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Author Topic: SIFM issues and intermod calcs  (Read 302 times)

Chris Eddison

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SIFM issues and intermod calcs
« on: March 19, 2017, 11:23:19 am »

Hi all
First of all, I realise a lot of PSW users are from the US. I'm in the UK so a quick translation of frequencies for you;
We tend to "live" in empty tv channels, hence the use of channel names.
Channel 38
606-614MHz. Licensed under a shared license - I have one of these.
Channel 65
823-832MHz. Just been added to our shared license, so i'm licensed for this too.
Channel 70
863-865MHz. Bandit country! This is licence-free and is where most radio kit sold over the counter to schools, DJ's etc. lives.

I'm trying to crunch some numbers in SIFM. I've always just used it with the numbers that came straight back, but I also know you can leave it for a while longer (like, >5 days!) to get more accurate results and potentially a couple more channels. I've never had the time for this in the past, but I've got ages now until I have another show, my windows laptop was sat doing nothing so I thought, why not? Always useful to have a list of intermod free channels to hand.
This is all being driven because I've just ended up picking up 6 Sennheiser G2 systems in channel 70 (and their tuning range also encompasses the top 2MHz of channel 65). I'm considering sending my 4 x channel 70 Trantec S5.3's off to MLEC to be adjusted so they can do channel 65 as well (new thing they're offering - looks to just be a software tweak). I'm trying to work out how many channels I can squeeze in busing my 12 x channel 38 Trantec's, my 4 x (soon to be) channel 65 Trantec's and my new (but old) 6 x Sennheiser G2's in the top 2 mHz of 65 and 70. I'm pretty sure I won't be able to run all 22 simultaneously without intermods, but it'd still be nice to know how many I can use. I'm cheating and putting the Trantec's in to SIFM as G2's. They have similar switching bandwidths and tuning steps, but I know it's a bit naughty.


My problem is, SIFM comes back with its' usual "checking (xx)" where xx is the number of channels it's already found, and then the usual percentage remaining to be checked (ticking upwards very slowly!). I figured I could leave this laptop sat for a few weeks if needs be and see what comes back (Sennheiser reckon that you might get another couple of channels out of it if you leave it). I leave the laptop for a day, come back and SIFM has closed - I presume from a crash.
I've switched off all power saving functions, hard drive sleep, etc. etc. and have tried this on 2 different machines now. Same every time.
I've no idea how far it's getting, or how many channels it's found.


Has anybody else had similar issues? Does anybody have another clever tool that could run the numbers instead (I know of Wireless Workbench, and Audio Technica's simple frequency checker tool).
I'm considering accepting a few intermods providing they're on my less-used mics (channel 65 and channel 70). I've (unwittingly) actually been running with a few intermods for a few years (I used a recommended list of frequencies, but running it through various intermod calculators comes back with loads! - should have checked it for myself but I was too trusting!). As long as I protect my channel 38 frequencies, which is where my principal actors end up, I don't mind a few on the others used for chorus work or one-liners. I'm trying to think of a neat way of calculating this in SIFM. The easiest way I can envisage is to come up with a list of good ch38 frequencies, and then a list of channel 65/70 frequencies with a few intermods between them (maybe untick the 3TX 3rd order intermod box but keep 2 TX 3rd order ticked) and cross reference them to check the 65/70 list doesn't intermod in to 38, but I don't think SIFM can do that.
Any thoughts? How many people actually worry about 3TX intermod in real life?
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Pete Erskine

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Re: SIFM issues and intermod calcs
« Reply #1 on: March 19, 2017, 06:50:07 pm »

How many people actually worry about 3TX intermod in real life?

Triple beats are really only important when using combined IEM TX through an active combiner.  Absolutely no advantage when selecting mic freqs.

More info in this thread:

http://forums.prosoundweb.com/index.php?topic=156032.0
« Last Edit: March 19, 2017, 06:53:29 pm by Pete Erskine »
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Chris Eddison

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Re: SIFM issues and intermod calcs
« Reply #2 on: March 22, 2017, 12:05:10 pm »

Thanks Pete
I've managed to get a set of frequencies sorted that'll behave nicely, so all's good. Never did manage to keep SIFM running long enough to complete a full set of calculations.
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Diogo Nunes Pereira

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Re: SIFM issues and intermod calcs
« Reply #3 on: March 22, 2017, 07:21:54 pm »

I'm trying to crunch some numbers in SIFM.

Hi, it's been a long time since I've done that.

Quote
I figured I could leave this laptop sat for a few weeks if needs be and see what comes back ...

Does anybody have another clever tool that could run the numbers instead (I know of Wireless Workbench, and Audio Technica's simple frequency checker tool).

Yes...  I would recomend you to give a try to Shure Wireless Workbench (WWB6).  It's a very powerful software and somewhat more intuitive than Sennheiser Wireless Systems Manager (WSM) in my opinion. Both programs are free, and you can achieve what you're trying to obtain in both - without waiting for the next day.

Other options - frequency coordination programs -  exist but either cost money (RF Guru/IAS) and/or I've never tried them (Clearwaves/...)

In WWB I've managed to get all 22 frequencies you need in a few minutes.

I'm attaching some files for you to play around. Just change the extensions and import in WWB.

. Equipment profiles for you Trantec gear (change the extension from .txt to .eqp).
. Inclusion group with all UK Licence Free + Ch38 Bands (change extension from .txt to .ils)

Have fun. Cheers,

D
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Diogo Nunes Pereira
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Chris Eddison

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Re: SIFM issues and intermod calcs
« Reply #4 on: March 26, 2017, 07:40:02 am »

Wow! Thank you so much Diogo!
I'll definitely have a play with WWB. I was always put off by the fact that none of my gear was Shure (which is daft - that's exactly what I was doing with SIFM!) but it does look like pretty easy software to handle.
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