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RF scanning?


cedric12
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Hi all,

 

Pretty new to field sound. Ive recently been having issues with scanning for clear freq's. i have 4 lectrosonic 411a's.  maybe im doing it wrong? 

 

my way: Turn on all receivers and transmitters. let sit for a couple seconds. then, turn off all transmitters. Scan with all 4 receivers ( blocks 19,20,(2)21's ) at the same time. find the clearest location on each rx and tweak on all matching tx's. 

 

everything is fine until i place them on the talent. It seems like i cant be any more than 10 feet away from all 4 without losing full signal. any suggestions would be great. thanks

 

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Using the scanner function does not prevent IM problems you may be creating with your final choice of frequencies. After scanning I try to use the frequencies suggested on the printed table provided with the lectrosonics which are coordinated to avoid IM.

 

Dan.

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Turn on the receivers. Scan with the first one, pick a frequency. Set the transmitter, leave it transmitting and move it a few feet from your bag, then start scanning with the second transmitter and repeat the process. You also have to take inter modulation into consideration as you select frequencies. Either use the charts or get the FreqFinder smartphone app. With experience you will get to know if the loss of range is intermodulation or some other issue.

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Hi all,

 

Pretty new to field sound. Ive recently been having issues with scanning for clear freq's. i have 4 lectrosonic 411a's.  maybe im doing it wrong? 

 

my way: Turn on all receivers and transmitters. let sit for a couple seconds. then, turn off all transmitters. Scan with all 4 receivers ( blocks 19,20,(2)21's ) at the same time. find the clearest location on each rx and tweak on all matching tx's. 

 

everything is fine until i place them on the talent. It seems like i cant be any more than 10 feet away from all 4 without losing full signal. any suggestions would be great. thanks

Please post or email the actual 4 frequencies you used when your range went to 10 feet. Something weird is going on here. Even if you chose the wrong frequencies, intermod should not rear its ugly head if the transmitters are more than 15 feet from the 411 receivers and the transmitters are more than 5 feet from each other.

 

This sounds like a strong interferer, not intermod.

Best Regards,

Larry Fisher

Lectrosonics

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thanks for all of the responses.

 

the transmitters are about 5 feet away from each other and im no more then 15 feet away from all. and its usually just 1 transmitter that will give me issues out of the 4. No camera tx's either.  I'm gonna read more into the tutorial and try a couple things that were suggested. 

 

 

a friend suggested grouping since i have 3 of the same block? again, dont really understand what this means or if it will be helpful. sorry, i obviously have to study up on alot of stuff. 

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" have to study up on alot of stuff... "

The Lectro wireless guide is basic and thorough...

also other manufacturers have similar guides on their sites.

several of them include  walk-test set-up procedures you should study, and follow...

 

I note a lot of significant additional information in your last post...

(which makes intermod seem even less suspect!)

unfortunately professional use of wireless is not plug and play....

besides some reading, there is also "trial and error" involved.

and helpful, knowledgeable tech support is just a toll-free phone call away...

Edited by studiomprd
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Freq Finder (app for smartphones) will be a big help here. 

 

This may also help you out:

 

https://www.dropbox.com/s/mz3y8isudsn218y/TV%20Channel%20Wireless%20Frequency%20and%20Block%20Layout.pdf

 

This is a document I have that matches up the channel numbers with the frequencies and which block they reside in. Very helpful when dealing with finding a clear channel based on what little info you might have.

 

Now, I also have Freq Finder with the TV database add-on. I set a location for downtown Miami (I've worked down in Dadeland recently) and had a look. It doesn't look good for the blocks you have.

 

Block 19: 

Channel 17: Westgate Fl, approx 55dB in the downtown area. They may not be online yet, this may be your best hope in this block.

18: WPBT from downtown. 96 dB. Don't bother.

19: WSFL, permit for construction right now, might be OK... but not for long. 97dB.

20: WLRN, 93dB and online. Don't bother.

 

Block 20:

21: WDLP from Pompano. 57dB, and online. If you are indoors, this might be almost acceptable. Marginally.

22: WFOR. 98dB, downtown Miami, don't even bother.

23: WLTV, 94dB and online. Again downtown... Don't bother.

24: W24DE 52dB from Miami, I'm not certain what this one is, maybe a low power college station? It says they are licensed, so they could be online too. Don't know. Indoors might be possible in this band.

 

Block 21:

25: WIMP, 15kw station, 54dB. This might be possible depending on where you are. Looks like they broadcast southwest toward Hialeah and hit N. Miami and Miramar.

26: W16CC - Construction permit, looks like another low power from Westgate broadcasting southwest. 53dB.

27: WXEL out of West Palm Beach. 48dB, but they are certainly online. Shouldn't have any problems indoors in this channel.

28: WFLX also from WPB. 50dB, same as WXEL. Outdoors... You probably will still have issues.

