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Stacking Winegard HD-6065P antennas
On Sun, 12 Jan 2014 11:48:13 -0500, Jerry Stuckle
wrote: I'm not talking about fiber, and I'm not talking about some half-assed gadget cooked up in your basement. I'm talking about a real, professional-grade TDR. Make and model please? I used to drag around a Tek 1503 but rarely used it. It was most useful for find broken cables, usually where the rats chewed through the wires. Also, for measuring the length of cables on a roll that didn't have ft markers. One day, I needed it, and it was dead, probably from bouncing around in my truck. Rather than fix it, I sold it as-is. http://www.ebay.com/itm/131091152872 I was already carrying a scope, so I saw no reason to buy another scope just to get a TDR. So, I designed and built a TDR, mostly checking CAT5 and telco wires, not coax. Something like this: http://www.epanorama.net/circuits/tdr.html We use expensive stuff because it gives accurate results. I use cheap stuff because I know its limitations and can work within those limitations. Much as I value my money, old test equipment is good enough for most things. http://www.learnbydestroying.com/jeffl/pics/home/slides/test-equip-mess.html You stated that the losses come primarily from the "impedance bump" presumably produced by the non-50 ohm connector or adapter in the line. Well, time to put that to the test. I didn't say anything about a non-50 ohm connector. The connector can be 50 ohm and still get an impedance bump. With a TDR you can see every connector on the cable (as long as they are far enough apart - typically 3-4 feet). If the connectors were a prefect 50 ohms, you wouldn't see any reflection. Therefore, either the connectors are not quite 50 ohms, your coax is not quite 50 ohms, you have a high resistance shield connection, or this is one of your cases where theory fails to accommodate your reality. That's theoretical. Reality is much the same. First of all, we don't crush cables to try to emulate something we can easily see in real life. I crush, chop, dissect, and set fire to cable to see how they're built. Amazing what you find if you look inside of things. However, since you have an aversion to crushing coax able, you can get the same effect with a short length of different impedance coax cable and some adapters. Just insert where I suggested you crush the coax, and you should see it clearly on the TDR. Then replace it with an identical length of the correct impedance cable and compare the losses. At worst, the loss difference will be fractions of a dB. That suggests that your "impedance bump" isn't really responsible for much loss. Of course, you have set fire to plenum, non-plenum, and riser CAT5 cables to see how they burn. I think you might be surprised. Learn by Destroying(tm). Second of all, you can gimmick up something all you want with signal generators, spectrum analyzers, crushed cables, all you want. For those that believe theory, proof by bench testing is possible. For those who do not believe or understand theory, no amount of test equipment will ever prove anything. Theory and testing go hand in hand. If there's a discrepancy, then either one of them is wrong, or the procedure is flawed. We SEE the results in real time in real installations with the appropriate test equipment. You see the results, but for some odd reason, I haven't seen your results or list of appropriate professional test equipment. Why always so vague and non-specific? FoN (Fear of Numbers)? So? Dipoles aren't 50 ohm antennas. They're typically closer to 75 ohm. I guess you missed my point. If you can tolerate the 1.5:1 VSWR, the reduced attenuation and cost of 75 ohm coax makes the effort worthwhile. No, it's worthwhile because your coax will more closely match the antenna. And you can easily match the coax to the transmitter with a tuner. Tuners can be lossy. Try this T-tuner Java app on the lower bands. http://fermi.la.asu.edu/w9cf/tuner/tuner.html The starting values (hit the AutoTune button) produce a 2dB loss at 160 meters. The losses are much less on the higher bands. Q=100 for the inductor seems a bit high. Please re-read the article: www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm http://www.microwaves101.com/encyclopedia/why50ohms.cfm I read the article. Unlike you, I understand what it is saying. What part of the following do you disagree with and why? (It's all in the above articles). Please try to be specific: 1. Loss for approximately equal size is less for 75 ohm cable. 2. 