Using CTCSS or DCS to filter traffic

[VK3TKO]

G'day people, newbie here.I need help on the use of repeaters. My situation: I live in central Victoria and chat with my brothr in northern Victoria, sometimes via HF and sometimes via VHF. With VHF we make contact via the Mt.Alexander repeater which uses tone access, 91.5 Hz.
My brother's in the habit of leaving his radio (we each have TYT TH-9800 quad band receivers) on all day to pick up when I call. However often there's too much traffic and it can be distracting. I'd like to use CTCSS so he can filter out that traffic. Then the only transmission he'll hear will be that from me.
My questions:
When I transmit on the repeaters uplink my TYT transmits a 91.5 Hz tone to cause the repeater to pass my audio to its transmitter. Does the repeater also pass my 91.5 tone to its transmitter?
If the answer to the preceding is yes, then when my brother's transceiver is set to use the Mt.Alex repeater does it block reception of signals lacking this tone? Or does it receive all, such as nearby simplex traffic?
Can I transmit a DCS with my tone and have my brother set his radio to filter out transmissions that lack this DCS? The idea is to limit his reception to my transmissions and not all Mt.Alex traffic.
Sorry for the long post but I'm new to this. I may be asking too much of the repeater. Things were simpler back in simplex days.
regards, Rob

[VK4ADC]

Rob

DCS tones should pass through any repeater BUT you need to also transmit the 91.5 access tone to activate the repeater itself. Most repeaters require the control tone to open but do not re-transmit them.

It may seem a bit complicated but if your existing radio does not allow concurrent transmission of both signalling methods (however unlikely) then a work-around might be to..
(1) use an external 91.5 CTCSS module and inject that into your audio and set up the radio for DCS; 
(2) transmit 91.5 plus a much higher CTCSS control tone that your brother's radio can decode on. The issue with #2 is that the repeater's receive audio bandpass may filter out the whole of the CTCSS tone range so it will not be re-transmitted. You wouldn't know until you tried it.

At this point you probably need to read your user manual to see what your radio can do : CTCSS, DCS or CTCSS plus DCS..

One point you need to consider : the repeater is an open use facility and the LCD/Regs say you must listen before you transmit so as to avoid interference to other repeater users.  If you use DCS for squelch control 100% of the time then you won't hear other users and that is a big issue.  You may become a significant target for the repeater owners.

73 Doug VK4ADC

[VK3TKO]

Thanks Doug. That's a very nice way of advising me to read the manual first. Good suggestion. You've also clarified my understanding of how a repeater works. Your point about transmitting over others is important. I expect to use my radio's monitor function before each call to open its audio to non-coded transmissions.
Time to hit the books.
Rob

[VK4ADC]

Another thought rumbling around in the brain box : your radio may be able to send DTMF tones plus the CTCSS, maybe 5 tone sequential, but does it have any DTMF or 5-tone decode option ? Unlikely, but possible.

[VK3TKO]

My radio does permit transmission of DTMF tones, two and five tone DTMF but you've lost me. What would the DTMF do? The radio documentation shows I can send CTCSS Encode and CTCSS Encode/Decode. I can also send DCS Encode/Decode in conjunction with CTCSS so I'll try that.
If I and my brother set our radios for CTCSS encode and decode then they will only pass to audio those signals containing the repeater's CTCSS tone. However the repeater includes the CTCSS tone in all transmissions to that will do nothing to reduce audible traffic. It looks DCS is the most promising solution.
regards,
Rob

[VK4ADC]

Rob

The 'I can also send DCS Encode/Decode in conjunction with CTCSS so I'll try that.' has me in doubt a bit. Can you actually set that up - have you tried it ??

As I mentioned previously, you will need continuous 91.5 Hz CTCSS to open the repeater and keep it open and then you would need to see how faithfully DCS would pass through the repeater and that DCS is set to open the remote receiver (not CTCSS). My recollection is that DCS signals are basically square wave in shape and may not go through without distortion. Trial and error.

Transmitting the 91.5 plus one other CTCSS tone is probably the best possibility, the 91.5 opens the repeater and the second tone is what the other transceiver CTCSS decode is set to. CTCSS encoders are small these days too.  Pick a high-ish CTCSS tone (near 250 Hz) as that is more likely to pass through the repeater receiver/transmitter combination.

