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Coax recomendations
Charlie wrote:
Roy the kind of test results you cited would be extremely evident whether someone has a network analyzer or just an swr meter. That defense is sorely transparent in my opinion. To suggest that most amateurs would not even have any interest if their bent or coiled 9914 suddenly jumped off the scale for loss and mismatch is ludicrous to say the least. Would you really notice if your cable loss was about 3 dB higher than specified at 400 MHz and if it varied by a dB or two when the cable is flexed and bent? What measurement equipment do you use which would cause this amount of extra loss to "jump off the scale"? And what causes you to think that increased loss would cause mismatch to "jump off the scale"? Increased loss will improve, not degrade, the impedance match. Let me be clear ...I am not disputing what you claim you got as test results. My conclusion is either the 100ft length you had was bad or something skewed your calibrated setup. What you have as evidence is Davis' spec on the one hand, and my measurement report on the other. You've chosen to believe that Davis' cable all meets its published specifications. I have exactly the same evidence, but know my capabilities and that of my equipment, so I believe my measurements -- but always keeping in mind that it's a single sample. Additional measurements made by someone else on another piece of the cable would increase the knowledge base, although I'm sure there are people who would choose to ignore the evidence no matter how much is presented. My career was in microwave r&d and I know that it takes repeatable test results to form a valid, verifiable and publishable data. That's great! Then you have the background to be able to make decent measurements, and you said you're using some of the cable. Why not just measure the loss in a length of it and report your results? This is not personal Roy....but it is somewhat stimulating. I hope it's caused a few people to think a bit about how they evaluate evidence to determine the truth of a matter. It's something which too many people are woefully unable or unwilling to do. Roy Lewallen, W7EL |
Coax recomendations
"Roy Lewallen" wrote in message ... I've got some of that which I purchased new, and did some extensive tests on it with a network analyzer. The loss varies all over the map depending on how you coil, bend, or flex the cable, and I never saw loss anywhere near as low as the spec says. A typical value at 400 MHz was more like 5 - 5.5 dB/100 ft. Glad you're happy with it. Roy Lewallen, W7EL Roy what kind of coax do you recommend along the same type ? I soon plan on putting up several beams, tribander for the low bands, 6 meter, 2 meter and a 432 antenna. Should be running about 125 feet or so. While I know hardline would be best for the VHF , I don't want to (can't spend the money, easy to install for the rotator) so I want to stay with one of the 9913/lmr400 types. I have had a piece of 9913 up for about 10 years and it seems to be ok, no water I can tell, I still would like to go with a solid foam type instead of the hollow core . Just looking at the specks and advertising can sometimes be deceiving. de KU4PT |
Coax recomendations
Owen with all due respect there is no "question" why 9914 has not replaced
Heliax and that is due to loss factors. BTW 9914 is impervious to water in and of itself..so evidently you have not done much homework on this particular coaxial cable. Davis 9914 is recommended for rotator loops. Your supposed quandary about "9914 replacing Heliax" is contrived in my opinion to murk up the waters of this issue and maybe steer focus away from what obviously, at least to me, is an unfortunate one-time testing experience by Roy. Yes I suppose we should always be "suspicious" of manufacturer's claims but do you exercise that philosophy across the board? How about the tires on your car? How about the prescription medicines you may take and also over the counter meds? How about those fast food burgers? How about your drinking water? Are you as equally "suspicious" of these products or is this philosophy of yours only revealed to others when you want to discredit someone else's data. I think the later and not the former sir. Owen....I give you a salute for being an obvious "spin doctor" for Roy's one time, one sample, one conclusion, years ago test cycle. A job well done on the surface..however the underlying facts remain. Davis BuryFlex has been sold for well over 10 years in the "real world" and these same real people, government agencies, municipalities, and service agencies have used thousands of miles of it with no apparent issues. Cite similar tests to Roy's and I'll reconsider. As for me I'll go with the Davis data, once it arrives, and do a calibration standards trace on their test station. Was Roy's test bench's calibration traceable? It is preposterous you would continually cast aspersions towards a company that has been in the wire and cable business for over 25 years and promote and crusade for a one time shot-in-the-dark independent so-called "test". You do not fool me sir....best regards..... -ps How many times do you think Davis has tested their 9914 in the past 10+ years? More than the one single time Roy has perhaps? -- Charlie "Owen Duffy" wrote in message ... On Sat, 10 Dec 2005 19:46:15 -0600, "Charlie" wrote: Owen it is NOT brand loyalty. It is the publicly published data by RF Davis (for the past 10+ years) vs. Roy's one-shot test setup some years ago. I'm not out to discredit Roy...I even shook his hand once at a Hamfest. We should be a little suspicious of manufacturers claims. Davis' can be expected to support their product. Roy's single poor experience is concerning, indicating either a quality control issue, or more general non-compliance with spec (both are issues for Davis). An independent test of stock cable and possibly Roy's sample would be most interesting. I know I have made measurements and adjustments at times and in searching for possible explanations, the cable quality is on