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Antenna Cable


Daniel McIntosh
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I imagine you've already considered it and have good reasons otherwise -- but another option would be to remote a couple of receivers next to the antennas and run a dual audio cable.  You'd no longer have the loss in the antenna cable.

Sorry, if I'm pointing out the obvious (and for not answering the actual question).  Depending upon how your cart's configured, it may be a pain to reconfigure the receivers.

John B., CAS

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There is tremendous loss in 100' of antenna cable.  Unless there is a compelling reason (like you only have a Venue and not enough/any portable receivers), then sending out the receivers and running back XLR, as suggested above, it the wise choice.

For 50 ohm BNC, I believe I use Belden 5289.  I simply use small zip ties about every 2ft or so to keep my 2 x 50' cables together.  But I rarely use these, and typically only if I am improving line of sight in a tough location by sending them up a stairwell or through a hole in a solid wall or something.

Robert

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I imagine you've already considered it and have good reasons otherwise -- but another option would be to remote a couple of receivers next to the antennas and run a dual audio cable.  You'd no longer have the loss in the antenna cable.

Sorry, if I'm pointing out the obvious (and for not answering the actual question).  Depending upon how your cart's configured, it may be a pain to reconfigure the receivers.

John B., CAS

+1

Plus, I've got a cat5 solution for remoting RX that would give me up to 4 channels to and/or from, and up to 1000 lossless feet through one light, manageable cable. Much more attractive for my time, stress, and money.

-- Jan

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I don't know what "+1" means (stupid me) but add me to the list of people who think using 100 feet of coax, no matter how low loss the cable, is not a good idea. Remotingv the receivers, as suggested here, and just sending audio back down cable is a much better way to go.

-  Jeff Wexler

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I did my own bonehead tests years ago, when I went from VHF wireless to UHF.  With my Ramsay-homebrew log periodics and a passive minicircuits splitter with Belden "mini8" type 50 ohm coax I found that the longest cable I really wanted to use was about 30' (no amplification).  Not very much when you factor in the height of a stand or mast too.  I've also been amazed at the range I get with just the onboard antennas on my RX, so I tend to move them (or myself with them) closer to the action and not use the cabled antennas much except for stage work, anymore.

phil p

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I have a 125' pair of rg58 wrapped in nylon sheathing.  Everyone is right, the loss is incredible, BUT it does come in handy to get me line of sight.  I've used it for chase scenes on roof tops (I stay safely at street level and run the antenna tree up to the roof), or street scenes that go from an exterior to a rear apartment or deep stairwell.  I like Jan's Cat 5 suggestion.  I'm going to look into that.

Best

Billy Sarokin

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For what it's worth, I ran a 150' pair of "low-loss" cables to a  control room for a reality show I did early this year. We were sending 12 lectrosonics UM400a as talent mics to a hard disk recorder for isos, as well as 3 UM400s sending IFB audio from each mixer to the Director/Producers, all through 3 Venue Receivers. I had these combined through a Lectro multicoupler, which was fed by 2 dipole Lectro antennas.

"Remoting" the receivers was not a possibility, do to the nature of the show: gut renovations of New York businesses in 4 days, in the dead of winter, shooting around the clock.  It was a brutal gig, to say the least, both on our bodies and the [rental] gear.  Did I mention there were no a2s? But I digress...

I wish that I had written down the model number of the cable because it worked like a champ. It was about 1/2" thick, weighed a TON, and was nearly impossible to coil when we changed locations (only once a week, thank goodness). The production sourced it for me through VER in New York. If you're interested, you might want to contact Craig Ellefson there, and ask him which cable I used on "construction intervention".

I know it seems to be the consensus that this was the "wrong" way to do it, but I must say, we always had tremendous range using this system, sometimes as far as 200-300 feet (which is pretty awesome in New York city). Its my belief that with the heaviest of heavy-duty RF-shielded coax cable, the line loss is minimal (at least up to the 150' we were using it at).

E.

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Great stuff Jeff and Jan

I used a long low loss cable when I was mixing Hercules bit it was thick as water hose but was quick to apply.

For my last drama in Fiji I bought a 150 foot 14way drum - big but it was an ideal solution for busy jobs

Happy New Year

mike

post-17-130815092822_thumb.jpg

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I don't know what "+1" means (stupid me)...

Eh, it's these young whippersnapper's short-hand way of saying "I agree with that."

As to antenna cable: I think Blake Wilcox helped me out with some Belden 9913F, which is very good low-loss stuff that's actually pretty flexible; also lighter-weight than the standard RG-8 stuff. I think it's maybe $1.29 a foot or something, not too expensive. I think this is the Mini8 stuff referred to above. I haven't tried the LMR400 cable, but it's a lot cheaper (half the price).

The Insta-snakes do look very cool!

--Marc W.

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Credit where credit's due: this is Wexler's fine cat5 solution that I've adopted. The thread to which he previously herein linked shows the thinking / science well.

Billy's examples of situations in which he uses RF cable / remote antenna have made me imagine how I might tackle 'em using the remote RX. I've made up a 6U rack case that includes a 4U drawer with all the pieces/parts, into which I would mount the 1U RX4900 receivers, power, antennas, and Comtek TX. Imagine mounting that case on a rolling cart for the exterior --> interior movement or rooftop run. Think that would work equally well as a third hand-wrangling an antenna mast.

I'm at this point always more likely to remote the RX rather than the antennas for the following reasons:

  • Safety. Have not yet met the RF cable that will safely lay down and play nice. Maybe this thread will yield a solution to this objection :) One can always hope.
  • Ease of use. See above. One of my prime concerns in equipment choice is making it safe and easy for my team and colleagues.
  • RF cable loss. Suppose this could be solved with an amp in line, but see above.

