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RF Venue Diversity.


Prahlad Strickland

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Loving this,  the range is phenominal with my QRX200's and great for portable simple setups since it has both dipole / shark in one, works great indoors too.

 

My question is,  in Dual mode on qrx,  both channel A and B are using both shark / dipole correct?  I'm heavily presuming based on what I have read that both channels use both whips / both antenna channels.    

 

A production friend (who's a dp here in hawaii) was wondering why i'd mix dipole / shark since channel A would use shark, and channel b would be on dipole.   

 

Anyways,  I told him both use both.  But wanted to confirm in case i'm off my head again.

 

cheers

 

Prahlad 

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In the video, they say that each channel operates individually, so i guess one is the fin and the other the dipole

 

i'm sure the manufacturer knows the answer to that question.

 

also, there's a whitepaper available: http://cdn2.hubspot.net/hub/316692/file-353615134-pdf/Diversity_Fin_Antenna_and_Polarization_Diversity.pdf?t=1382404904000&t=1426371917000

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I use my QRX100 more in dual mode than single and can attest that at least for the 100, they will switch antennas.  If a receiver has too low of a signal on Al, it will switch to B, and remain on B while the signal is good, even if lower than A, but as soon as a problem, then switch back to A.  You can easily confirm this by simply unplugging one of the SMA leads on a receiver.

 

There are many instances where I have just hooked up 1 shark fin when in a bag just when I needed that extra range, and even hand held the fin while tracking super long beach shots for example.

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Yes, and? That's what I said. But I'm pretty sure that inside a QRX both receivers have access to both antennas, just like on any other dual channel diversity receiver.

Just confirming what you said.  I'm unsure what the QRX does within their antenna circuitry, but both Rx should be getting a mixture of both antenna signal.

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Lots of confusion here about diversity reception. I will try and clear up some of it (but since I am not an expert I may end up just muddying the waters further). Regarding diversity in general: there are 2 types --- antenna diversity and receiver diversity. Lectrosonics uses antenna diversity. Zaxcom and Audio, Ltd. (and IU don't which others) use receiver diversity (clarification to follow). Using the RF Venue single piece antenna with Lectrosonics (or any other antenna diversity system) both the antennas are available to the receiver. The diversity reception decides which antenna is giving the best signal and then switches to that antenna. Several people have weighed in on the potential and relative advantage of using a pair of antennas that are of different types or two of the same variety (for example, 2 shark fins) but polarized (orientation) differently. With the RF Venue the advantage, beyond just the obvious one piece design, is that the receiver will have the chance to receive the signal picked up by two different style antennas, each with their own characteristics, strengths and weaknesses.

 

Now, Zaxcom and Audio Ltd. receivers are all diversity, dual receivers in one box and each receiver gets its signal from the 2 antennas (whether they are sharkfins, dipoles or a mixture of the two as in the RF Venue). The diversity system determines which receiver has the best signal, chooses that receiver to output audio to your mixer's input. My understanding is that this receiver switching is preferable to antenna switching (but obviously antenna diversity switchings works for the most part otherwise no one would ever be using Lectrosonics wireless). Zaxcom wireless being all digital have an advantage utilizing a diversity system because they can actually compare with checksum verification the integrity of the data packet that is the signal. I should clarify that Zaxcom receivers in single mode work just as I have described but in dual mode (where each receiver is used to receive 2 channels of audio) the diversity system is antenna diversity (like Lectro) not receiver diversity. Again, it all seems to work.

 

So, the only thing we are actually trying to determine here is whether it really works to utilize 2 antennas of different types, whether this is an advantage or of no significance or a liability. I think the only way this can be determined is to get enough people field testing the RF Venue and comparing it to the typical and common use of 2 identical antennas. These tests can be done with ANY of the wireless out there that use either diversity system in their receivers.

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A succinct and clear explanation, Jeff. I have a follow up question, which may be more in Larry Fisher's wheelhouse, about the practical benefits of Lectrosonics SR series Ratio Mode. Is it a combination of antenna diversity and receiver diversity? If it is, how am I benefitting from using it, since with the SRs, I'd be using the same two receiver antennas in fixed positions for each integrated receiver in the SR which will have (presumably) identical range and reception to the worn transmitter? What does Ratio Mode do that is better than plain ol' antenna diversity?

Sent from my iPad using Tapatalk

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Hi all, 

 
I work at RF Venue, and have some thoughts. 
 
The Diversity Fin will work well on the QRX200, but not for all of the reasons discussed here. 
 
Jeff, you are correct that one of, but not the “primary” advantage, of the Diversity Fin is that it is feeding two different types of antennas into the diversity receiver. I will get to this in another paragraph. 
 
The primary advantage of the Diversity Fin is that it eliminates multi-path interference and cross-polarization fades through polarization diversity. There are many, many, many different things that can cause a dropout. Multi-path interference is one of the most common. 
 
Polarization is a restriction of the movement of orientation of the electric field in an electromagnetic wave. I thought I had a blog post on the subject but can’t seem to find it right now. This video does an OK job describing polarization in the context of the Diversity Fin. 
 
On the Diversity Fin, the LPDA element and dipole element are oriented at right angles to one another, and hence branch A and branch B of the receiver are able to choose signals from two antennas that vary in polarization. 
 
