hey all. Quick opinion question.
I'm working on getting a UHF ham repeater up and going. It'll be about 40 watts around 442MHz with about 50 feet of feedline into a single-bay UHF folded dipole.
We have, at our disposal, RG-8 and RG-214 coax. I don't mind spending some $$ for 9913, LMR-400 or something like that, but what's your opinions as to the best kind for the buck?
I know RG-8 is pretty frowned upon for repeaters but what are your thoughts?
Repeater coax
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bellersley
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bellersley
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Well, the problem is that the other people working in our group are hard-set on the fact that RG-8 is the way to go. When I explained that most sites won't even LET you use anything less than LMR/9913, they said that I don't know what I'm talking about. One of the people in our group is a broadcast engineer, they use RG-8 for some of their VHF/UHF comm. and STL equipment, so according to them, "if it's good enough for them, it's good enough for us".
I'm trying to convince them that anything less than 9913 or LMR is probably not a good idea, but that doesn't seem to work. Aparantly their thinking is that just because RG-8 and RG-214 have pretty close to the same loss, it must be the same cable, which everyone knows isn't the case.
So yes. How much does 100 feet of LMR400 go for these days? I'm halfway tempted to go and buy some myself
I'm trying to convince them that anything less than 9913 or LMR is probably not a good idea, but that doesn't seem to work. Aparantly their thinking is that just because RG-8 and RG-214 have pretty close to the same loss, it must be the same cable, which everyone knows isn't the case.
So yes. How much does 100 feet of LMR400 go for these days? I'm halfway tempted to go and buy some myself
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bellersley
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If it were up to me, it'd be fed with a healthy dose of LDF4-50, or at least 2-50.
Unfortunatly, it seems that I have no say in what happens with the project...the "powers that be", so to speak, are hell-bent on using RG-8 type coax. I put an N connector on the RG-8 we have now, and it's certainly NOT the best braid in the world, although it is one of the better ones I've seen for that type of coax.
Real-world, what could we expect with 50 feet of RG-8 type coax at UHF, running 45 watts? Looking at all the figures I can find, we'd be lucky to see 20 coming out of the antenna.
It's my view that this should be done properly, from day one, but it seems the goal is to get it on the air "now" instead of "right", but that's just my opinion.
Unfortunatly, it seems that I have no say in what happens with the project...the "powers that be", so to speak, are hell-bent on using RG-8 type coax. I put an N connector on the RG-8 we have now, and it's certainly NOT the best braid in the world, although it is one of the better ones I've seen for that type of coax.
Real-world, what could we expect with 50 feet of RG-8 type coax at UHF, running 45 watts? Looking at all the figures I can find, we'd be lucky to see 20 coming out of the antenna.
It's my view that this should be done properly, from day one, but it seems the goal is to get it on the air "now" instead of "right", but that's just my opinion.
FYI, you can Google this stuff...
For typical cheap-:o Belden 8214 RG-8, you're talking 4.2dB/100'. You'd lose 2.1dB in the feedline, plus figure another 1dB for connector losses. In round numbers, call it 3dB, which means you'd see 22.5 out of the antenna assuming you have a perfect match (none of them thar swerrs...)
The average Times/Andrew Cinta/9913/etc. cable will be about half that, which is approaching reasonable, but not great.
Bear in mind, these are ALL garden hoses. Waterproof all you want - these cables WILL get waterlogged sooner or later. And, there have been many discussions about coaxial-type cable being used in repeater service.
Again, I'm saying LDF4. Coax has its place, but for a repeater/tower run, you want feedline, not coax. You'd be talking 1.4dB/100' which is much more reasonable, plus less connector loss (assuming you know how to install Heliax connectors properly). You could probably get away around 1.2dB of loss for the overall connectorized run. And your feedline won't turn into garden hose.
I've got the same issue with hamhumps... I get criticized because my amateur repeater is built to commercial specs (no mobile radios or that there RG-8 for me, thank you). Then they get all amazed that my repeater will give solid handheld coverage (as in, on your belt, not stuck up in the air) for a 30-mile radius. Duh.
