Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
[EMAIL PROTECTED] wrote: There is no 'reverse burst decoder' per se in a tone decoder - it is just driven with the out of phase energy long enough to cause it to close very quickly. All tone decoders react to the reverse burst, not just one that is specially configured to react to a reverse burst. I don't know of any special circuitry in a tone decoder that makes it more susceptible to a reverse burst than a normal tone decoder. 73 - Jim W5ZIT The cheaper decoders that don't have good 'talk-off' immunity will have a delay cap in the output to keep it open for a period of time no matter what. Some of them are so long that even 'chicken-burst' won't work. Even the early TS-32's were like that. Many newer 'decoders' are actually in software/firmware in the radio, and sense the phase inversion in S/W. In fact, many new radios do everything in S/W except the actual RF filtering and amplification. Feed the high-IF in one pin, get audio out another. -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
skipp025 wrote: I'm heading toward the question of is it better to reduce or remove (mute) the ctcss after the phase shift or just not worry about it?. As mentioned in one reply... there might be enough time for some fast decoders to re-lock on the inverted ctcss before the tx drops. 200 mS might not be much time but... is/does it possibly confuse some of the reverse burst ctcss decoders? It does vary quite a bit. I've seen some that close so fast that most radios will open it back up again, and others that close so slow that most radios go away before it closes. I think a good value to use would be 160-180 mS-my opinion... -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
At 1/19/2007 18:25, you wrote: Actually, the electronic CTCSS decoders react about the same as the old reeds. The physics of the matter causes the filters that can discern for instance - 100 Hz from 97 Hz or 103 Hz to be very narrow, and they ring - even when the driving tone is removed. By reversing the tone phase for a short period of time, the energy in the filter is driven to zero very quickly, and if the tone is removed from the decoder input at the right time, the tone decoder closes very quickly, and you get very short squelch bursts at the end of a transmission. I was never able to get a ComSpec TS-32 decoder to respond to reverse burst of any kind. Bob NO6B
Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
wa9zzu wrote: --- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: Re: Reverse Burst Comments (Com Spec RB-1) If you add a circuit like the Com Spec RB-1 board to the typical repeater system using a ts-32/ts-54 board... the tx ctcss is not disabled or removed before the RB-1 delayed ptt line drops. So you have the phase inverted ctcss present for at most up to 200 ms typical before the tx drop. If you don't remove the ctcss source the inverted ctcss remains up until the tx off/drop... Any of you actually running the RB-1 board with a true reverse burst type ctcss decoder (built into your radio)? Is a true reverse burst decoder in your commercial radio completely fooled by the phase inverted ctcss before carrier drop function. Or do you actually still hear some minor difference from the rb-1 type operation vs an original true Motorhead (Motorola) encoder - decoder operation? Thinking out-loud about having to possibly mute the ctcss at some time after invert and before the delayed ptt drop as a requirement to get the full/true reverse burst quiet squelch close. Any of you been down that road already? skipp Skipp, I find your comments interesting in that the purpose that Motorola had in using reverse burst of the PL tone was to quickly damp the mechanical reed in the PL decoder to close the squelch and eliminate the user from hearing the noise burst. But of course you knew that. However, in later model radios there is no mechanical vibrating reed to abruptly dampen and stop the vibrating from being detected. So where is the need for a inverted burst if there are no receivers using mechanical reeds as PL tone decoders? Incidently Motorola did not use an inverted reverse burst of 180 degrees. Their designs used 270 degrees since the PL reed then stopped vibrating faster and the amplitude of the burst was also increased to hasten the reed to stop. Don't modern day receivers use electronic circuitry to detect PL tones, and aren't the detectors not using a ringing decoder? If so isn't the purpose of having a reverse burst unnecessary? I can remember many years ago that some hams used a circuit which they refered to as polish PL which turned off the PL tone before the xmtr dropped and had no reverse burst. It seems like I'm hearing more of the same. Where am I going wrong here? Allan Crites The problem with just turning the tone off is that most all decoders take a MUCH longer time to just coast to a stop, rather then be told 'I'm about to go off the air, close now'. Digital squelch (CDCSS, or DPL in Motorola terms, DCG for GE folks) sends a short burst of 133hz tone for the same purpose-to let the decoder know that the transmission is over and to close. And everything I saw had Motorola's original R/B at 120 degrees, not 270. But as someone wise once said, I could be wrong. -- Jim Barbour WD8CHL
RE: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
