PL / CTCSS on AM CB

We have had CBs in our cars and a base in the living room for years, with a 5/8 wave vertical on the roof of the house. We've been plagued by skip and other RF garbage, and my wife is tired of hearing spanish, "AUUUDIO", and bleed-over from channel 6 (we use 1). Short of her getting her ham ticket (not likely, but not for a lack of trying) and switching to GMRS, I'm short on options. Turning the gain down and squealch up really cuts down on the range, and skip still usually opens the audio.

I want to put CTCSS encoder / decoder boards in my radios (Cobra 29, 148, and radio shack base). I don't see any reason this won't work (though the carrier will always be modulating at 88.5 hz, 110.9 hz, or whatever freq), which could reduce the life of my finals, or reduce peak power (not too concerned, I'm not running amps, and the radios are stock modulation or 70% at most).

Before I drop a hundred bucks on two PL boards, I'm wondering if anyone has tried this, or has a technical explaination for why it shouldn't work. It even seems to me that I could make a box with the PL board inside, mount two 4 pin mic sockets, and two 1/8 inch sockets for an external speaker, and be able to move the box from radio to radio (powered by batteries or 12v).

Any thoughts would be great. If I do try it, I'll post a diagram and pics with my results. It seems the good people at Uniden would have already thought of this, as it would be a helpful feature, but we'll see.

Thanks and 73

Matt

Instead of spending all that money to upgrade CB radios, spend $75 and get your GMRS license, and a couple of GMRS radios. You and your wife are covered under 1 license, you'll get clean FM audio, none of the CB garbage (HELLLO AUDIOO!), and with the permission of repeater owners you can use GMRS repeaters to increase your range. Depending on how far you need to talk to each other you might do well with a pair of mobile radio's at 50 watts. I'm not sure if handheld GMRS radios would cover your needed range, but might with good external antennas. You'd come out spending a little more money than upgrading the CB radios, but would get away from all the garbage on that band.

As to the tone boards, I'm unsure how well they would work on AM. Maybe someone else can chime in that has had more experience testing it. If it were me (and I wasn't a ham radio op) I'd do anything to get away from the noise of "skip land."

Additional thought on CTCSS with AM, exclusively on CB:

I imagine that the channel you're using would have to be absolutely quiet. If there was another station on the frequency and the "heterodyne" sounds of two stations doubling would probably create a noise that would be louder than the PL tone.

I could be wrong, but I know when you hear all that skip garbage coming in the carrier has a lot of high pitched whine on the receiving end.

Way back in the early days of CB a couple of manufacturers had two-tone signaling, pretty much the same as quick call to allow you to mute the radio until another unit sent the tone sequence to un-mute the receiver. As already pointed out get yourself GMRS radios to replace the CB stuff, your wife will enjoy the silence.

I would expect the overwhelming noise on the CB bands would distort the PL tone to the point it could not be decoded reliably.

The above commenters are offering good advice: UHF radios can be had cheap on ebay. Programming software and cables are readily available, a GMRS license is simple to get.

The added features of certain brands of radios would make a set up like yours handy.

Kenwood has Fleetsync built in.

Text messaging on your radio system.

Quite an upgrade from CB.


Regards,

JD

I tried CTCSS years ago and had no luck with it. If the channel was quiet sometimes it would work but not dependable at all. Go with GMRS .

Thanks for the advice, you're probably right about the range being cut by the rx radio not being able to hear a sub-aud tone in the first place - and narrowbanding has put a lot of cheap surplus UHF stuff onto the eBay market for GMRS. If I find a box of cheap PL boards at a hamfest somewhere I might try it as an experiment, but with after everyone's input and some extra thought I'm glad I didn't sink anything into the idea yet.

EF Johnson and Regency and I think SBE used some selective calling option back in the 70's but I never got to play around with it.

73,
n9zas

And the real question is WHY? There are too many good alternatives than the HHHHHHEEEEELLLLLLLLLLLLLOOOOOO crappy bands.

Could be because, once in a blue moon someone comes along and figures out what it takes to make an old idea ( or crappy band) work better for them?

Selective calling in the right configuration can make that work.

73,
n9zas

Subaudible signaling on AM might not be legal because it would increase the bandwidth of the signal.

Back a LOOOOOG time ago, I tryed doing tone board on a couple CB's and found that 1) they have to be hard wired into the TX RX circuits on the main board, 2) when (if) they get installed, the TX RX audio
went to hell.

Had not effect on the radios power out or range.

Back in the late 60' early 70' there were a couple makes that also tryed this and do to being AM they phased them out real quick.

The FCC also got in the act as by adding these type of signalling did change the modulation type which were against the FCC rule.

As everyone else as sayed, get a GMRS, ham, or even a commerical license and you will be better off.

thanks

Good to know, thanks. I scrapped the idea and put together a simle GMRS repeater with a couple mobiles and a homebrew controller...narrowbanding sure has created a surplus of UHF gear for GMRS. Anyway, just waiting on the duplexer to arrive and that will be that.

Thanks for all the input.

Instead of trying PL on the CB, you can use DTMF selective switching.....

The Base station has a DTMF receiver/decoder on the RX audio output and the speaker is squelched closed until the proper DTMF signal is received and decoaded to open the squelch on the speaker of the base radio....Then, the mobiles you use have a DTMF encoder that with the push of a button, sent the DTMF code.

