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Question of the Day: What's the most interesting small town you've visited in South Africa?
Sentech dish
- Thread starter f1man5
- Start date
stoke
Honorary Master
ME 2.
Howz about a - I live in this general area - hint as well ?
My last dish I dropped from the roof, and it still works, but i think I could be better if it was symetrical.
Howz about a - I live in this general area - hint as well ?
My last dish I dropped from the roof, and it still works, but i think I could be better if it was symetrical.
OK - this is where I got it from.
There is a pic included (I think its the 40cm version)
Check it out at
http://www.miro.co.za/stage/intranet/wireless.php?section=AntennasDish
There is a pic included (I think its the 40cm version)
Check it out at
http://www.miro.co.za/stage/intranet/wireless.php?section=AntennasDish
desraid
Expert Member
is it better than the flat panel one?
bdt
Executive Member
...define"better"
-that depends on the version of "better" you're running -and which flat panel one you mean. Oh- and, while we're at it, which dish he's referring to! Admittedly hf1man5 seems to think that he's got a 40cm dish there which'd mean an 18dBi gain device (notwithstanding the 9dBi feed is uses). This combo is cheaper than the significantly less powerful 13dBi flat panel antenna, so that'd qualify as "better" alright.
But dishes are somewhat less friendly to put up on poles, something flat panels are rather better at- a loss there!
.
So, as to "better"? It depends.
-bdt
desraid said:
-that depends on the version of "better" you're running -and which flat panel one you mean. Oh- and, while we're at it, which dish he's referring to! Admittedly hf1man5 seems to think that he's got a 40cm dish there which'd mean an 18dBi gain device (notwithstanding the 9dBi feed is uses). This combo is cheaper than the significantly less powerful 13dBi flat panel antenna, so that'd qualify as "better" alright.But dishes are somewhat less friendly to put up on poles, something flat panels are rather better at- a loss there!
.So, as to "better"? It depends.
-bdt
so I thought I'd had it all figured. but no.
bdt, are you saying the only reason it's better is because it's cheaper?
I'm trying to understand the theory here. An 18dBi gain dish gives me 18dBi gain right?
Adding the 9dBi feed horn, does that give me 27dBi gain? or does is only "catch" 9dBi?
And then, I add 10metres of LMR400 cable, at 0.2dBi loss per metre. I end up(in theory) having a 7 or 25dBi gain on the far end of the cable?
3dBi is supposed to be 100% improvement in signal, according to some guy.
So, if I start off with 11% signal, in theory, I should get about 35% signal if I get 7dBi gain?
But all of this doesn't help if I'm more than 5.7km from the tower?
according to http://rational.co.za/MyWireless I'm 6.7km from the closest tower, but 9.9km from the one my modem picks up. obviously I can't connect at all.
Geez I'm confused...
bdt, are you saying the only reason it's better is because it's cheaper?
I'm trying to understand the theory here. An 18dBi gain dish gives me 18dBi gain right?
Adding the 9dBi feed horn, does that give me 27dBi gain? or does is only "catch" 9dBi?
And then, I add 10metres of LMR400 cable, at 0.2dBi loss per metre. I end up(in theory) having a 7 or 25dBi gain on the far end of the cable?
3dBi is supposed to be 100% improvement in signal, according to some guy.
So, if I start off with 11% signal, in theory, I should get about 35% signal if I get 7dBi gain?
But all of this doesn't help if I'm more than 5.7km from the tower?
according to http://rational.co.za/MyWireless I'm 6.7km from the closest tower, but 9.9km from the one my modem picks up. obviously I can't connect at all.
Geez I'm confused...
Klaas, you close.
1. The antenna gain.
Gain is measured in dBD and not dBi
Most antenna manufactures specify their antenna gain in dBi because it looks better and fools the public, the same as many appliance manufactures will advertise Input Power rather than Output power, it just looks better.
The i in dBi stands for Isotropic and that is what they are referncing there gain against and it could be a piece of wet string, which would make the antenna look very good
At the end of the day, if an antenna specifies its gain as dBi then immediately subtract 3 dB so as to reference it against a known factor like a dipole which in air has 0 dB gain.
So now your 18 dBi antenna has a usefull gain of 15 dB.
