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Help with Cart Antenna System


Zack

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Due to my lack of knowledge about wireless mechanics/physics, I'm asking for help with piecing together the most ideal (for the cost) set-up, parts, and strategy for incorporating an antenna system for cart use.  So far, I have thought of getting a PSC Multi Dual...to feed what I currently use ( 2x 411's and 1 SRa) and have plenty of room for more wireless units I get in the future.  As for what else is needed I'm not 100% sure about.... type of antennas, amplifiers or not, proper deployment, etc..etc.  Please feed me your suggestions :)

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Check out the Lectrosonics FAQ section on antennas. Although it's a bit vendor specific you can glean a good deal of info. Also, before diving into an antenna system, have you considered placing the wireless closer to set? The cost of an instasnake with cat5 costs less than, antennas, distro, power etc

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" have you considered placing the wireless closer to set? "

the loss thru audio lines is less than the loss thru antenna lines (coax)!

Clarity: there is virtually no loss when passing audio at line level through cables. It is not the use of coax cable that causes the loss. Passing RF, not audio, through the coax cable from antenna to the receiver is the problem. Placing the antenna closer to the transmitters improves the signal at the antenna but that signal will be drastically reduced by the loss on the cable back to the receiver.

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Clarity: there is virtually no loss when passing audio at line level through cables. It is not the use of coax cable that causes the loss. Passing RF, not audio, through the coax cable from antenna to the receiver is the problem. Placing the antenna closer to the transmitters improves the signal at the antenna but that signal will be drastically reduced by the loss on the cable back to the receiver.

True.  And the trade off on location is that RF type 50 ohm coax that does not make for a lot of signal loss is very fat, heavy, stiff, expensive and requires connectors or adapters to get down to BNC.  When I first made my dual sharkfin rig I also made some cables like this, and ended up using them maybe twice.  For higher loss cables I found the best compromise was a cable no longer than about 30 ft.  As has been said, having a small cart that can work "close in", the antenna mounted to the cart and very short cables works very well, another trick is to remove the RX from the cart into their own rack/box/rig w/ power, and put that as close to the action as you can while running audio lines back to your cart.  The whole scrum of dealing w/ RF cables/antennas etc etc was one of the things that pushed me back towards using bag like rigs more often that I could take very close to the action, w/ RX, boom op, and monitoring all wireless on individual rubber duck RX and TX antennas.  This helped speed up our moves and keeps us flexible and able to instantly respond to lighting and camera changes w/o moving cables.

Philip Perkins

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Due to my lack of knowledge about wireless mechanics/physics, I'm asking for help with piecing together the most ideal (for the cost) set-up, parts, and strategy for incorporating an antenna system for cart use.  So far, I have thought of getting a PSC Multi Dual...to feed what I currently use ( 2x 411's and 1 SRa) and have plenty of room for more wireless units I get in the future.  As for what else is needed I'm not 100% sure about.... type of antennas, amplifiers or not, proper deployment, etc..etc.  Please feed me your suggestions :)

I use dual Lectrosonics folding dipole antennas that stay on a mast on my main cart, using cables just 10' long. This system has been very reliable with impressive range. If I need the antennas to be closer, I just roll my cart closer.

Glen Trew

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It is my firm belief that most Rf reception problems can be solved by using appropriate antennas. I have never been happy with rigs that are remote from the cart (the Rx bank) and sending back audio through a snake cable.

Either I can get closer to the action, which is possible MOST of the time. Or I use appropriate antennas in situations where it's not possible to move closer. Like real outdoor locations - streets highways etc.

Like Glen, I use the Lectro whips in normal situations on the Six Pack, and then the SNA most of the time, and then the PSC sharkfins, and when opportunity permits I will definitely get at least one helical antenna.

-vin

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In today's production environment (fast and loose), I am a big fan of not having to remote ANYTHING - Antennas or receivers.  It makes moving to the next spot slower, and puts my gear in harm's way.

A smaller cart that will fit close to set when range is an issue is a very important thing to me.  I use 12' 50 Ohm antenna cables (not the thick ones) to my antenna mast, which is attached to the cart, and goes directly to the receiver, no barrel or patching.

