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RF Splitter education


Michael P Clark

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I've been using Dipole antennas for several years now, and am thinking about Sharkfins alot. I typically only run 4 wireless at once, and figured I am fine with 1 Sharkfin antenna rig. I have noticed that most of you cart based mixers are using 2 sharkfins in an array. So here comes the questions....

How many is too many wireless for 1 Sharkfin?

Any Signal loss the more wireless are placed on 1 Sharkfin?

What is the ideal seperation of 2 Sharkfin antenna in an array?

Longest cable run before an RF Boost is needed?

Do you want to connect 1 or both antennas from the receiver, to the same or different Sharfin Antenna?

Do you like Yagi's better than Sharkfin's?

I know it's alot to ask but it would all coome out eventually. Thanks in advance!

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Michael, I've been using shark fin antennas for a while now and like them quite a bit. I had a situation where I needed to be over 300 feet away from four actors in a sewer tunnel and called Gordon at Lectro asking how I could remote four antennas on an antenna tree that far away from the receivers. He told me to use 50ohm video cable up to 100 feet, which I did with great results. I've used 100 feet of antenna cable on many occasions, mostly during cold weather so that I can stay on the camera truck in the warm!

Peter Devlin uses Swiss army antennas on his rig, which are omni directional. I have one for my IFB, but prefer the SFs for directionality with my Lectros.

Regards

Mick

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Michael Wrote:

"I've been using Dipole antennas for several years now, and am thinking about Sharkfins alot. I typically only run 4 wireless at once, and figured I am fine with 1 Sharkfin antenna rig. I have noticed that most of you cart based mixers are using 2 sharkfins in an array. So here comes the questions...."

"How many is too many wireless for 1 Sharkfin?"

- Would not run more than 2 without some sort of active splitter with built in amplification to make up the loss of adding more receivers.

"Any Signal loss the more wireless are placed on 1 Sharkfin?"

- As with ANY antenna system, you can count on approx 3dB of loss PER split when splitters are PASSIVE.  In other words, with a 2 way split, there will be approx 3dB of loss per output.  With a 3 way splitter (1 in 3 out), you can figure on about 6db loss per output, etc.

"What is the ideal seperation of 2 Sharkfin antenna in an array?"

- At least 0.5 wavelengths of operating frequency apart.

"Longest cable run before an RF Boost is needed?"

- Completely depends on quality of cable, RF frequency, the sensitivity of your receivers, and the quality of the splitters!  Note that the higher your freq, the more loss per any given distance of cable.  I would not recommend much more than 100 feet, even with the best available antenna and a good active splitter.

"Do you want to connect 1 or both antennas from the receiver, to the same or different Sharfin Antenna?"

- The 2 antenna inputs on your receivers need to be connected to 2 different antennae for the diversity system to function.

"Do you like Yagi's better than Sharkfin's?"

- Yagi's are cut to a specific frequency.  Log Period antenna (shark fin) are useable across a broad range of frequencies and are often therefore more suitable to frequency agile RF systems.  Yagi's can be more durable and can be more suitable for all weather use.  However, Lectro now has a Shark Fin that overcomes these shortcomings as well.

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Here is a very basic cable loss chart that I found by googling "RF cable loss":

http://www.northcountryradio.com/Articles/cables.htm

Here are the spec sheets for some passive RF splitters that are considered to be some of the best available.  I was going to upload them but it appears that Jeff's upload folder is full.

http://www.minicircuits.com/pdfs/ZAPD-1.pdf

http://www.minicircuits.com/pdfs/ZA3PD-1.pdf

Personally, I would recommend using an active splitter if you are splitting more than 2 ways.

Hope this is helpful.

-Darren

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Big vote for the sharkfin log periodic.  My wireless stuff, collected piecemeal over the years, is in 3 different blocks, so the widebandness of the LPs works well for me.  I have passive MiniCircuits splits in a home-made quadrack, hooked to a home made dual sharkfin rig (fins from Ramsey).  I generally don't put more than 30' of mini 8 50 ohm cable on this, and it has worked better than any solution I've had before.  I'd guess that the commercial solutions w/ powered splits, antenna amps, purpose built antennas and beefier cable would work that much better--that sewer pipe story is a great example.  Although it wouldn't have worked for that shot, a good old fashioned solution to keeping the antenna runs short is to put the receivers out closer to the action (w/ the antennae) and run audio lines back to your cart.  We end up doing this a fair amount--a bit more work to hump everything around, but more solid reception in dicey or distant setups with pretty low-budg gear.