50 ohm cable will tolerate a higher power due to a higher voltage breakdown. 3. Maximum power is with about 30 ohm coax cable. http://www.microwaves101.com/encyclopedia/coax_power.cfm 4. Mismatch loss from 75 ohm cable in a 50 ohm system is 0.18dB. 5. If the mismatch loss from using 75 ohm cable is less than the difference in attenuation for a comparable 50 ohm cable, and there are no high power levels involved, then it is better to use 75 ohm cable and tolerate the mismatch. You don't know our installations. We've been in business for several years, with lots of satisfied customers. Trying to tell a professional what their job is only makes you look stupid. I only debate a persons ideas and never attack them personally. If you are unable to do that, you lack "professionalism" which presumably goes with your professional title. No MoCA installations? http://www.mocalliance.org Nope. It's used by few professionals. Coax ends up with too many problems. Category cable for runs under 100M or so and fiber for longer runs. Fiber is generally better and much more expensive. I also do fiber where possible. However, when faced with a large apartment complex, with no possible way to economically rewire the building, I was forced to consider what could be done with the existing wiring. The building had CAT3 going to all the apartments, but CAT3 is useless (no twists). Even DSL had crosstalk problems. I tried to use the CAT3 as a pull line to drag in CAT5, but that also failed (no smurf tubes in the walls). I also tried 2.4/5.7 wireless, which proved erratic because of aluminum foil backed insulation, untouchable firewalls, and interference from existing Wi-Fi systems. So, I tired MoCA and it worked. http://www.netgear.com/service-providers/products/in-home-connectivity/moca-bridges/ http://www.netgear.com/service-providers/products/in-home-connectivity/moca-bridges/wm2500rp.aspx They're now bringing in Comcast TV, internet, and phone via coax, using MoCA to distribute internet around each apartment. Depending on wiring, Jperf shows about 100-300 Mbits/sec between clients (16 maximum). Speedtest shows whatever was ordered from Comcast from/to the internet, typically 22/2 Mbit/sec. To be honest, things did not go smoothly. MoCA is expensive. The isolation between apartments on the main Comcast splitter was not enough to prevent leakage between bridges. Using couplers instead of splitters were a big help. I also needed to select a different channel, which is not allowed by every MoCA unit. I started with Actiontek, which was cheaper, but does NOT offer channel selection and was therefore useless. Some of the apartments had satellite TV, which had to be accommodated with diplexers. However, the worst problem was that I rapidly became the single point of contact for any problem with the system. Fortunately, I was conveniently underbid for the maintenance contract by another service company, which has taken over the system. To the best of my knowledge, it's still running nicely after about 18 months. Next time you run into a situation that does not economically allow a retrofit of fiber or CAT5/6, and there's existing coax, think about MoCA. Find a different distributor or ask for it by part number. Thomas and Betts SNS1P6U. We use several distributors - both U.S. and international companies. Did you any of them if they specifically carry T&B or stock T&B SNS1P6U connectors? Where we left off, you were having difficulties finding a stocking distributor. Are either of your unspecified distributors on the T&T distributor search page? http://www.tnb.com/ps/dls/dls?ca=corp Within 25 miles of your location, it shows 5 stocking distributors with 13 locations. Quick check: Stocked by Allied, Newark, Tessco, Farnel(UK), MCM. Not stocked by Digikey, Mouser, Arrow. T&B distributor search: http://www.tnb.com/ps/dls/dls?ca=corp These are consumer (retail) outlets. They are not used by most professionals. None of those listed above have a retail (brick and mortar) store. Many do sell online and from catalogs, but even the largest distributors do that. Legally, if they charge sales tax, they are a "retail" operation. Offhand, I can't think of a single large distributor that does not accept taxable sales or requires a resale permit in order to process an order. There used to be those as B2B (business to business) operations, but not any more, because the growth of internet commerce has made retail processing a necessity. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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