2. The Feed Horn.
A Feed horn is just a fancy name given to an Wave guide to cable converter, and to overcome the losses occured in this conversion they make it an active device giving it around 6 to 9 dB gain.
This gain is normally also to make up for any cable losses you may occur provided its not too long.
So if your 10 meters of cable has 2 dB loss, the conversion loss is 3 dB and provided there is no interference on your antenna, then yes, you should realise around 19 dB gain at the modem.
The 11% you speak of is that at the modem inside the house, as you need to add it to whatever the modem has where the antenna will go.
In my case I have a 19 dB panel with no amplifier/convert/horn etc just 12 meters cheap RG214 cable (because its very flexible) and it pushes my 27% (on the roof) to 43%
The greatest advantage of using an antenna is the SNL improvement as that far outways the signal strength.
Mine went from 7 to 17 dBm
Remember a 10% signal with 12 dBm SNL is 1000 times better than say 40% signal with 10 dBm SNL, just keep that in mind when you line up your antenna.
So with the antenna you can pull in the closer tower.
try getting someone to test for you first.
1. The antenna gain.
Gain is measured in dBD and not dBi
Most antenna manufactures specify their antenna gain in dBi because it looks better and fools the public, the same as many appliance manufactures will advertise Input Power rather than Output power, it just looks better.
The i in dBi stands for Isotropic and that is what they are referncing there gain against and it could be a piece of wet string, which would make the antenna look very good
At the end of the day, if an antenna specifies its gain as dBi then immediately subtract 3 dB so as to reference it against a known factor like a dipole which in air has 0 dB gain.
So now your 18 dBi antenna has a usefull gain of 15 dB.
2. The Feed Horn.
A Feed horn is just a fancy name given to an Wave guide to cable converter, and to overcome the losses occured in this conversion they make it an active device giving it around 6 to 9 dB gain.
This gain is normally also to make up for any cable losses you may occur provided its not too long.
So if your 10 meters of cable has 2 dB loss, the conversion loss is 3 dB and provided there is no interference on your antenna, then yes, you should realise around 19 dB gain at the modem.
The 11% you speak of is that at the modem inside the house, as you need to add it to whatever the modem has where the antenna will go.
In my case I have a 19 dB panel with no amplifier/convert/horn etc just 12 meters cheap RG214 cable (because its very flexible) and it pushes my 27% (on the roof) to 43%
The greatest advantage of using an antenna is the SNL improvement as that far outways the signal strength.
Mine went from 7 to 17 dBm
Remember a 10% signal with 12 dBm SNL is 1000 times better than say 40% signal with 10 dBm SNL, just keep that in mind when you line up your antenna.
So with the antenna you can pull in the closer tower.
try getting someone to test for you first.
Thanks a lot Pro. I think I get what you're saying and it's nice to hear from someone who seems to know how these things work. The people who sell the cable and stuff doesn't seem to. Less so the okes at nowire
Anycase, I think I was a bit optimistic about using it where I stay now. Spent sunday afternoon in and on the roof, and it's simply useless, the signal I'm getting. I get 11% signal but between 0 and 2 SNL, and every time I try to connect it says that the remote computer did not respond. I presume it's because of the distance. That tower is 9.9km (Menlo Park) from me. The one at 6km's looks like it's behind a hill(Zita Park),and the other(ElardusPark) I can't even pick up when I'm 2 km from it at my parents' place, So I don't have hope as I'm in the same direction, just way further.
Nice. Now what do I do with a contract that's got 8 months to go?
Anyone?
Anycase, I think I was a bit optimistic about using it where I stay now. Spent sunday afternoon in and on the roof, and it's simply useless, the signal I'm getting. I get 11% signal but between 0 and 2 SNL, and every time I try to connect it says that the remote computer did not respond. I presume it's because of the distance. That tower is 9.9km (Menlo Park) from me. The one at 6km's looks like it's behind a hill(Zita Park),and the other(ElardusPark) I can't even pick up when I'm 2 km from it at my parents' place, So I don't have hope as I'm in the same direction, just way further.
Nice. Now what do I do with a contract that's got 8 months to go?
