Mr_DNS
join:2005-09-07
Laredo, TX | Minimum cable length Anyone know the minimum cable length for WB setup?
I'm hearing from 50' to 75' now.
What happens if cable is say only 20' long? |
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 grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY
4 edits | I was quite surprised by this WildBlue "minimum length" stipulation, and quite frankly I don't understand it. Surely it can't be a hangover from the old days when the cable guy would leave a few extra feet "in case you move the television some day"....can it ?
Cable loss is a function of frequency X distance, and conventional wisdom is to use only the minumum amount of cable necessary. On lower frequency and/or non-coaxial configurations, standing waves can be an issue. But the wavelength on this Ka-band stuff is so very very short, that I can't see how SWR could possibly come into play.
Any WB engineers care to explain the rationale for minimum cable length?
//greg//
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DW4000CE/1.2 Ghz Tualatin/512 PC133 - W2K Pro/SP4 - SRS G11/1370H - RSL83/ACP81 - v4.2.1.10C - RWIN 513920/MTU 1500 - proxy switch - Gateway/DNS 205.177.62.91/66.82.4.8 plus rollovers - Firefox 1.02 |
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 fjholler
join:2005-08-21
Stamping Ground, KY
1 edit | said by grohgreg:I was quite surprised by this WildBlue "minimum length" stipulation, and quite frankly I don't understand it. I read an explanation of this on one of the forums a few weeks back, and now I can't find it. Worst of all, I can't recall the precise rationale. Old age causes me to do that sometimes.  I believe that the upshot of it was that it was pure B.S. My cable is not more than 25-30 feet long.
Actually, now that I think about it, it might have been the old "in case you move the television some day" ploy. |
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Mr_DNS
join:2005-09-07
Laredo, TX | said by fjholler:I was quite surprised by this WildBlue "minimum length" stipulation... In RV literature for datastorm unit,
»www.motosat.com/downloads/intern···tion.pdf
I could not find any references to cable length.
Since the Modem to TRIA cables are running about 950 Mhz signal, I can't figure out why shorter cables would affect performance....over at that other forum, it was suggested a higher dB uplink signal is the end result....but who knows.
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fjholler
join:2005-08-21
Stamping Ground, KY
1 edit | said by Mr_DNS:over at that other forum, it was suggested a higher dB uplink signal is the end result....but who knows. Maybe that's what I'm thinking of. |
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Mr_DNS
join:2005-09-07
Laredo, TX | reply to Mr_DNS
After reflecting on this topic, if the TRIA has a variable uplink output, then most likely the modem "drives it."
But, I understand there will be a software update for these modems, so after this update is done, maybe NOC will have better control of output.
Maybe having a hotter uplink signal may "bleed over" into adjacent beams; that's the best speculation I could come up with at a consumer ground level viewpoint;) |
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quote:
Actually, now that I think about it, it might have been the old "in case you move the television some day" ploy.
Don't mean to drag this off topic, but if they're paying for the cable, what exactly is the "ploy" here? |
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grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY | Read the whole thread Jeff. He was just responding to a comment I'd made earlier. Perhaps "ploy" wasn't the best choice of words, but the intent was understood
//greg// |
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| reply to Mr_DNS
Well there are two reasons for a min cable length.
1) The power supply needs to draw a min of current to function properly, so if you take the DC resistance of the cable at 50 feet, there will always be enough current draw to ensure the power supply is within its linear design curve.
2) Most important. The modem will adjust its output power to the TRIA to range in at the nominal power to the SMTS (Hub). There is only so much range adjustment on the modem. SO if you place a modem in a hot part of the beam with too little cable, the modem cannot be adjusted low enough to get it within the nominal range on the hub. This could cause the burst demods not to be able to adjustt fast enough to catch the next burst. So with 75 feet we have the modem in a nice linear range that we can control not over driving the hub and causing issues. |
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grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY | said by in the bush :
Well there are two reasons for a min cable length. #1 - pure gibberish.