For typical cheap-:o Belden 8214 RG-8, you're talking 4.2dB/100'. You'd lose 2.1dB in the feedline, plus figure another 1dB for connector losses. In round numbers, call it 3dB, which means you'd see 22.5 out of the antenna assuming you have a perfect match (none of them thar swerrs...)
The average Times/Andrew Cinta/9913/etc. cable will be about half that, which is approaching reasonable, but not great.
Bear in mind, these are ALL garden hoses. Waterproof all you want - these cables WILL get waterlogged sooner or later. And, there have been many discussions about coaxial-type cable being used in repeater service.
Again, I'm saying LDF4. Coax has its place, but for a repeater/tower run, you want feedline, not coax. You'd be talking 1.4dB/100' which is much more reasonable, plus less connector loss (assuming you know how to install Heliax connectors properly). You could probably get away around 1.2dB of loss for the overall connectorized run. And your feedline won't turn into garden hose.
I've got the same issue with hamhumps... I get criticized because my amateur repeater is built to commercial specs (no mobile radios or that there RG-8 for me, thank you). Then they get all amazed that my repeater will give solid handheld coverage (as in, on your belt, not stuck up in the air) for a 30-mile radius. Duh.
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bellersley
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Well, here's the equipment that I personally have for the project.
I have a UHF MSF5000 with a 45W PA, I also have the 100W PA we could use as well. I've also got a single-bay UHF dipole (Sinclair). Only thing missing is a duplexer, but I'm working on a Sinclair 4 Cavity "Res-Lok" style.
However, the others in the project want to include such things as a broadcast audio processesor, NRHC repeater controller, etc...
Space IS a serious concern at this site, but given the space we have, there's no reason it can't be done.
My attitude is that it should be done to commercial specs. There's no reason it can't be, as we already have the stuff to do it! The most popular repeater in town is using a 15 watt Stornophone mobile as it's transmitter with a home-brew controller...it sounds like CRAP, nevermind it's coverage range sucking, considering it's on top of the CN Tower. Other machines running the same power at lower altitudes have a better coverage range, so. Yes.
Anyway, enough of my ranting! tvsjr, you've answered my question, now the hunt is on for some LDF!
I have a UHF MSF5000 with a 45W PA, I also have the 100W PA we could use as well. I've also got a single-bay UHF dipole (Sinclair). Only thing missing is a duplexer, but I'm working on a Sinclair 4 Cavity "Res-Lok" style.
However, the others in the project want to include such things as a broadcast audio processesor, NRHC repeater controller, etc...
Space IS a serious concern at this site, but given the space we have, there's no reason it can't be done.
My attitude is that it should be done to commercial specs. There's no reason it can't be, as we already have the stuff to do it! The most popular repeater in town is using a 15 watt Stornophone mobile as it's transmitter with a home-brew controller...it sounds like CRAP, nevermind it's coverage range sucking, considering it's on top of the CN Tower. Other machines running the same power at lower altitudes have a better coverage range, so. Yes.
Anyway, enough of my ranting! tvsjr, you've answered my question, now the hunt is on for some LDF!
The MSF5000 is a great box (when the PAs aren't dying, but that's a grumble for another time). We've got a few in our statewide linked repeater system.
My personal repeater is as follows:
Kenwood (gasp!) TKR-750 version 2 repeater, making 5 watts
Midland LMR PA (it was free, and it's a *hoss*) making 150 watts
TxRx 6-can BpBr duplexer
Appropriate isolators
Andrew 1/4" Superflex for all internal jumpers
Andrew 1/2" Superflex jumper from cabinet to antenna
Polyphaser lightning protection
Old GE ferroresonant power supply (another hoss)
300Ah of in-cabinet battery backup with a Samlex charger/controller
Andrew 1-1/4" Heliax feedline (~450ft.)
Decibel DB-264 antenna (150-160 supposedly, but it's 1.05:1 at 147).
The Kenwood repeater is really cool because it has all the basic controller functions built in... DTMF control, courtesy tone, ability to switch channels when the system dumps to battery (backs power output down, changes IDer, shortens hang time, etc.) It's also an all-around tight repeater, RF-wise. And they're cheap.
