Antenna Mast

[filmfreak]

Greetings Group

I am about to build my premier cart setup and even though I have covered most of the aspects after thorough investigation and feedback there are still some issues that need to be solved.

The cart I am getting is the rast order vk cart --> http://www.rastorder.com.au/product_vkmain.htm  because the design and sturdiness really suit my needs and I like very much the modular design concept plus Rob is a very helpful and enthusiastic individual who is up for modifying each cart to suit specific needs.

Ii is still not 100% clear to me which antenna setup I should use and also how to setup the mast.

The VK cart has a dedicated antenna pole holder so it is clearly suggested to set up the antenna mast on the given position.

I 've noticed that most of the cart setup pictures have their antenna mast at the back of the cart and on a vertical axis that is usually at the the center of the cart's width.

I guess that it is not that important as to where exactly the mast will be positioned and it comes down to practical issues considering the cart's ergonomics and functionality.

I 've decided to use the given position on the cart, in order to have the back side of the cart free to place boom poles . I am thinking of a possible 3rd boom at the back of the cart but would like to ask the group if anyone knows possible benefits of positioning the mast at the back side of the cart instead of the right hand side.

Some highlights regarding the mast installation :

 

i)  How many metres should the pole be extended ? I know that the higher the receivers are the less interference they face and also they can cover the transmitters if they are on a   

    higher position than other equipment on the set but is there a critical height that the pole should be extended to ?

ii)  Which materials should be favored / avoided in order to build up the mast's pole from scratch ?

    Which antenna poles are there available on the market ?

iii) Regarding antenna types, I know that the best possible combo for a conference hall p.e. is a mixture of shark fins and omnis - sharks to direct the signal and omnis to cover a wide area.

    I noticed that most carts are using sharks in parallel but there are also some carts that use sharks in combination with an omni like the Sennheiser A5000CP.

    A sound engineer advised me to use Yagis. they come in reasonable prices and depending on how many parts they are made of  their receivability is increased.

    Which type is more commonly used and does it have to do with how wide the area we want to cover is and also how much is the receiving signal amplified or does it come down

    to certain flexibility and downfalls of sharks versus omnis versus yagis ?? 

iv) Should the receivers be always in pairs so the horizontal as well as the vertical frequency waves will be received in the best way possible ?

    Should the antennas be placed parallel or should they be placed - on a pair  -  vertical versus horizontal for optimum results ?

v) Is it possible for someone to break down the signal flow from the antennas to the amplifying and distributing stage of the chain all the way down to the inputs of the mixer ?

vi) Is there a critical distance of the antennas between them that is related to the angle of the coverage ?

    In other words in the case that I will make a horizontal bar and mount 2 shark fins is there a distance to angle ratio of the distance between the 2 fins that I should take in account ? 

I will not purchase a vr field which looks like a really neat and compact solution, so this option is not on my plans.

Thanks in advance and I hope that these questions can benefit other engineers who are also building up their premier cart setup.

Happy New Year and Warm Wishes for an innovating and prosperous 2009 to everyone !

Regards

  Aris

[RPSharman]

Aris,

Visit the Lectrosonics website, and also listen to the RF seminar recently given here in Los Angeles.  There's a link somewhere in this forum.

Antenna type and placement is an inexact science.  I use 2 x batwings, but if I determine the gain is "too high" and it's bringing in interference, i might move closer to set and use the whips.  Or I might put the portable receivers right on set.  The real trick is using short 50ohm cables with 50ohm connectors.  If you have the antenna on a long cable, then run it out the length of the cable.  There's no point putting on a 50ft cable to run the antenna an extra 6ft.  Signal loss down the cable is a major contributor to poor signal, but I haven't experienced the improved reception being worth the inconvenience of the THICK 50ohm cable.  I would also take the rugged convenience of the batwing over a Yagi.

Placement of the antennas in relationship to the transmitters simply comes with experience, and even then you'll discover that even with identical circumstances, results will vary!  Good times.

Robert

[filmfreak]

Thanks Robert and Scott

I guess it is a mix and match scenario based on experience Robert, just wanted to take precautions and examine various parameters.

Scott,thank you very much for the detailed urls and the really detailed info on your exact antenna mast setup.

