Another ham and I have been experimenting with Hear-Clear (HC) on our GTX and MaxTrac radios. We're working through a repeater that does NOT have HC.
So far, our experience has been interesting. The noise and crackles due to weak signals into the repeater are just about gone. Either you're in and solid, or you're out and gone entirely. Signal fade from the repeater output seems to be reduced quite a bit too. The recovered audio (with HC on at both ends) sounds much softer than when HC is off, but it has a telephone-like quality, with very little outside interference or noise, almost like you're having a private conversation. The voice seems quite natural after listening to it for a while. Not quite as wide-band as I'm used to, but then a lot of the high-frequency noise is reduced or missing.
When one of the radios is not using HC, the results are hard to explain. I found that the compression/expansion can be quite noticeable, almost like speech processing on HF, and HC transmissions, when heard on a non-HC receiver, seem to lose the softer components of the speech, so the voice peaks really get accentuated.
I'd be interested in hearing about anyone else's experiences and comments regarding Hear-Clear. Do you think we should activate it (if possible) on the repeater, or will it work quite nicely on a machine with relatively flat response and unity audio gain? Unfortunately, the local 900 repeater was not built with HC in mind, so it may not be very easy to implement.
Thanks.
Bob M.
Any experiences with Hear-Clear on 900 MHz
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CTAMontrose
- was grem467
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Well, we're using it now. My experience with it is just as Bob said... It is definatly an improvement. I have this horrible ignition noise on my truck and it was rendering my GTX's receiver almost useless. With the Hear Clear in use now, it is clear as day. Everyone on the repeater has a Motorola radio so it hasn't been a problem yet.
"I'll eat you like a plate of bacon and eggs in the morning. "
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
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EOppegaard
- Posts: 287
- Joined: Mon Nov 24, 2003 9:07 pm
both matt and I are onthe same repeater. It is an awesome improvement, gets rid of any background "hiss" that is there. Using a GTX mobile as a control station.
Eric Oppegaard
Where's Oppie?
Where's Oppie?
Hearclear is a combination of two techniques to improve audio quality by decreasing the effects of Rayleigh fading and by compensating for the narrow channel bandwidth.
The narrow bandwidth is compensated by companding which lowers the noise floor and expands dynamic range by 1:2 on a logorithmic scale.
Rayleigh fading causes rapid drops in signal strength. This effect is more pronounced at higher frequencies such as 900 MHz due to the shorter wavelength. The second part of Hearclear - "Flutter Fighter" - uses RSSI to dynamically reduce receive gain during fades to minimize the audible effect of the noise bursts.
Bench testing doesn't show off the Flutter Fighter part of Hearclear - so if you really want to evaluate it - try it in the field.
Other brands of radios may have companding but not Flutter-Fighter so even though they may be 'compatible' the Motorola technology may sound better.
The narrow bandwidth is compensated by companding which lowers the noise floor and expands dynamic range by 1:2 on a logorithmic scale.
Rayleigh fading causes rapid drops in signal strength. This effect is more pronounced at higher frequencies such as 900 MHz due to the shorter wavelength. The second part of Hearclear - "Flutter Fighter" - uses RSSI to dynamically reduce receive gain during fades to minimize the audible effect of the noise bursts.
Bench testing doesn't show off the Flutter Fighter part of Hearclear - so if you really want to evaluate it - try it in the field.
Other brands of radios may have companding but not Flutter-Fighter so even though they may be 'compatible' the Motorola technology may sound better.
Thanks XMO. I have run some audio tests between radios and graphed the compression and expansion, but as you noted, the flutter-fighter is not something that can be easily synthesized or tested on the bench. Even with non-mobiles, there's still picket-fencing going on, and hear-clear does seem to get rid of just about all of it. Signals are either there and full quieting, or gone entirely.
Bob M.
Bob M.
NoiseCom and TAS have manufactured Rayleigh fading simulators that can be used in the lab to evaluate a radio's performance in a simulated real world environment.
Someone had one listed on ebay a while back for around a grand. As much of a test equipment nut as I am - I passed on that. Other than playing with it - I couldn't see that I could DO anything with it.
Still - it would be interesting to experiment....
Someone had one listed on ebay a while back for around a grand. As much of a test equipment nut as I am - I passed on that. Other than playing with it - I couldn't see that I could DO anything with it.
Still - it would be interesting to experiment....