If I need to remote the antennas, I use a maximum of 50' of 50 Ohm BNC (directly into the Venue with no barrel) and get the antennas as close to the set as possible.  This is typically done outside to improve line of sight around solid objects.  In terms of just distance, there is almost no difference sending 50' of cable out than staying on the cart with short cables.  The RF loss through the cable cancels the improvement in distance.  In these cases I move closer, or run a portable receiver attached to an XLR as a last resort.

Using barrels or using 50' of cable to get the antennas 20' closer are mistakes that should be avoided.

Robert

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I took a page out of Mark Ulano's set up.  I work in corporate and stage type productions sometimes where sound and video are in another part of the building.  Though more expensive, the Aviom units allow up to 64 channels of audio up or down one Cat 5 cable.  I also use USB to Cat 5 convertors to allow the control of the Venue systems from the mixer point.  With the two Cat 5 cables, I can be up to 150m from the set, send and receive audio and control the wireless receivers.  The Venue receivers and Aviom input and output units are in an SKB case with the antennas on folding arms that store in the back of the case.

David Rogers

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check out the flatpanel sharkfin we sell (yea its an ad of sorts)

http://wolfvid.com/datasheets/Antenna_UHF_flat_panel.pdf

here is something I wrote for AM video reception - not really that different from SOUND FM ( pardon the lousy formatting)

  •     Log Periodics (SharKfins) compared    We recommend for general use the WSV green flat panel  Antenna. This is a high gain flat log periodic antenna. All antennae are good  at short range. Where they differ is in the extreme end of range. In a bad  multipath environment at short range, any directional antenna is better than a  non-directional one. The omni rubber ducks are non-directional or omni  directional. So if you can, use a directional antenna.

    The gray CIT ultra has a little more gain than the other  three we tested: WSV aluminum, Lectrosonics flat panel, PSC flat panel and WSV  green flat panel. 

    In normal transmitting distances with a decent signal, there  is no difference between these antennas. At low signal strength there are very  subtle but discernable differences between the antennae and between cable types  used. 50W  black Belden cable is preferred. Generally, the CIT (gray) antenna is a little  more sensitive to low level signals at high and low frequencies. This shows up  on the DX-404 tuner as one or two additional LEDs lighting up. The WSV (green)  antenna seems a little more sensitive to reflections from objects within 3 ft.  of antenna. The Lectrosonics (black) and WSV (green) seem to be very similar  otherwise.

    What this means in practical terms is: if you’re receiving a  small transmitter at the end of a 100 yard football field, the CIT antenna  would be good for 100 yards, whereas the others will be good for 98 yards.

    Again, this is splitting hairs at the extreme far end of the  receiving range. The new DX-404 tuner seems to switch antennae without any  color phase shifts in the picture.

    Relative position  (where you put the antenna) is much more important than the exact direction you  point it or the brand of antenna.  So  move your antennae 6" to left or right or up and down for best  pictures.  This demonstrates the radical  effect multipath has on the signal.  The  reason the picture is bad 6" away from the original position is only  multipath.  So when you see a picture  get bad, and then good, when one end of the transmission chain is moving, you  are observing the different patterns of multipath.  Therefore you should continuously experiment with better  positions.

    The CIT antenna is very bad below channel 14. Our WSV Log  Periodic is not as sensitive to accurate pointing.  It has a wider pattern. With low signal strength use the side  lobes (30° off  center) rather than on axis.  CIT is  very sensitive to horizontal - vertical position.  For best results, it has to be perfectly parallel (the same  spatial plane) with the modulator’s antenna, especially at the higher channels.  (This is the price you pay for the high gain.)  WSV Log Periodic has slightly less gain than others but is much easier  to point.  Antennae in order of gain:  CIT Ultra Antenna, Lectrosonics, PSC, and WSV. Remember to experiment with  antennae positions all the time.  The  best solution is four antennae spaced by 3 ft. for the diversity receiver of  course.

    Look at the artwork below and  think a little. If the transmitter is vertical, the receiver also has to be  vertical. Note the difference in vertical or horizontal radiation pattern. This  is called phase of a transmitter signal.