Anyone?
bdt
Executive Member
klaas said:
You seem to simply be out of range -and out of luck. Your options definitely include ceding it to someone else: ie, they'd buy the remainder of your 8 month contract; no harm, no foul -and you walk away. Also you could simply byte the bullet and take a hit on the balance of your contract: far less desirable! A third possibility might be to get your contract made dormant (I know they've done this from time to time) and be reactivated at some later date when you CAN use the service.
I don't know that the last would work for you/is even really possible, but I am going for a canonical answer here. Just FOI ("our"), what contract you on?
-bdt
bdt,
I am on MyWi 128, so it goes for R649/month. Anyone that's interested or know of someone who might be, let me know please! Besides the modem with USB cable, there is also an ethernet cable that would go with it. The contract runs out in May 06 I think...
I am on MyWi 128, so it goes for R649/month. Anyone that's interested or know of someone who might be, let me know please! Besides the modem with USB cable, there is also an ethernet cable that would go with it. The contract runs out in May 06 I think...
bdt
Executive Member
cable clarification
Up 'til now I've been under the impression that RG214 wasn't rated for this kind of SHF work, hence staying with LMR 195 & 400; the latter being my headache. It works well enough but it's a compleat bitch to work with, as I'm sure you know.
So: IS RG214 something I could consider using, from both practical and economy viewpoints?
ProAsm said:
Up 'til now I've been under the impression that RG214 wasn't rated for this kind of SHF work, hence staying with LMR 195 & 400; the latter being my headache. It works well enough but it's a compleat bitch to work with, as I'm sure you know.
So: IS RG214 something I could consider using, from both practical and economy viewpoints?
At these frequencies the size of the wavelength becomes a problem hence the reason for using LMR 400 as its dialectric renders it to have a velocity factor in the region of .8 so as to make the cable useable at these frequencies, also it does have a lower loss factor simply due to the dialectric properties, however, if its only a matter of cable and provided its not too long and you dont mind the extra loss (about 50% more) then RG214 is excellent and a first choice in our book simple because of the flexibility.
Positioning of the antenna where we achieve the greatest SNL (Signal to Noise) is far more important that a high signal strength, thus the loss in RG214 becomes irrelavent
Positioning of the antenna where we achieve the greatest SNL (Signal to Noise) is far more important that a high signal strength, thus the loss in RG214 becomes irrelavent
bdt
Executive Member
ProAsm said:...if its only a matter of cable and provided its not too long and you dont mind the extra loss (about 50% more) then RG214 is excellent and a first choice in our book simple because of the flexibility.
Positioning of the antenna where we achieve the greatest SNL (Signal to Noise) is far more important that a high signal strength, thus the loss in RG214 becomes irrelavent
Okaaay, in practical terms what's this come to? As an example, I've got a site where I installed a 24dBi
grid (the one Miro sells) and used 7m of LMR400 (cos they were *really* finicky about sig strength- they're in the radio game in another area) and ended up with: 36% sig, 18 dBm snl, -69dBm RSCP & -87dBm ISCP -as measured with MySignal 5.0 Based on what you're saying, this would've been a prime candidate for using RG214 instead of LMR400, yes? Could you get a thumbsuck of what I'd've ended up with using RG instead of LMR cable? ..and on a related note, how much does that stuff typically cost, per metre of course, anyway??
Ta for the input so far
-bdt
TheRoDent
Cool Ideas Rep
I grabbed the Dish. Good luck Anthony. All the best in Oz.
RichardP
Banned
bdt said:
I know its a late posting ;-) but LMR400 cable is R25/Metre.. just a FYI, the N-Type connectors are about R60 each for some good ones.
bdt
Executive Member
slight correction
...maybe to you it is, but I definitely don't buy either LMR400 or N-type connectors at those prices! (but I would pay more for Telegartners than I do for the (so far, entirely acceptable)) non-branded connectors I _am_ using ATM.
Oh, BTW: I *was* asking about the price of RG214, but I can see how my bad phrasing of the question may have led to confusion..
RichardP said:
...maybe to you it is, but I definitely don't buy either LMR400 or N-type connectors at those prices!
(but I would pay more for Telegartners than I do for the (so far, entirely acceptable)) non-branded connectors I _am_ using ATM.Oh, BTW: I *was* asking about the price of RG214, but I can see how my bad phrasing of the question may have led to confusion..