Deviation ...

Hi all

The RSGB recently had a bit of a dig (RadCom Aug 21) reminding us that on 2M FM simplex we should be using narrow FM deviation, not wide, in order to be compatible with 12.5 KHz channel spacing. We have had 21 years to adapt, so what’s wrong with us ?

However many transceivers (certainly most HT’s) don’t switch to narrower Rx filters when set to narrow mode, although they do limit the Tx deviation.

When activating on 2M FM I have generally used narrow but have sometimes been told “your audio is a bit quiet”. Also, when choosing frequencies, everyone still limits themselves to 25Khz slots - “up 1” still generally means 145.525 and very few people ever select the intervening channels. If you do, there is a good chance of getting splattered by someone transmitting wide on the adjacent frequency.

Simple question - what is everyone else in the SOTA community using ?



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Some fool gave all the non-HF licensees access to HF and 80% of the 2m users vanished overnight rendering the need for more FM channels very, very moot.


25Khz channel spacing.


Also I’ve never heard anyone using the V16 to V47 chan names, people still use and understand the old names (S8 to S23).


Indeed Andy, it’s not as if there is a shortage … in theory of course the “any mode” part of the band is available to FM users too.

Unanimous so far on channel spacing - are you using wide deviation ??

Yes, I’m a massive deviant. :wink:

I’m not sure when you got your M5 so you may have not been on the air before the M5 licence was introduced. I had G7 issued in (must check) July 1990. Back then I lived on The Wirral at a stunning 25m ASL. Using average sensitivity 2m FM box with a 5/8 colinear on the gable end would be quite a challenge in the evening to find anywhere to talk to people, all the channels were just busy all the time. Even those in the all modes section. There was always a collection of goons using FM on beacons squashing them. Even the repeaters had traffic and not just during the morning and evening commutes.

So making more FM channels available was a sound idea. But as soon as people could use HF with no effort the majority of the 2m FM traffic disappeared. There are many conclusions you can draw from this fact some of which are guaranteed to start a war of words so I’ll not state them. :slight_smile:

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:rofl: I was waiting for that, it had to come sooner or later

I’m a recent M5 (2020) having waited till I retired to get into the hobby (should have done it years ago)

Looks like I’m a wide boy from now on, no need to deviate from the norm

Of course I use 12.5 kHz. I do not want to disturb others with my transmission. By the way, some repeaters make problems if they are set for 12.5 kHz and the transmitter of the OM is set for 25 kHz. The squelch of the repeater can close with too large a deviation, then the transmission from the repeater is chopped off.

73, Peter - HB9PJT


The funny thing is that when using 12.5 kHz TX deviation, you regularly get a “You have a very low modulation, i must increase the volume…” :smiley:

As everyone is going to use FT8, it’s not a problem anymore… :rofl: :rofl:

I use 25 kHz standard, just to be “like others”, even on 12.5 kHz designed repeaters with the problem described by Peter HB9PJT.
Living in a low density aera, i’m not concerned about adjacent repeaters.

73, Patrick TK5EP

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I’m not concerned about any repeaters.


Fine to use narrow on repeaters, I was discussing simplex … and you won’t find me on repeaters anyway


Oops ! I should have better read the original post… :smiley:
Of course are repeater QSOs not valid for SOTA.

So my answer : i’m not concerned by simplex QSOs during SOTA, still for the same reason, no local activity !

73 Patrick TK5EP

There is not much activity here generally, hardly a CQ on the calling channel except SOTA - maybe SOTA is keeping 2M FM alive in this area due to a few dedicated activators

I don’t get the old names, despite being licensed for 15 or more years. I was coming off a summit a couple of weeks a go calling CQ and some GM4 came on asking me to QSY to S… That was the last I heard of him. I really don’t know why he couldn’t have just said the frequency. It’s folk stuck in the 1970’s or trying to confuse newer amateurs I think.

As for FM, I run all my kit narrow, however generally use 25KHz spacing. I sometimes use the ft-3 for ISS stuff and have that set to 5KHz steps, which can be tedious.

73, Fraser

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You only had a 2 digit display if you were posh. Other rigs may have a printed number in a window.

It made sense to give the channels numbers and a descriptive letter.

So S20 is Simplex channel 20 and as each channel is 25kHz it’s 20*25 = 500 making
145 + (20 * 25) = 145.500 simplex i.e. the calling channel

R3 is channel 3 and repeater so the input is 145+(3*25) = 145.075 and the output 145.600


Back to that 7500 on ch 24 and the simple/repeater switch is on S so it’s on S24 which is actually R4 output. It couldn’t be any simpler.

EDIT As Damir said it should be 145.675 but I can’t type and think at the same time.


Thanks for the explanation. That’s the first time I’ve actually seen it described.

Like I say, it belongs in the past!


R3 is 145,675 because it is 600 kHz shift

I still us “old” names. They are simple and easy to calculate. And a channels are 12,5 kHz plus

S10 is 145,250 S10a is 145,2625
S20 is 145,500 S20a is 145,5125

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Here is Australia it seems that 25kHz channel spacing is still standard - it’s what the repeaters round here use - and I’ve just checked the WIA bandplan (WIA = Wireless Institute of Australia - more or less the equivalent of the RSGB) and it states that simplex FM channel spacing is 25kHz, while digital channel spacing is 12.5kHz.

Repeaters though, can use 12.5 or 25kHz spacing, apparently…

Sadly, out here, it’s very rare to hear any FM simplex at all :cry: at least at my QTH anyway, the long distances (and mountains) are a limiting factor in terms of coverage.
I suppose somewhere like Sydney there could be more activity, but I’m told that most of the FM repeaters lie silent most of the time, while the digital repeaters on DMR and similar are buzzing. You can draw your own conclusions!
I suppose this is off topic, as the original question was about the UK situation, but I thought this might be of interest anyway.
73, Steven


Thanks Steven for bringing this information to the VK hams. Yes it is of interest, thanks for your effort.

73 de Geoff vk3sq

Still on 25KHz on FM because my FM radio does not have 12.5 channel spacing.