Got loads of homework  now !!

Regards

[ve7kjr]

Hi Aris, Years ago before the shark fins came along, I would have my antenna system mounted on a c stand and sand bags borrowed from the grip dept. The system consisted of a dipole(lectrosonics sna600) and a 6 element yagi for gain and distance.The arm of the c stand was horizontal with the antennas at each end, I used very low loss coax cable about 25 ft. and even mounted the comtek transmitter in the center of the c stand. The height depended on how far I was from set or how far away the actors were. I remember long shots where the actors might be 1/8 of a mile away with a very long lens. I had no problems with the rf. Putting the comtek transmitter up there solved reception problems at video village as well.If it was a panning shot my third could rotate the stand to keep the yagi on the actors, remember a yagi is very directional just like a shotgun mic. The down side to this was the amount of time it took to set up and take down each day and every time you had to do a move you had to disconnect the cables from the sound cart. Ever time you connect and disconnect an rf connector you are causing wear and tear on that connection, if you do this several times a day you will end up with less than ideal rf reception over time.I have made it a point to change to new connectors on the cables and cart once a year where connections are connected and disconnected. I inspect and listen to the rf cables to see and hear if there is any breaks in the shield, if there is you will hear a noise as you move the cable. When working in rain, I protect the connections on the antennas and the antennas themselves. Water in the coax is not a good thing and the antennas are water resistant not water proof.

Ok lets jump to present day. The fastest and easyest setup are the antennas mounted on a single boom pole, an old one you don't use anymore for booming but will work well for a mast. A shark fin (log Periodic) with the ambient "quicklok" "quick release tip" mounted to the shark fin and boom pole. No fuss no muss, on and off in seconds. A lectrosonics sna600 folding diopole antenna with some sort of clamping adaptor so you can clamp it a foot or so below the shark fin on the boom pole. Both antennas should be vertical, 10 or 12 feet of low loss coax cable (9913f has a loss of 1.9db per 25 ft. at 700 mhz which is not very much) should be more than enough, tape or heat shrink the two cables every foot to keep them neat but leave enough seperation at the ends of the cables so you can connect them to the antennas and to your cart.The most important point of all is to add a strain relief at both ends of the cable, a piece of sash cord will work fine. Way too many times I have seen coax cable get pulled right out of the connectors, had there been a strain relief on the cable it wouldn't have happened.Have two sets of cables made up,one for back up.You should be able to mound the boom pole on the back of your cart on either side or the middle of your cart whatever works for you as I have not seen your cart. The beauty of this system is 1 an easy fast setup.2 when it comes time for a short move all you have to do is lower the pole and don't have to undo any connections. The boom pole will give your antennas more than enough hight to receive your transmitters and you can be some distance from the set. If working in the rain just put a plastic bag over the antennas/connectors to keep the water out.I hope this is all make sense to you, over the years I have found this to be the fastest/easyest and a very reliable setup.

Phil (VE7KJR)

[filmfreak]

Hi Phil

That's very descriptive and the way you also wrote about your early days set up cleared many questions in my head.

Thank you for putting so much time in.

I can see that you changed from a horizontal setup to a totally vertical one.

Any particular reasons for doing this move over the years ?

Why did you substitute the 5 element Yagi antenna with a log periodic shark ?

Does it have to do with signal reception, design sturdiness, very directional ( Yagi ) versus directional ( Shark ) or a bit of all 3 factors ?

Rf cables inspection is a very useful hint and I will definitely bear this in mind.

I can see your Ambient quicklock suggestion and that is a very helpful one. I will rather "snap" off than twist whatever is on top of the pole. Handy ! 

Could you please post a picture of the strain relief loops ?

As you underline it is a very important issue in order to protect your cables.

Are you amplifying the signal and are you also using a router before you will feed the 2 antennas on your wireless ?

I noticed that the Lectrosonics sna600 folding dipole antenna is common in your's and Scott's setup. I will investigate the product further.

Let me see if I got that right :

Place the Shark on top of the pole and then clamp a Lectro sna 600 at least a foot below it, both on the same vertical axis which should just cross the dipole in half of its length.

