LarryF Posted June 22, 2011 Report Share Posted June 22, 2011 Here's an interesting (to me) problem that finally seemed to have a simple cause. I've reordered the history so the oldest email is at the top. An interesting conclusion is that there is a need for a lighter solution than using 2 x 150 foot runs of Belden 9913F which would weigh 15 lbs for each run and is bulky when rolled up. If this is too long, skip to the end to find out who killed Colonel Mustard in the drawing room with an RE20. ******** From: Bartek Swiatek Sent: Tuesday, June 14, 2011 10:42 AM To: Larry Fisher Subject: Switching antennas noise Hi Larry, I'm on a show in Atlanta, a very wireless heavy show, and I'm using a Vrfield with lp650's. I am experiencing switching in between antennas noise. A static like pop, everytime the venue switches in-between my two sharkfins. I have an SR receiver piped into the venue for multicoupling, but those seem to be unaffected. The SR tx are SMQV's on blk 470. The venue tx are SMV's on blks 21, 25, 26, two each. I power my lp650 with the BIAST's from my Meon. When I switch to passive lp 620's the issue goes away. Any help would be appreciated. Bartek Swiatek ****** On Jun 14, 2011, at 12:54, Larry Fisher <larryf@Lectrosonics.com> wrote: Hi Bartek, I'm not sure what is happening here. How much loss do you have between the LP650's and the Venue input? That would be cable loss plus any splitters. If you don't know your cable loss, just tell me the type of cable (or diameter in inches) and the cable length. Also, are you aware that the Venue has a "bias T" built in? That is to say, it will provide power from its input antenna ports if the internal jumper is set. You can check to see if the antenna power is enabled with a voltmeter by checking the voltage from the Venue antenna "in" port. Measure between the center pin and the BNC shell. I'm not absolutely sure what happens if the internal power is on with an external bias T, though it was designed to be OK. Best Regards, Larry Fisher Lectrosonics ******* Sent: Tuesday, June 14, 2011 1:29 PM Larry, I'm using 150 foot runs of westpan 807. I verified continuity of the run, as well as the voltage of the venue antenna outputs as negative. 0V. Bartek ******** On Jun 14, 2011, at 15:47, Larry Fisher wrote: Hi Bartek, I can't find the "westpan 807" using a Google search so I don't know what your loss is. Is there any other information on the cable you can give me? Also, it is odd that the passive LP620's work fine but the amplified 650 units don't. Massive out of band RF, plus amplification in the LP650 could be overdriving the Venue where the 620 would deliver less out of band RF and not over drive the Venue but that is a real stretch of the imagination. What distance is the talent from the antennas? Is there any funny RF on the set such as RF video transmitters? Sorry I'm not giving you much help here but this is a weird one. Best, Larry F Lectro ******* From: Bartek Swiatek Sent: Tuesday, June 14, 2011 2:43 PM Larry, the cable comes from XXX, YYY is I believe the guy who is in charge of that project. The distance from the antennas differs but the switching "pops" occur sometimes as close as 50' away. And as for RF the usual suspects... Canotrams in our case. Bartek Swiatek ********* On Jun 14, 2011, at 16:54, Larry Fisher wrote: Shut off CanaTrans and see if the problem goes away. They have a nasty reputation for interference and are not legal for use in the U.S. They should have an FCC sticker but I bet they don't. Best, Larry F Lectro ********* > From: Bartek Swiatek > Sent: Wednesday, June 15, 2011 9:26 AM Larry, Would it be possible to ship the LP650, cable, BIAST, and the jumpers to you guys for evaluation? Something is off and I just can’t wrap my head around it. In addition to the switching noise the antennas are also underperforming.... As for the Canotrans I don't have an opportunity to test with and without, it's an all wireless show sound and video Bartek Swiatek ******** On Jun 15, 2011, at 11:33, Larry Fisher wrote: Hi Bartek, Send them to my attention and include a copy of this extended email. This is in case I'm not around so service will have an idea of what to do with the equipment. You can test without the CanoTrans by moving your gear to a different site away from the CanoTrans. After all, what else do you have to do between 2am and 6am in the morning. Best, Larry F Lectro ******* Here is an internal email from Dean regarding the antennas and the 2.5 foot jumper cables that Bartek shipped to us. Hi Larry, As we thought, the non-standard BNC to BNC cable (yellow) was intermittently bad (real bad). I corrected the intermittent, but not sure if I totally trust the cable. All other functions with all other pieces sent for evaluation checked good. The ALP650L/E had the 4dB attenuator installed so the resulting gain is 8dB. Please let me know if there are any further tests you would like run. Thanks, Dean ******* Then Bartek sent us the 150 foot cables. Hi Bartek, Well, this is the rest of the problem. These