I'm taking about 1.5dB of loss in the cabinet (duplexer, isolator, jumpers, etc.) and another 1dB in feedline to the antenna. The antenna is 6dBd gain (omni pattern), so my ERP is in the neighborhood of 375 watts. The system sensitivity is 0.21uV for 12dB SINAD. It hears as well as it talks.
Point is, if you're going to put a class machine on the air (like an MSF), don't hamsexy it up with a bunch of addon crap (they sound just fine in stock configuration), and do spend the time and money to do things right. It's worth it in the long run (not to mention you won't spend trip after trip going back to the site to fix some broken hamsexy accessory.)
Have fun...
My personal repeater is as follows:
Kenwood (gasp!) TKR-750 version 2 repeater, making 5 watts
Midland LMR PA (it was free, and it's a *hoss*) making 150 watts
TxRx 6-can BpBr duplexer
Appropriate isolators
Andrew 1/4" Superflex for all internal jumpers
Andrew 1/2" Superflex jumper from cabinet to antenna
Polyphaser lightning protection
Old GE ferroresonant power supply (another hoss)
300Ah of in-cabinet battery backup with a Samlex charger/controller
Andrew 1-1/4" Heliax feedline (~450ft.)
Decibel DB-264 antenna (150-160 supposedly, but it's 1.05:1 at 147).
The Kenwood repeater is really cool because it has all the basic controller functions built in... DTMF control, courtesy tone, ability to switch channels when the system dumps to battery (backs power output down, changes IDer, shortens hang time, etc.) It's also an all-around tight repeater, RF-wise. And they're cheap.
I'm taking about 1.5dB of loss in the cabinet (duplexer, isolator, jumpers, etc.) and another 1dB in feedline to the antenna. The antenna is 6dBd gain (omni pattern), so my ERP is in the neighborhood of 375 watts. The system sensitivity is 0.21uV for 12dB SINAD. It hears as well as it talks.
Point is, if you're going to put a class machine on the air (like an MSF), don't hamsexy it up with a bunch of addon crap (they sound just fine in stock configuration), and do spend the time and money to do things right. It's worth it in the long run (not to mention you won't spend trip after trip going back to the site to fix some broken hamsexy accessory.)
Have fun...
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bayfire300
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belersley:
i asked the same question last week and what i learned from these guys here on the board is .if your gonna do it?...do it right.
go w/ lmr-400 w/ n conectors and if you can afford itgo w/ 1/2" andrews heliax you can find info on both at http://www.cablexperts.com
try e-bay for cable also
try to get a 6 cavity duplexer for better isolation also w/ n connectors
i have a little 40 watt repeater myself and i learn all this stuff from these guy last week,,,,,,,,,,their knowledge here is invaluable
otto
i asked the same question last week and what i learned from these guys here on the board is .if your gonna do it?...do it right.
go w/ lmr-400 w/ n conectors and if you can afford itgo w/ 1/2" andrews heliax you can find info on both at http://www.cablexperts.com
try e-bay for cable also
try to get a 6 cavity duplexer for better isolation also w/ n connectors
i have a little 40 watt repeater myself and i learn all this stuff from these guy last week,,,,,,,,,,their knowledge here is invaluable
otto
I don't want to be a lead weight in a ballon race, but the LMR type cable is not a good choice in repeater service. There have been a large number of threads over time on this subject. Most of us older radio geeks or what ever label we have this week, all seem to agree.
Over time, you will find that the LMR coax cables will develope noise in repeater service. The solution seems to be to replace it with a better quality cable like some kind of heliax. This is not just one person saying it, but a large number of the radio service group on the board here.
Do what you will, but be fore warned that if you do use the LMR cable, don't come back here asking for help to solve a noise problem on your repeater system.
Jim
Over time, you will find that the LMR coax cables will develope noise in repeater service. The solution seems to be to replace it with a better quality cable like some kind of heliax. This is not just one person saying it, but a large number of the radio service group on the board here.
Do what you will, but be fore warned that if you do use the LMR cable, don't come back here asking for help to solve a noise problem on your repeater system.
Jim
If the learning from one's own mistakes it what the ham group want to do, then by all means use RG8 and shortly after that upgrade to LMR400 and in the end settle on LDF4-50 Heliax. Inferior cables will work for a short period of time in repeater use but eventually get noisier. Personally I prefer to learn from someone else’s misfortunes. Some people only learn from their own mistakes.