The sna 600 should be placed vertical and the antenna setup would be something like an m/s setup ( if you would just look at the polar patterns ) where the sna 600 would be the equivalent of a figure of 8 ?

Thanks and hope I am not tiring you with loads of questions.

I want to break down all components of the setup as radio signal and communications are an integral part of today's demands.

I am definitely checking the rf seminar on locationsound.com soon . 

[studiomprd]

" with an omni like the Sennheiser A5000CP. "

that antenna is very directional. neither vertical nor horizontal, it is circularly poloroized.

" A sound engineer advised me to use Yagis "

you actually often get the best information on antennae from RF engineers, including HAM radio folks.

[FSBELLA]

Hey guys, Rode re-designed there boom poles ($99.00) and they are perfect for a 9' antenna mass. early on when they 1st came out with the poles, I sold them strictly for that application, but they had some knuckle problems. the RODE rep said they fixed the issue. (just ordered a couple 9' poles for a sound mixer to use exactly for this deal)

the bang for the buck factor- you cant go wrong.

mixers have used, mic floor stand, and ofcourse flex arms.

good luck

[Richard Lightstone, CAS]

Frank,

Well I went through 2 of the Rode poles - all breaking at the very top. Switched to a more expensive K-Tek and have never been happier.

My two previous poles had the supposed "lifetime guarantee". They were never replaced by Rode and might be in the trash by now.

RL

[Jeff Wexler]

Well, I will weigh in on this since I have had to configure a few antenna masts in my time. For years while using my Audio, Ltds., I really got away with just using 2 short whips mounted to the back of my cart. They were fitted with right angle connectors, I would park them face down and when we had to do a shot that needed the wireless (rare) I would rotate them upright and I was almost always close enough. Not the case these days, as we all know, and when using log periodic sharkfin type antennas I knew I had to get them up in the air. On the last 2 carts I used the center section of lightstand tripod, mounted to the side of the cart. The new cart using a very lightweight Lowell stand --- I just pull the tripod legs off and devise a way to mount it to the cart. This has worked well for me.

-  Jeff Wexler

[soundtrane]

I got a pair of "boom poles" machined to specs - i wanted the poles to sit inside my aluminum upright tubes on the two sides of my cart. The poles go up to 12 ft. Standard 3/8" studs are on the top and i use an acrylic bar, 1 1/2" by 2 1/2 feet long with holes on the ends and one in the center to put on the poles. I use the Lectro SNA or the PSC sharkfins for my Sixpack. I also have SNA's for my Sennheiser IEM Tx x 2 which I use to feed audio to boom ops and director/scripty/video village.

Start of the day setup involves pushing the boom poles into the upright tubes on my cart and fixing the acrylic bars with 3/8" female nuts. Then depending on the situation, either the SNA or the sharkfins go up.

I also hoist the Ambient TC slate Tx up one of the poles using a small pouch and a re-suable cable tie.

I find this setup very light and easy to use. Erecting and dismantling take just about two minutes.

-vin

[ve7kjr]

Hi Again Aris,

To answer some of your questions, The switch from c stand setup to a single pole setup was made for a faster setup/ takedown/ or a move. Remember how I said I would have to undo and redo the bnc connectors every time I would have to move the sound cart and how this causes wear and tear on the connectors. Chances are really good that you will have to move your sound cart several times a day as the set changes or you need power and the electric dept. has moved their drop to somewhere else. Then there were days where I would have perfect cart parking, not having to move all day and could cover several sets on one stage, just swing the antennas a bit to hit the set we were shooting on. I used wireless boom all the time for several reasons, faster setups/ two man crew/ rapid set changes etc. etc. Some mixers will cringe at the idea of a wireless boom but over the years the transmitters sound pretty good when setup right,,, never as good as a hard cable but still pretty good.

Yagi verses Shark Fin

The yagi antenna design has been around for a long time and has proven itself to be one of the best antennas for rf gain. The more elements there are the more rf gain you will have (3db per element) however they are very directional and need to be pointed or amied just right. They also offer great front to back rejection.