Skipp, I find your comments interesting in that the purpose that Motorola had in using reverse burst of the PL tone was to quickly damp the mechanical reed in the PL decoder to close the squelch and eliminate the user from hearing the noise burst. But of course you knew that. However, in later model radios there is no mechanical vibrating reed to abruptly dampen and stop the vibrating from being detected. So where is the need for a inverted burst if there are no receivers using mechanical reeds as PL tone decoders? Because the software-based decoders respond the same way as a mechanical reed to the reverse burst. When the phase shift occurs, the correlation routines lose lock causing the processor to signal the audio gates to close. Eventually the software routine would regain lock at the new phase, but the transmitter drops before that can happen. Hardware-based designs that don't look for change of phase but rather just the presence or absence of tone are another story, but fortunately those aren't very common nowadays. Some of the early non-reed non-software decoders used what were basically very narrow bandpass filters followed by a detector. They could care less what the phase of the incoming tone was as long as the frequency was right - you always heard the squelch crash when the transmitter unkeyed. Chicken burst, or transmitting no PL before transmitter drop, was invented as a means of getting those types of decoders to mute before the transmitter dropped. I can remember many years ago that some hams used a circuit which they refered to as polish PL which turned off the PL tone before the xmtr dropped and had no reverse burst. Yeah, chicken burst, same thing. --- Jeff -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.410 / Virus Database: 268.17.0/639 - Release Date: 1/18/2007 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.410 / Virus Database: 268.17.0/639 - Release Date: 1/18/2007 Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * Your email settings: Individual Email | Traditional * To change settings online go to: http://groups.yahoo.com/group/Repeater-Builder/join (Yahoo! ID required) * To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
I played around with using the RB-1 board on my repeater transmitters using motorola and several other receivers in tone squelch. Eventually I found it was better to remove the capacitor which causes the RB-1 to send NO tone for the last 100ms (or what ever the timing is). --- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: SNIP Any of you actually running the RB-1 board with a true reverse burst type ctcss decoder (built into your radio)? Is a true reverse burst decoder in your commercial radio completely fooled by the phase inverted ctcss before carrier drop function. Or do you actually still hear some minor difference from the rb-1 type operation vs an original true Motorhead (Motorola) encoder - decoder operation? Thinking out-loud about having to possibly mute the ctcss at some time after invert and before the delayed ptt drop as a requirement to get the full/true reverse burst quiet squelch close. Any of you been down that road already?
Re: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1)
Actually, the electronic CTCSS decoders react about the same as the old reeds. The physics of the matter causes the filters that can discern for instance - 100 Hz from 97 Hz or 103 Hz to be very narrow, and they ring - even when the driving tone is removed. By reversing the tone phase for a short period of time, the energy in the filter is driven to zero very quickly, and if the tone is removed from the decoder input at the right time, the tone decoder closes very quickly, and you get very short squelch bursts at the end of a transmission. There is no 'reverse burst decoder' per se in a tone decoder - it is just driven with the out of phase energy long enough to cause it to close very quickly. All tone decoders react to the reverse burst, not just one that is specially configured to react to a reverse burst. I don't know of any special circuitry in a tone decoder that makes it more susceptible to a reverse burst than a normal tone decoder. 73 - Jim W5ZIT -Original Message- From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Fri, 19 Jan 2007 2:27 PM Subject: [Repeater-Builder] Re: Reverse Burst Comments (Com Spec RB-1) --- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: Re: Reverse Burst Comments (Com Spec RB-1) If you add a circuit like the Com Spec RB-1 board to the typical repeater system using a ts-32/ts-54 board... the tx ctcss is not disabled or removed before the RB-1 delayed ptt line drops. So you have the phase inverted ctcss present for at most up to 200 ms typical before the tx drop. If you don't remove the ctcss source the inverted ctcss remains up until the tx off/drop... Any of you actually running the RB-1 board with a true reverse burst type ctcss decoder (built into your radio)? Is a true reverse burst decoder in your commercial radio completely fooled by the phase inverted ctcss before carrier drop function. Or do you actually still hear some minor difference from the rb-1 type operation vs an original true Motorhead (Motorola) encoder - decoder operation? Thinking out-loud about having to possibly mute the ctcss at some time after invert and before the delayed ptt drop as a requirement to get the full/true reverse burst quiet squelch close. Any of you been down that road already? skipp Skipp, I find your comments interesting in that the purpose that Motorola had in using reverse burst of the PL tone was to quickly damp the mechanical reed in the PL decoder to close the squelch and eliminate the user from hearing the noise burst. But of course you knew that. However, in later model radios there is no mechanical vibrating reed to abruptly dampen and stop the vibrating from being detected. So where is the need for a inverted burst if there are no receivers using mechanical reeds as PL tone decoders? Incidently Motorola did not use an inverted reverse burst of 180 degrees. Their designs used 270 degrees since the PL reed then stopped vibrating faster and the amplitude of the burst was also increased to hasten the reed to stop. Don't modern day receivers use electronic circuitry to detect PL tones, and aren't the detectors not using a ringing decoder? If so isn't the purpose of having a reverse burst unnecessary? I can remember many years ago that some hams used a circuit which they refered to as polish PL which turned off the PL tone before the xmtr dropped and had no reverse burst. It seems like I'm hearing more of the same. Where am I going wrong here? Allan Crites Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.
