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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 => Wireless and Communications => Topic started by: Pete Erskine on September 02, 2015, 09:35:01 pm

Title: RF coordination simultaneous example using IAS and Workbench
Post by: Pete Erskine on September 02, 2015, 09:35:01 pm
Here is an expansion on my videos about IAS and WB. 
It is divided into 2 - 12 minute videos.

Part 1 (https://youtu.be/-BmBRX70O68)

Part 2 (https://youtu.be/kzGP4KWLpA4)
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Neil White on September 03, 2015, 09:56:18 am
Here is an expansion on my videos about IAS and WB. 

Hi Pete,

Thanks for the detailed videos. I think the most interesting thing is the noticeable difference in the equipment profiles between the two pieces of software. The WWB6 profiles seem to be more conservative than the IAS ones. Are these settings something that can be calculated from an equipment's spec sheet?

Neil
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Pete Erskine on September 03, 2015, 10:13:30 am
Hi Pete,

Thanks for the detailed videos. I think the most interesting thing is the noticeable difference in the equipment profiles between the two pieces of software. The WWB6 profiles seem to be more conservative than the IAS ones. Are these settings something that can be calculated from an equipment's spec sheet?

Neil

NO, these are arbitrary settings set by the software designer.  Not much to do with eq specs.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Jens Palm Bacher on September 04, 2015, 02:43:30 am
NO, these are arbitrary settings set by the software designer.  Not much to do with eq specs.
Well you could if the specs showed the intermodulation attenuation  etc. It is clear that a Sennheiser 5212 transitter in "low intermod" mode will have better specs than a cheap Shure unit, but it is not easy to read from the spec sheet.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: peter dakin on September 05, 2015, 07:08:38 am
great videos Pete.

Can I ask what device your using for scans, does this pump out a file format compatible with WW6 or do you need to convert it?


Cheers
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Henry Cohen on September 05, 2015, 08:12:24 pm
Well you could if the specs showed the intermodulation attenuation  etc. It is clear that a Sennheiser 5212 transitter in "low intermod" mode will have better specs than a cheap Shure unit, but it is not easy to read from the spec sheet.

Whereas it would be nice to know the IM suppression number, it's really kind of irrelevant: Whereas one device (the transmitter) may not be producing the IM product, another device might be; the preamp in the antenna, the multi-coupler or the receiver front end. The IM software programs are merely pointing out the math of potentially problematic frequencies and in no way negates the need for a "war game" or other walk test.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Pete Erskine on September 05, 2015, 08:57:11 pm
Can I ask what device your using for scans, does this pump out a file format compatible with WW6 or do you need to convert it?

Scans are from TTI.  More detail on how I did it can be found at http://www.bestaudio.com/spectrum-analyzer-setups

Normal TTI scans can be used in WB as long as you edit out the Headers using a text file.  All of the scans listed on my website have the headers removed and can be imported into either IAS and WB.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Jason Glass on September 05, 2015, 11:31:18 pm
Whereas it would be nice to know the IM suppression number, it's really kind of irrelevant: Whereas one device (the transmitter) may not be producing the IM product, another device might be; the preamp in the antenna, the multi-coupler or the receiver front end. The IM software programs are merely pointing out the math of potentially problematic frequencies and in no way negates the need for a "war game" or other walk test.

With this always in mind, I often adjust the intermod bypass window settings in IAS to generate more usable frequencies in large channel-count coordinations, gradually reducing the bypass bandwidths as required.  It's less risky than completely abandoning triple-beat calculations.  The risk can be further mitigated by setting and adhering to a strict band plan, where like-type equipment is assigned to specific areas of spectrum, with large guard bands between the different types.  This technique is also a reason that I try to stay away from broadband RX antenna amplifiers if possible and use passive higher gain antennas on the front end.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Henry Cohen on September 06, 2015, 09:15:51 am
This is technique is also a reason that I try to stay away from broadband RX antenna amplifiers if possible and use passive higher gain antennas on the front end.

I can't stress enough the validity of this statement. Amplified antennas and other in line preamps cause far more problems than they solve 99% of the time. Their use has limited applications, and not has a band-aid for other inadequate system implementations.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Neil White on September 06, 2015, 03:22:36 pm
I can't stress enough the validity of this statement. Amplified antennas and other in line preamps cause far more problems than they solve 99% of the time. Their use has limited applications, and not has a band-aid for other inadequate system implementations.

It is interesting that some manufacturers seem to market active antenna as their recommended product for radio mic receive antenna. Is the correct application to make up for cable losses, not to compensate for rf path loss?

Are there any rules of thumb for how far to keep transmit and receive frequencies separated by in a spectrum band plan?
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Jens Palm Bacher on September 06, 2015, 04:37:12 pm
It is interesting that some manufacturers seem to market active antenna as their recommended product for radio mic receive antenna. Is the correct application to make up for cable losses, not to compensate for rf path loss?