The Shark Fin

The shark Fin has been around now for a number of years and is a log periodic dipole design, it has a very wide bandwith 450 to 862 MHZ say (depends what they are cut for)and has a gain factor of 4 dbd over a dipole. Do they work, yes they do,and I use them all the time now, do they have a much gain as a yagi, no. Would I put one on a long cable run, no. However with that being said Lectrosonics now offers a "shark fin" design with an rf amplifier that is phantom powered and adjustable up tp 12db gain right at the antenna. I have not played with one yet so it is not fair for me to pass judgement on the design, but in

theory would work well on a long run of cable.Nor I have not used the sennheiser a5000cp which is a (circular polar helical design), a design that has been around for a long time as well and now is beign introduced to the ET industry, offers 8dbi gain, wide bandwith 450- 960 mhz / very directional / and weight 3lbs. (A bit much) Do the work,,, sure they do ! Would I use one,,, only if the situation called for it.Seldom is the rf arriving at your your antennas in the phase that you would like it to be in, as rf travels at light speed it will bump into it own reflections, bounce of just about anything and turns itself  from vertical to horizontal and back and forth many times over. What happens is a lost in rf siginal level at the recieving end. This is the beauaty of the a5000cp design, to be able to deal with this problem. The other way around is SmartDiversity, which  is a microprocessor controlled technique that automatically analyzes audio content and RF levels to determine optimum timing for the switching activity. Active analog antenna phase switching techniques use both antennas at the same time, with 180 degree phase switching to help keep the received signals in phase and minimize dropouts. When the overall RF signal strength quickly drops, the phase of one antenna is switched 180 degrees. If the switch increases the RF level, it will remain latched in that position until the RF level quickly drops again. Both antennas are used at the same time, so overall operating range is also improved. As far as antennas spread apart,,, they only need to be a 1/4 wavelength apart from each other, doesn't matter if they are beside each other in a horizonal plane or one below the other in a verical plane as long as they are 1/4 wavelength apart.If you want to spread them more, go ahead if that will make you happy.

I feel I'm getting too deep into this for you, The bottom line is, you will have to think about the kind of work you are about to do and what antennas will work for you. Antennas are just tools, to do the job by. Understanting what works for you and what doesn't work will be the key for you. Rf is crazy stuff, trying to understand it fully can take a lifetime. Experience will be your best teacher ! You really don't want to have to shout out "another for sound please" and then the director asks WHY and you have to say I had a drop out in the radios SIR.  Sure drop outs will happen even to the best of us from time to time, remember I said rf is crazy stuff. If you are using wireless a lot, and most of us are forced to for whatever reason, having a good antenna system will save your bacon and you might get the next job the producer is working on. Antennas are the first stage of how the rf and sounds that come with it get into your cart so think about that. And yes there have been times when I just used the "rubber ducks" that came with the receivers on the bnc mounts on the cart, why,,, because I just knew it would work.

You asked about a strain relief for the rf cables, well I use a piece of sash cord at both ends, top of the pole and at the cart,works just fine or you can get velcro ties that will work as well but you will have to replace them as the velcro wears out. I do hope this has helped you out, got you thinking a bit more before you start spending you cash.

Phil (VE7KJR)

[Scott Clements, CAS]

I got the Lectro antenna amplifier (ufm230) a couple of years ago, and can't live without it:

http://www.lectrosonics.com/catalogs/UniversalCatalogPages/FilterAmp.htm

I keep a 150 foot run of 50ohm Belden cable on the cart.  Not the bulky stuff, it's the size of regular video cable.  I keep a SNA600 dipole antenna on a flex arm with the Lectro antenna amplifier.  When needed, I unplug one of the antennas and run the 50ohm cable out to set.  The antenna amplifier (at the antenna end) compensates for the cable loss.  It's like having my venue sitting on the set, except there's only one small cable to run.  It works really, really great! 

Sometimes 150 feet seems WAY to long, and sometimes it seems way to short (like on a really long pier with a 2 to 3 page walk and talk).  I never thought I needed this rig until I got it.  Now I can't imagine life on set without it.

