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Author Topic: Directional antennas for *finding* interfering sources?  (Read 5227 times)

Scott Helmke

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Directional antennas for *finding* interfering sources?
« on: November 04, 2016, 09:50:48 am »

Any recommendations for very directional UHF antennas for tracking down interference & uncoordinated sources?

I do the frequency coordination for a local Big Ten football stadium, and we have a couple TTi spectrum analyzers and a nice R&S FSH spectrum analyzer. Handy gear for checking on things, beyond the Axient spectrum manager that keeps scanning the bigger picture. 

I rarely have problems with non cooperating media, but it would be nice once in a while to have something really directional to try to track down unknowns. What's available (or could be built reasonably) in the UHF TV spectrum?  I really can't justify something huge to carry around, though.
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Pete Erskine

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Re: Directional antennas for *finding* interfering sources?
« Reply #1 on: November 04, 2016, 09:59:33 am »

Any recommendations for very directional UHF antennas for tracking down interference & uncoordinated sources?

I do the frequency coordination for a local Big Ten football stadium, and we have a couple TTi spectrum analyzers and a nice R&S FSH spectrum analyzer. Handy gear for checking on things, beyond the Axient spectrum manager that keeps scanning the bigger picture. 

I rarely have problems with non cooperating media, but it would be nice once in a while to have something really directional to try to track down unknowns. What's available (or could be built reasonably) in the UHF TV spectrum?  I really can't justify something huge to carry around, though.

A standard directional UHF Paddle like a Sennheiser A2003 will work.  Additionally you will need an adjustable pad to control the level so that it is not overloading your meter or SA.  The trick is to start at the back of the room., for example, and to aim the back of the antenna and turn it to minimize the signal.  The direction that the back of the antenna faces is the direction where the freq is on your first heading.   Then move to the side of the room and to the same.  the intersection is where your freq is.
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Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #2 on: November 04, 2016, 10:00:35 am »

Hi Scott,

These are perfect:

http://www.wa5vjb.com/products1.html

Just add a cable, connector, and a handle made of PVC pipe.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Scott Helmke

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Re: Directional antennas for *finding* interfering sources?
« Reply #3 on: November 04, 2016, 10:35:24 am »

I usually do carry a Sennheiser A2003 for trying to find stuff... but it's generally not been something I've had much success at.  I do like Peter Erskine's null approach, though. Will have to try that next time.
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Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #4 on: November 04, 2016, 11:40:01 am »

I usually do carry a Sennheiser A2003 for trying to find stuff... but it's generally not been something I've had much success at.  I do like Peter Erskine's null approach, though. Will have to try that next time.
Pete's method works well. Also, it helps to disable the instrument's preamp and add any internal attenuation that it may have.  I also find that orienting the antenna for horizontal polarization helps.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Pete Erskine

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Re: Directional antennas for *finding* interfering sources?
« Reply #5 on: November 04, 2016, 11:45:00 am »

I usually do carry a Sennheiser A2003 for trying to find stuff... but it's generally not been something I've had much success at.  I do like Peter Erskine's null approach, though. Will have to try that next time.

The back of the antenna has a sharper null than the front which is very wide.  Couldnt find an actual plot but this shows what i mean...
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Russell Ault

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Re: Directional antennas for *finding* interfering sources?
« Reply #6 on: November 04, 2016, 04:11:47 pm »

This may be a stupid question, but, at your level, do you ever use Doppler-shift-based antenna arrays for finding RF sources?

Thanks!

-Russ
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Lyle Williams

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Re: Directional antennas for *finding* interfering sources?
« Reply #7 on: November 04, 2016, 08:39:20 pm »

I don't do large wireless audio installs, but my experience of doppler systems (I have a simple one) is that they are better suited to wide area work where you just want to be able to drive to the vicinity of a signal than to close in work.

I agree with previous posts that a desireable feature in a handheld search antenna is a sharp and deep null.
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Russell Ault

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Re: Directional antennas for *finding* interfering sources?
« Reply #8 on: November 05, 2016, 01:39:14 am »

I don't do large wireless audio installs, but my experience of doppler systems (I have a simple one) is that they are better suited to wide area work where you just want to be able to drive to the vicinity of a signal than to close in work.

That makes sense. I was thinking of a Doppler system in combination with a hand-held antenna: mount a Doppler system at the side of the room and use it as one of the two points of directional reference for triangulation (bonus points if the if the system can be remote-controlled).

