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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Wireless and Communications => Topic started by: Nathan Riddle on January 02, 2018, 02:55:13 PM
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MPD Digital rg8x-bnc-antenna-cable-12in RG-8X
Anyone used these / are they good?
I don't have tools to roll my own (yet).
RG8X seems better than buying RG58/9 even for shorter cables.
https://www.amazon.com/MPD-Digital-rg8x-bnc-antenna-cable-18in-MILSPEC-Connectors/dp/B00I9EHY0S/ref=sr_1_cc_4?s=aps&ie=UTF8&qid=1514921766&sr=1-4-catcorr&keywords=rg8x%2Bbnc&th=1
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I want to use them as short interconnects for my distro -> passive splits since I have more receivers than distro outs.
[RF diversity fin] ->
[RF Distro 3x (+3dB) + 1 cascade(0dB)] -> [4x SLX receiver]
[RF Distro 1x (+3dB)] -> [2x1 split] -> [2 x SLX receiver]
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MPD Digital rg8x-bnc-antenna-cable-12in RG-8X
Anyone used these / are they good?
I don't have tools to roll my own (yet).
RG8X seems better than buying RG58/9 even for shorter cables.
https://www.amazon.com/MPD-Digital-rg8x-bnc-antenna-cable-18in-MILSPEC-Connectors/dp/B00I9EHY0S/ref=sr_1_cc_4?s=aps&ie=UTF8&qid=1514921766&sr=1-4-catcorr&keywords=rg8x%2Bbnc&th=1
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I want to use them as short interconnects for my distro -> passive splits since I have more receivers than distro outs.
[RF diversity fin] ->
[RF Distro 3x (+3dB) + 1 cascade(0dB)] -> [4x SLX receiver]
[RF Distro 1x (+3dB)] -> [2x1 split] -> [2 x SLX receiver]
I've had good experiences with MPD and wouldn't hesitate buying more of their cables.
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MPD Digital rg8x-bnc-antenna-cable-12in RG-8X
Anyone used these / are they good?
I don't have tools to roll my own (yet).
RG8X seems better than buying RG58/9 even for shorter cables.
https://www.amazon.com/MPD-Digital-rg8x-bnc-antenna-cable-18in-MILSPEC-Connectors/dp/B00I9EHY0S/ref=sr_1_cc_4?s=aps&ie=UTF8&qid=1514921766&sr=1-4-catcorr&keywords=rg8x%2Bbnc&th=1
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I want to use them as short interconnects for my distro -> passive splits since I have more receivers than distro outs.
[RF diversity fin] ->
[RF Distro 3x (+3dB) + 1 cascade(0dB)] -> [4x SLX receiver]
[RF Distro 1x (+3dB)] -> [2x1 split] -> [2 x SLX receiver]
I didn't know cables could be digital :o
I wouldn't classify a single braid shield construction as "low loss", but for short jumpers within a rack they'll be fine.
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I didn't know cables could be digital :o
I wouldn't classify a single braid shield construction as "low loss", but for short jumpers within a rack they'll be fine.
HA!!
Henry,
I'm pretty sure in this case 'MPD Digital' is a proper noun.
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Are they better than: Shure UA802 RG58C/U UHF coaxial cable 2ft?
I don't have tools (yet) to roll my own and LMR400 is probably too inflexible for short jumpers.
I'm inexperienced to building RF racks, and the builds I've learned off of were made out of 'crappy' cable (at least it seemed to me).
If I'm using them with passive splits I want the 'best' (within reason) cable.
I need to go read http://www.astronwireless.com/topic-archives.asp I believe.
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Are they better than: Shure UA802 RG58C/U UHF coaxial cable 2ft?
Possibly, but it also might not matter much. Cable loss is typically quoted as a certain number of dB lost per 100' for a given frequency (the higher the frequency, the greater the loss).
While every cable is different, RG58 (and it's ilk) typically cause somewhere in the neighbourhood of 13 dB/100' of attenuation at 500 MHz. RG8X is more like ~9dB/100' at 500MHz, or about 4dB less attenuation per 100' at 500MHz.