My guess is that the broadcast engineer doesn’t normally work with weak signals. When people here say that Heliax is the only way to go, it is because they found out the hard way. Commercial outfits use Heliax not because it is more expensive but because they don’t want to replace the cable every year.
For a 50 feet run the difference in feed line loss is not very large but that is not the only item to look for in a feed line for a repeater. Since you are looking for weak signals in the 0.25 uV range in the presence of a transmit signal that is around 50 volts peak from a 25 watt signal, you need a solid low noise cable like Heliax.
I just realize that you are located in Mississauga. That pretty well is Toronto and the noise level produced by the city may be even higher than that produced by the cable.
For more info:
http://batboard.batlabs.com/viewtopic.php?t=24173
Nand.
My guess is that the broadcast engineer doesn’t normally work with weak signals. When people here say that Heliax is the only way to go, it is because they found out the hard way. Commercial outfits use Heliax not because it is more expensive but because they don’t want to replace the cable every year.
For a 50 feet run the difference in feed line loss is not very large but that is not the only item to look for in a feed line for a repeater. Since you are looking for weak signals in the 0.25 uV range in the presence of a transmit signal that is around 50 volts peak from a 25 watt signal, you need a solid low noise cable like Heliax.
I just realize that you are located in Mississauga. That pretty well is Toronto and the noise level produced by the city may be even higher than that produced by the cable.
For more info:
http://batboard.batlabs.com/viewtopic.php?t=24173
Nand.
Last edited by Nand on Sat Oct 22, 2005 5:12 am, edited 1 time in total.
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bellersley
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Okay! Well, we managed to secure 100 feet of LMR-400 and the proper N connectors. This is being fed into our antenna and an MSF on the other end. Reflected power dosent exsist (that is, for 40 watts out, not even 1 is getting back).
The repeater isn't in Mississauga, its in Toronto. Using a ham portable on our antenna/feedline, I'm hitting repeaters as far as 200km full quieting...not bad
The eventual plan is to use heliax, but for now I think were good. As always, thanks for you input!
The repeater isn't in Mississauga, its in Toronto. Using a ham portable on our antenna/feedline, I'm hitting repeaters as far as 200km full quieting...not bad
The eventual plan is to use heliax, but for now I think were good. As always, thanks for you input!
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Mike in CT
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transmission line
Old buzzard here with 30+ yrs in tower business...
Stay away from LMR-400. it WILL introduce noise into your system. For a bit more $ than 9913, you can find 1/2 inch or 7/8 inch hardline.
I would recommend (for 450MHz) to go with 7/8 line. Sure it will cost a bit more, but when you spread that cost difference over the next 10-20 years, it will be negligible and you will be glad you did it!
Use the best you can afford. Cable repair/replacements are not only expensive, but a royal pain. DO IT ONCE, DO IT RIGHT and you will never regret it!
And remember to go first class on the weatherproofing!
73,
Mike in CT
KM1R
Stay away from LMR-400. it WILL introduce noise into your system. For a bit more $ than 9913, you can find 1/2 inch or 7/8 inch hardline.
I would recommend (for 450MHz) to go with 7/8 line. Sure it will cost a bit more, but when you spread that cost difference over the next 10-20 years, it will be negligible and you will be glad you did it!
Use the best you can afford. Cable repair/replacements are not only expensive, but a royal pain. DO IT ONCE, DO IT RIGHT and you will never regret it!
And remember to go first class on the weatherproofing!
73,
Mike in CT
KM1R
Mike in CT is right on the money. As for broadcast engineers, most I've met are much more open minded and much more astute than the crowd you're saddled with, but part of the success in my 40+ years in the business has been due to the business provided by "broadcast engineers" dabbling in the 2 way radio business. I can understand using an RG-8 cable for temporary duty or in an attempt to induce a loss in a feedline for attenuation tuning, but even that's a bad idea due to the fact that the cable deteriorates so rapidly. Maybe those broadcast engineers who wanna use RG-8 should take a look at how well their broadcast systems and STL links work, or maybe how poorly.
curmudgeon.....and I like it.