Are there any rules of thumb for how far to keep transmit and receive frequencies separated by in a spectrum band plan?
I also avoid broadband amplified antennas whenever possible. If i need to use long coax, i try to use antennas or amps with filtering, such as the Sennheiser A 12 AD or the AB 1036. It is interesting to see that Sennheiser have moved away from broadband amplifers in their 9000 series, and are going back to filtered antennas.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Jason Glass on September 06, 2015, 04:49:05 pm
It is interesting that some manufacturers seem to market active antenna as their recommended product for radio mic receive antenna. Is the correct application to make up for cable losses, not to compensate for rf path loss?

Are there any rules of thumb for how far to keep transmit and receive frequencies separated by in a spectrum band plan?

It is, indeed, only suitable to make up for cable losses and/or passive components like splitters, and is unnecessary for simpler systems.  The LPDA alone has +5dBi of gain, and if you use a helical, its gain is roughly 8-9 dBi (11-12 dBi gain minus 3dB polarization mismatch loss).  If you use high quality 3/8" low loss cable your losses are in the neighborhood of 3.5dB to 4.5dB per 100ft at the middle of the UHF-TV band (585MHz).

The question of band spacing is more difficult to answer.  Every urban area in the USA has different areas of the UHF-TV band available for use, so we are forced to be very flexible in our band planning.  You really just try to keep them as far apart as is practical and do your best to stick to it.  Unfortunately, someone almost always shows up late with a piece of gear that will only tune to a band where you don't want that type.  You just have to make it work as best you can.

Having a good spectrum analyzer helps very much to examine the spectrum at potential assignment frequencies to see if they have low enough noise, and to determine if predicted IMD products are really being transmitted by your equipment, although you are rolling the dice on what's happening inside the front ends of your receivers.  This is where expensive high-end gear helps, because its receiver channel filtering helps to reduce internal IMD products dramatically.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Jay Rigby on September 07, 2015, 01:29:31 am
Scratch that, just realized you are using Parallels.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Karl Winkler on September 07, 2016, 10:26:53 am
I can't stress enough the validity of this statement. Amplified antennas and other in line preamps cause far more problems than they solve 99% of the time. Their use has limited applications, and not has a band-aid for other inadequate system implementations.

Absolutely. Like audio gain structure, this concept can not be reiterated often enough!
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Ike Zimbel on November 22, 2016, 09:48:26 pm
Here is an expansion on my videos about IAS and WB. 
It is divided into 2 - 12 minute videos.

Part 1 (https://youtu.be/-BmBRX70O68)

Part 2 (https://youtu.be/kzGP4KWLpA4)

Hi Pete,
I've been experimenting with this and one thing I'm finding pretty consistently is that it's very difficult to get the two programs to agree on even basic intermod calculations. In this instance, I did the initial coord in IAS (nothing too challenging, about 30 freq's, all Shure except 4 Lectro IFB's to avoid). Since I will be handing this show off to an A-2, I decided to re-enter it all in WWB-6 on the laptop included with the rig. Well, even though I had used the most restrictive IAS settings, WB didn't agree with about 1/3 of the frequencies I'd selected...so I did a re-calc in WB-6. Once it was happy, I punched those numbers back into IAS, and was quite surprised to have some of them be called out as 3rds...and so on, back-and-forth. It's working, RF wise, but I find this interesting. What I think is happening is that the results vary depending on where the calculations start, ie, in what order the frequencies are being calculated against each other.
Title: Re: RF coordination simultaneous example using IAS and Workbench
Post by: Pete Erskine on November 22, 2016, 10:50:15 pm
Hi Pete,
I've been experimenting with this and one thing I'm finding pretty consistently is that it's very difficult to get the two programs to agree on even basic intermod calculations. In this instance, I did the initial coord in IAS (nothing too challenging, about 30 freq's, all Shure except 4 Lectro IFB's to avoid). Since I will be handing this show off to an A-2, I decided to re-enter it all in WWB-6 on the laptop included with the rig. Well, even though I had used the most restrictive IAS settings, WB didn't agree with about 1/3 of the frequencies I'd selected...so I did a re-calc in WB-6. Once it was happy, I punched those numbers back into IAS, and was quite surprised to have some of them be called out as 3rds...and so on, back-and-forth. It's working, RF wise, but I find this interesting. What I think is happening is that the results vary depending on where the calculations start, ie, in what order the frequencies are being calculated against each other.


IM calculations are like the lotto.  First a random number in the range is picked, then each additional freq is located working away from the first.  Every time you do a recalculate a random number starts the process.  So not only is it gambling but the actual calculation methods aren't exactly the same either.  Seems like the numbers chosen correctly by one program should test OK in another.  for this inconsistency I blame the calculation methods.