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Antenna system from DCaudiovisuel


Jeff Wexler

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Vin posted this antenna system he found from the French company, DCaudiovisuel. I am hoping someone who really understands RF and antenna technology can shed some more light on this type of system. No mention of what it costs (other than it rents for 46 euros a day.

dcaudiovisuel.com

Regards,  Jeff Wexler

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Jeff, the system is 1. the antennae, 2. the distributor and 3. the RF analyzer. If it costs 46 Euro to rent, it should be quite expensive to buy, I am sure... But what seems very interesting is that you can 'hands-on' change orientation of the antennae and get to better signal strength by looking at the signal on the analyzer... very interesting.

-vin

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  • 2 weeks later...
  • 2 weeks later...

I work as an RF Tech for large live broadcast events (Republican Convention, Presidential Candidates’ Debates,  Network Entertainment Shows etc) as well as a third or boom on Feature Films and Episodic TV.  So I have the luxury of seeing two different, however related, worlds.  This antenna system seems like a combo of the two.  Pretty cool!  It’s a 2x8, 50 ohm active wide band UHF antenna splitter,  A spectrum analyzer, and a couple of UHF dual quad antennas.  It’s kind of like what we would use on a big show shrunk down into a portable package.  Although, to be honest, I’ve never seen UHF Quads…..that’s pretty cool. 

Here’s a list of off the shelf components here in the States that would get you the same results .  (and I’m going with the CHEAPEST ingredients….we’re in a Recession/Depression…right?!)

ANTENNAS:

UHF Quads are cool….but Log Periodics are cheap and easily available! 

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

That link will take you  to a guy that makes them for 25 bucks and it’ll give you 18 to 20 dB of gain in the frequencies that we want!  I own 10 of these and they are GREAT! 

ANTENNA SPLITTER:

I couldn’t find a 2 x 8 cheap …but I found this.

http://www.digital-loggers.com/multi.html?gclid=CIra2sCXwZkCFdBM5QodgQWjuQ

Above is a link for a 1 x 16 Wideband active 50 ohm splitter.  It’s only one input ….so you’ll have to buy two.  But at only $295 each you can afford it and you will be able to upgrade to 16 receivers! (the Shure, Sennheiser and PSC are all good units….this is just the most bang for the buck)

SPECTRUM ANALYZER:

Here is the sticky one….. I use an ICOM PCR-1500 computer based radio with a bit of software called “Spectrum Commander”.  It’s not great, but it does the job.  The two items, WITHOUT the laptop required to run it, cost about a thousand bucks.  For that money I should have bought a cheap Chinese Spectrum Analyzer like this:

http://www.ntscope.com/Merchant2/merchant.mvc?Screen=PROD&Return_Screen=CTGY&Store_Code=MTC&Category_Code=TAM&Product_Code=AT5011

I used this model at the Republican National Convention last year and it performed really, really well.  It’s on the short list of new toys in my future.

Throw in some RG-8x cable with BNC ends, flat black spray paint for the Antennas and you are at  less than  2 Grand for the whole set-up!  Rent it for $65 per day (today exchange rate) and you have a pretty good  Return on  Investment!

Of course, I’m kind of throwing this all out there as a bit of a joke….but it would all actually work about the same as the system from the website. I will say one thing, none of my equipment has been as valuable as the Intermodulation Analysis System software from Masque sound.  That program is GOLD!

Kevin Parker

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<<That link will take you  to a guy that makes them for 25 bucks and it’ll give you 18 to 20 dB of gain in the frequencies that we want!  I own 10 of these and they are GREAT!  >>

How does one mount these antennae - will need some way to put it on a 3.8" thread bolt (end of an antenna mast)...

-vin

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Vin,

I bought a cheap, universal microphone mount.  I then removed the spring loaded "mic clip", leaving behind the threaded base and a slot with a screw in it. I mounted this to the antenna with rubber washers taking up the slack. Once the mic thread was mounted I could use any hardware designed for microphones. Also, when in a pinch, I screw in a short microphone arm from weighted table stand (about 3.5").  This then acts like a "stud" that can be mounted in the knuckle of a c-stand.  It's hard to describe....maybe I'll get some pictures up.  Keep in mind, the green PCB can be drilled and altered without any effect on the preformance of the unit (just avoid the trace) and try to use plastic hardware (if possible).

I'll try to get pictures for you to see...in the mean time, have a good weekend!

Kevin Parker

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I had a local plastic shop bend a strip of Lexan into a U shape. Then I drilled appropriate holes to attach the Lexan to a mast fitting and smaller holes to fasten on the antennas. Of course, I drilled matching holes in the fiberglass antenna, careful to avoid the trace.

