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Old April 6th, 2014, 19:32   #1
Cobrajr122
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Radios and You

Radios In Airsoft and You: Basics of Telecommunications

So before I start - I would like to state:
NOTICE : If you disagree with using 4 watt transmitters on the FRS or GMRS bands, or want to challenge the legalities, or are deathly afraid that the police will drop out of the ethosphere and bust you for using overpowered radios, please STOP READING HERE.

--------------------
Because people have doubted my advice in the past, I will put this at the top so I don’t have to say it again later.

I grew up in a family of techies, I have spent the last 6 years of my life studying, designing, implementing, using, diagnosing, and repairing radios and related hardware/software. Telephony is my background in schooling, its my career, and hobby. I know what I am talking about.
--------------------

As opposed to just command level comms, telecommunications at an individual level has become more and more important in both real and simulated warfare over the past few decades. To achieve this, radios that have specific capacities are used. This guide will be to help you choose a radio system that will allow you to have an effective means of communications in every situation.

I believe that if you have a piece of kit on you, it should have a real function within the confines of your mission, and you should know how it works.
Since everybody should have radios on them in milsims, everybody should have a good base knowledge about them.
This post is to just give anybody reading it a good basic knowledge of what the radios systems are that we use, and how they operate.


-We shall start off with some basic telephony knowledge-

For our purposes, as unlicensed operators we have been given the use of 22 channels (soon to be 27) for use of voice communications. Each channel has a specific frequency and other parameters assigned to it. Operation outside of these frequencies and other ISM Bands by a non licensed individual is strictly prohibited and will NOT be tolerated at any event.

The 27 channels are divided into 3 categories, FRS, GMRS, and MURS.

FRS - Family Radio Service - UHF Band ~462MHz and ~467MHz
FRS consists of channels 1 through 14 with channels 1 through 7 being “shared” with GMRS. Each channel has a bandwidth of 25KHz and a maximum RMS output of 0.5 Watts

GMRS - General Mobile Radio Service - UHF Band ~462MHz
NOTICE: GMRS requires a licence to use in the US. DO NOT USE GMRS WHEN YOU ARE CLOSE TO THE BORDER. This goes double for GMRS channels 5, 6, and 7 (19, 20, and 21) as they are emergency channels.

GMRS has 8 channels that we list as 15 to 22 with all 8 of them being “shared” with FRS.
Each channel has a bandwidth of 25KHz and a maximum RMS output of 2 Watts.
Mobile stations, base stations (vehicle and building “permanent” installations) and repeaters are prohibited from use on the GMRS band.

MURS - Multi Use Radio Service - VHF Band ~151 MHz and ~154MHz
Not in service until [UNKNOWN]
MURS consists of 5 channels that are not shared with FRS or GMRS channels.
Channels 1, 2, and 3 have a Bandwidth of 11.25 KHz while 4 and 5 have a bandwidth of 20KHz.
The lower bandwidths means that the current programmable radios will not be permitted on these channels unless they can be programmed to use the permitted bandwidths.

Frequencies (MHz)

(forum formatting fail)

1 GMRS/FRS 462.5625
2 GMRS/FRS 462.5875
3 GMRS/FRS 462.6125
4 GMRS/FRS 462.6375
5 GMRS/FRS 462.6625
6 GMRS/FRS 462.6875
7 GMRS/FRS 462.7125
8 FRS 467.5625
9 FRS 467.5875
10 FRS 467.6125
11 FRS 467.6375
12 FRS 467.6625
13 FRS 467.6875
14 FRS 467.7125
15 GMRS 462.5500
16 GMRS 462.5750
17 GMRS 462.6000
18 GMRS 462.6250
19 GMRS 462.6500
20 GMRS 462.6750
21 GMRS 462.7000
22 GMRS 462.7250

(MURS is not yet in service in Canada)
1 MURS 151.820
2 MURS 151.880
3 MURS 151.940
4 MURS 154.570
5 MURS 154.600

--------------------

Comms 'Bleeding'

-What is it
-Why it happens
-How to prevent it


What is it
I am sure by now that just about everybody has heard it. You are listening to your radio and somebody else starts to talk who obviously does not belong on that channel. You can hear them but they cannot hear you.