I saw this exact setup a few years back that a farms her for his home setup because his wife complained of the exact same thing, so this was his solution and I saw it and it worked pretty good. He had the DTMF encoader wired to him mic PTT, so each time he keyed up, the DTMF encoder would be sent out to open the base speaker....pretty nifty idea...He had one on him mobile in his pickup truck and one setup in his tractor

None of these 'tone' schemes are going to do away with the doubling and interference when your receiver is 'opened' by them. You just won't hear all the typical stuff when the receiver is not 'opened' by the tones. There's no 'magic' 'cure' for a congested band. And those 'tones' do not mean your conversation won't be heard by anyone else, that's a common misconception too.
The GMRS suggestion is one answer. Maybe not the 'cheapest', but still cheaper than the typical cell phone. But then, not nearly as reliable as a cell phone. Oh well...
- 'Doc

Until about ten years ago there was a courier firm in Portland that used DTMF squelch on single-sideband CB. Had a five or six-tone sequence at the beginning of each transmission and a single "end of transmission" tone burst at the end. You wouldn't hear the start code but you'd sometimes hear a couple milliseconds or so of the stop tone before the squelch closed.

I used to know somebody who worked for the company and he showed me the rig in his car. I don't remember the rig's brand or model, but it was a fully self-contained under-dash unit about the size of an external CD drive, including the DTMF receiver and BFO (likely implemented on a chip.)

So, although PL squelch probably wouldn't work on CB, DTMF/selcall might be worth looking into.

"But then, not nearly as reliable as a cell phone."

In fact, it's probably more reliable. Even with batteries and generators, telco switches and cell phone ground stations only have a finite service life during an extended power failure, and forget using your cell phone during a major disaster, as was learnt most recently during Sandy. Telephony 101.

I hate to be the gadfly here, but am ctcss simply doesn't work unless you can modulate the entire waveforme and detect it. Kaar corproration and Giannini Scientific that took over Hammerlund did try it with early AM business band I know of, but had to resort to a AM equivelent of 1/2 of a sideband and carrier processed through a "leaky" balanced modulator . It worked it a quiet channel with uhf early class A cb that could be either am or ssb and they also did it with vhf high and low, at least Kaar did.
Anyone claiming otherwise is suspect.

Now on the issue of sideband. This is an area that I do have expertise on selective calling. The problem is frequency stability. To achieve tone purity to lock withing a PLL capture range using the archaic 565 chip as reference, the stability would have to be 10-ppm or better. That can be achieved with all references ovenizied or using TCXO and would be common to marine or aviation where still at that level you would have issues with clarification and voice color. It's good enough for data though providing the capture range of the tone decoding is pretty broad. Necode used in marine and the Australian outback standards would appply as would many other systems based on narrow stability and using a data train. This wasn't reality with free running IF's and BFO's that were room temp in conversions unless the entire reference system was ovenized or TCXO's like today's GMDSS marine SSB units.Don't know a thing about current amateur.

Their was a work around for free running SSB systems that would work very well, but was very inexpensive to implement at least by the 90's. It was based on a two tone system and Bramco was the pioneer in this. This system worked on not the actual tones of the selective calling, but the difference of the two tones. Think about it. Even way off frequency, the two tones generated would still produce a preselected tone to decode. That was implemented in either a single recovered tone or a data train that an AFSK demodultor would decode. Very common in terrestrial 2-7mhz point to point systems in developing countries using unovenized crystals and single 9-10 mhz single conversion receivers. The most popular system was a pulse train sending a single ASCII character very slowly using two tones followed by a two tone dtmf system that the difference was decoded. The selcall units cost often as much as the units themselves. I worked on and integrated units used by Transworld, Stoner,Kachina, Bramco, and variations of that system as well as Necode and Loral telcom's octl9 bit systems. Motorola did a very poor attempt at using a reed based single tone system using a pilot carrier hence AM compatible for the selective call and went to tightly controlled FSK sytem with future systems that were totally frequency controlled by oven or TCXO.

AM systems tended to be single tone or DTMF. Single tone was the basis of the original attempt at CB's HELP plan and offered as an accessory with Regency, Lafayette, and Johnson systems that was really based on Motorola's early quick call system in the 60's. FWIW, these systems were called "ringers" during their day as were marine systems like Necode.

Necode's octal system was the first to display the unit calling you in a digit system rather then an all call system and also provided a return confirmation tone that was hotly contested by the FCC as unatteded operation. Motorola's early Micom and Nautilus systems were cited under the same issue.


Selective call under SSB and AM has always been a contentious issue with single tone being the standard for AM and was never reliable. Only Johnson perservered during the 70's using it that I know of after everyone else either never delivered the units like Lafayette. CTCSS took an act of god and specialized am generation to pull it off.

If your building a GMRS repeater, you could look into doing split tones (Motorola mobiles don't pass tone from RX to TX when used as a mobile based repeater) to keep people off. Not perfect but it's simple and easy to do.

You're making no sense here. Most repeaters couple the audio from the discriminator and strip the tone via a high pass network. The tone is regenerated at the transmitter. This isn't ham radio. You don't build repeaters legally for GMRS out of mobiles unless they are certified for base station stability at .0025%. It's either type accepted as a base station or repeater with appropriate stability then that of a mobile or control station at .005% last I recall. Mixed tones are easily circumvented since most programmable radios allow specification of any tone tx or rx, so you have no security there. You're better off using DPL that virtually any commercial transciever nowadays supports. GMRS supports either, but using something exotic such as MDCxxxx or any of the other digital protcols that are similar were not legal on GMRS besides 2 tone sequential and dtmf for paging and selective calling.