The mounting screws and nuts are nylon to avoid antenna coupling as much as possible. Ordinarily I wouldn't concern myself with brand names but, in this application, it's important to use Lexan. Ordinary plexi will be weakened at the bend and tend to break when you bump the cart into something on a move.

David

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David,

I love it!

Here are a few of mine

antenna.jpg

antenna2.jpg

antenna1.jpg

I used the widest microphone stereo bar I could find (I always try to maintain a full wavelength of physical separation).  It disassembles quickly and stores "flat" for easy travel.  Also, when I am running two antennas next to each other (as above) it is usually for two seperate receivers, not for diversity.

Kevin Parker

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i would have also said more separation between antennae, unless of course they are going into separate rx. In my case, I got the PSC antennae which have worked very well on my last feature and since the Sixpack does the multiplexing of the rf, no need to bother about multiple antennae, just a pair, but with proper separation.

Thanks Dave and Kevin for the nice ideas. :)

-vin

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nice, David, but for better "diversity" results, I prefer more separation!

Sorry, I should have been more clear.

I have two antenna masts to achieve diversity. The one mast pictured has two antennas because I still have a receiver on Block 27. All the rest of my gear is Block 21 or Block 22 but that single Block 27 unit is still handy now and again. And, I have a separate receiving antenna available for the occasions I use it.

I didn't event think of diversity, a non-issue here, because I was focused on illustrating the mechanics of the mount.

i would have also said more separation between antennae, unless of course they are going into separate rx

Yes, Vin, exactly. Separate receivers.

By the way, one reason for the use of a U-shaped mounting bracket is to move the antenna away from the metal mast. Ideally one wants to keep the antenna apart from anything metal because a certain amount of "coupling" occurs. (I'll leave it to Mike Michaels to explain this more coherently as the phenomenon stains my limited understanding of radio wave behavior. As a long-time ham operator, he is more conversant with these issues.)

Anyway, a U-shaped bracket is a useful design even if one were attaching only a single antenna.

David

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While we are on the subject of diversity - imho - the sharkfin antenna is usually a wide band antenna and IF the working blocks of two separate wireless Rx is covered within this bandwidth then the antennae should be properly physically separated (there's a wavelength or so required if i remember rightly) nevertheless.

I remember Larry Fisher telling me how i should keep my SNA's (for the Sennheiser IFB) away from the sharkfins. I think he was saying this for the same reason as i stated above.

-vin

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I remember Larry Fisher telling me how i should keep my SNA's (for the Sennheiser IFB) away from the sharkfins. I think he was saying this for the same reason as i stated above.

Vin, I'm not sure if I understand correctly. I would have thought there should be no problem having two RECEIVING antennas in reasonably close proximity. I thought Larry Fisher's admonition was to keep a receiving antenna well separated from transmitting antenna for your IFB system.

But, are you asserting that even two receiving antennas should be spaced a wavelength apart?

David

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I think that science and reality differ greatly when it comes to antenna placement.  My friend Steve Morrow has used the Zaxcom antennae (the ones mounted no more than 8" apart) with long, thin cables for years.  Having worked for him when he first bought his venue and these antennae, they work great and he gets fantastic range.  I went with two PSC sharkfins on flex mounts, because they seem more durable and easier to pack up.  Also, I can aim them individually, and I can break one off for long walk and talks, etc.  But under normal configuration, they aren't the "proper" distance apart.  I know my range is as good as anyone I worked for in the past with antenna spread the "proper" distance.  It's simply impossible to apply lab conditions to a field application.

Robert

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Dave, you're right about the Tx-ing versus the Rx-ing antennae. But I think a wavelength apart is what is prescribed. As Rob writes here, it's possible to get good range with even lesser distances apart, but maybe one is not getting ALL the range possible with the antennae. I must admit that I am no expert here, so others who are experts could possibly help clear the mystery.

-vin

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I must admit that I am no expert here, so others who are experts could possibly help clear the mystery.

-vin

I am no expert either and I have discussed this "how far apart should the 2 antennas be" hundreds of times and still I do not have a clear answer. One thing, though, regarding diversity and range: it is my understanding that the diversity part of the antenna receiving system (whether it be antenna diversity of receiver diversity) works primarily to deal with phase cancellation and nulls in the signal that can cause RF drop outs. Each receiver, even diversity equipped receivers, are only using the signal from ONE antenna at a time, so that in a "fixed" situation, transmitting antenna in one spot, receiving antenna in one spot, no diversity switching even occurs. If you have good RANGE with just one antenna, the other antenna, even if it is spaced 1/4 wave apart, 1/2 wave apart or full wave apart, does not increase the range. The diversity switching does, however, protect from phase cancellation and nulls. Now, if you space the two antennas really far apart, 20 or 30 feet lets say, you are able to increase your "range" (coverage) not because of any diversity system but because you have provided 2 antennas with the further one serving to increase your coverage (it will be closer to the transmitter as the subject moves closer).

