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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Loren Aguey on May 12, 2011, 11:40:29 am

Title: HME Pro 850 Wireless Com-Howling Issues
Post by: Loren Aguey on May 12, 2011, 11:40:29 am
This unit is among the nicer wireless com units I've used. Highly configurable and sound quality is very clear, and properly configured the range is very good.

I'm on a show right now and every once in a while someone on wireless will go to talk and there's a high pitched howling, almost oscillating sound that is transmitted through all the wireless and RTS in the chain. It doesn't quite sound like normal feedback its more electronic sounding. Its not the normal sound of RF interference I've heard in the past.

This is one of the smaller rooms on the MS campus and we've had normal RF interference issues in the past with our other HME system UHF system 800, which is fixed frequencies in the 400 range.

This is a rental unit so I'm going to call them on my next break just wondering if anyone has any thoughts on this.

Thanks.


Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Henry Cohen on May 12, 2011, 10:31:26 pm
Is it only one or two beltpacks causing the problem or is it random beltpacks? Where is the offending beltpack when the noise occurs?

Are the beltpacks set to PTT or PTTx?
Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Mac Kerr on May 12, 2011, 11:03:07 pm
Also, what kind of headsets are used with the HME packs? It might be mechanical, or electrical feedback in the headset.
Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Loren Aguey on May 13, 2011, 08:20:26 pm
Is it only one or two beltpacks causing the problem or is it random beltpacks? Where is the offending beltpack when the noise occurs?

Are the beltpacks set to PTT or PTTx?


Well I though it was one of the beltpacks but after it was swapped it happened again a couple more times throughout the day. It always happened within 10-15 ft of the base station.

And I'm not familiar with the setting PTTx. After a quick check in the manual I didn't see anything about it. This was something I didn't have to configure but there was no function to lock the push to talk button if that's by what you're asking.

Also, what kind of headsets are used with the HME packs? It might be mechanical, or electrical feedback in the headset.

I'm not sure the exact model but they were lightweight headsets similar to these.

http://www.rftechnostore.com/php/proddetail.php?prod=RF6

It did kind of sound like that. Any way to determine in the future if that's what it was? We don't own these it was a rental but I imagine I'll come across them again.

Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Henry Cohen on May 13, 2011, 09:47:56 pm

Well I though it was one of the beltpacks but after it was swapped it happened again a couple more times throughout the day. It always happened within 10-15 ft of the base station.
Sounds like the beltpacks are in high power (100mW) and  saturates the front end of the base RX when too close. The RF overload of the demodulator caused enough bleed resulting in the squelch opening. This was one of the issues with the first generation of Pro850, since resolved. Set the beltpacks to AUTO (if not already) and reposition the antennas [higher] so it's not likely a pack will get close enough to trigger the problem.

Quote
And I'm not familiar with the setting PTTx. After a quick check in the manual I didn't see anything about it. This was something I didn't have to configure but there was no function to lock the push to talk button if that's by what you're asking.
PTT = Push To Talk, meaning the pack's transmitter is always on, the talk button merely opens the audio circuit.

PTTx = Push To Transmit [and talk]. Transmitter is off until the button is pushed.

Quote
I'm not sure the exact model but they were lightweight headsets similar to these.

http://www.rftechnostore.com/php/proddetail.php?prod=RF6
Interesting you would point to a headset supplier in a different industry, as opposed to referencing an example from a pro audio supplier or manufacturer.
Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Loren Aguey on May 14, 2011, 10:55:15 pm

Well I though it was one of the beltpacks but after it was swapped it happened again a couple more times throughout the day. It always happened within 10-15 ft of the base station.
Sounds like the beltpacks are in high power (100mW) and  saturates the front end of the base RX when too close. The RF overload of the demodulator caused enough bleed resulting in the squelch opening. This was one of the issues with the first generation of Pro850, since resolved. Set the beltpacks to AUTO (if not already) and reposition the antennas [higher] so it's not likely a pack will get close enough to trigger the problem.