4dB less attenuation sounds great, but let's consider it in the context of usage: 2' of RG58 (the Shure cable) will cause ~0.26dB of loss at 500MHz, while 18" of RG8X (the MPD cable) will cause ~0.14dB of loss at 500MHz, for a difference of only ~0.12dB which, in the grand scheme of things, isn't very much.
In my mind, for short intra-rack coax runs, the type of coax is less important than other considerations (quality of cable and connectors, durability of assembly, cost, etc.); even if you did something crazy and wired up your rack with RG316, by my math you'd still likely be looking at less than half a dB of attenuation per link from the cable.
-Russ
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In my mind, for short intra-rack coax runs, the type of coax is less important than other considerations (quality of cable and connectors, durability of assembly, cost, etc.); even if you did something crazy and wired up your rack with RG316, by my math you'd still likely be looking at less than half a dB of attenuation per link from the cable.
One reason for using low loss coax (braid over foil, double braid or corrugated shield) within a rack is for RFI immunity. Remember that a standard single braid shielded coax is not just lossy, meaning RF energy escapes, but that same porosity that let's RF energy out lets unwanted RF energy into the coax and can contribute to a number of maladies including IMD, gain stage saturation and receiver desense.
For a typical wireless mic receiver rack, low loss coax won't make a substantive difference, unless the rack is also loaded with a significantly "noisy" digital equipment, IEM transmitters with less than stellar shielding, or other potential RFI/EMI sources.
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Possibly, but it also might not matter much. Cable loss is typically quoted as a certain number of dB lost per 100' for a given frequency (the higher the frequency, the greater the loss).
While every cable is different, RG58 (and it's ilk) typically cause somewhere in the neighbourhood of 13 dB/100' of attenuation at 500 MHz. RG8X is more like ~9dB/100' at 500MHz, or about 4dB less attenuation per 100' at 500MHz.
4dB less attenuation sounds great, but let's consider it in the context of usage: 2' of RG58 (the Shure cable) will cause ~0.26dB of loss at 500MHz, while 18" of RG8X (the MPD cable) will cause ~0.14dB of loss at 500MHz, for a difference of only ~0.12dB which, in the grand scheme of things, isn't very much.
In my mind, for short intra-rack coax runs, the type of coax is less important than other considerations (quality of cable and connectors, durability of assembly, cost, etc.); even if you did something crazy and wired up your rack with RG316, by my math you'd still likely be looking at less than half a dB of attenuation per link from the cable.
-Russ
Thank you for giving me the 'damping factor' of sound for RF applications calculations/math. That definitely puts things in perspective :)
I found this site:
http://www.qsl.net/co8tw/Coax_Calculator.htm
And thoroughly enjoyed learning about the coax types and losses associated with them! I needed that so badly to get the light'bulb to go off in my head about RF.
The mud isn't as thick to see through now!
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What about something like this?
3.3dB @ 450MHz for 100ft according to spec sheet. $166
https://www.showmecables.com/by-category/cables/wifi-microwave/bnc-male-to-bnc-male-low-loss-400-ultraflex-coaxial-assembly
https://www.showmecables.com/media/specs/SMC-400UF-Wifi-Assemblies.pdf
LOW LOSS 400 ULTRAFLEX CABLE - 100FT BNC MALE TO BNC MALE
Designed to deliver high performance with minimal loss, Low Loss 400 UltraFlex (LMR-400UF equivalent) assemblies are the standard for the wireless LAN industry. With a durable Polyethylene jacket, these cables are suited for indoor and outdoor installations.
Features:
Connector 1: BNC Male
Connector 2: BNC Male
Cable Type: ShowMeCable Low Loss 400 UltraFlex (LMR-400UF Equivalent)
50 Ohm
Polyethylene (PE) Jacket suitable for Indoor or Outdoor Use
Stranded Center Conductor for Maximum Flexibility
Applications: Wi-Fi, Antenna Cables, Ham Radio, Patch Cables, Jumper Cables, WLL, GPS, WLAN, LMR, WISP, WiMax, SCADA, Mobile Antennas
I know it's probably one of those: buy once cry once kind of deals, but I don't have big tour budget to get the best, just what is needed/works.
