Split Frequency and Tone Operation For Simplex Conversations

[Linus]

All,

Has anyone set up their radios to operate on simplex using split frequency and tone operation? I wrote up a use case here:

https://greyscale.zone/split-frequency-and-tone-operation-on-gmrs.html

Basically, two radios are independently set up to transmit and receive on different channels and tones. The reasoning is to make it so that outside listeners hear only one side of the conversation, and it makes it harder for them to interfere with an ongoing conversation. I understand that there is no expectation of privacy in GMRS. A user can make it harder for outsiders to interfere with a conversation by removing context (one sided conversations) and the quick ability to scan tones and interfere. Assume in this use case that both channels are checked for the presence of others before starting a conversation.

 

The example below illustrates the programming for two Wouxun KG-805G radios. 

 

Radio One Program Setup

 

| Radio Slot | Radio Receive | Radio Decode | Radio Transmit | Radio Encode |

| ---------- | ------------- | ------------ | -------------- | ------------ |

| 39         | Channel 3     | DN174        | Channel 6      | DN205        |

 

Radio Two Program Setup

 

| Radio Slot | Radio Receive | Radio Decode | Radio Transmit | Radio Encode |

| ---------- | ------------- | ------------ | -------------- | ------------ |

| 39         | Channel 6     | DN205        | Channel 3      | DN174        |

[WQQQ874]

I’m guilty of doing this set on my radios. It’s something we’ve done on the commercial two way side of the world and I’ve implemented it on my gear. Another thing I’ve done is using non standard DPL’s and PL’s on my radios. It’s not perfect but when you want a little extra protection it’s not a bad idea. The caveat is that your radios should of similar capability.

[Radioguy7268]

What happens when you add a 3rd Radio into the mix? You can decide to program it to either your A or B profile, but then when you try to key up on the 3rd radio - one of the other units (which is programmed the same as your 3rd unit) isn't going to hear what's being said.

 

Taxi cabs used to do a setup similar to this in the 1950's and 60's on VHF.  The dispatcher keyed up on a 152.xx frequency, which all the mobile radios listened to. The mobiles would talk back in on a 157.xx frequency - and the dispatcher normally had a separate receiver tuned to that receive channel - even when he/she was keyed up & transmitting.  Taxi units could not hear each other, and could not talk to each other, which eliminated chatter between units.

 

Unless you want to enter your Louie DePalma Dispatcher mode, it's not very useful beyond 2 units.

[Linus]

Good Point! Three or more radios turns this idea upside-down.

 

Any thoughts on scaling up to more users?

[Lscott]

I think Radioguy7268 pointed out a possible solution. Select one memory slot and program one GMRS channel for TX and another for RX. You can use a mix of analog and digital tones for TX and RX. Then select your next memory slot using the same idea but using different GMRS channels and tones for TX and RX. Setup as many memory slots as you like. All the radios should be programmed identically.

 

During communications you just announce that everyone switch to another preprogrammed memory slot on their radio periodically. Anybody trying to jam or monitor your communications will get frustrated fairly quickly trying to figure out what channels and tones you’re using every time you switch memory slots.

[JohnE]

did  this for a customer who didn't want all his men BSing all the time. only foemen or supervisors could talk to them radios 3,4,5 ...... were set up like 2 and supers had 1.

[scorpion1200]

What i did is use a repeater channel as simplex...467.550 with a dcs code(DN023) for my setup...just make sure you don't key into a repeater using that code.

I got tired of all the kids using their bubble packs interfering...I needed more frequencies...i added all repeater channels as simplex in my Wouxun KG-1000g and my Wouxun KG-805G.

If you don't add a ctcss or dcs you will hear someone keying into some repeater...Now the bubble packs can't hear me or transmit ever...LOL

[SteveC7010]

What i did is use a repeater channel as simplex...467.550 with a dcs code(DN023) for my setup...just make sure you don't key into a repeater using that code.

