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 🙂 

[Harris K]

On 9/4/2024 at 6:18 PM, Constantin said:

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 

Since no one else piped in:

 

You're absolutely right that an RF wave wouldn't change polarity or phase in a pure vacuum. In the terrestrial spaces we're dealing with, there are many contributing factors. Air isn't a vacuum, there's plenty of matter for our wave to interact with on the way to us. While this generally won't be a significant factor at the distances we're dealing with, as temperature reach extremes and humidity increases this will play in more. There's also impedance to consider. In air this pretty much won't matter, but as our signal passes through other objects, reflection and distortion can occur 

 

There's also electromagnetic fields in a space to consider. Our hero signal passing through other fields can alter its polarity and phase. Again, this effect will usually be minimal in our use cases, but is impossibleA to quantify in the day. 

 

The biggest factor for us is probably surface interactions. A perfectly smooth surface exactly parallel to the emitting antenna would reflect our signal phase shifted 180°. When our reflective surfaces aren't perfectly parallel, the incident angles will be greater or lesser than 180°, and as we're in a three-dimensional space our polarity is going to be affected as well. With a less smooth surface, the interactions will get more complex. 

 

While not affecting the polarity of our direct wave, there's also  first order and second order reflection interference to consider, which spatial diversity of receiving antennae would also help. I'm pretty unclear on how much of a factor this is in the scenarios we're dealing with, so if anyone knows better or can point to a resource I'd love to learn more. 

 

Sorry for the wall of text.

[PMC]

I want a pair of glasses I can wear that will reveal all the RF waves around me with variable wavelength filters. Like the glasses Roudy wore in "They Live."

[Harris K]

On 8/31/2024 at 8:24 PM, cjh said:

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!)

CJH, I apologize for swerving this thread away from the intention so hard. 

 

I haven't really tried single zone multi anntenna, as my understanding is you'll just be opening up to a bunch of phase weirdness one way or the other when risking the same signal hitting two spaced antennae and being summed. I'm not sure how the BSRF AS-84 would be handling this electronically, so take me with a grain. 

 

But from the rest of your original post, it sounds like you have a lot of room to play. Having your antennae ~650mm apart is  roughly the bare minimum for the spatial separation of an antennae receiving 490mhz to be theoretically be doing anything at at least one full wave length apart. It is not the ideal or the rule or anything like that. Taking advantage of your diversity capabilities is getting those guys into different places for ideal reception. 

 

Single zone is not a good idea, to the best of my understanding. Which is also to say, you probably can't find much info on it because it's not a strategy that makes sense to implement. But if you have the units, play with it and report back. 

[Constantin]

On 9/21/2024 at 3:27 PM, Harris K said:

You're absolutely right that an RF wave wouldn't change polarity or phase in a pure vacuum

Actually, I have a feeling that this might not be true, but I am honestly not sure. In a vacuum and with weaker gravitational pull, I can imagine RF waves (and any other wave) to easily change polarity. Phase as I understand it would only be an issue when two waves interact or when one wave interacts with a reflection of itself. 
I am using polarity only because antenna manufacturers use it, when they say an antenna is horizontally or vertically polarized. This is definitely not the same as polarity in an audio signal. 
 

Here is a picture I stole off the internet that kind of helps to visualise what I mean by polarity: 

 

 

the pink line shows a signal radiating from a vertically polarised antenna, and the blue line from a horizontally polarised antenne. 
What I don’t understand is how pink can become blue. Yes, waves get scattered around and bounce off of surfaces, but the angle always stays the same (only in opposite direction). What I currently can’t imagine is a surface that would reflect pink line into blue line

[Constantin]

On 9/22/2024 at 9:32 AM, Harris K said:

Having your antennae ~650mm apart is  roughly the bare minimum for the spatial separation of an antennae receiving 490mhz

Not sure if I‘m understanding you right, here, but if so, then that is way off. 15cm is roughly 1/4 lambda which is the recommended minimum distance. Although there would be nothing wrong with spacing the antennas by 65cm or even 65 meters. 
 

[Constantin]

On 9/22/2024 at 9:32 AM, Harris K said:

single zone multi anntenna, as my understanding is you'll just be opening up to a bunch of phase weirdness one way or the other when risking the same signal hitting two spaced antennae and being summed.

I think your general conclusion is correct, in that summing two antennas into one input could cause problems, and I don’t know enough about RF to say any of the following or the preceding with any authority. 
But my understanding is that RF is not the same as audio. Phase issues aren’t really issues so much, unless actual cancellation occurs. Phase issues occur in normal setups, too, when the primary wave gets combined with its own reflection. As I understand it, Lectro’s phase diversity actually makes use of this to their benefit

[Harris K]

Constantin, maybe this should move to DM because this risks losing educational value for anyone. 

15 hours ago, Constantin said:

In a vacuum and with weaker gravitational pull,

Fair enough. 

 

15 hours ago, Constantin said:

Yes, waves get scattered around and bounce off of surfaces, but the angle always stays the same (only in opposite direction). What I currently can’t imagine is a surface that would reflect pink line into blue line

An uneven, non-uniform surface. Maybe a perfect 90 degree rotation is unlikely, I really don't know, but the reflections are occurring in three dimensional space, and the incident angle will happen in three dimensions. 

 

15 hours ago, Constantin said:

15cm is roughly 1/4 lambda

I always remembered this as minimum distance being at least one wavelength apart, though on re-researching this now I'm seeing a variety of sources claiming 1, 1/2 and 1/4 are each the best practice (although this seems to be largely sound people discussing it so now I really don't know).  So at minimum I retract my confidence in my assertion. 

 

14 hours ago, Constantin said:

Phase issues aren’t really issues so much, unless actual cancellation occurs

I agree, and agree that in a single antenna situation first and higher order reflections are also a problem. However, in a system with two antennae in the same space being summed, you're almost guaranteed to have slight timing differences between the two, which upon summing would be a great way to try to create phase interference. 

 

There is not, to the best of my understanding, a concern about comb filtering as in audio, so agreed there. 

 

Edit: This was exactly wrong, you will absolutely see comb filtering. It won't produce the same audible effect as in audio.