Either this cable or RG8X for 150 with 8dB loss can't exactly afford RG8 (Belden 9913)@ 2.8 dB loss for $300.
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Also, this is really for remote mounting of antenna from TX or RX, correct?
I'm still not completely convinced remote mounting the antenna (closer to stage) with associated cable loss is better than having antenna at FOH with less cable loss. Though I guess the logic here is that air losses is greater than coax losses.
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LMR-400 UF (basically what you quoted) Is what we use for the majority of our RF cables..... Well, what we purchase at least for between antennas and receivers/distros.
We also use LMR-240, usually it is what most of the manufacturers/distributers are sending out now with large RF orders (or RG8). The few extra dB loss per run for the majority of our applications, it doesn't make a considerable difference between the two (<50ft).
However, for longer runs (100's of feet) LMR-400 is the way to go (or bigger, or fibre for 1000's of feet).
But do realize, that with the larger numbers (LMR-400), it is as thick as a 15A AC cable, and not nearly as flexible. You can fit a few hundred feet (probably a thousand+ feet) of coiled RG8 in the same space as 100ft of coiled LMR-400.
Get in the habit of doing path loss calculations over free space and cable. Find out what your receiver needs for signal strength and figure out what cable best suits your needs. If LMR-240 fits the bill, save some money and get that. But if you really need LMR-400, get the LMR-400.
BRad
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I'm still not completely convinced remote mounting the antenna (closer to stage) with associated cable loss is better than having antenna at FOH with less cable loss. Though I guess the logic here is that air losses is greater than coax losses.
Coaxial cable losses at the distances we're working with will always be less than than free space path loss.
Pick a coax cable, any coax cable (and a frequency): http://www.qsl.net/co8tw/Coax_Calculator.htm (http://www.qsl.net/co8tw/Coax_Calculator.htm). For safe measure, add 2dB to account for worn connector losses.
Now check the path loss at that same frequency (use "0" for transmitter and receiver gain): https://www.pasternack.com/t-calculator-fspl.aspx (https://www.pasternack.com/t-calculator-fspl.aspx).
This is why it's just about always better to get the antennas as close to the transmitters as possible.
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Get in the habit of doing path loss calculations over free space and cable.
Now check the path loss at that same frequency (use "0" for transmitter and receiver gain): https://www.pasternack.com/t-calculator-fspl.aspx (https://www.pasternack.com/t-calculator-fspl.aspx).
In the spirit of Merlijn van Veen ("if your mental estimate is within a decibel, it's close enough"), you can do quick-and-dirty Free Space Path Loss calculations for UHF microphones (etc.) in your head using the following equation:
FSPL = 20log(d) + 27
where 'd' is the distance between antennas in meters. For VHF devices, replace the 27 in that equation with an 18. This should get you within 2 dB of the Pasternack calculator; if you need more accuracy than that, you can use the following:
FSPL = 20log(d) + 20log(f) - 27.5
where 'd' is the distance between antennas in meters and 'f' is the frequency in MHz. This equation is not frequency dependent, and should get you well within a decibel every time.
(If you're wondering how "quick-and-dirty" and "20log(d)" go in the same post together, just remember that it's exactly the same mathematical operation you'd use for figuring out point-source SPL drop over distance.)
-Russ
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FSPL = 20log(d) + 20log(f) - 27.5
where 'd' is the distance between antennas in meters and 'f' is the frequency in MHz. This equation is not frequency dependent . . .
[Emphasis added]
How is this equation not frequency dependent?
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How is this equation not frequency dependent?
Sorry, I should have been clearer: the second equation can be used for any given frequency, whereas in the first equation the constant used (and therefore the equation itself) changes with frequency; to my way of thinking this makes the first equation itself frequency-dependant, whereas the second equation merely has a frequency-dependant result (as do all FSPL calculations).
-Russ
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Sorry, I should have been clearer: the second equation can be used for any given frequency, whereas in the first equation the constant used (and therefore the equation itself) changes with frequency; to my way of thinking this makes the first equation itself frequency-dependant, whereas the second equation merely has a frequency-dependant result (as do all FSPL calculations).
