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You guys seem to be my de facto sounding board...

I am nearing completion of the first version of the FreqFinder app for iPhone and Android. It keeps track of all of your transmitter channels in use and then calculates the intermodulation products between them and tells you if any channels are being affected by intermodulation products. It is meant to be a replacement for the Lectrosonics intermod chart. It will also test all of a transmitter's options against the channels in use and provide a list of usable channels for when the need arrises to change frequencies.

An add-on will provide a comparison against the fcc tv station database for users located in the US.

First supported transmitters will be Lectrosonics and Comtek, but more will be added over time.

The price will be $30 for the base app and $15 for the US TV add-on.

Also, current front runner for the name is FreqFinder, but TXCentral is also an option.

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A little primer for anyone:

Intermodulation is a phenomenon that occurs when two separate frequencies are summed and then put through any non-linear circuitry. This causes the two frequencies to produce other frequencies at the frequency sum and difference of the original frequencies. The products themselves then produce their own intermodulation products which produce their own products, etc. Each iteration of this process is known as 2nd order, 3rd order, etc, and is weaker in effect with each subsequent iteration. Despite 2nd order products being the strongest, they usually lie much further from the target spectrum in use and are not as often considered as 3rd and other odd order products which generally lie much closer to the target spectrum.

Transmitters experience this effect because a signal broadcast from one transmitter can actually be intercepted and summed in with another transmitter's signal, causing intermodulation products. The effect is stronger with proximity and can occur between 2 or more transmitters, although the average distance between 3 or more transmitters is generally much larger and therefore products generated by numerous transmitters are considered less important. However, higher order products can be generated by 2 transmitters alone and are also important considerations.

The different possible combinations of transmitter frequencies together at even a small number of orders increases drastically as more transmitters are added (10 transmitters calculated to the 7th order produces approximately 434,000 products) and so the calculation is obviously the job of some sort of calculating machine I'm sure will be invented soon if it doesn't already exist. And we travelling sound mixers often have to find ourselves new channels, so having a portable version of this calculation would be ideal. And that is the purpose of this app.

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Making of the app:

This app is designed for relatively small wireless setups on the go. While there are virtually no limits to the number of transmitters supported, more transmitters increase the calculation time exponentially. 12-20 transmitters max is recommended. Sadly no 40 channel reality shows for the moment.

Despite the processing powerhouses our iPhones are now (and I only have an iPod touch 4G), the challenge of this app is making it fast. Without optimization a single calculation of a full intermod, 7th order, 10 TXs would take about half a second. However, the most common use of the app, I believe, will be to suggest which channel options are viable for when a new channel needs to be selected. Lectrosonics blocks contain 256 channels, and an intermod would have to be calculated for each of them to determine which channels are viable. In the field, waiting for 128 seconds to find a new channel would be useless.

So I have employed a fair amount of trickery to get the time down considerably, but in my opinion it currently isn't enough. My goal was to provide flexibility in the strictness of filtering the channel options but at the moment, it would be too slow. So instead, the algorithm is set to a fast but useable filter. My hope is that I will be able to, in future versions, add some gpu accelerated calculation to increase speed and open up the options.

The TV add-on requires data connectivity and accesses the FCC TV database to find the location and radiated power of local television stations. That information will then be provided with a transmitter's general info as well as during channel finding in order to better select channels.

This is the very most useful part of the app, in my opinion. I have been using a not commercial ready version of the app for a while now and nothing can compare to avoiding the local television stations in terms of performance on these transmitters. Mind you, there are plenty of other things out there transmitting and they also intermod with each other. That is beyond the scope of this app.

Expanding the TV add-on to other countries is a future goal. It would of course require an accessible database and research into the rules of any particular country, but it is something I feel is worth working on, for anyone who wants help when travelling.

The app will have support for switching to your LectroRM app to change a frequency. :)

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I'm in! I'll buy it no matter what it's called, but FreqFinder probably the more descriptive app name.

Important note: I have burned by using the top-level info from the FCC database in the past. Sometimes, stations that are listed as CP are actually operating, while others shown being licensed are in reality not transmitting. The actual info is sometimes buried in the authorized letter section. Very frustrating.

Hopefully this will settle down in another year or two after the new frequency allocations for terrestrial broadcast get worked out. Based on what is happening in major markets, we are going to need all the help we can get...

--Scott

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Thanks for the support guys! This is why I come to you.

To answer a few comments/questions:

Scott: Thanks for the heads up on the FCC data. I can't say I've been burned by the data before, but it is only one piece of the puzzle. That said, I'll see if there are ways to keep the FCC data honest from the stand point of the app.

Jim: Allowing for user created devices is not out of the question. It's not a simple thing though as the calculations are optimized to the list of channels built in and a non-trivial sized UI would need to be built specifically for it. The program will expand, however, and I'll be looking for ways to make it faster and more flexible. What transmitters were you looking to use with it?

Bernie: I can't say a computer program is in the foreseeable future. iPod touch might be the way to go.

Phillip: The app will be supported by any iOS device that supports iOS 4 and higher. (iPhone 3G and higher)

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Those of us who use digital radios don't need the intermod calculator, but an app that frequently updates all the tv stations in use would be a wonderful thing! (especially if there was an Android version)

Billy Sarokin

You guys seem to be my de facto sounding board...

I am nearing completion of the first version of the FreqFinder app for iPhone and Android. It keeps track of all of your transmitter channels in use and then calculates the intermodulation products between them and tells you if any channels are being affected by intermodulation products. It is meant to be a replacement for the Lectrosonics intermod chart. It will also test all of a transmitter's options against the channels in use and provide a list of usable channels for when the need arrises to change frequencies.

An add-on will provide a comparison against the fcc tv station database for users located in the US.

First supported transmitters will be Lectrosonics and Comtek, but more will be added over time.

The price will be $30 for the base app and $15 for the US TV add-on.

Also, current front runner for the name is FreqFinder, but TXCentral is also an option.

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Those of us who use digital radios don't need the intermod calculator, but an app that frequently updates all the tv stations in use would be a wonderful thing! (especially if there was an Android version)

Billy Sarokin

Billy,

Please forgive my ignorance, but why would an intermod. app. not be necessary for digital radios? They still use RF, right? To which radios are you referring? Do yours have some sort of intermod. avoidance functionality built in? What am I missing?

~tom

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