Why it happens
FRS/GMRS radios operate using a 25KHz bandwidth. These bandwidth have built in guard spacing that 'should' eliminate the bleeding, but the cheaper china radios tend not to colour inside the lines so well.
For Ch 1-14 (FRS) this spacing is fine and does not cause any issue between any of them.
When you add Ch 15-22 (GMRS) this causes an issue.

Ch 15-22 operate very closely with Ch 1-7

Some people believe that some interference they get is simply from the power level of near by transmitters on different frequencies. I have tested this with up to 70W on adjacent channels with a few different receiving radios (2 types of blister pack, a Puxing 888, and a Motorola XTS2500), none of them receive any interference. So, these guys either have REALLY, REALLY shitty radios, or they were experiencing interference due to the bandwidth issues as described in this section below, which is far more likely.

Bandwidth - A channel uses more then one single frequency to work. To effectively transmit voice(or anything really) a chunk of frequencies are used with the carrier being the main one that is programmed into the radios.
This chunk of frequencies for FRS/GMRS is split in half and the carrier is the middle frequency.

For a 25KHz bandwidth, this means that a frequency of 462.5625 (Ch1) actually uses from 462.550 to 462.5750
462.550 and 462.5750 are the carriers for ch 15 and 16, which have their own 25KHz bandwidths as well.

This means that the channels have 12.5KHz overlaps with each other. Ch 1-7 and 15-22 all overlap with each other.

I have tried to illustrate this with a couple channels.



As seen, 1 overlaps with 15 and 16, and 2 overlaps with 16 and 17(not shown)

HOW TO PREVENT IT

There are many options to avoid this from happening, I will cover 2.

1. -Do not use Ch 15-22 or 1-7.
Instead restrict comms to 1-14 or 8-22

This ensures that there will be no bleeding and blister pack radios can still be used.
Limits the amount of ch that can be used, not good for very large games.

2. -Change your bandwidth settings to 12.5KHz instead of 25KHz on Ch 1-7 and 15-22 (This does not always work)
Also known as Narrow band. (Narrow - 12.5KHz, Wide - 25 KHz)
Not to be confused with the Channel STEPPING setting.
This will eliminate all overlapping, but slightly degrade audio quality.

This ones only works if everybody has non blister pack radios, which, as anybody who has read my game comms briefs knows I advocate.

I know this is possible on the Lintons and Puxings I own, but not sure about any other brand. It seems to be a popular option to add to these radios so I would assume most have it.

My tests on some china radios, higher and lower grade, has shown sporadic results though - this does not always work.


I am sure there are a few other things that can be done, but these are just a couple options that will work just fine.

I have not covered the difference between the CDN and US frequencies because we all use the US ones anyways. It also seems that no matter how hard I try, Blister pack radios will still be at massive mil sims like this, and you can ONLY get those with US frequencies.

--------------------

'Sub' Channels

Sub channels are bad and they should feel bad.

-What are they
-How do they work
-Why are they bad


What are they

Sub channeling is a method used to block all incoming traffic on a particular channel that does not contain a specific squelch tone.

How do they work

These sub channels operate using a squelch tone.

Squelch - Without squelch, you would constantly hear noise. Squelch turns off your receive circuit until it is triggered either by a specific signal, or a signal with X strength. At this point, it opens up your receive circuit until the tone/signal stops.

While the squelch is open, you can hear EVERYTHING on the frequency you are tuned into.

With FRS/GMRS there are two different technologies used to create 'sub channels' using squelch.
1. CTCSS
2. DCS

They are both quite different in their nitty gritty operation, but achieve the same result.

