Single zone multi antenna setup

[cjh]

Currently in RF rebuild mode on the cart and have installed a BSRF AS-84 antenna distro which has the option to have 2 antenna diversity pairs. I understand the multi zone set up scenario but keen on some user feedback re single zone multi antenna set up. Consistent coverage is getting harder given sets have much more rf as well as the general increase in environmental rf. I Also run digital (zax) wireless which suffers a little more from line of sight issues so interested in options of getting antenna coverage from more than one direction of a set. I understand cable loss, gain matching, the use of combiners / splitters and when / where to use or not use active gain. 
My decades long standard set up has been a pair of fins above the cart about 650mm apart. Long coax runs (up to 50m) when I’m remote from set work fine, it’s not signal strength I’m after but more coverage area, ideally from another direction. 
 

Standard single diversity antenna - I’ve rarely separated my fins more than the antenna bar width, on occasion when in a jam I’ve run one off on long coax to give more coverage area but often last minute and not we’ll set up re coax loss etc. 

 

Things I understand but am not 100 on:

 

The pros and cons / best practice of a diversity setup when antenna are separated from each other. One on cart, one nearer set but opposite side, or either side of set left / right etc. 

 

Overlapping antenna coverage area, mainly using fins but all other antenna designs on the table re best set up.
 

The RF Venue spotlight looks great, has anyone used this in a diversity set up, what / where was the second antenna etc. 

 

Apologies for opening the RF can of worms again, it is indeed a black art but one I am enjoying a deep dive into. Have watched multiple online tutorials re this and lots of good info but most of it is about multi zone setup not single zone multi antenna set up (which was never really req back in the day of clear rf!)

 

Thanks,

Chris. 

 

[The Documentary Sound Guy]

You already know more than I do on this topic, but since you're using Zaxcom I'd chime in and suggest experimenting with using at least one dipole in combination with ZHD modulation.  At least indoors (i.e. studio), dipoles can allegedly outperform sharkfins because they can capture reflected RF.  And ZHD allegedly does better in high-reflection environments (bonus:  this can mitigate line-of-sight issues).  Testing out this combination is something that's been on my mind ... since you are also testing, I figured I'd toss it out there as a suggestion.

Beyond that, I only have the standard advice of getting the antennae up high and keeping them apart so that multiple lines of sight are possible.

[Constantin]

7 hours ago, cjh said:

The pros and cons / best practice of a diversity setup when antenna are separated from each other. One on cart, one nearer set but opposite side, or either side of set left / right etc. 

 

I think there is no rule to this. Whip antennas as found on the transmitters radiate in an omni pattern, but the body they are attached to will block a lot of signal in that direction. If that is where your antennas are you’d lose a bit of signal strength, it would make sense to have another diversity pair on the opposite side of the set. But it kind of depends on how your actors are moving around. Ideally,  you should have antennas there where the signal isn’t obstructed by the actor‘s body. 
I would say this could be achieved with a single pair as well. I did try this once and it worked really well to extend the coverage area. But with two pairs you‘re definitely better off
 

Using omni antennas on your receiving end will not mitigate this and they also don’t have the signal boost quality that comes with the shark fin design

[Fred Salles]

Just now, Constantin said:

Using omni antennas on your receiving end will not mitigate this and they also don’t have the signal boost quality that comes with the shark fin design

For the first time I dare to disagree with Constantin here 😉

First there are several omni active antennas that includes gain and filters, (Wisycom AFDA for example). Or were you talking about actual quality as in performing better?

Secondly I found that when working indoor the combination of one omni and one directional antenna for the diversity duo works very well. I believe you do benefit from reflected RF signal from the omni when in tricky situation. Sometimes I use both omni and remoting one away from the cart (example: tracking shot following characters walking within two or several rooms in a house.)

 

[Constantin]

9 hours ago, Fred Salles said:

For the first time I dare to disagree with Constantin here 😉

Really? This is the first time? I‘m surprised!

 

I think I actually wanted to write: „omni antennas wil not mitigate this, BUT they don’t have the …“

Anyway.
Yes maybe the omni can work well, too. I suppose they may well worl better indoors and sharks probably perform better in more rf congested areas. 
But while I don’t have any measurements or other proof ready to strengthen my theory, to me it always seemed like when I am really far away from the transmitter, my sharkfins could still receive a signal (when they were pointing in the right direction), when omnis were already crapping out. 
but, YMMV. I‘m fine with that

[Fred Salles]

I have the same experience outdoor with the sharkfins pointing at the actors, they surely outrange the omnis.

Indoor however, especially in a place where you have one or several rooms between the antenna and the actors, the omnis perform better in my experience. Again, choosing both in problematic indoor locations, one directional and one omni is worth the try and if your rx allows it you can see which one of the 2 antennas is chosen by the machine.

[Constantin]

22 hours ago, The Documentary Sound Guy said:

dipoles can allegedly outperform sharkfins

Just to pick this up before a develops a life of its own: sharkfins are dipoles. It‘s in their actual name, LPDA where the D is for dipole. a dipole can be made to be either omni-directional or directional. The classic whip antenna is a monopole and it is omni-directional, as is Betso‘s Bow-tie, for example, which is, well, a bow-tie antenna, but it’s also a dipole. 

4 hours ago, Fred Salles said:

one directional and one omni is worth the try

It certainly is worth a try. I did try it a few times, but I have not been able to produce significant improvements over two sharkfins, but that was only in that given situation and I never made any real comparisons. What you are saying about the reflected signal possibly reaching the antenna from the side rather than straight on, does appear to make sense. 