    [img height=211 width=362]http://jwsound.net/SMF/file:///C:/DOCUME%7E1/HP_ADM%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_image002.gif

    YAGI or Flat panel FOR RECEPTION    ·            A Yagi is an antenna  that looks like your rooftop TV antenna.  Mount antenna on "C" (Century) stand up high (7 ft.) for  safety sake.  Reception is better the  higher the antenna. Use our new stand extender (5ft).

      Single channel Yagis have several advantages that may be critical in difficult  situations:

    ·            Selectivity:  Some are tuned only for one channel only some for a few.  The antenna will reject adjacent broadcast  channels that  are usually much stronger  than low powered modulators.

    ·            Directivity:  Front-to-back ratio is as high as 20 dB.  The angle of acceptance of a signal is very narrow. This is  especially noticeable at long range.  Experiment with very small directional increments when pointing the  Yagi.  Hold antenna on central rod in  rear if necessary. At short range directivity goes away but you can optimize  reflecting signals (multipath) by rotating antenna to null out reflections.

    ·            The general TV type Yagis have gain forward and  rejection of signals from the rear.

    ·            Make sure you mount it vertically polarized  (opposite from what you see on most rooftops), matching modulators antenna  orientation.

    ·           

    A good large Yagi if you really need  range:  http://www.antennasdirect.com/91XG_HDTV_antenna.html 

    Needs  with some  good accessories. Antennas Direct, 1699 West 5th Street - Suite F, Eureka, MO  63025    877-825-5572

        Antenna Distance vs. Cable Distance?   

    Question: 

    Is it better to place the Rx antenna far from the Tx and use  a short 50Wlow-loss  cable between the antenna and Rx tuner, or to have the Rx antenna close to the  Tx and use a long 50Wlow-loss cable between the antenna  and Rx tuner?

    Short Answer:

    It is always best to keep the  Rx antenna close to the Tx, even if you have to use a 100 foot 50W  low-loss  cable to the Rx tuner.  Why?  You may lose 10db of signal in the long  cable, but you benefit in Tx signal strength over interference and noise. The  gain in performance is because the Tx is stronger than the background  signals.  Background signals may be off  channel, but can still induce flicker and rolling pictures.  So, 100 feet of cable is not the killer you  always thought it was.  **

    Best Answer:

    Place the Rx antenna as close to the Tx as possible and mount the Rx tuner directly on your  antenna stand while using a short 50Wlow-loss cable between the antenna and the Rx  tuner.  You can then run a 75W video cable up to  1000 feet from the video output of the tuner to your video assist recording  system or monitor.

    [img height=357 width=350]http://jwsound.net/SMF/file:///C:/DOCUME%7E1/HP_ADM%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_image008.jpg

    ** In general, it is best to use antenna cables that are no  longer than 25 feet.  If you still need  to use a longer cable, then you should use a powered in-line signal amplifier.  Using an antenna pre-amp like this will allow you to use either 50Wor  dual 75Wcable  up to 300 feet between the antenna and Rx tuner.  An adequate device to use is the Radio Shack (yes, Radio Shack)  model 15-1170, which runs about $50 w/tax and shipping.  Online order only: http://www.radioshack.com/product/index.jsp?productId=2103913 

    Multipath AGAIN:    [img height=146 width=193]http://jwsound.net/SMF/file:///C:/DOCUME%7E1/HP_ADM%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_image010.jpg [img height=143 width=180]http://jwsound.net/SMF/file:///C:/DOCUME%7E1/HP_ADM%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_image012.jpg

    Reception with no multipath              Multipath looks like 2 images (moving!)

    CHOOSING THE best  WHIP ANTENNA FOR TRANSMITTING    An antenna is an antenna, is an antenna . . . correct?  Actually, an antenna is just a radiator of  RF signals, but there can be good ones, bad ones and ugly ones.  The properties that make an antenna a sweet  one are the same for receive or transmit.

    Omni antenna designs go from unity gain 0dB to 10dB and  higher. The more gain, the further the reach. The higher the frequency, the  shorter the antenna.  The higher the  gain, the longer the antenna.  The  higher the gain, the higher the radiation or receive pattern.

    Examples:

    UHF 3dB gain Antenna @ 470 MHz (TV Channel 14) is about 6”  long;

    for 6dB gain, it is about 12” long. 

    for 9dB gain, it’s about 36” long.