Philip Perkins

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Thanks everybody for their input. I value the real world experience that this forum provides. I checked out Lectrosonics FAQ about these questions and they didn't answer them all for me. It has alot of info on antennas, but not a whole lot on log periodics. If I decided to go with Log Periodics, it would seem smarter to go with 2 in order to keep the diversity system of my wireless intact. But the $$$ doubles. Would I be stupid to go with just 1 Log Periodic? At some point I can see myself getting a diversity setup, but would I be wasting my time getting one and saving up for another?

I already run the wireless out up to 100' feet when needed, like Philip. I even built a box fitted for 4 wireless and a BDS system with a junior plug on the bottom. But running that out and taming 4 XLR's is getting tiresome. Seeing 1 BNC(or 2) and a much lighter C-stand, seems like a great option. I already have this system down, and this costs less($0.00) then getting a diversity log periodic setup($1000+) that won't get additional rental.

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Phillip,

I've seen those Ramsey antennas for sale on ebay, they're green right?

How do you mount them?

Also, semi pertinent, have you guys ever bought any loc-line to make your own flexi mounts? The stuff is dirt cheap compared to buying PSC's 65$ mount.

LL

Yeah, but they aren't that expensive right from Ramsey.  There's also another guy who sells a similar fin for even less, but I forgot his name, sorry.  I mounted the fins together on a single bar with a baby-receiver that goes on a C stand etc.  I sandwiched together 2 pieces of plastic and a simple angle iron and drilled thru them all.  Bolted everything together, then bolted the other side of the angle iron to the aluminum bar.  The fins can pivot sideways (towards each other) which makes a flat package for travel.  They've worked very well for me for several years now, but I don't do episodics....  The coolest fin for exterior use that I've seen is the Lectro "skeleton" model.

I could not find any Locline locally.

Philip Perkins

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"Would I be stupid to go with just 1 Log Periodic? At some point I can see myself getting a diversity setup, but would I be wasting my time getting one and saving up for another?"

If your diversity system is an **antenna phase** diversity system such as Lectro's, you could get away with 1 directional antenna without any ill effects and still see some benefit.  However you would not get the range nor rejection that you would get with 2 directional antennae.

Not recommended with diversity systems that actually switch between the two inputs as you may have an acceptable signal on the LP, but have nothing when the system goes over to the whip.

-Darren

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Guest Jeff Colon

Hello Michael, all

This is the ebay source for the PCB plate to roll your own log period dipole... for me they have worked great... certainly, not bad for 35 bucks in parts (cable connector etc.)

http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZkeb3985

I was under the impression that diversity antennas needed at least quarter wave separation to actually have each antenna see a "diverse" signal.  Lectro has a great book on RF, Last I saw, I think it was downloadable at their site.

Question,  If I were to use two fins on multiple diversity systems would I want to use 2 RF multis or other active splitters ?

ThX, All Best,

Jeff c

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Some people I've talked to have actually recommended matching a sharkfin to a less directional antenna. Sometimes, particularly as you near the limits of the system, the receiver will make frequent shifts between antennae if the performance is very similar. Although these are theoretically imperceptible, sometimes there is a faintly audible click on the switch-over. By using a system where one antenna pulls a bit more signal than the other, you minimize this liability.

But the most effective way to employ your resources shouldn't involve crippling your system, essentially shooting one element in the leg to make it go slower. For this reason, I wouldn't recommend using a sharkfin paired with a 1/4 wave whip. But using a sharkfin for one diversity antenna and a something like the SNA 600 makes some sense. The dipole is tunable to your frequencies and provides additional gain compared with the whip. Being omni-directional, it ensures that your system can receive good signal even when people wander from expected marks (and away from optimal sharkfin reception).

I don't know if this represents the best system or not; there's too much voodoo in RF reception to make definitive statements without extensive testing. I asked Larry Fisher about this set-up during the LSC sponsored radio seminar and he thought it might be a good plan but stopped short of committing to it.

David Waelder

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Hello Michael, all

This is the ebay source for the PCB plate to roll your own log period dipole... for me they have worked great... certainly, not bad for 35 bucks in parts (cable connector etc.)

http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZkeb3985

I was under the impression that diversity antennas needed at least quarter wave separation to actually have each antenna see a "diverse" signal.  Lectro has a great book on RF, Last I saw, I think it was downloadable at their site.

Question,  If I were to use two fins on multiple diversity systems would I want to use 2 RF multis or other active splitters ?

ThX, All Best,

Jeff c

2 splitters of any kind.  The passive ones are fine (MiniCircuits) for most work.

That Ebay site was "the other guy" I was think of (who sells LP antenna parts cheap).

Philip Perkins

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Jeff wrote:

"I was under the impression that diversity antennas needed at least quarter wave separation to actually have each antenna see a "diverse" signal"

Thank you for pointing out my typo.  I meant to write 0.5 wavelengths apart and I will modify my original post.  It is my understanding that  1/4 wave whips need to be at least 1/4 wave apart and other antennae that emulate half wave antennae such as Yagis, LP's, and dipoles should be at least 0.5 wavelengths apart.  My own system does not use any 1/4 wave whips so all of my antennae are at least 0.5 wavelengths apart.