So, that is a lot of explanations, assumptions and mostly speculation by me, NOT an expert (so I may be all wrong on most of this) but certainly encourages someone here who IS an expert to clear this all up.

-  Jeff Wexler

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From Vin

But I think a wavelength apart is what is prescribed.

From Jeff

I am no expert either and I have discussed this "how far apart should the 2 antennas be" hundreds of times and still I do not have a clear answer

I think we may be talking at cross purposes here.

As I already explained, the two antennas* on one mast in my photo show two RECEIVING antennas feeding different receivers.

It is acknowledged that two DIVERSITY antennas should be more widely spaced for best results.

It is also acknowledged that a RECEIVING and a TRANSMITTING antenna should be more widely spaced.

The question (as I understand it) was, Do two receiving antennas need to be more widely spaced for maximum performance? That is, does one receiving antenna interfere with another closely spaced receiving antenna.

* Robert, I am open to correction on this point, however, I understand that, for radio use, the plural of antenna is antennas. For insect anatomy, the plural of antenna is the Latin antennae. (But I could be mistaken and acknowledge this may fast track me into the Pedantry Hall of Fame)

David

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* Robert, I am open to correction on this point, however, I understand that, for radio use, the plural of antenna is antennas. For insect anatomy, the plural of antenna is the Latin antennae. (But I could be mistaken)

David

I am sure you are right, David.  I started with antennas, but then had doubts and "corrected" it incorrectly!  I only wish my spell check knew what I was writing about.  Or perhaps it does, and thought I was stripping these poor insects of their antennae to use for my antennas.

Robert

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Two receiving antennas placed in close proximity to each other may effect the expected characteristics of the antenna, that may be good, that may be bad. (more forward gain/less forward gain....holes  the frequency response of the antenna....etc).  On transmit the problems could become amplified.

Lectro recommends placing the two diversity antennas at least 3 to 4 feet apart and 3 to 4 feet away from metal surfaces. This seems like really sound advice.

Placing a transmit antenna close to a receive antenna may cause the receiver to "de-sense" and experience limited range or outright interference.

And for Larry Long, I think the non-pro version of that software would be wise investment!

Back to BBQ and Beer!

Kevin

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CQCQCQdeWA8ARZ...

there are lots of interactions that occur amongst radio antennae (antennas?) in space, as well as interactions with other stuff, and in both theory and practice, more spacing is usually preferred, unless you desire that interaction. this applies to any and all combinations of receiving and transmitting antennae, so I would try to separate my receiving antennae even if they are going to different RX's.

and BTW, not all diversity systems are "either-or" antenna selection,  many are combining systems (includes blending and phase flopping).

actually, beam antennae, like LPDA's and Yagi's are utilizing the interactions amongst their individual elements, so are dipoles, and ground plane antennae!

The (usually bi-annual) ARRL antenna book $45.00 http://www.arrl.org/catalog/9876/ is a good source of information, and just looking at it might give you an idea how complex the subject is!  as radio amateurs, we are constantly discussing, designing, building, rebuilding and experimenting with our antenna farms! there is a lot of math and physics in radio antenna theory and practice.  while we sound folks wish it were, it really isn't "Plug 'n Play!!

sometimes things that should work well don't, and often things that shouldn't work well surprise us and work exceedingly well!

but even in practice, it usually works better if good theory is being applied.

" Since the first edition in September 1939, radio amateurs and professional engineers have turned to The ARRL Antenna Book as THE source of current antenna theory and a wealth of practical how-to construction projects. Use this book to discover even the most basic antenna designs-- wire and loop antennas, verticals, and Yagis--and for advanced antenna theory and applications. Many of the antennas in this edition benefit directly from advances in sophisticated computer modeling.

This 21st edition has been extensively revised to include information you can use to build highly optimized or specialized antennas. The book includes new content on Near Vertical Incidence Skywave (NVIS) techniques, phased arrays, S-parameters as used in modern vector network analyzers (VNA), Beverage receiving antennas, mobile “screwdriver” antennas, ionospheric area-coverage maps, and much…much more.

"

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