: 2/30 = 7/30
I assume so
From: NicosiaNomad Sent: 10/12/2005
No B0ssies I'm not a teacher or lecturer, just a simple comms techie.
Although I've not played with or tested Tx/Rx units with less than the full 8 channels I'd have to say yes. Just as the basic frequencies are internationally agreed, so the CTSS subaudio frequencies and DCS codes would have to be the same for all Tx/Rx, otherwise you would only be able to communicate effectively with another unit set up the same (non-standard) way and it would not be a true PMR446 radio. According to the bumf for my Alan 456R CTSS sub code 30 uses a sub-audio frequency of 186.2Hz. DCS sub code 30 = 205.
If you have a 3 channel set turn the CTSS/DCS coding off (ie to 00). Try to determine which of the 8 basic channels match the channels you have, for example by setting your set to channel 2 and stepping through the 8 channels on another unit, transmitting on each channel until you get comms. When you've obtained the basic channel match try setting the same CTSS sub channel on both sets, you should still be able to communicate.
Out of interest what PMR unit do you have?
Steve
From: Biff Sent: 10/12/2005
Hey Steve,
I've got a Kenwood UBZ-Lj8.. group code 30 on that is 186.2hz as well....
but on my Icom F22SR Group code 30 is 165.5hz
Why don't they make them all the same ??
Biff
From: B0ssies Sent: 10/13/2005
Steve, I just asked because you made it so clear for all to understand.
I have the Cobra from Maplins that a number of us got on "Special"
From: NicosiaNomad Sent: 10/14/2005
Why don't they make them all the same ??
Having agreed an international standard you'd think the manufactures would stick to the standard, because by not doing so would make them incompatible. However it seems to be that some manufacturers don't stick to the standard.
Have a look at the FAQs from the link IBS posted. www.446user.co.uk/faq_cat_1_PMR446.html#6
If your kit doesn't match this (like your Icom) it's non-standard. Not a problem if you want to talk with someone else with the same non-standard set up, but not much fun for trying to figure out the differences with the standard.
Steve