With CTCSS ch 1 (67 Hz) enabled, your radios squelch will only open up your receive circuit when it receives a 67 Hz tone.


Why are they bad

They are bad because it gives you the false illusion that you are on a private channel and can talk whenever you want without interfering with anybody else.

For this example I will be using CTCSS squelch tones.

---

Scenario:
-You are allotted FRS Ch 2.
-You want to have 3 nets
- Sect 1
- Sect 2
- Sect 3

FRS - 2 - Sub 1 = Sect 1
FRS - 2 - Sub 2 = Sect 2
FRS - 2 - Sub 3 = Sect 3

Radios will be programmed as such.

Sect 1 = 462.5875 MHz CTCSS 1 (67 Hz)
Sect 2 = 462.5875 MHz CTCSS 2 (71.9 Hz)
Sect 3 = 462.5875 MHz CTCSS 3 (74.4 Hz)



A member of sect 1 keys up to talk. All member of sect ones radios are activated and all sect 1 members can hear. Sect 2 and 3 do not hear this traffic.

Because members of Sect 2 and 3 do not hear sect 1 traffic, they do not know that there is traffic being passed. Therefor they do not know that the net is in use and not to key up.

A member of sect 2 keys up. All Sect 2 radios are activated.
A member of sect 3 keys up. All sect 3 radios are activated.
All members of sect 2 and 3 can now hear all traffic - This is a collision - bad.

A member of sect 1, 2 and 3 all end up keying up during the same transmission.
More collisions, more bad.

Because the transmitting stations can't hear the net, they do not know that they are talking at the same time as others. 2 people attempting to talk on the net at the same time is incoherent.

--------------------

Hardware

Blister Pack Radios (THEY ARE BAD AND THEY FEEL BAD)

Blister Pack Radios are the ones you find at canadian tire, wally world, the corner store, etc. Usually packaged, in blisterpacks.
They are bound by law, meaning low transmitting power and fixed, SHORT antennas. Some of them even use slightly off, or completely different frequencies for the channels. making them not work with other brands. They often have roger beeps enabled, sometimes permanently.

AVOID AT ALL COSTS


4W Programmable Radios

These are the the ones you want. There are numerous brands, models, and price points out there and can seem intimidating to somebody new to the world of radios.

They often have far more functionality and abilities that the blister pack radios do not offer.

Because these radios are programmable, and sold to an international audience, they do not come with the FRS/GMRS channels pre-programmed, therefore it is VERY important that you only use the radio within the 22(27) frequencies that we have been granted use of.

Some of the more popular radios include;

Puxing 777
Puxing 888
Puxing 888k
Baofeng UV-5R b,c, etc

The list goes on.

It is very important that when choosing a radio you get one in the correct frequency range, usually 400-470MHz. You should also make sure that it has the standard antenna and headphone/mic ports. (SMA Male and Kenwood 2-Pin)



Larger Radios(more power)

Larger radios such as man packs and vehicle mountable radios usually come with 20W+ power ratings. Some people see that higher number and think they need it, because more is better.
While it is very true that higher power is better with telephony, it is definitely not required for our application, and could land us in some shit. As mentioned above, the 4W radios that we use violate the law. They usually just slip by and nobody cares, but they are starting to get noticed because people are using them improperly. If we start parading around the EM spectrum with overpowered china grade transmitters, somebody will definitely take notice - especially when there are Industry Canada guys on these forums.

4W is MORE than enough for our applications. With the stock antenna I was able to keep loud and clear comms out to just past 4KM in medium/dense forest. Which is very close to the limit of Line of sight comms, which is roughly 4.41 KM at the height of my face.

So, these larger radios are simply not needed, and not suggested. The use of vehicle and base mounted radios is specifically outlined as being against the law, let alone their transmitting power.

Batteries

This one is pretty sweet and simple
BUY EXTRA BATTERIES!

