Re: [Elecraft] Transmission line loss
In a message dated 11/17/07 12:02:32 AM Eastern Standard Time, [EMAIL PROTECTED] writes: For today's discussion, let's assume the power is 100 watts, total run is 100 feet, that I can tune this vertical up to 50 MHz, and the SWR at the antenna hits 5:1 (it won't, as I'll have a remote tuner there, but just for discussion...). For comparison, check out the online loss calculator at: http://www.ocarc.ca/coax.htm Davis RF-brand RF-9914F Bury-Flex has a published matched line loss of 1.1 dB/100 ft at 50 MHz. Per the Handbook, a 5:1 SWR at the load will add around 1.2 dB of loss, for a total of 2.3 dB over the run, for about 60% efficiency. (I'm still fuzzy on the percentage calculations.) According to the online calculator, the matched loss of that coax is 1.009 dB/100 ft. It shows the additional loss due to 5:1 SWR as 1.13 dB, so the total loss is 2.139 dB and about 62% efficiency. Insignificant difference between your calculations and the online calculator. . A variety of brands of RG-8X have a matched line loss of 2.0 dB at 50 MHz per 100 ft. A 5:1 SWR adds 1.7 dB, for a total of 3.7 dB loss, for a little over 42% efficiency. The online calculator shows Belden 9258 (which is RG-8X type) as having slightly higher matched loss (2.188 db/100 ft @ 50 MHz) which makes the SWR loss 1.784 dB and the total loss 3.972 dB. Efficiency almost exactly 40%. Again, an insignificant difference between your calculations and the online calculator. . Am I reading something wrong here, or is the 1.4 dB difference between the two cables correct? Can you extrapolate that to an S-meter at 6 dB/S-unit? If so, I'd say the 1.4 dB would be barely noticeable on the receiving end at best, and the extra cost of lower loss coax isn't worth the money. Operation at HF would be even less of an difference than at 50 MHz. All the numbers I have are close to the numbers you got. But there are other factors to consider. First is the actual coax length. IIRC, you need 128 feet, not 100 feet, and that pushes the losses up a bit. In practice the coax length will probably need to be greater - maybe 150 feet when all is said and done. For example, you want to leave some slack at both ends of a buried cable. Second is the cost of a dB. If the difference between a K3/10 and a K3/100 is ten dB and the price differential is $380, that's $38 per dB - but only on transmit. If better coax reduces the overall loss by, say, 2 dB, and the cost differential is $50, that's $25 per dB. And it works on both transmit and receive, not just transmit. Remember too that a lot of the 'cost' of the installation will be in the work it takes to put it up. Third is maxing out performance. While an S-unit of loss will normally not be noticeable most of the time, when things get tough it can be the difference between a QSO and no QSO. This is one big reason the big guns work stations the rest of us don't. Fourth is purely esthetic - some folks like knowing that they have the highest efficiency reasonably possible. 73 es GL de Jim, N2EY ** See what's new at http://www.aol.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Transmission line loss
The bigger difference between RG-8X and 9914 is power handling capacity. Also, there are some low-loss RG-8X cables out there that cut the loss difference by half again. I bought a 500' spool at a hamfest some years ago. It's double shielded. I've used short runs to UHF antennas for satellite work with good results. But, no doubt that the 9914 Bury-Flex is among the best of the half inch flexible cable money can buy. Doug -- K0DXV Mike B wrote: First of all, I have to congratulate the posters in the earlier thread on line loss, etc., for prompting me to actually get my calculator ARRL Handbook out and read up on transmission line loss, dB calculations, etc. My interest has come up as I'm planning on installing a flag pole vertical in my yard, due to CCRs, and the coax run will be around 100 feet outside the house, plus 28 feet inside. Here's my take on line loss, and please correct me if I'm wrong. For today's discussion, let's assume the power is 100 watts, total run is 100 feet, that I can tune this vertical up to 50 MHz, and the SWR at the antenna hits 5:1 (it won't, as I'll have a remote tuner there, but just for discussion...). Davis RF-brand RF-9914F Bury-Flex has a published matched line loss of 1.1 dB/100 ft at 50 MHz. Per the Handbook, a 5:1 SWR at the load will add around 1.2 dB of loss, for a total of 2.3 dB over the run, for about 60% efficiency. (I'm still fuzzy on the