Normally when you are putting one antenna into branch A of the receiver and another into branch B of the receiver you are practicing spatial diversity, which lowers the probability of encountering a multi-path null considerably because it is very unlikely that a dropout will occur across both antennas simultaneously when those antennas are spaced a physical distance apart. 
 
The Diversity Fin offers a significant improvement in multi-path/phase related dropouts over spatial diversity systems. It will be most effective in *indoor* environments where there are an abundance of reflected signals, but it will also do the same thing outdoors. 
 
I am thrilled to hear Prahlad is experiencing improved range on his system using the Diversity Fin, but I want to make sure that the production sound community knows that The Diversity Fin is not designed to maximize range. Certainly, the higher gain of the LPDA element will give improved range over a lower gain antenna or a poorly designed directional antenna under the exact same conditions, but pitting the Diversity Fin head to head against high gain directional antennas by walking a Tx out until a drop defeats the point. 
 
If you are looking to maximize range, a pair of high gain helical antennas is likely to give more range. RF Venue manufactures a collapsing helical antenna called the CP Beam. Other manufacturers also make helicals, probably the highest gain you can get comes from PWS. (But remember the higher the antenna gain, the narrower the beam width!) 
 
Location sound pros enjoy the Diversity Fin because it is more effective at reducing phase related dropouts than two paddles but only takes up half the space, a good thing on the cart. 
 
They also like it because, as Jeff points out, there are two different types of elements and, paired with a diversity switching circuit, nearly gives the benefits of having two antenna coverage types in one, somewhat like having an antenna that is both directional and omnidirectional at once. Ie., if the talent wanders out of the coverage area of the narrow LPDA, the receiver will usually switch to the dipole. 
 
And speaking of receivers, there are a lot of different diversity receive methods out there. Broadly, as Jeff has discussed, I think they can be grouped in two categories. 
 
- A single receiver circuit that switches between two antennas. I have heard this called “antenna switching.”
 
- Two independent receiver circuits that switch depending on which is receiving the stronger signal from two antennas. I have heard this called “receiver switching.”
 
I have seen block diagrams for all sorts of permutations of these and I won’t propose to be an expert on all of them, or any. I am not an engineer by training. Also I’m not sure the terminology is used consistently across manufacturers. 
 
I do know that receivers with a single receiver circuit that passively combine two antenna signals without any kind of “intelligent” switching or combining are rare. That is, a receiver that simply combines the two attached antennas and treats them as some sort of single array or single antenna—those guys are hard to find.  
 
I do not know what the “dual” and “single” modes in the QRX200 refers to exactly. How they are described on Zaxcom’s website leads me to believe that “dual” might be some sort of receiver switching, and “single” may be antenna switching. However I doubt that “single” mode is a passive combine mode where both attached elements are treated as a single antenna. Whatever they are I’m sure Zaxcom has a good reason to use them as they make some great gear.
 
The benefits of the Diversity Fin will be present in both modes as the probability of a encountering a null will be nearly zero either way. 
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Thank you, Alex, for adding to this discussion. You have clarified a number of things and one of the things I learned is the term that describes antenna orientation: polarization diversity. I did mention antenna orientation but didn't go far enough to point out that people have experimented with using 2 antennas of the same type but orienting them, one horizontally "polarized" and one vertical. This is in an attempt to have a diversity system to deal with multi-path (which we all seem to know something about) AND cross-polarization issues. The RF Venue does this one better by utilizing 2 separate TYPES of antennas and orienting them to deal with polarization.

 

One correction regarding Zaxcom: each receiver has actually 2 separate receivers in the box. In SINGLE mode the diversity system uses receiver diversity, switching between the 2 receivers, which ever is getting the best signal. In DUAL mode, it has to use both receivers, each one for their own received signal, so receiver diversity is not possible. In dual mode, each individual receiver utilizes antenna diversity.

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I did mention antenna orientation

 

Sorry, missed that. 

 

About the QRX200, do you mean that in dual mode the two receiver circuits are actually used as non-diversity receivers for different signals on different frequencies?

 

If so, then the Diversity Fin would not provide any benefit over just attaching a dipole antenna to one branch and a LPDA to the other. 

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Ok. I've noticed, with MY RX-12 that there is no diversity whatsoever when using the receivers in Dual mode. If you unplug the B antenna, the B channels all go to hell while the A channels stay strong. Maybe mine is not setup correctly, and the box is very new to me, but it doesn't appear that I have antenna diversity in Dual mode. Glen Trew once explained to me the way the venue does its thing, and it was quite different from the way I imagined it. Maybe he or Larry can weigh in on that one.

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It should share antennas internally with internal circuitry providing amplification and switching appropriate to the design. Each receiver switching to the best antenna signal... Trew told me, however, that this isn't exactly how the RF Venue goes about its business.

 

So in theory it should still work with one antenna? 

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Ok. I've noticed, with MY RX-12 that there is no diversity whatsoever when using the receivers in Dual mode. If you unplug the B antenna, the B channels all go to hell while the A channels stay strong.

Todd, any diversity system requires 2 antennas. If you unplug one of the 2 antennas it's not surprising that you have "no diversity whatsoever".  Am I missing something?

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