[The Documentary Sound Guy]

Thanks for the correction.  I was thinking about omni dipoles (à la Lectro SNA600, or Betso Bow-tie).  Was trying to distinguish that from monopole whips.

Aren't LPDA technically arrays of multiple dipoles?  I wouldn't have categorized a sharkfin as a dipole for that reason, but I certainly have lots to learn on the topic.

[Constantin]

1 hour ago, The Documentary Sound Guy said:

Aren't LPDA technically arrays of multiple dipoles?

Yes, that’s what the A is for. 😉
log-periodic dipole array

[cjh]

Thank you for the replies, keep ‘em coming. 
 

Anyone used the rf venue spotlight? Was it in a diversity configuration with 2 of them or another type of antenna?

 

Anyone switch from fins to helical antenna who can provide user review. I recently got a used pair of the big psw helicals and will test A/B test them with fins. They’ll be studio use only though as big sails in the wind. 
 

Heres the new build, will be testing rf side soon. 
 

[Harris K]

A while back I had a long chat with a NASA engineer about how they approach diversity radio receiving for interstellar communication, and I've kept a paradigm he gave me in mind since then. 

 

In those types of radio systems, they consider two kinds of diversity: spatial diversity and phase diversity. Spatial diversity they are thinking of in terms of countries and hemispheres, but the approach they have is a lot simpler than I'd assumed. Get the second antenna where the first one won't be receiving. It's not very magical, but it keeps working out for me. 

 

Phase diversity is also kind of simple. When you can't space out your antennae, you can diversify to optimize for the orientation of the Tx signal. We all know it's best practice to have your Rx antenna in the same orientation as you Tx antenna. However in the real world, if you're not getting line of sight then it's impossible to determine the phase of the original signal by the time it's reflected to you. I tend to think orienting your antennae for phase diversity doesn't make sense indoors, but can start making a lot of sense in certain exterior situations or for bag work where spatial diversity is close to zero. 

 

Anyway, I guess my point is sometimes it makes sense to be dumber about this. The intention of diversity radio systems is to set yourself up for success. If both your receiving antenna are in basically the same problematic position, you're not really giving the diversity system any advantages. 

[Constantin]

7 hours ago, Harris K said:

you can diversify to optimize for the orientation of the Tx signal

I always thought this was polarisation not phase, but in any case I was always curious about this. Some wireless manufacturers used to sell their receivers with one antenna sideways and the other straight up. It’s rare that I would have a transmitter sideways, but it does happen and it’s good to have a sideways antenna ready for that. However, I don’t understand how a rf wave can change its orientation once it’s gone from the transmitter. So I can’t see an advantage in having both at the same time, but like I said, just because I don’t understand it, doesn’t mean it won’t happen. 
phase diversity as I know it is how Lectro receivers work(ed) for a long time. 
But at this point we probably need @LarryF  in this room

[Harris K]

Polarity does seem like a better descriptor, but I'm repeating the language used by someone else, so blame him.

 

My understanding is that reflected signal's orientation will change relative to its incident angle, so the concern is when you don't have direct signal from the Tx. Moreover, in the real world there's no way to calculate that new orientation in an actual and complex space, so that's where it starts becoming more art than science.

 

If I'm wrong about anything here, I would appreciate being corrected.

[Constantin]

3 hours ago, Harris K said:

If I'm wrong about anything here, I would appreciate being corrected.

Hence my page for Larry, if anyone knows it’s him. 
I just can’t imagine how the wave would change orientation mid-air. I guess if it hit a parabolic dish or something it could happen.

in space on the other hand, maybe it rotates all the time, who knows, that is certainly easier to imagine for me

[cjh]

There are also very good resources via the RF Venue website. Keeping it simple and not overthinking it is good advice too. The phase vs polarity is a good question and Google nailed it, they both describe the shifting of  the of the original waveform where polarity is a complete 180 degree shift and phase is used to describe a shift of anywhere between 0 and 180 degrees. So from our POV we are dealing with phase which particularly indoors constantly varies with changes in reflection angles. Clean line of sight coverage fins are going to get solid reception but when line of sight is blocked the strongest signal getting to your antenna may well be a reflection which will have a varying amount of phase difference. Helical antennas really making sense here. I presume we all generally have fins because they are smaller more suited for location use and for years they have been ok but now with the world of congested RF I’m thinking helicals are a better option. 

 

 

[Constantin]

I‘m not sure if Google really did nail it. With regards to audio waves it seems correct, but antennas can be vertically polarised or horizontally polarised. That shouldn’t really affect phase as the moment in time a signal radiates from an antenna would still be the same, but with horizontal polarisation the rf wave sort of lays on its side, whereas with vertical polarisation its upright. 
I‘m just curious how it could change from one to the other, but I don’t want to take this thread too far from its original question, so maybe I have to find this info elsewhere 

[cjh]

40 minutes ago, Constantin said:

I‘m not sure if Google really did nail it. With regards to audio waves it seems correct, but antennas can be vertically polarised or horizontally polarised. That shouldn’t really affect phase as the moment in time a signal radiates from an antenna would still be the same, but with horizontal polarisation the rf wave sort of lays on its side, whereas with vertical polarisation its upright. 
I‘m just curious how it could change from one to the other, but I don’t want to take this thread too far from its original question, so maybe I have to find this info elsewhere 

Yeah I get your point, my description is easy to understand sound wise but less so RF wise in that regard. Helicals tho, def going to experiment with those. It’s these kinds of questions and the replies to them which bit by bit help to decipher the black magic of RF. Well they’re helping me anyway 🙂