    The vertical radiation pattern of antennas vary according to  design.  For now, let’s assume similar  design, just more or less gain.  The  simple description is that with little gain (3dB), the pattern resembles  “Mickey Mouse ears.”  The higher the  gain, the more the pattern resembles a round pie. The higher the gain, the  further the reach.  If you are close and  you have more gain than necessary, you are not wasting anything.

       

    Side View of Vertical Antenna    [img height=166 width=437]http://jwsound.net/SMF/file:///C:/DOCUME%7E1/HP_ADM%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_image014.jpg

    Choose the antennas you use with thought.

    Avoid using the 6” Rubber Duck antenna.  They are the ugly black ones:  not tuned, inefficient and ineffective.

    Conclusion:  Longer antennas give more gain = better signal, less flicker, more  range. We happen to be selling some custom made ½ wave whips. You can find the  instructions for homemaking here 

    Under: http://movies.groups.yahoo.com/group/VideoAssist/files/ 

    A file called: whip.PDF  you have to sign into the group, its easy and safe. Or:

    http://f1.grp.yahoofs.com/v1/UGx_SwmdVhBMCfAgDhXAVN9FwashtBiizi80RgjI1oNrO0vqJ7LvLwDuvsHVw35PtYPwb0G2VNcAXw-Knbie_tqO7hs-3t7qeTY/whip.PDF 

    Dipole vs. Yagi vs. Log Periodic, What’s the  difference?    A dipole is the simplest antenna. The Radio Shack amplified  box with rabbit ears is really a dipole. It receives from all directions  equally. This is not good. You will be receiving reflected signals (result of  multipath) as much as direct signals. These will cancel each other out and make  the video look like a cheap ass rolling and flickering TV transmission.

    Advantage of Yagis and Log Periodics: they are  directional.

    Yagis are tuned for one frequency (one channel) (±10MHz).  Log Periodics work for a wide band of frequencies. (400-1000MHz or TV channel  14-69). For the same physical size as a log periodic, the Yagi has slightly  more gain (up to 10dB). That means it may have 20% longer range (1200 ft.  rather than 1000).

    The reception patterns are pretty similar, but the Yagi has  a tighter pattern, therefore more gain.

    If you know you will be using one frequency only, you are  better off using a Yagi. It acts like a filter and rejects all other signals  (TV stations) that you don’t want. Unwanted signals make a mess out of your  receiver’s front end (input stage) and show up as weird patterns or less  sensitivity (less range). Of course in TV reception you never use Yagis, as you  want to be able to receive lots of channels.

    Use a log periodic (flat panel) to receive:

    Advantages: covers all channels (14-69), pretty good  directionality, therefore it’s better with multipath. Decent gain.

    Most important also are new, short, clean, low loss  cables between antenna and receiver (or transmitter).

    Use half wave antenna for  transmitters –

    always better than the ugly  6” black whip.

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Thanks for all the help people... I got some reading/research to do now :)

@senator.... in a similar thread some weeks ago you had a link for a book or web page that gave some great info about antenna theory or building them as well?  I can't seem to find it again and was hoping you might be able to repost that?  thx

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probably the ARRL antenna handbook, one of the most popular books for HAM radio operators!!

http://www.arrl.org/shop/The-ARRL-Antenna-Book/

BTW, I mentioned in another thread about the fact that 1/2 wave whip) antennae (sic) are better than 1/4 wave whip antennae (sic); Wolfie has called attention to the fact that antenna stuff applies to TX's as well as RX's.  I have some 1/2 wave antennae (sic) that I use on TX's for range / performance improvement! the 'drawback' is that they are, of course, twice as long as the 1/4 wave antennae (sic) that come with the units, but they are still shorter than the old VHF antennae (sic) were, and I have some flexible ones that I can sort of wrap around the body a bit for a bit of extra help (getting the antenna to a better position relative to the RX)!

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Hey Zack,

I started a thread a little while ago about who is using what antennas, mounting and placement.  Check it out, it gave me some ideas about what I wanted to do.