No problem. I haven't used RPN since college ;D
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One reason for using low loss coax (braid over foil, double braid or corrugated shield) within a rack is for RFI immunity. Remember that a standard single braid shielded coax is not just lossy, meaning RF energy escapes, but that same porosity that let's RF energy out lets unwanted RF energy into the coax and can contribute to a number of maladies including IMD, gain stage saturation and receiver desense.
For a typical wireless mic receiver rack, low loss coax won't make a substantive difference, unless the rack is also loaded with a significantly "noisy" digital equipment, IEM transmitters with less than stellar shielding, or other potential RFI/EMI sources.
I thought the term "low loss" referred to the heavier inner conductor, not the completeness of the shield.
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One reason for using low loss coax (braid over foil, double braid or corrugated shield) within a rack is for RFI immunity. Remember that a standard single braid shielded coax is not just lossy, meaning RF energy escapes, but that same porosity that let's RF energy out lets unwanted RF energy into the coax and can contribute to a number of maladies including IMD, gain stage saturation and receiver desense.
For a typical wireless mic receiver rack, low loss coax won't make a substantive difference, unless the rack is also loaded with a significantly "noisy" digital equipment, IEM transmitters with less than stellar shielding, or other potential RFI/EMI sources.
I just wanted to add to this for those that are new to digital wireless systems. Digital transmitters are sending data (ones and zeros) so there is no dynamic range component to the signal (in standard terms). The transmitters are always running at full power compared to analog systems. There is likely much more energy running through your jumper cables and so a much bigger potential for interference.
For this reason you should use higher grade cables (RG8x or LMR-195) when connecting to your distro. It's also a best practice to NOT neatly lace all the cables together. A rat's nest will likely work better.
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I just wanted to add to this for those that are new to digital wireless systems. Digital transmitters are sending data (ones and zeros) so there is no dynamic range component to the signal (in standard terms). The transmitters are always running at full power compared to analog systems. There is likely much more energy running through your jumper cables and so a much bigger potential for interference.
For this reason you should use higher grade cables (RG8x or LMR-195) when connecting to your distro. It's also a best practice to NOT neatly lace all the cables together. A rat's nest will likely work better.
Thanks for this golden nugget :)
I'm a bit OCD when it comes to cable management so my RF rack looks spic'n'span; I'll have to go clutter it up :(
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LMR-400 UF (basically what you quoted) Is what we use for the majority of our RF cables..... Well, what we purchase at least for between antennas and receivers/distros.
We also use LMR-240, usually it is what most of the manufacturers/distributers are sending out now with large RF orders (or RG8). The few extra dB loss per run for the majority of our applications, it doesn't make a considerable difference between the two (<50ft).
However, for longer runs (100's of feet) LMR-400 is the way to go (or bigger, or fibre for 1000's of feet).
But do realize, that with the larger numbers (LMR-400), it is as thick as a 15A AC cable, and not nearly as flexible. You can fit a few hundred feet (probably a thousand+ feet) of coiled RG8 in the same space as 100ft of coiled LMR-400.
Get in the habit of doing path loss calculations over free space and cable. Find out what your receiver needs for signal strength and figure out what cable best suits your needs. If LMR-240 fits the bill, save some money and get that. But if you really need LMR-400, get the LMR-400.
BRad
Thanks for simplifying all this for me and pointing out the specifics!
Coaxial cable losses at the distances we're working with will always be less than than free space path loss.
Pick a coax cable, any coax cable (and a frequency): http://www.qsl.net/co8tw/Coax_Calculator.htm (http://www.qsl.net/co8tw/Coax_Calculator.htm). For safe measure, add 2dB to account for worn connector losses.
Now check the path loss at that same frequency (use "0" for transmitter and receiver gain): https://www.pasternack.com/t-calculator-fspl.aspx (https://www.pasternack.com/t-calculator-fspl.aspx).
This is why it's just about always better to get the antennas as close to the transmitters as possible.
I played with both; I wasn't sure about the gain at first but once you stated using "0" it worked itself out. Thanks!
Makes a ton of sense now to use coax to get the antenna closer than leaving the antenna further away.
I need to figure out how to calculate the dB loss of couplers, connections, & cable differences [a rule of thumb].