cables weren’t intermittent like your shorter ones but the losses are incredibly high. The 21 dB of loss at 500 MHz would be about 27 dB at 600 MHz. Your system didn’t have a prayer of operating properly. No one should have sold you 150’ of small cable for a UHF antenna link. If you had been sold the correct cable, such as RG-8 equivalent or our 9913F cable, your loss would have been 6 dB at that distance and the 8 dB gain in your LP650 would have more than made up for it. The larger cable is more expensive and much heavier but it would have worked. RG-8 is 0.4” in diameter as is the 9913. Loss is ALWAYS inversely proportional to co-ax diameter. The small cable you have (0.25”), no matter what it is called, will be high loss. Incidentally, RG-8 mini is not RG-8. RG-mini is a small diameter co-ax (like yours) and is therefore high loss. Let me know if you have any questions or need further help with this. Also, we need a return shipping address. I’m available at 800 821 1121. Who made the 3 foot cables you sent us on the first round? Best Regards, Larry Fisher Lectrosonics ****** Larry, First of all thank you so, so much for taking the time to deal with this. I know you have more important things to deal with than dealing with poorly constructed cables. As for the jumper cables, both were made either made by me or my utility, I really don't remember, but the blame should fall squarely on my shoulders!!. I was always suspicious of those right angle connectors, but it somehow slipped my mind. Another problem I had was the fact that they passed a continuity test, and since I'm in the field I don't have access to proper diagnostic tools. As to the westpenn "snake" that is the cable that XXX builds. The crazy thing here is that I know of at least 5 other mixers that have build a similar setup, 100' runs, and 125' runs, at 8dB gain at the LP 650. I went a bit further arguing that if 125' functions with a 8dB bump, I should be able to pull of 150' and have the latitude to compensate for the additional length. Hhahahaha. 27dB!!!! that is truly shocking! "The 21 dB of loss at 500 MHz would be about 27 dB at 600 MHz" This makes all the sense in the world now, considering that the ill effects of my system were especially pronounced on the blocks 25/26! As to the 9913F, is that the very large diameter cable with the non standard BNC connections? (the stock that I won at the Ramps Party? and thank you) Most of the mixers I know will use that cable for runs under 20' ...ironically, for either runs to Helical antennas or on car rigs! The reason being the cable is a bit impractical for long runs (heavy, and does not lay well on the ground... trip hazard, and that the non-standard BNC connections are not easy to deal with in the field. I would definitively call this a case of me following the herd without thinking it through!! Lesson learned!! The show I'm on at the moment and will be until thanksgiving, "The Walking Dead" is incredibly rough, wireless heavy, and shot at very fast pace! With your input it becomes brilliantly clear that I have to find a compromise here, I don't think I can rock out 100' + of the heavy cable and at the same time I have a necessity to remote my antennas!! Shooting on rooftops without access, etc! One more thing: I'm a bit confused about the cable stock, I have always believed that RG-58 is what, wireless antennas needed to live on (50 ohm), Is RG-8 simply a low loss version (thicker conductor) of RG-58? And is the 9913F a Belden equivalent of the RG-8? or are there differences? The package is coming your way. Bartek Swiatek ******** Hi Bartek, The right angle connectors on the short cables needed to be soldered on the ground terminal and the hot terminal. Then they would be OK. The loss in those connectors is high compared to high quality right angle connectors but by high, I mean 2 dB rather than 1 dB. With the antenna amplifier in the system, you would be able to compensate for that. The kind of cable you used for your short cables is fine since the loss is very low for a short run of 2.5 feet. RG-8 is a larger co-ax with less loss than RG-58, which is important only for runs longer than 15 feet. The Belden 9913F is a version of RG-8, i.e., in the RG-8 family. It is slightly lower loss, more flexible and slightly lighter due to use of a foamed polyethylene rather than solid polyethylene insulation. It is also double shielded. The F designator is for flexible (ha!) since the center conductor is stranded rather than solid. This adds a ½ dB of loss at 100 feet but is a reasonable trade off for better handling. The foam insulator also means it is a little less rugged when run over by a truck tire. RF is always a compromise. Here’s an excellent site with all kinds of co-ax calculation: http://www.timesmicr...in/calculate.pl The RG cables are at the bottom of the “Product” menu in the calculator. You want “Total Run Attenuation (dB)”, not the Attenuation(dB/100 feet). The real problem here is the 150 foot RF run. The larger, lower loss coax is a problem