percentage calculations.) A variety of brands of RG-8X have a matched line loss of 2.0 dB at 50 MHz per 100 ft. A 5:1 SWR adds 1.7 dB, for a total of 3.7 dB loss, for a little over 42% efficiency. Am I reading something wrong here, or is the 1.4 dB difference between the two cables correct? Can you extrapolate that to an S-meter at 6 dB/S-unit? If so, I'd say the 1.4 dB would be barely noticeable on the receiving end at best, and the extra cost of lower loss coax isn't worth the money. Operation at HF would be even less of an difference than at 50 MHz. I realize there may be other considerations as to the type of coax used that could sway one's decision. In my case, I want direct buriable, and I haven't come across any 8X that allows this. Longer runs and higher SWR would obviously sway the argument as well. RG-6 seems to be in between the RG-8X and Bury-Flex as far as loss, but the cost may be much better (from what I've read here). In my searching, I came across a pretty handy document from Cisco relating to dB loss and gain: http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a00800e90fe.shtml Thanks for your input. 73, Mike KW1ND ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Transmission line loss
[EMAIL PROTECTED] wrote: Third is maxing out performance. While an S-unit of loss will normally not be noticeable most of the time, when things get tough it can be the difference between a QSO and no QSO. This is one big reason the big guns work stations the rest of us don't. Right on, Jim. This is a very important point. What's the difference between a signal just barely above the noise floor that you can copy and a signal just below the noise floor that you can't copy? (A) About a dB or dB-and-a-half, and (B) A new country/grid/zone/state, or not. That dB wouldn't be even measurable if the guy's signals were S9 and 50 dB above the noise -- but when you get down to the bleeding edge in weak-signal work, that last dB or dB-and-a-half is what separates the big guns from the wanna-be's. :-) There's the difference in your coax right there. Fourth is purely esthetic - some folks like knowing that they have the highest efficiency reasonably possible. What's the difference in cost, twenty or thirty bucks? Come on, you spend that much for dinner with the XYL, and by the next day, it's all down the drain. Literally. :-) Your coax will be there helping (or hurting) you for years. Get the best stuff you can. You'll never regret it. Bill W5WVO ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Transmission line loss
Mike, Take a look at the loss from 0.40 inch diameter 75 ohm coax that may be available free as cutoffs from your cable installing company - it is burial rated and will often outperform the 50 ohm coax when you do the loss calculations. You are correct that the matched line loss will vary with frequency, but the added loss due to SWR is independent of frequency - it only depends on the SWR and the matched line loss. 73, Don W3FPR Mike B wrote: First of all, I have to congratulate the posters in the earlier thread on line loss, etc., for prompting me to actually get my calculator ARRL Handbook out and read up on transmission line loss, dB calculations, etc. My interest has come up as I'm planning on installing a flag pole vertical in my yard, due to CCRs, and the coax run will be around 100 feet outside the house, plus 28 feet inside. Here's my take on line loss, and please correct me if I'm wrong. For today's discussion, let's assume the power is 100 watts, total run is 100 feet, that I can tune this vertical up to 50 MHz, and the SWR at the antenna hits 5:1 (it won't, as I'll have a remote tuner there, but just for discussion...). Davis RF-brand RF-9914F Bury-Flex has a published matched line loss of 1.1 dB/100 ft at 50 MHz. Per the Handbook, a 5:1 SWR at the load will add around 1.2 dB of loss, for a total of 2.3 dB over the run, for about 60% efficiency. (I'm still fuzzy on the percentage calculations.) A variety of brands of RG-8X have a matched line loss of 2.0 dB at 50 MHz per 100 ft. A 5:1 SWR adds 1.7 dB, for a total of 3.7 dB loss, for a little over 42% efficiency. Am I reading something wrong here, or is the 1.4 dB difference between the two cables correct? Can you extrapolate that to an S-meter at 6 dB/S-unit? If so, I'd say the 1.4 dB would be barely noticeable on the receiving end at best, and the extra cost of lower loss coax isn't worth the money. Operation at HF would be even less of an difference than at 50 MHz. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