I got tired of all the kids using their bubble packs interfering...I needed more frequencies...i added all repeater channels as simplex in my Wouxun KG-1000g and my Wouxun KG-805G.

If you don't add a ctcss or dcs you will hear someone keying into some repeater...Now the bubble packs can't hear me or transmit ever...LOL

While I get your plan, it’s not permissible under FCC rules:

 

95E.1763c 467 MHz main channels. Only mobile, hand-held portable, control and fixed stations may transmit on these 8 channels. Mobile, hand-held portable and control stations may transmit on these channels only when communicating through a repeater station or making brief test transmissions in accordance with § 95.319©. The channel center frequencies are: 467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000, and 467.7250 MHz.

[SUPERG900]

Non-standard splits->

 

This is one of those things where, although technically possible, isn't really all that useful. It's really (half?) a solution in search of a problem.... If privacy is an issue, a commercial license and some digital radios will do the trick.

 

There's no privacy allowed on GMRS, nor Amateur bands, either.

[Blackmar401]

What i did is use a repeater channel as simplex...467.550 with a dcs code(DN023) for my setup...just make sure you don't key into a repeater using that code.

I got tired of all the kids using their bubble packs interfering...I needed more frequencies...i added all repeater channels as simplex in my Wouxun KG-1000g and my Wouxun KG-805G.

If you don't add a ctcss or dcs you will hear someone keying into some repeater...Now the bubble packs can't hear me or transmit ever...LOL

i literally asked about doing this a couple weeks ago and upset alot of people. I think it was on reddit though

[Linus]

A few comments to address here. Previously I stated "I understand that there is no expectation of privacy in GMRS".

 

Commercial Radios: Thank you for the comment above, commercial radios may offer that option, but I am not seeking privacy. The use case is a remediation method that makes it more difficult for malicious activity to reach two radio users during a conversation. I am not talking about kids using a bubble pack radio as a toy. I am referencing a radio user honing in on the context of the conversation and interrupting with creepy and objectionable comments. The use case (rarely needed) sets up predefined TX and RX pairs that can be switched a few times until the two radio users are in contact with each other via cell phone or in person. Think hiking or camping in an area without cell phone connectivity and a radio user out there is potentially a threat (preferably just an annoyance).

 

Regarding the repeater input comment. Others may try that, but it is not permitted in the use case that I describe. I am referencing a simplex conversation. The repeater inputs are used for repeater contacts and part of a conversation to a wider audience.

[SUPERG900]

A few comments to address here. Previously I stated "I understand that there is no expectation of privacy in GMRS".

 

Commercial Radios: Thank you for the comment above, commercial radios may offer that option, but I am not seeking privacy. The use case is a remediation method that makes it more difficult for malicious activity to reach two radio users during a conversation. I am not talking about kids using a bubble pack radio as a toy. I am referencing a radio user honing in on the context of the conversation and interrupting with creepy and objectionable comments. The use case (rarely needed) sets up predefined TX and RX pairs that can be switched a few times until the two radio users are in contact with each other via cell phone or in person. Think hiking or camping in an area without cell phone connectivity and a radio user out there is potentially a threat (preferably just an annoyance).

 

Regarding the repeater input comment. Others may try that, but it is not permitted in the use case that I describe. I am referencing a simplex conversation. The repeater inputs are used for repeater contacts and part of a conversation to a wider audience.

 

A determined harasser/jammer can easily find out that you're on separate frequencies - and yet still - they need only transmit on just one of them to break your stride. There just aren't that many GMRS frequencies.

 

Now, if it's simply a matter of avoiding hearing somebody else's objectional and uninvited comments - PL tones, or even better, DCS codes work quite well. Remember - nothing can stop someone from transmitting on (any) channel - but you can filter them out - easily. It's exponentially way more work for them to flip through codes and tones than it is channels. Filtering is the purpose of PL and DCS - it only opens squelch when it sees a signal with the code you have programmed in. Really, hearing an unintended party is only an issue if you have no PL or DCS set for a channel. (...and this is why repeaters use PL tones....)