in portable situations. I do have two possible solutions for you below: The first is to run 100 feet of 9913 and then for the last 50 feet use RG-58 for easy handling. Your loss would be 5 dB for the RG-58 (at 50’) and 2 dB for the 9913 (at 100’). The 8 dB of gain in your antenna amp would be nearly perfect. The second is to use 150 feet of RG8X (also known as RG-8 mini) and your loss at 600 MHz would be 15 dB. Set the internal amp for max gain of 12 dB and you again are solid. The -3dB of gain (3 dB loss) is minor and I think the amp gain is a touch higher anyway. RG-8x is a lower loss RG-58 version and is the same size as the XXXX you were using. One last item: Can I post all your travails on JWS and save some other mixers the same problems? I will change the names to protect the guilty and will leave out your name if you wish, though it will have more impact if it is real. I’ll send you the text for a final OK. I am not happy with XXX about this though they are generally excellent. Anybody can make a mistake and that’s OK as long as they learn. Best Regards, Larry Fisher Lectrosonics ***************** This is the end of the emails. Bartek was kind enough to leave it "real". The westpan 807 cable he mentioned is actually West Penn 807, an RG-8X cable which is closer to RG-58. This 807 cable was not a good performer in our measurements, not even as good as generic RG-58. It had 27 dB of loss at his 150 foot length. Maybe it was very old or had been walked on too many times. As a result of this, Lectro is making up some RG-8X mini cables in a 125 foot length for testing, that when used with an amplified antenna, either the LPD650 or our in line antenna amp, the UFM230, will have losses that just match the max gain of the amps. This means that maybe, for some moderate coin, you could have a light weight cable system with good long length performance. Best Regards, Larry Fisher Lectrosonics Quote Link to comment Share on other sites More sharing options...
Whit Norris Posted June 28, 2011 Report Share Posted June 28, 2011 Here's an interesting (to me) problem that finally seemed to have a simple cause. I've reordered the history so the oldest email is at the top. An interesting conclusion is that there is a need for a lighter solution than using 2 x 150 foot runs of Belden 9913F which would weigh 15 lbs for each run and is bulky when rolled up. If this is too long, skip to the end to find out who killed Colonel Mustard in the drawing room with an RE20. ******** This is the end of the emails. Bartek was kind enough to leave it "real". The westpan 807 cable he mentioned is actually West Penn 807, an RG-8X cable which is closer to RG-58. This 807 cable was not a good performer in our measurements, not even as good as generic RG-58. It had 27 dB of loss at his 150 foot length. Maybe it was very old or had been walked on too many times. As a result of this, Lectro is making up some RG-8X mini cables in a 125 foot length for testing, that when used with an amplified antenna, either the LPD650 or our in line antenna amp, the UFM230, will have losses that just match the max gain of the amps. This means that maybe, for some moderate coin, you could have a light weight cable system with good long length performance. Best Regards, Larry Fisher Lectrosonics Thanks Larry and Bartek for posting this. Larry and am waiting to here the report of the testing of these cables. Thanks, Whit Quote Link to comment Share on other sites More sharing options...
Marc Wielage Posted June 29, 2011 Report Share Posted June 29, 2011 I found out the hard way on my first wireless job about 7 years ago that RG59 does not work well for receivers. Luckily, I did not get any major hits or dropouts during circled takes. I doubt that even half of the available signal was making it through my cable, and this was maybe 30' at best (to get around a corner and a metal door). Right after the shoot, I did some checking up and was stunned to learn how severe the dB loss is with UHF frequencies through RG59 cable, and immediately changed over to RG8. Absolutely no issues now. Live and learn. (I make different, more interesting mistakes today, but I try to never repeat the same mistake twice.) I also read and re-read Lectrosonics "white paper," Wireless Microphone Systems: Concepts of Operation and Design, and realized the complexities of RF systems like this. Lotta black art here, and some of it's unpredictable. --Marc W. Quote Link to comment Share on other sites More sharing options...
Bartek Posted August 12, 2011 Report Share Posted August 12, 2011 Marc. that was a rg 58 cable in question :-) Quote Link to comment Share on other sites More sharing options...
Marc Wielage Posted August 13, 2011 Report Share Posted August 13, 2011 I can't remember -- it was five or six years ago that I ran into this. It seems like all the best lessons in life (especially for sound) are the hard ones. --Marc W. Quote Link to comment Share on other sites More sharing options...
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