Quote
And I'm not familiar with the setting PTTx. After a quick check in the manual I didn't see anything about it. This was something I didn't have to configure but there was no function to lock the push to talk button if that's by what you're asking.
PTT = Push To Talk, meaning the pack's transmitter is always on, the talk button merely opens the audio circuit.

PTTx = Push To Transmit [and talk]. Transmitter is off until the button is pushed.

Quote
I'm not sure the exact model but they were lightweight headsets similar to these.

http://www.rftechnostore.com/php/proddetail.php?prod=RF6
Interesting you would point to a headset supplier in a different industry, as opposed to referencing an example from a pro audio supplier or manufacturer.

Thanks for the help Henry I'll definitely look into those settings next time. For this situation would you recommend PTT or PTTx?

As for the headset I linked, I didn't even notice they were drive through headsets I just googled hme headsets real quick picked those because they looked closest to the ones we rented.

Title: Re: HME Pro 850 Wireless Com-Howling Issues
Post by: Henry Cohen on May 15, 2011, 07:42:22 pm
Thanks for the help Henry I'll definitely look into those settings next time. For this situation would you recommend PTT or PTTx?

PTTx is recommended for most situations except with those users who are too impatient to wait the split second for the transmitter to fully key up, or who really do need to talk instantly (life-safety).
Title: Re: PTTx
Post by: Mac Kerr on May 15, 2011, 08:01:51 pm
PTTx is recommended for most situations except with those users who are too impatient to wait the split second for the transmitter to fully key up, or who really do need to talk instantly (life-safety).

If I am wrong here maybe Henry will correct me, but I think there are two advantages to PTTx vs PTT. The first and most obvious is the increased battery life in the portable packs when they are not transmitting all the time. The second is that it creates a binary condition for the channel squelch. Rather than have a slowly weakening signal try to hold the squelch open as a user goes out of range, that channel is already fully squelched. This avoids some of the "swishing" interference we have all experienced. If the user tries to talk from out of range, either it will not work, or there may be some of the weak signal artifacts, but they will only happen while hey are trying to transmit, not the whole time the are borderline out of range.

Mac
Title: Re: PTTx
Post by: Henry Cohen on May 16, 2011, 12:09:09 pm
If I am wrong here maybe Henry will correct me, but I think there are two advantages to PTTx vs PTT. The first and most obvious is the increased battery life in the portable packs when they are not transmitting all the time. The second is that it creates a binary condition for the channel squelch. Rather than have a slowly weakening signal try to hold the squelch open as a user goes out of range, that channel is already fully squelched. This avoids some of the "swishing" interference we have all experienced. If the user tries to talk from out of range, either it will not work, or there may be some of the weak signal artifacts, but they will only happen while hey are trying to transmit, not the whole time the are borderline out of range.
Mac is correct on both counts. And of course the less active transmitters running around, the quieter the RF noise floor, which in turn means greater range and less chance of RF saturation of various RF gain stages.

BTW, the corporate I'm doing now is a good example. Out of 20 BTR beltpacks, only two are on constant transmit (PTTx); one is for the SM who has to make a some automation (safety) calls and the other is for the AD who's simply not able to 'push, pause, talk'.
Title: Re: PTTx
Post by: Loren Aguey on May 16, 2011, 06:38:39 pm
Mac is correct on both counts. And of course the less active transmitters running around, the quieter the RF noise floor, which in turn means greater range and less chance of RF saturation of various RF gain stages.

BTW, the corporate I'm doing now is a good example. Out of 20 BTR beltpacks, only two are on constant transmit (PTTx); one is for the SM who has to make a some automation (safety) calls and the other is for the AD who's simply not able to 'push, pause, talk'.

Thats great info thanks guys. I never considered the battery life aspect of that. I wonder if that was why when we had to rent the Tempest900 they absolutely devoured the batteries in very little time. Either that or maybe some high power tx boost setting or something I didn't have time to troubleshoot it.

Anyway, now I know a couple more things to look out for. Thanks again.