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HF/MW/LW General Discussion General discussion on monitoring the HF (High Frequency), MW (Medium Wave), and LW (Long Wave) spectrum (0.5 - 30 MHz)

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  #21 (permalink)  
Old 01-22-2006, 8:26 PM
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Lets just add modat or MDC1200 for 11mtrs
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  #22 (permalink)  
Old 01-23-2006, 12:18 AM
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Hi good buddies,

I'm going to derail one train of thought right now, you can't use PL on a CB rig without modding out the audio section. The passband is limited to 300-3000Hz and simply won't pass the tone. The mod is perfectly legal though, you're not going to touch anything affecting modulation percentage, frequency or power output which would void FCC certification (formerly type acceptance). The HUGE drawbacks are in the very nature of CB, there's no such thing as a "private" channel so you're likely to step on someone without provisions to disable the PL and monitor before transmitting which further complicates things. Being AM or SSB inherent noise would undoubtedly mask the PL tone since it's transmitted at 20% modulation with voice at 80% meaning you'd have pretty miserable voice audio too. That's why PL is only used with FM to begin with and FM is illegal on CB in the US. Even at 100% modulation CBers who are awfully fond of "power mics" always say you have low audio while thier overmodulated distortion gives you ear bleed.

It's much easier to add in (audio) band signalling which was common on some Polytronics (Poly Call), E.F. Johnson (Selectacall), Lafayette (?) and other CBs in the late 60s. In theory at least all you need is a tone oscillator to inject a tone burst into the transmit audio and a highly selective tuned circuit tap in the receive to send the tone to a control circuit that un-mutes the receive and activates an optional alarm. L-C tuned circuits were used but now an op-amp with an R-C feedback circuit will provide the needed selectivity. Any design engineers out there?

Since false activation can occur with just the right heterodyne and CB being what it is I suggest a more appropriate radio system. It's interesting to note that when the number of legitimate users outweighed the hobby banders there were actually channels you could set up on and expect little interference. When the trend became a hobby oriented chit-chat band the 23 channels became crowded and drove legitimate users off the band, selective calling was discontinued as an unprofitable accessory, no market for it. The CB history lesson ends here and the 40 channel era begins...
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Old 01-23-2006, 8:44 AM
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Very well put Warren,thank you.
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Old 01-23-2006, 7:11 PM
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Default Interesting how a simple question can get out of hand..

Yes it legal to operate ctcss on 11 on CB. It's in part 95. That being said, before making a call, one should always check the channel by deactivating the decode to make sure the channel is clear before calling. I know... who's going to do that today? Back in the days when you had to pay $20 for your licence and when personal and businesses used CB, it was (& still is) a good thing to have so that your rig wouldn't be sqawking all the time.

It's not encrypting the audio at all.

Anyway, I've found tone boards in the AES catalog; forgot to bring it home; will get back on that.
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Old 01-24-2006, 4:44 AM
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Default Here's what I found:

from Norcom:
nc-101 encoder $21.99
nc-104 " $26.99
nc-106 encoder/decoder $62.99
nc-401 encoder $62.99

From communcation specialists:
ss-64 encoder $28.99
ts-64ds encoder/decoder $57.99
te-32 encoder $49.99

All except the te-32 are boards that can be installed inside the radio. The te-32 is an external box.

Only a qulified tech can legally install a board on a cb!
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Old 01-24-2006, 2:13 PM
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Interested parties may want to check out something called "SELCAL" for ideas on a simple system used on aircraft HF systems. Uses audible DTMF type tones and a simple decoder. The receiving end has a pre-defined code setup; the audio is fed into the device and it emits a sound and visual indication when the proper tone is received.

Long story short, no mods required to the radio. The sender needs a way to input DTMF tones though. Anybody savvy enough with electronics could whip up the decoder end and run the radio's audio through it. Worth all the work for CB? Not in my opinion, but I would admire anybody who loves radio and electronics enough to try it.
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Old 01-28-2006, 6:44 PM
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Hi again,

I do believe I wrote "The mod is perfectly legal though..." but what you missed was "Being AM or SSB inherent noise would undoubtedly mask the PL tone since it's transmitted at 20% modulation with voice at 80% meaning you'd have pretty miserable voice audio too." Maybe it was "That's why PL is only used with FM to begin with and FM is illegal on CB in the US." that confused you. I don't understand why all the convoluted gyrations when it's totally impractical.

"Interested parties may want to check out something called "SELCAL" for ideas on a simple system used on aircraft HF systems."
That's an acronym for selective calling and we already went through that too. Still it's a lot of trouble and needless expense for a lousy CB rig. Putting a DTMF mic on it is the easy part, the decoder isn't all that hard either, the technical part is simple but due to the nature of the beast it becomes a logistical nightmare.

Like I said, if you're going to go through all that you may as well opt for a proper radio system and avoid all the headaches. CB is too far gone for any serious communicating, you can't turn back the clock to 1965 and even then serious users found it was unsuitable because HF and VHF are different as night and day. It's a long story but in a nut shell the FCC considering it "equivelent spectrum replacement" when class A CB was reallocated to public service was one of the biggest mistakes they ever made, class D never panned out.

If you think I preach doom and gloom now, just wait a few years and once again all you'll hear is "skipland" wrapping the needle around the stop. This was the equivelent of UHF? I hardly think so!
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  #28 (permalink)  
Old 01-31-2006, 10:39 PM
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I know it's a lot of trouble, we were just wondering if we could do it. I'm not really as interested in PL tones. I'd just like a two-tone sound that I could play to activate different radios. I dont want to mute everyone else out, I just dont want to have to hear everyone talking all the time. All of my friends live close together, so our signals will override all of the others.
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Old 02-02-2006, 12:05 AM
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Hi again CSL and all,

Oh yeah it can be done, just not worth it is all.

"I dont want to mute everyone else out, I just dont want to have to hear everyone talking all the time."
HUH? If you don't want to hear everyone else talking you HAVE to mute them out. (;->)

"All of my friends live close together, so our signals will override all of the others."
Yup, crank the squelch to the max and stomp on 'em, that's CB for ya.

Now I'm wondering why you asked in the first place.
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Old 03-25-2006, 8:15 AM
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Quote:
Originally Posted by Joseph11
HillbillyUHF: You quoted the post that CSL126 wrote about adding a CTCSS Encoder/Decoder box. When you quote a post, you're supposed to be replying or talking about that post. You, sir, are trying to stir things up.
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Old 04-03-2006, 5:45 PM
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Some of the others are right, PL won't work with AM modulation. I believe that's why they have never offered it.
I can vouch for the old Lafayette system. I had a system set up years ago and those tones would get through and open the speaker when voice was too far down in the noise to hear.
It worked very well. It was a "two tone simultanious" format that prevented false tripping.

Later.....
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