-Russ
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Dan Currie

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Re: Directional antennas for *finding* interfering sources?
« Reply #9 on: November 05, 2016, 04:29:30 am »

Scott,
  Maybe a receiver like an Icom R20 would help.  It has easily adjustable gain settings and a pad which are useful in zeroing in on the source.  It can also demodulate FM signals which you can listen to on it's internal speaker.
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Lyle Williams

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Re: Directional antennas for *finding* interfering sources?
« Reply #10 on: November 05, 2016, 06:53:18 am »

The other thing about searching for interfering signals - if you aren't allowed to turn them off there is no point in physically finding them.  See them on the spectrum analyser, avoid them.
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brian maddox

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Re: Directional antennas for *finding* interfering sources?
« Reply #11 on: November 05, 2016, 10:42:21 am »

The other thing about searching for interfering signals - if you aren't allowed to turn them off there is no point in physically finding them.  See them on the spectrum analyser, avoid them.

Of course it is helpful to know where they are so you can deploy your antennas in the most strategic way to avoid them as well.
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Pete Erskine

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Re: Directional antennas for *finding* interfering sources?
« Reply #12 on: November 05, 2016, 02:20:05 pm »

This may be a stupid question, but, at your level, do you ever use Doppler-shift-based antenna arrays for finding RF sources?

Thanks!

-Russ

I have looked a some but this is too complicated for casual use.  The directional antenna, not requiring power, one flat paddle, can do the same job just as easy.
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Scott Helmke

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Re: Directional antennas for *finding* interfering sources?
« Reply #13 on: November 05, 2016, 10:02:39 pm »

The other thing about searching for interfering signals - if you aren't allowed to turn them off there is no point in physically finding them.  See them on the spectrum analyser, avoid them.

Granted, but my situation is a football stadium - I don't think I have my actual "lettre de marque" from the head of the athletics department in my laptop case any more, but I'm reasonably sure I could shut somebody down if I needed to.
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Ike Zimbel

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Re: Directional antennas for *finding* interfering sources?
« Reply #14 on: November 07, 2016, 04:22:07 pm »

Any recommendations for very directional UHF antennas for tracking down interference & uncoordinated sources?

I do the frequency coordination for a local Big Ten football stadium, and we have a couple TTi spectrum analyzers and a nice R&S FSH spectrum analyzer. Handy gear for checking on things, beyond the Axient spectrum manager that keeps scanning the bigger picture. 

I rarely have problems with non cooperating media, but it would be nice once in a while to have something really directional to try to track down unknowns. What's available (or could be built reasonably) in the UHF TV spectrum?  I really can't justify something huge to carry around, though.
I use this baby with my TTI. I find that the futuristic Star Trek-ish styling makes folks think that I can pick up far more with it than I actually can...
On a serious note, be aware that signals can bounce around and appear to come from somewhere other than where they're originating from. Case in point, I spent an hour, with the aid of the GDC and two other guys with SA's tracking down this rogue signal at an empty MetLife stadium this past summer. At one point, the signal really seemed to be strongest coming from an area in the upper stands, to the left of one end zone...and there just happened to be someone from the press sitting up there with a laptop. The GDC was working that area and he went over and checked it out...no dice. It was around this time that I started to look in the opposite direction, and shortly thereafter realized that the signal was coming from our own tech world which was set up in the concrete bunker formed by the end zone seats (ie under the seats). The offending device was a single PSM-1000 Tx that I had walked by 67 times by that point, sitting on a road case by the monitor console. The ME had pulled it out of the rack (which was under a tarp a few hundred feet away) to use as a local cue mix, and he had TOLD me as much. What he didn't tell me was that it was an additional channel to the ones I had allocated. In any event, my point is that the signal was basically being channeled out of that bunker and up into the stands.
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Diogo Nunes Pereira

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Re: Directional antennas for *finding* interfering sources?
« Reply #15 on: November 09, 2016, 03:59:07 pm »

Additionally you will need an adjustable pad to control the level so that it is not overloading your meter or SA.

Hi. Any suggestions on such a device? I already own a selection of in-line Mini-Circuits attenuators with SMA connectors, but it seems like something adjustable would be more practical.

Is this something you can buy or have you built your own?

Thanks.