 

When I say "don't bother" I mean that you will be asking your tiny 150mw transmitters to compete against a megawatt tower. Think about standing on the 50 yard line in a full stadium, and whispering to someone in the end zone. Yea, it is that bad. Your receiver doesn't even have a chance. With the power down in the 50dB range, you *might* get a clear signal through to your RX, but you are still competing against a dull roar that is pretty 'loud' in comparison. You might want to consider swapping blocks with someone from an area that blocks 19-21 aren't so trashed. 

 

Good luck.

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I'm curious what happens if only one person wears a transmitter, while all four receivers are on. Can you receive the signal then? 

 

I generally never do a scan with my own transmitters on, since that just adds to the confusion. I just look at the sweep, find a valley (as opposed to a peak) channel that's clear, then look for some more. Every time we move -- sometimes as little as a block -- there's always the risk of another source of RFI. New Endian's FreqFinder is a great app to have, but I only dial the frequencies in to check for intermod once I'm sure everything works. If it doesn't, chances are a couple of clicks either way solves the problem.

 

Lectrosonics' free Wireless Guide has some great theory that applies to all brands of wireless transmitters, especially when it comes to avoiding interference and selecting the right antennas. In fact, I'd say Lectrosonics is among the best in the industry for clear, easy to read (and understand) text on all this stuff. 

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Here is the proper way to setup your wireless system, as indicated in Lectrosonics MANUALS...yes, read 'em!

 

1. Set up the system for testing.
Place antennas in the position in which they will be
used and connect to the receivers. Place transmitters
about 3 to 5 feet apart, about 25 to 30 feet from
the receiver antennas. If possible, have all other
equipment on the set, stage or location turned on
as well, especially any mixing or recording equipment
that will be used with the wireless system.

 

2. Set all receivers on clear channels.
Turn on all receivers, but leave the transmitters off.
Observe at the RF signal strength indicator for each
receiver module. If a signal is present, change the
frequency to a clear channel where no signal is
indicated. If a completely clear channel cannot be
found, select the frequency with the lowest RF level
indication. Once all receiver modules are on clear
channels, go to step 3.

 

3. Turn each transmitter on one at a time.
Start with all transmitters turned off. As you turn on
each one, look at the matching receiver to verify a
strong RF signal is received. Then, look at the other
receivers and see if one of them is also picking up
the signal. Only the matching receiver should indicate
a signal. Change frequencies on either system
slightly until all channels pass this test, then check
again to see that all channels are still clear as done
in step 2.

 

4. Turn each transmitter off one at a time.
With all transmitters and receivers turned on, turn
each transmitter off one at a time, in turn, and look
at the RF level indicator on the matching receiver
module. The RF level should disappear or drop to a
very low level. If it does not, change frequency on
that receiver and transmitter and try it again. When
a clear frequency is found, turn the transmitter on
and move on to the next channel.

 

IMPORTANT: Any time a frequency is changed on
any of the systems in use, you must start at the
beginning and go through this procedure again for
all systems. With a little practice, you will be able
to do this quickly and save yourself some “multichannel
grief.”

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Set all receivers on clear channels. Turn on all receivers, but leave the transmitters off. Observe at the RF signal strength indicator for each receiver module. If a signal is present, change the frequency to a clear channel where no signal is indicated. If a completely clear channel cannot be found, select the frequency with the lowest RF level indication.

 

Gee, I dunno. I'd rather do a frequency scan. Page 16 of the 411a manual says the same thing, and that's the way I've always done it. That way, I know if I'm on the hairy edge of a brick of localized interference.

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I'm curious what happens if only one person wears a transmitter, while all four receivers are on. Can you receive the signal then? 

 

I generally never do a scan with my own transmitters on, since that just adds to the confusion. I just look at the sweep, find a valley (as opposed to a peak) channel that's clear, then look for some more. Every time we move -- sometimes as little as a block -- there's always the risk of another source of RFI. New Endian's FreqFinder is a great app to have, but I only dial the frequencies in to check for intermod once I'm sure everything works. If it doesn't, chances are a couple of clicks either way solves the problem.

 

Lectrosonics' free Wireless Guide has some great theory that applies to all brands of wireless transmitters, especially when it comes to avoiding interference and selecting the right antennas. In fact, I'd say Lectrosonics is among the best in the industry for clear, easy to read (and understand) text on all this stuff. 

Hi Marc,

Just trying to correlate what you do with my usual method.  I have two 211s in block 27 and two in block 24.  They are in my mixer this way.  channel one block 27, channel two block 24, channel three block 27, and channel block 24.  I have my D-4 camera hop turned on as well as my Nomad Zaxnet.  All talent receivers turned off to start.  I start with channel one and scan.  I find the clearest spot and set the corresponding tx to that frequency and leave it on.  I move to channel two and do the same thing and leave that tx on, and on down the line.  Reading Sound Art Films post and your post indicates that my method may not be the best.  I've been having some interference problems in some areas and I'm going to give these techniques a try and see if I get better results.

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