Odd sounding rx audio on 900 Mhz
I just started using a GTX mobile and a GTX handi talkie on 900. The local repeaters are running hear clear and I have the radios programmed with hear clear turned on. The audio quality in the receiver is very odd. I can only explain it as "mushy" almost as if there is some kind of AGC with a slow attack / decay time. For example when the repeater identifies, rather than a crisp sounding sine wave "beep" quality it sounds kinda like "bweep bweep" as if the amplitude is increasing as the next beep starts up. I thought it was a problem with my radio, maybe in the audio amp until I listened on multiple radios and to different repeaters all which exhibited the same odd sound.
Is this typical hear clear, the GTX radios, or am I nutz!
George
KJ6VU
Is this typical hear clear, the GTX radios, or am I nutz!
George
KJ6VU
Yes, certain things do sound odd at times. You are not nuts !
Our local repeater is NOT running hear-clear, but all the users are, a combination of GTXs, MaxTracs, and Spectras. The repeater is setup for equal audio in/out and uses a wide-band receiver. The locally-generated CWID does sound mushy and like an AGC circuit is detecting the tone near the end. This is how it sounds on my hear-clear receivers. I think this is normal. Repeated audio using hear-clear enabled radios, however, sounds great.
Hear-Clear does some compression at the transmitter end, and expansion at the receiver end. It also tries to eliminate a lot of hiss, pops, and crackles. The difference is truly amazing. Signals can be very noisy without hear-clear, but completely noise-free and usable with it. You're either there and full-quieting, or not there at all, and it does try to keep you there as long as possible.
You may want to see if the repeater operators would try disabling hear-clear, and see if it still sounds OK. It does mean that every user would need hear-clear activated to benefit from the system, but this could be how it's done elsewhere as well. Users without hear-clear can still use the repeater. Their audio will sound different but not bad enough to complain about.
Bob M.
Our local repeater is NOT running hear-clear, but all the users are, a combination of GTXs, MaxTracs, and Spectras. The repeater is setup for equal audio in/out and uses a wide-band receiver. The locally-generated CWID does sound mushy and like an AGC circuit is detecting the tone near the end. This is how it sounds on my hear-clear receivers. I think this is normal. Repeated audio using hear-clear enabled radios, however, sounds great.
Hear-Clear does some compression at the transmitter end, and expansion at the receiver end. It also tries to eliminate a lot of hiss, pops, and crackles. The difference is truly amazing. Signals can be very noisy without hear-clear, but completely noise-free and usable with it. You're either there and full-quieting, or not there at all, and it does try to keep you there as long as possible.
You may want to see if the repeater operators would try disabling hear-clear, and see if it still sounds OK. It does mean that every user would need hear-clear activated to benefit from the system, but this could be how it's done elsewhere as well. Users without hear-clear can still use the repeater. Their audio will sound different but not bad enough to complain about.
Bob M.
I am visiting the Boston area this week and I brought my GTX portable. Yesterday, a friend keyed up the local repeater with his MTX9000 with hearclear turned OFF and I keyed it up with my GTX with hearclear turned ON. I could hear the mushy "bweepy" CWID sound from the repeater on my GTX on the local repeater while the '2000 HT with no hearclear had crisp, clear "beep" like CWID quality.
The radio without hearclear sounded much better with better frequency response but in fringe coverage areas, there was alot more squelch noise like you would expect in a normal HT. The GTX with hearclear made the repeater sound more "solid" and there were much fewer snap, crackle, pop sounds.
Bottom line: Hear clear does a great job getting rid of annoying noise in fringe reception areas at the expense of crisp audio fidelity. Like most things in life, its a tradeoff.
for me, If I am in an area where the repeaters are strong, I would opt to turn hear clear off.
George
KJ6VU
The radio without hearclear sounded much better with better frequency response but in fringe coverage areas, there was alot more squelch noise like you would expect in a normal HT. The GTX with hearclear made the repeater sound more "solid" and there were much fewer snap, crackle, pop sounds.
Bottom line: Hear clear does a great job getting rid of annoying noise in fringe reception areas at the expense of crisp audio fidelity. Like most things in life, its a tradeoff.
for me, If I am in an area where the repeaters are strong, I would opt to turn hear clear off.
George
KJ6VU
I agree, but I don't really care if the CWID sounds good, bad, or not at all. Most of the people using our repeater are either mobile or handheld, and noise, pops, and flutter just go with the territory. Hear-clear does get rid of 99% of it, and people sound just great. I will admit that the audio on a non-hear-clear receiver sounds crispier, but then all the noises come through even louder.
Once you get used to it, either way works well.
Bob M.
Once you get used to it, either way works well.
Bob M.