My only beef with the design is that there is not a battery compartment.  It only accepts external power.  I rubber band a 9 Volt on and that seems to work pretty well.  The battery (ipower) will last about 3 hours.

scott

[berniebeaudry]

Phil (VE7KJR)

Your post was a wealth of knowledge and I thank you for taking the time to explain it so clearly.  I haven't had the chance to do sound for a feature, but one of my regular gigs is as an audio assist for pro sporting events.  Of course in that venue we use rf often and much of what you talked about translates to what I have to deal with occasionally.

Thank you very much!

Regards,

Bernie

[ve7kjr]

Hi Bernie, I remember doing the big set ups on the sporting events as an a2 as well, a day to set it all up and have it working, the game might be 2hrs and then take it all down. Never did like the take down part, what a mess of cable, camera cable, video cable,intercom cable all stacked in a big pile next to the moible.Like a big pile of spaghetti ! You would have to take your time and use caution getting the cable out so as not to pull the connectors right off.The nice part was when someone finished with their cables they would help another dept. camera helping sound lighting etc.There was a brotherhood there among the crew. I haven't done a moible in a long time, but it is like riding a bike, you never forget.

I have several books on antenna design from the ham radio hobby, as I have said most of the antenna desings we use today have been around for some time, it is easy to make your own if you like building things and have the time and tools. The formulas for doing such are in the books all you have to do is the Math. In the end what is important is that you have confidence in your system and know what it can and can't do. What works at one location may not work at another location or the same location on a different day. There are so many factors to take into consideration, so a little thought might go a long way. It's not just plug and play.

Phil (VE7KJR)

[filmfreak]

Hi Phil

Thank you very much for spending so much time in analysing everything so thoroughly.

No worries about getting too far or over analyzing.

Wasn't tiring or confusing at all !

Every single bit of your posts is very much informative, descriptive and straight forward.

I am also happy that the topic seemed interesting to many other engineers and they felt like chiming in.

Seems like I 'll be heading towards the Lectro sna 600 dipole combined with a log periodic shark.

Looks like a really rugged and very important! compact solution.

Space is limited in my car so a compact as well as a rugged solution is a winner in my case.

I am finishing work on a series I am on in 3 days so I will be able to investigate and spend the time needed for the "antenna mast" project starting at the end of the week.

First step is to thoroughly examine the Lectro RF seminar and I will take things from there.   

As said by all posts here there is no silver bullet and no solution that will help for all setups but after reading the posts here I am concluding that I should take the plunge with the sna dipole + shark combo and then adjust according to needs and experience over the years.

Once more thanks for the feedback and happy that it turned out to be an interesting topic for everyone.

[RPSharman]

Scott,

The UFM230 seems like a great solution.  I though about adding another type of antenna for those difficult situations, but even putting the whip on this unit close to set on a 100ft cable would offer a great option for those difficult locations.  If I were starting from scratch and needed to buy the minimum, I'd buy one batwing and a UFM230.

Robert

[FSBELLA]

Frank,

Well I went through 2 of the Rode poles - all breaking at the very top. Switched to a more expensive K-Tek and have never been happier.

My two previous poles had the supposed "lifetime guarantee". They were never replaced by Rode and might be in the trash by now.

RL

RL,

Rode just replaced 2 shockmount in a week, never asked for the bad mounts and had free shipping- for there" lifetime warranty"

your sales rep should have and still can (please dont say it was me-lol) replace the poles for you.

and I was a bit concerened with the poles, but they did fix the issue. they seem "stronger" so we will see.

later,

[Steve Nelson, CAS]

Here's another way, one that eliminates the need for long coax runs, RF line amps, and so forth: Put all your receivers on a small, light cart - I use a PSC - with its own power. Run all the outputs into an Aviom system which gives you a 16 in/16 out network that runs back to your main cart through practically as much inexpensive and rugged Cat-5 cable as you can imagine (down the street and around the corner if you need it). Also put all your transmitters there, too (Comtek, IFB, etc.).

This is a more expensive option but it allows you to get your antennae AND your receivers as close to the action as possible (on the roof, in the rain, in a tiny set, upstairs, etc., etc.) while allowing the mixer to position him/herself in a more desirable location. Yo can also run any other line or mic ins and outs through it. And since the RF cart has its own power and has only one Cat-5 cable back to the mixer cart it is fast and easy to move if things suddenly change. This may add a cart to your setup and is probably not for purists, but once you get it running it ca make a huge difference in your daily functionality by eliminating most of the RF/distance issues we so often encounter. The Aviom system is transparent to my ears, consumes little power and has been completely reliable.