Antennas

The antennas that come with the radios are usually sufficient, but if you want to edge out your reception in dense forest. or in a large building you will want to get a longer antenna.
Anything longer is better, and the higher you can get it on your body the better.

The ‘average’ wavelength of FRS/GMRS frequencies is ~25.44 inches.
Obviously an antenna that long would be unwieldy, so we need to reduce the size of it in fractions of the wavelength. I personally use one that is 14” long, or ½ wavelength. To get it away from my body and a bit higher up, I use an antenna relocation kit.

1/4 wave = ~6.5"
1/2 wave = ~14"
5/7 wave = ~18"
3/4 wave = ~19"
1 wave = ~25.44"

Because we are working with more than one frequency, you are not limited to the numbers above, anything within those values will work. However, using an antenna above 1 Wavelength is not preferable, nor should you weave it into your gear to such a point that it is no longer roughly straight. Having too much of a curve in the antenna will change its EM map and may be detrimental.

Headsets / microphones

I do not know enough about repro gear to really write about this.
What I do know is that after going through 2 sets of repro in one season I bought MSA Sordins, and a real U94 PTT and have never looked back.

It basically comes down to - buy what you can afford, and what is functional. But remember that if you buy shit, you get shit, and you will become shit to your team when your comms go down or start fucking up.

There are numerous options out there for headsets, mics, and PTTs.
One important thing to remember is that you should not use a speaker. Speakers are loud and they give away your position when you are trying to be sneaky.
If you do not like wearing a full headset, look into a shoulder mic and an ear bud like this:


Find what works for you and stick to it.

Another important thing about PTTs is placement on your gear.
Spend a long time deciding where you want to put your PTT. It must be in a spot where it can not be accidentally activated. If you end up hot micing you will be hunted down by your teammates and castrated.

fin
Maybe?
This could get bigger if people have questions, and it depends on how lazy I am.

Feel free to ask questions, comment, and add to it... especially in areas I am lacking like repro ancillaries.

Last edited by Cobrajr122; February 2nd, 2016 at 11:53..
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Old April 6th, 2014, 21:51   #2
Redneck Jimbo
 
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When using a longer antenna say? A 25in and folding it 2-3 times (like the mil/blade type antennas) down to 6-8in or so, decrease the clarity of the transmissions/receptions? Or is it over all length of the antenna whats important?
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Old April 6th, 2014, 22:20   #3
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Very good read thanks for putting the time and effort to educate Hopefully people will take heed to this.
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Old April 6th, 2014, 22:53   #4
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Very good, and very understandable.

I am going to re-read my radio manual in the AM and post a couple questions.
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Old April 7th, 2014, 00:09   #5
r.d.fretz
 
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Now this is the kind of thing needed by those of us who are either new to airsoft or only use radios at work, which are FAR less complex. I've read the post 3 times now and am begining to get it. At least I think I'm getting it... Either way, I'm rethinking the use of radios in the field. Having never owned a radio like the Puxing 888, this is all new to me. I was thinking about maybe getting one, but now, I think I need to do some research and learn more. Right now I only have a pistol, but I know how it basically works and why. Radios shouldn't be different. if you have it, you should know the basics of how it works.

I'm guessing from this post, there are many people who go to games who need and use such radios. So now I'm asking, how important is it to those who have radios? I have hunted large game for years and haven't yet used a radio, maybe I should have been...
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Old April 7th, 2014, 00:34   #6
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This is a superb write up. Thank you so much for this. I just re-programmed my 777 properly using what I learned from this.
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Old April 7th, 2014, 13:44   #7
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Like this article, will keep it for reference. I do have a question. Apart from hand programming a radio are there any good software program that can be used to do the programming. Then plug in the radio to up load the fregs?
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Old April 7th, 2014, 14:29   #8
Danke
 
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The software programs are unique to the handset. Most you can program by cable from a laptop or copy over from a second handset.
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Old April 7th, 2014, 17:05   #9
Cobrajr122
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Quote:
Originally Posted by Redneck Jimbo View Post
When using a longer antenna say? A 25in and folding it 2-3 times (like the mil/blade type antennas) down to 6-8in or so, decrease the clarity of the transmissions/receptions? Or is it over all length of the antenna whats important?
Folding those blade antennas electrically shortens the length and will decrease the reception properties.