------------------------------------------------------------------------------

David Wrote:

"Sometimes, particularly as you near the limits of the system, the receiver will make frequent shifts between antennae if the performance is very similar."

I believe that, at least in the case of Lectro diversity systems, "most" of the Lectrosonics systems (not certain about the venue) are actually antenna phase diversity where the system changes the phase relationship between the antennae rather than switching between the antennae themselves.  I believe what is occurring as one reaches the end of one's range, is that the signal is low enough for the software to determine that it should try reversing the phase in hopes that the signal strength will improve.  When it does not improve (because the range is just too far and the signal is just too weak), it switches back.  This cycle continues to repeat itself as the software is not capable of determining if the weak R.F. signal is due to the system being at the limits of its range as compared to multipath, phasing, or anything else.  Of course there are many diversity systems available that do actually switch between antennae as well.

Cheers,

Darren

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Guest Jeff Colon

Thanks Darren,  I was not aware of the need for .25 and .5 difference in physical separation 'tween whips and dipoles, etc.  As some mentioned previously, using two different antennas i.e. a whip and a sharkfin.  My version of this is to extend one of the whips using a piece of coax as an extender.  I wish I had kept the picture of the hard hat with the antenna mounted on top... it was a decent solution in a room with a few hundred PCs (msoft training seminar)... got a few laughs as well...

Am I correct in my assumption that Your Explanation to DW re: the Antenna phase scheme explains why the whips are 3 inches instead of three ft' apart on Lectro Diversity receivers.

Thx,

Jc

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Hi Jeff,

I believe that 1/4 wave antennae, whips or otherwise, require a ground plane.  When the antenna is mounted directly to the receiver, the receiver is the ground plane.  If you extend your antenna with a piece of coax, you either need to add a ground plane or ensure that you are using an antenna that doesn't need a ground plane such as a yagi, LP, or dipole.

Lectro once made a portable ground plane for exactly this application, but unfortunately they stopped making them.  I *think* that Lectro used to include them with their original non-diversity distribution systems.  I'll bet there are still lots of them floating around out there owned by mixers that no longer need them due to how popular the Lectrosonics dipoles have become.

http://www.lectrosonics.com/manuals/agpuman.pdf

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Hello Michael, all

This is the ebay source for the PCB plate to roll your own log period dipole... for me they have worked great... certainly, not bad for 35 bucks in parts (cable connector etc.)

http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZkeb3985

ThX, All Best,

Jeff c

Whoa, those are cheap compared to the Lectros and PSC. Almost too cheap! But worth a test.

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Guest Jeff Colon

The biggest drawback with the bare PCB antennas is durability... Performance wise, an antenna by any other name...

If you are hesitant about putting on the connectors or making a mount, try these.

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

I'm with Phillip and many others who now extend audio lines from receivers placed close to the transmitters.  If I can get the recieving antenna within 35' of the transmitter on a clear freq. I rarely get a hit.  Best Practice seems to be proper antenna placement, no barrels interconnecting antenna cable and a max of 2 splits when using a passive device.

these Cheapo pcbs are wonderful for uhf video assist or watching Superbowls at home ;-)

Jeff c

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The biggest drawback with the bare PCB antennas is durability... Performance wise, an antenna by any other name...

If you are hesitant about putting on the connectors or making a mount, try these.

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

I'm with Phillip and many others who now extend audio lines from receivers placed close to the transmitters.  If I can get the recieving antenna within 35' of the transmitter on a clear freq. I rarely get a hit.  Best Practice seems to be proper antenna placement, no barrels interconnecting antenna cable and a max of 2 splits when using a passive device.

these Cheapo pcbs are wonderful for uhf video assist or watching Superbowls at home ;-)

Jeff c

Those $175 Wolf PCB fins are no better than what I made from a Ramsey fin for about $40.

If you need episodic-in-the-jungle level durability, I'd get the Lectros.

Philip Perkins

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How is it Wolf's PCB board is getting 10dB gain where all the PCB boards I am finding and what you guys have shown me are 6dB gain? It doesn't appear to have any RF Boost built in.

And thanks for all the input, it will surely save me and others money in the future.

But that ALP620 looks so sexy:)....

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I have been using the "green PCB", from Ramsey for a few years now.  I LOVE them.  Is you are hooking up the cable yourself, remember to run the cable from the front where it is located, to the rear where you are mounting it, in a straight line.  If it goes down, at say a 45% , it will "short out" the range.  I had a person with a degree in physics explain this to me..  I could not explain how it works.  Just a "head's up"

Coleman

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