 

Now it may be that you initiate a call on a channel for which you have no squelch code programmed (and third parties can talk on and you hear them too) - but you can easily switch to another channel for which you do have programmed on both radios same squelch code - obviating the need for a split operation.

[laneends]

The BTech 50-x1 has a frequency hopping feature, but this requires everyone to be using that radio

[Radioguy7268]

I wonder if anyone has pointed that out to the FCC?  Seems that an automated frequency hopping system in GMRS would not be monitoring the channel prior to each transmission as it hops around - potentially causing interference to anyone who is already transmitting on the channel. I'd also wonder how it handles identification on the 4 channels that it just transmitted on.  Or, do you need to stop every 15 minutes to go back and manually key up on the channel(s) in question and properly identify?

 

Type acceptance under Part 95 probably doesn't allow for such a feature. I'm not a lawyer.

[Lscott]

 I'd also wonder how it handles identification on the 4 channels that it just transmitted on.  Or, do you need to stop every 15 minutes to go back and manually key up on the channel(s) in question and properly identify?

 

 

The FCC rules requires one to identify but doesn't specify if that must take place one each channel used. Really what would be the difference if one were to switch channels manually every 10 minutes so long as every 15 minutes the operator ID's? It's really the same thing.

 

§95.1751   GMRS station identification.

Each GMRS station must be identified by transmission of its FCC-assigned call sign at the end of transmissions and at periodic intervals during transmissions except as provided in paragraph © of this section. A unit number may be included after the call sign in the identification.

(a) The GMRS station call sign must be transmitted:

(1) Following a single transmission or a series of transmissions; and,

(2) After 15 minutes and at least once every 15 minutes thereafter during a series of transmissions lasting more than 15 minutes.

( The call sign must be transmitted using voice in the English language or international Morse code telegraphy using an audible tone.

© Any GMRS repeater station is not required to transmit station identification if:

(1) It retransmits only communications from GMRS stations operating under authority of the individual license under which it operates; and,

(2) The GMRS stations whose communications are retransmitted are properly identified in accordance with this section.

[laneends]

I can only assume that the FCC is aware of this feature. If they are not, it's a major oversight on their part given that this is published in the copy of the manual listed on their own page for it's type acceptance. Interesting though it's listed as menu item # 58 in that copy of the manual, and #60 in the other one I posted...

[mbrun]

Spread spectrum is not permitted on GMRS. This feature is a crude poor-man’s variant of that. I would venture to guess that the only logical legal conclusion would be that identification rules apply to each frequency of operation, no different than if you manually switch channels and keyed up. Just like it would not be legal to hold two radios, one tuned to channel 1 and one tuned to channel 2 and announce yourself only on channel 1 every 15 minutes but then do your talking on channel 2 but never announce yourself there.

 

 

Michael

WRHS965

KE8PLM

[Radioguy7268]

I'm pretty sure that the FCC would tell you that you need to identify on each and every channel that you're transmitting on. That's kind of the whole concept of ID'ing - it's a way to identify who is transmitting, so that any issues of interference can be more easily resolved. If you transmit on channels 1,3,5, and 7 - but only transmit a partial ID on Channel 5 and 7 (because the radio switched channels halfway through your voice identification) then I don't think you've properly identified. 

 

How does the radio accomplish monitoring the channel to make sure it's open and available before automatically switching?  

[MichaelLAX]

On 3/2/2021 at 4:36 AM, SteveC7010 said:

While I get your plan, it’s not permissible under FCC rules:

 

95E.1763c 467 MHz main channels. Only mobile, hand-held portable, control and fixed stations may transmit on these 8 channels. Mobile, hand-held portable and control stations may transmit on these channels only when communicating through a repeater station or making brief test transmissions in accordance with § 95.319©. The channel center frequencies are: 467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000, and 467.7250 MHz.

So it is permissible per this FCC rule for two Fixed Stations talking simplex on these frequencies.