D
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Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #16 on: November 09, 2016, 04:08:07 pm »

I use this baby with my TTI. I find that the futuristic Star Trek-ish styling makes folks think that I can pick up far more with it than I actually can...
On a serious note, be aware that signals can bounce around and appear to come from somewhere other than where they're originating from. Case in point, I spent an hour, with the aid of the GDC and two other guys with SA's tracking down this rogue signal at an empty MetLife stadium this past summer. At one point, the signal really seemed to be strongest coming from an area in the upper stands, to the left of one end zone...and there just happened to be someone from the press sitting up there with a laptop. The GDC was working that area and he went over and checked it out...no dice. It was around this time that I started to look in the opposite direction, and shortly thereafter realized that the signal was coming from our own tech world which was set up in the concrete bunker formed by the end zone seats (ie under the seats). The offending device was a single PSM-1000 Tx that I had walked by 67 times by that point, sitting on a road case by the monitor console. The ME had pulled it out of the rack (which was under a tarp a few hundred feet away) to use as a local cue mix, and he had TOLD me as much. What he didn't tell me was that it was an additional channel to the ones I had allocated. In any event, my point is that the signal was basically being channeled out of that bunker and up into the stands.
Stepped attenuators like these are excellent for many applications including "sniffing" for interference sources:

http://m.ebay.com/itm/JFW-10dB-2-2G-Ad-justable-Variable-Attenuator-50DR-193-/301310803858

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #17 on: November 09, 2016, 04:10:02 pm »

Hi. Any suggestions on such a device? I already own a selection of in-line Mini-Circuits attenuators with SMA connectors, but it seems like something adjustable would be more practical.

Is this something you can buy or have you built your own?

Thanks.

D
Stepped attenuators like these are excellent for many applications including "sniffing" for interference sources:

http://m.ebay.com/itm/JFW-10dB-2-2G-Ad-justable-Variable-Attenuator-50DR-193-/301310803858

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Diogo Nunes Pereira

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Re: Directional antennas for *finding* interfering sources?
« Reply #18 on: November 11, 2016, 05:24:36 pm »



Stepped attenuators like these are excellent for many applications

Thank you Jason.

Ordered one from that link you provided.

Expected delivery date, January 4th...

Such is life in Europe.

Cheers,

D

Sent from my Xylophone using Tapatalk...

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Diogo Nunes Pereira
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Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #19 on: November 11, 2016, 05:28:11 pm »


Thank you Jason.

Ordered one from that link you provided.

Expected delivery date, January 4th...

Such is life in Europe.

Cheers,

D

Sent from my Xylophone using Tapatalk...
Hi Diogo,

Make sure you also have some SMA-m to BNC-f adapters!

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Diogo Nunes Pereira

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Re: Directional antennas for *finding* interfering sources?
« Reply #20 on: November 11, 2016, 05:36:56 pm »

Yep. Of those I have plenty now... my spectrum analyzer being the RF Explorer.

I found I gave a lot of them away before to colleagues who bought RFEs or RTL-SDRs, so when I needed a stock refill just went double-digit.

Sent from my Xylophone using Tapatalk...

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Diogo Nunes Pereira
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Jason Glass

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Re: Directional antennas for *finding* interfering sources?
« Reply #21 on: November 11, 2016, 05:37:53 pm »

The other thing about searching for interfering signals - if you aren't allowed to turn them off there is no point in physically finding them.  See them on the spectrum analyser, avoid them.
I may be a bit spoiled on this issue; I'm an NFL GDC. :-D Also, I make it a point when negotiating my terms with a client that if I'm to be held responsible for RF frequencies, then I must have their full backing and authority to the extent of the law to shut down uncoordinated operations. I never abuse this privilege and always work to keep the RF peace.

That said, it's almost always prudent to find a new clean frequency immediately for the party being stepped on, and hunt down the offender later.

Regarding the law, one of the few perks of having a Part 74 license is knowing that Part 15 users are tertiary and must immediately cease operation when notified that their equipment is causing interference to licensed primary and secondary operators.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Diogo Nunes Pereira

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Re: Directional antennas for *finding* interfering sources?
« Reply #22 on: November 11, 2016, 05:58:47 pm »



Regarding the law...

Or not regarding it at all.

In the show I am setting up today, I built a custom profile in WWB for a Wisycom transmitter called CRT36 that the OB crew brought in to do IEMs.

When fired up, both CRT36 units totally slammed a Sennheiser 100 (with whip) that was close by, on a clear DVB channel. That's a tottaly unlicensed 2W system!!!

 Had to run an XLR for the ew100 system to be on the opposite side of the stage.

Senn 500 and Shure UHF series had no serious desending (and had remote antennas), so we kept them SL.

Again, so is life in Europe. (Spain at least...)

Sent from my Xylophone using Tapatalk...

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Diogo Nunes Pereira
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ProSoundWeb Community

Re: Directional antennas for *finding* interfering sources?
« Reply #22 on: November 11, 2016, 05:58:47 pm »


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