Think of it like a net, the larger the net, the more of the signal you are receiving. However, if your net is larger your net, the more potential there is to pickup the background noise and whatnot, especially when you move past 1 wavelength.

Quote:
Originally Posted by jakster View Post
Like this article, will keep it for reference. I do have a question. Apart from hand programming a radio are there any good software program that can be used to do the programming. Then plug in the radio to up load the fregs?
There are programming cables that you can get, however the drivers and the software are sometimes difficult to install and make work. When you only need to use it presumably once, it is not really worth the money to me.
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Old April 7th, 2014, 17:26   #10
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[QUOTE]There are programming cables that you can get, however the drivers and the software are sometimes difficult to install and make work. When you only need to use it presumably once, it is not really worth the money to me./QUOTE]

Yep got the cable but for the life of me can't find a good program to upload
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Old April 7th, 2014, 18:54   #11
ThunderCactus
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Gotta use the manufacturer software
The wouxun UVD1P is not only an excellent radio all round, but also has very simple software that's free.
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Old April 8th, 2014, 00:23   #12
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Thank you, I think im going to go with the Baofeng UV-5RD with the stock anenna and pic up an extra 14in~ just in case. Thank you again for straightening this hole bag of snakes out.
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Old April 8th, 2014, 11:25   #13
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Thanks for this! Reading some of your earlier posts (which it looks like you've moved here) helped me get a firm understanding on frequencies and bleeding in the past.

Quote:
Apart from hand programming a radio are there any good software program that can be used to do the programming.
Generally, you'll only be using the radio on the FRS/GRMS frequencies. If you know the first frequency, and the bandwidth (25 khz), you can step through pretty easily.
I also have them written on a piece of card paper, with "secret radio codes" scribbled at the top.

I have a few questions:
MURS: This is the first I've heard of MURS. Do you expect that it will become more common world wide? As in, will international radios start having these lower frequencies built in? Do you expect that game hosts will start using them?

Wavelength: This is sort of unrelated, but do you know of any simple resources online that explain why an antenna that is shorter than the wavelength of the signal, would be sufficient? I'm at work, and can't really wrap my head around that at the moment, but I'm curious as to how it works.
...I don't know how radio signals are transmitted, so I suppose that might help me understand better, haha.

"Real" headsets with Chinese radios: I bought a pair of MSA Sordins on a whim, assuming that they'd work fine with my Puxing 888 and Chinese PTT, without doing much research. Obviously they won't work, because of the impedance difference (maybe add a little about impedance to the original post?). I've started out doing a little research, and from what I saw, I would need to either replace the microphone with a low impedance mic, or I would have to buy a real PTT and radio.
If I get a real PTT, will I need to buy a different radio as well? Or would a PTT be all that I need to make my Sordins work with 888?
If I can't use the 888, do you have a recommendation for a decent radio? I'm having trouble finding good advice for something like that, since I don't need a ton of bells and whistles.
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Old April 8th, 2014, 12:16   #14
w1lp33
 
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Send your sordins to Srs tactical to change the mic, cost you $100. Personally is recommend getting a real nexus ptt from them as well, cost you $150. Nexus ptt + MSA sordin works great with a puxing 888 once you swap the mix (and plug if need be).

It's fast too, shipped my headset out, had the work done and had it back in my hands in 3 business days. (And while it's there, if you don't already have gel ear cups, buy them, they're worth every penny of the $45.)
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Old April 8th, 2014, 14:15   #15
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Thanks w1lp33, I'll look into it. I'm gonna have to save up some money, but that's probably what I'll end up doing.
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