Look forward to hearing more details about Dan's particular situation.

-- Jan

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Hi Mike,

I agree about the cable loss.  Unless you are using something the size of a fire hose it is substantial (for example, at 680 mHz, the cable loss is over 12db in 100' of rg58 cable), but I disagree about the amp.  I usually find that rf amps at the end of a run boost the unwanted signals as much as the wanted ones and never seem to help (though I haven't tried using any in years so perhaps things are better now!).

Usually the only time the cable loss is justified is if the cable gets you line of sight. The cable loss is much less than the signal loss going through multiple walls or buildings.

All the Best,

Billy

" Its my belief that with the heaviest of heavy-duty RF-shielded coax cable, the line loss is minimal "

it depends...

on what you consider minimal...

with any long cable run, an amp at the distant end is advised.

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Hi Mike,

I agree about the cable loss.  Unless you are using something the size of a fire hose it is substantial (for example, at 680 mHz, the cable loss is over 12db in 100' of rg58 cable), 

[sNIP]

All the Best,

Billy

I agree with others about avoiding long antenna runs whenever possible, but I must say I am intrigued by Steigs' suggestion of LMR400.  As an alternative to wrangling with RG-8 (likely what you used on your construction show, Ethan) the loss seems way better than RG58 or RG8X.  According to this page it is 2.7 dB/100' at 450 MHz and 3.9 dB at 900MHz.  That's nearly a fourth of what Billy quoted above for RG58.

LMR-400 COAX

Paul

Addendum:  I found this loss calculator and I find it hard to believe:

http://www.timesmicrowave.com/cgi-bin/calculate.pl

LMR-400 has significantly lower loss than even RG-8??!! What gives? Please enlighten if you are still checking in, Steigs. In my experience, RG-8 is the standard and as unwieldy as it is, it seems folks wouldn't insist on it if better results could be achieved with something that's easier to handle. Anyone?

PG

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I know that there is loss in 100' of RG58 50ohm cable.  I did non-scientific testing, i.e. I swapped out a 15' cable with a 100' cable and saw no discernible difference on the Lectro UCR411a display RF LEVEL read-out, nor did I see the ANTENNA PHASE INDICATOR begin to flip more than usual.  What I did see was that when my utility ran the long cable out to full length and "boomed" line of sight my reception improved and the shot was successful.  The kit mentioned here and in previous threads may be appropriate in some circumstances.  I think in the case of a 2 person walk and talk down a NYC street using a combination of 2 lavs and a wireless boom (on the same block, with a shared antenna pair), that remoting the receivers and/or using the CAT5 or other snake, may prove to be a bit over-kill.

I did look at the links provided though none seemed to point to a single snake containing two lines.

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I've looked for years but never found any dual rf cable.  A few years ago I had a cable company make up a custom cable (2 RG58's wrapped in nylon sheathing).  Now that I've learned about the low loss cable I'm thinking of having the same done with the LMR-200 cable.  The LMR-400 would be too unwieldy for me.  The 200 is the same size as 58 but with half the loss.

Billy

I know that there is loss in 100' of RG58 50ohm cable.  I did non-scientific testing, i.e. I swapped out a 15' cable with a 100' cable and saw no discernible difference on the Lectro UCR411a display RF LEVEL read-out, nor did I see the ANTENNA PHASE INDICATOR begin to flip more than usual.  What I did see was that when my utility ran the long cable out to full length and "boomed" line of sight my reception improved and the shot was successful.  The kit mentioned here and in previous threads may be appropriate in some circumstances.  I think in the case of a 2 person walk and talk down a NYC street using a combination of 2 lavs and a wireless boom (on the same block, with a shared antenna pair), that remoting the receivers and/or using the CAT5 or other snake, may prove to be a bit over-kill.

I did look at the links provided though none seemed to point to a single snake containing two lines.

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" rf amps at the end of a run boost the unwanted signals as much as the wanted ones "

you do mean the distant (aerial) end, right?

yes, that is how it works...

but what happens is that at the receiver end of the coax, after the loss, you have what you would have had if the RX was where the pre-amp is.  one should use just enough amplification as there is loss to follow.  of course if you use higher Q preamps, they only amplify what is in their bandpass, thus reducing some interference at the distant end.

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Useful thread, the LMR cable looks like the go, LMR240 has a better spec for a 1 millimeter increase in diameter, might be a hassle if it doesn't fit easily available RG58 BNC connectors which the LMR195 and 200 will. Def much better loss specs all round compared to any other 50 ohm cable I have seen.

Connector loss is something I'd like to know more about though, especially in regards to making short link cables to provide better access points on the rear of the cart (instead of the back of a venue module or the zax equivalent etc). In these cases you would be adding in the loss of 2 further male bnc connectors and one female joiner. (Presuming the cable length being only a foot or so would be negligible).

Seasons Greetings to all,

Chris.

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I've always heard that each jumper is a 3db loss, but it's possible I only heard that in my head after many good tequilas.

Useful thread, the LMR cable looks like the go, LMR240 has a better spec for a 1 millimeter increase in diameter, might be a hassle if it doesn't fit easily available RG58 BNC connectors which the LMR195 and 200 will. Def much better loss specs all round compared to any other 50 ohm cable I have seen.

Connector loss is something I'd like to know more about though, especially in regards to making short link cables to provide better access points on the rear of the cart (instead of the back of a venue module or the zax equivalent etc). In these cases you would be adding in the loss of 2 further male bnc connectors and one female joiner. (Presuming the cable length being only a foot or so would be negligible).

Seasons Greetings to all,

Chris.

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