The DTMF or 5-tone option would need an extra suitable decoder if the radio itself did not provide that function internally. It was just an idea floating round the brain at the time as I am sure that tones in that range would transit the repeater.

Older radios destined for Europe (plus others) had a 1750Hz tone generator in lieu of CTCSS but I think the idea has been dropped in more recent models. Of course you would need to decode that tone at the far end.

Probably time for you to 'think outside the box' as this is not a problem normally presented to the amateur fraternity : everyone listens to everything. 

No simple answers, but some experimentation may provide one.

73 Doug

[VK3TKO]

I've tried transmitting CTCSS in conjunction with DCS Doug but no go, you were right. Setting one on the radio results in the other dropping out. Another possibility: I've just learned that the Mt.Alexander repeater VK3RCV needs no CTCSS after all. I had been working from obsolete documentation. I don't know when it was changed. In that case I can include a tone in my transmissions and set my transceiver to ENC/DEC, i.e. to require the same code to pass received signals to the audio. As long as I keep an eye on the radio's display to ensure I don't barge into a conversatiton my brother and I can use the frequency in silence.
Do you see any hitch in that arrangement? I haven't tried it yet. My brother is currently on the road, broken down north of Dookie and I can't reach the Shep repeater from where I am. Thanks for your time.
Rob

The 'I can also send DCS Encode/Decode in conjunction with CTCSS so I'll try that.' has me in doubt a bit. Can you actually set that up - have you tried it ??

As I mentioned previously, you will need continuous 91.5 Hz CTCSS to open the repeater and keep it open and then you would need to see how faithfully DCS would pass through the repeater and that DCS is set to open the remote receiver (not CTCSS). My recollection is that DCS signals are basically square wave in shape and may not go through without distortion. Trial and error.

Transmitting the 91.5 plus one other CTCSS tone is probably the best possibility, the 91.5 opens the repeater and the second tone is what the other transceiver CTCSS decode is set to. CTCSS encoders are small these days too.  Pick a high-ish CTCSS tone (near 250 Hz) as that is more likely to pass through the repeater receiver/transmitter combination.

The DTMF or 5-tone option would need an extra suitable decoder if the radio itself did not provide that function internally. It was just an idea floating round the brain at the time as I am sure that tones in that range would transit the repeater.

Older radios destined for Europe (plus others) had a 1750Hz tone generator in lieu of CTCSS but I think the idea has been dropped in more recent models. Of course you would need to decode that tone at the far end.

Probably time for you to 'think outside the box' as this is not a problem normally presented to the amateur fraternity : everyone listens to everything. 

No simple answers, but some experimentation may provide one.

73 Doug

---

I've tried transmitting CTCSS in conjunction with DCS Doug but no go, you were right. Setting one on the radio results in the other dropping out. Another possibility: I've just learned that the Mt.Alexander repeater VK3RCV needs no CTCSS after all. I had been working from obsolete documentation. I don't know when it was changed. In that case I can include a tone in my transmissions and set my transceiver to ENC/DEC, i.e. to require the same code to pass received signals to the audio. As long as I keep an eye on the radio's display to ensure I don't barge into a conversatiton my brother and I can use the frequency in silence.
Do you see any hitch in that arrangement? I haven't tried it yet. My brother is currently on the road, broken down north of Dookie and I can't reach the Shep repeater from where I am. Thanks for your time. Rob

[VK4ADC]

The telling info " I've just learned that the Mt.Alexander repeater VK3RCV needs no CTCSS after all. I had been working from obsolete documentation. I don't know when it was changed. In that case I can include a tone in my transmissions and set my transceiver to ENC/DEC, i.e. to require the same code to pass received signals to the audio. As long as I keep an eye on the radio's display to ensure I don't barge into a conversatiton my brother and I can use the frequency in silence. "

The fact that the repeater is straight carrier-operated makes it possible to do either CTCSS or DCS, but you may need to pick a high CTCSS tone to make sure it transits the repeater without severe attenuation. Some commercial repeaters have a highpass audio filter to chop out frequencies below about 300Hz to stop control CTCSS tones going through, and depend on re-generation from a CTCSS encoder for outgoing tones - when required. The choice of a high tone should solve that one, if applicable.
I haven't tried DCS through a repeater but it might work for you. Try both options.

When you have it solved, make sure you re-post here so that others can benefit from your findings.

73 Doug

[VK3TKO]

That all makes sense Doug. As always, I'll try it and report back.
regards, Rob