I am just finishing up the cart with 411's Lectro umc-16b antenna distribution, 2 x Alp700a's and sna 600 with 216 adapter kit for the comtek transmitters.  All of these are mounted on one bar with the ability to mount on any boom pole I own with the Ambient quick pole release.  Inatial testing done with the comtek is impressive.  I hooked up a mic to Cantar with some music playing and I went for a walk... a really long walk.  So far so good.  I will be testing the lectros when I get back.  In my experience, it's always been line of sight,and height of the antennas, not width.

Thanks all

2 cents

B

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Brian, it is also width, prescribed distances between antennas if maintained will definitely provide better quality. it's physics. :)

as of now, your testing may prove your setup right, but one fine day it will show you real results.

It's great to see you using multiple types of antennas, that's the way to go imho and according to the serious experts in the field. :)

-vin

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Hey Vin,

I stand corrected.  I should have said that height in my opinion, outweighs the width.  If I could have one or the other I would take height over width.  My Antenna bar is only 35 cm wide so in  a pinch I can always take one off and move it to the other side to another free standing boom pole.  The limited with of my bar helps me be more mobile, keeps in compact and lighter weight, although not by much.  I have boomed for guys who use this configuration and we never got into range issues.

Thanks  We all know that wireless can be a little bit weird at times.  I know my testing is initially to test cables and overall performance.  Getting on a set is always a different story but I am confident of my particular setup.

B

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Senator thanks for the link, @ Brian thanks for that info.

I'm curious though, for these directional antenna, how "directional" are they?  If I had transmitters that ended up getting positioned further away from each other would I have loss from the transmitter(s) the antenna is not directly pointed at?  I'm not exactly sure how these multicouplers are supposed to be wired, but can you have a directional antenna in input A and a dipole (omni) in channel B.... then have a 411a be fed one output from each antenna input for diversity to figure out which is best to use..... or is that a completely wrong/bad approach?

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I'm not exactly sure how these multicouplers are supposed to be wired, but can you have a directional antenna in input A and a dipole (omni) in channel B.... then have a 411a be fed one output from each antenna input for diversity to figure out which is best to use..... or is that a completely wrong/bad approach?

Well I found the answer to this I guess going through the many .pdf's lecto has on their site: It is generally best to use two of the same type anten- nas on a diversity receiver, as some designs combine both antenna signals into a single receiver with a phase correction between them to maximize the resultant RF signal. If one antenna signal is significantly stronger than the other, the signal from the weaker antenna will do little to prevent multipath drop-outs that occur at the stronger antenna.

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Brian, glad i could be of help... if i remember correctly, the antennas should be at least or more than half wavelength apart. One would have to start at the lowest possible frequency one is going to use within whatever blocks one has... 

About height, usually it is good, but no point with too much height on an antenna that is not directional or a directional antenna not pointed in the right direction... i could have sharkfins that are directional high up and possibly totally lose the field of the tx which are way below... one has to check on the antenna characteristics and graphs and sort of commit to memory... this is what i have learned by experience/reading/groping around etc... Heh :)

-vin

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Vin,

Thanks dude.  Only when I start using the cart may I start to comment on the results.  Generally the Lectros are always reliable and I am always accepting of the fact that RF can be weird.  I think the lesson for all is to use the best equipment that you can, put yourself in a position to get the best reception and record away.

Vin, always nice to hear ya.  I am going down South to cover the oil spill with Discovery Canada.  I will send some pics of my trip, then the finished Cart based around the Cantar.

B

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  • 4 weeks later...

Going back to this topic, I can't seem to find a specific manual on lectro's site about their SNA600, so I'll ask here.  If I was to get 2 of these antenna, would I be able to just directly plug 1 SNA to each antenna port on a 411?  Basically, I'm not quite sure what I want to get yet as far as an array distribution (PSC multi-dual, or whatever), so I was hoping to just have the antenna mast available to test for just a single receiver at a time for now.

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Since I work out of a bag and sometimes on the cart I need a compact and simple system to help me with range I use a PSC RF Mulit http://www.professionalsound.com/specs/multi.htm and a

PSC Sharkfin.

http://www.professionalsound.com/specs/uhf_ant.htm

It is a very compact and effective system that is also easy to travel with

I've taken a look at these, but figured I would have to have 2 of them ... 1 per antena if I was to run a few 411's through it right?

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