#2 - see #1
//greg// |
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3 edits | reply to Mr_DNS
said by Mr_DNS:After reflecting on this topic, if the TRIA has a variable uplink output, then most likely the modem "drives it." Maybe having a hotter uplink signal may "bleed over" into adjacent beams; that's the best speculation I could come up with at a consumer ground level viewpoint;) Variable watt transmitter powered by modem....yep, I think you are on to something there...but not the part about "bleeding over" to adjacent beams,that part is, as Greg says, "pure gibberish"...more likely, 75' to 150' is the distance required for variable watt tria to get just enough, but not too much signal to ramp up or down.
I had to have an amplifier removed from my cable setup the other day because the DOCSIS modem in the DVR had a signal that was too strong...rendered HDTV inoperable. When removed, all was well.
...maybe relevant maybe not... |
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fjholler
join:2005-08-21
Stamping Ground, KY | reply to Island Jeff
said by Island Jeff: quote:
Actually, now that I think about it, it might have been the old "in case you move the television some day" ploy.
Don't mean to drag this off topic, but if they're paying for the cable, what exactly is the "ploy" here? It was a joke, son. Here's the smiley that I forgot to attach. |
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Mr_DNS
join:2005-09-07
Laredo, TX | reply to randyvsatus
said by randyvsatus:I had to have an amplifier removed from my cable setup the other day because the DOCSIS modem in the DVR had a signal that was too strong...rendered HDTV inoperable. Three Points -
1. Someone didn't configure the amplifier requirement,
2. Someone used a bad amplifier
3. Amplifier was not a high quality unit, and contained extra noises.
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3 edits | = Mr_DNS  1. Someone didn't configure the amplifier requirement, 2. Someone used a bad amplifier 3. Amplifier was not a high quality unit, and contained extra noises.
..in meantime, Adelphia made some improvements in our area and signal strength in on our node increased...well, now the amp (perfectly good amp) was pumping the signal too high for HDTV to work...remove it and all is well.
The point of my original post was that WB knows the distance a correct amount of wattage/amperage can go from the modem (which supplies power to radio/tria/transmitter (whatever you call it)and that appears to be between 75'& 150'...any closer than 75' and perhaps too strong a current...or perhaps they are BS'ing us, who knows.:D |
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grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY | said by randyvsatus:or perhaps they are BS'ing us, who knows. That's my guess
//greg// |
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fjholler
join:2005-08-21
Stamping Ground, KY | What possible motivation could there be for such B.S? Sell more cable? There's just too much at stake here for some engineer to just randomly drop in a spec to piss people off. I'll grant that the spec may be just dead wrong, but someone at WB has to think there's a good reason for it.
FWIW, my cable is roughly 30 feet long, and my system performs quite nicely. Today in light rain and heavy cloud cover all day long, 1.5 Mbps down, 250 kpbs up, and 595 ms ping. |
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| Maybe a email to: engineering@wild blue.com would give the one's who need to know .... the answer! |
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Mr_DNS
join:2005-09-07
Laredo, TX | reply to randyvsatus
said by randyvsatus:The point of my original post was that WB knows the distance...perhaps they are BS'ing us, who knows.:D .
I only skimmed the NRTC install manual, and so far, no minimun...but a maximun.
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Further, since WB's computers do monitor user's setup, I'm sure if an user was out of specs, the installer would be called upon to fix the "problem."
Since mine is most likely less than 20' [but it does go thru a surge protector], and I have been up for two plus months, then most likely, the WB Monitoring Cops are not going to bust me...
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said by grohgreg:said by randyvsatus:or perhaps they are BS'ing us, who knows. That's my guess //greg// It is with out a doubt BS. I have run these systems day in and day out on 8' test sets with no ill effect.:D |
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| after installing the system here with 25ft cables the systems would not work...tech said they now wanted 75ft cables minimum length but would not say why...changed the cables and did the release & renew and all worked well!
Surfbeam modem, Telsat/Anikast in Canada |
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