I finally listened to Mark Ulano on this one and I've never regretted it.

[Steve Nelson, CAS]

Sorry, that last post about the Aviom was from Steve Nelson (nelsound). (I hate unsigned posts!)

[Izen Ears]

  HELICALS!  Why even discuss any other option for remote antennas?

  I have 2 of them mounted on my cart and they receive stuff impossibly far away (like 1/4 mile outdoors) with no dropout.  I almost never have to unplug them ever since they live on the cart (maybe 5 times on an 8-week show), but if I do need a closer antenna I have the option to run out a 3rd antenna (sharkfin).  They like being close together at an X-Y pattern.  I fly them 10 - 12 feet and notice significant improvement over 8 feet.  They go around corners and through brick walls like nothing too, and they don't mind being tilted up to get a scene on a 2nd or 3rd floor from outside.  (I heard sharkfins want to always be horizontal.)

  They're expensive ($450 each) but they have freed up my brain to worry about other things.  Also I love having the receivers on my cart so I can see signal strength and also occasionally adjust gain.  They also give you a 14db boost in signal so on the extremely rare occasion I fly them out I don't worry about any antenna amps (100' on the fatty RG8 cables is the most I'll fly them out.)

  I couldn't afford them at the time I bought them, then after I got them I realized I couldn't afford NOT to have them!  (Prior to helicals I had used the PSC sharkfins but now I have Pro Wireless sharkfins and they work better.)

  Plus it's pretty awesome how many people (old-schoolers, producers, actors, PAs, even snooty ACs!) have never seen them and comment on how cool and sci-fi they are.  Straight out of Babylon 5 or something.

  Apologies if I sound arrogant; I don't know jack about RF technology but luckily with these I don't have to!

  Dan Izen

P.S.  I have noticed that the 50mw Zax 900 transmitters actually go farther than the 100mw Lectro 411s!  How weird is that?

[Richard Lightstone, CAS]

Steve,

Your Aviom system remote wireless concept sounds remarkably similar to that used by Mark Ulano.

Question to you is, who came up with the methodology first? Just for the record.

Whomever it was -- it is a great way to remote your entire audio chain. The Aviom could not only be used for your wireless racks, but also "hardwired" boom microphones, set playback, ifb's, comtek, audio to video and video return all with that one cat -5 cable!

Pardon me as this thread steers slightly off topic, but here is a link to Aviom:

http://www.aviom.com/News-1/Top-Stories-342/High-Tech-%3Cem%3EIron-Man%3C-em%3E-Relies-on-Aviom-Technology.cfm

Cheers,

RL

[Steve Nelson, CAS]

Richard,

I did cite Mark in the last line of my post and attribute my adoption of the technology to him. He'd been talking about it for a while and I was pretty much "Yeah, right" but once I checked it out and started using it, it's hard to imagine life on set without it.

It costs a few bucks to get it set up nicely (cart, power supply, the cable is cheap at least, and the units themselves aren't bad, but you need two pairs), but what a difference it makes.

At least I think it did...it's been so long...

---steve/n

[Richard Lightstone, CAS]

Steve,

OOPS! You are so right about the last line of your post.

My excuse: I wasn't listening....

I am also exploring using the same system....

Thanks and regards,

Richard

[Steve Nelson, CAS]

Richard - here we are having a merry old time on JW's two sites. Anyway, if I can be of any help to you or anyone else here about the virtues of Aviom and some little tricks, I've found true religion and I love preachin' it!

----steve nelson

[Jeff Wexler]

I find the PWS Helical antenna really intriguing, and not just the LOOKS. I used some helical-style antennas that Wolf was selling, these looked like white cake boxes since the antenna was enclosed in a round plastic enclosure. I think they used some of the same principles as the PWS. How many of these are in use now (by our unique group of production sound people) and why don't we see them at Coffey Sound and LSC? I freely admit that I am no expert on RF technology but I am curious why the people who we do rely on for these things haven't weighed in on this.

-  Jeff Wexler