the radar. In one of those cases, a mobile installation could not be trimmed properly, and the Taiwanese RG58 centre conductor was so far off centre, it was nearly touching the braid. We have all cut cables up and found inconsistent braid weave, open braid weave, voids in the dielectric, faulty stranding of inner conductor, off centre centre conductors. It is those kind of issues that downgrade a suppliers reputation, not their ability to select a good cable sample for laboratory measurement. Perhaps if you're a whiz, you should perform some measurements so you can report first hand your experience. We don't see the Davis stuff on this side of the world. The concept seems a good one, PE sheath, braid+foil outer, foam dielectric, stranded inner, but you have to ask yourself why they haven't displaced Heliax and its copies. I suspect the reasons include IM and noise issues associated with the braid+foil, mechanical issues with the foam, and resistance to water. Experience with noise and IM problems with braid+foil coax in fixed installations makes me wonder how it stands up in a rigorous test of flexing for a rotator loop, not anecdotal evidence, but a structured test. Owen -- |
Coax recomendations
To find ALL electrical characteristics and performance of
solid-polyethylene transmission line, use program COAXPAIR, from audio frequencies to UHF. Accuracy is of the same order as physical dimensions can be measured. Use a micrometer to measure inner conductor diameter and diameter over insulant. Or just guess at it. No need to unwind the cable off the drum! In a few seconds, download COAXPAIR from website below and run immediately. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Coax recomendations
On Sat, 10 Dec 2005 21:50:15 GMT, Owen Duffy wrote:
[good stuff snipped] | |Someone will probably suggest that LDF6-50 (32mm (1.25") hardline) |could achieve 0.3dB loss, but could you afford it, would it be good |value? I wasn't going to go that far, and I realize it's probably not common in ZL but I've bought lengths of LDF5-50 at ham flea markets. The last purchase, claimed to be about 10 meters worth, but by my estimation at least twice that long, and new and unused, cost me $10 U.S. Most of this stuff is leftover or removed from commercial two-way or cell phone use and shows up all of the time. LDF4-50 is even more common. I often buy short pieces that have been cut down, just for the connectors that are still on one end. I find it curious that Andrew cable is seen so often at these events and yet I've -never- even seen a piece of Davis cable, dispite the claims that miles of it are in commercial use. |
Coax recomendations
On Sun, 11 Dec 2005 05:39:27 +0000, Wes Stewart *n7ws*@ yahoo.com
wrote: I wasn't going to go that far, and I realize it's probably not common in ZL but I've bought lengths of LDF5-50 at ham flea markets. The last purchase, claimed to be about 10 meters worth, but by my estimation at least twice that long, and new and unused, cost me $10 U.S. Most of this stuff is leftover or removed from commercial two-way or cell phone use and shows up all of the time. LDF4-50 is even more common. I often buy short pieces that have been cut down, just for the connectors that are still on one end. I find it curious that Andrew cable is seen so often at these events and yet I've -never- even seen a piece of Davis cable, dispite the claims that miles of it are in commercial use. I agree with Ian's comments, the larger sizes are often available here as they are less attractive to hams. But if you buy 3 or 4 lengths of LDF5 or LDF6 and use connectors to join them, you will run into big $ unless the connectors come very cheap. Andrews has some braid+foil / foam coax, and they perform roughly similarly to LMR400, BuryFlex and 9913. To my mind LDF4-50 would be acceptable in this configuration, and the great advantage is that if water gets in somewhere, it doesn't wick right down the cable. I haven't handled BuryFlex, and I saw the claim it is waterproof, but I suspect it is not as waterproof as Heliax type cable where the closed cell foam dielectric is bonded to the inner and outer conductor with an adhesive, and there is no braid to form a natural wick. I am in the throes of replacing feedline on a HF dipole to repair damage by birds. The birds don't seem to eat PE irrigation tube, so I have fitted RG6 with a W2DU style balun inside 13mm PE tube to defeat the birds. The birds have attacked the LDF4-50 on the VHF/UHF antennas, but even if they make a hole in the copper, it doesn't seem to affect cable performance measurably, probably because the water can't travel up and down the cable from the hole. Still, parts of ZL have Keas, and they will eat anything, especially rubber or plastic! So I feel for our ZL friends running coax over 60m of ground. BTW, I added BuryFlex to my online line loss calculator, 9913 and C2FP were already there. I still like the open line option, but it will be real important to use effective baluns to adequately ensure balance. It used to be common commercial practice when HF Radio was used more widely for international telephony / telegraphy. Owen -- |
Coax recomendations
On Sun, 11 Dec 2005 06:06:08 GMT, Owen Duffy wrote:
On Sun, 11 Dec 2005 05:39:27 +0000, Wes Stewart *n7ws*@ yahoo.com wrote: I wasn't going to go that far, and I realize it's probably not common in ZL but I've bought lengths of LDF5-50 at ham flea markets. The last purchase, claimed to be about 10 meters worth, but by my estimation at least twice that long, and new and unused, cost me $10 U.S. Most of this stuff is leftover or removed from commercial two-way or cell phone use and shows up all of the time. LDF4-50 is even more common. I often buy short pieces that have been cut down, just for the connectors that are still on one end. I find it curious that Andrew cable is seen so often at these events and yet I've -never- even seen a piece of Davis cable, dispite the claims that miles of it are in commercial use. I agree with Ian's comments, the larger sizes are often available here as they are less attractive to hams. But if you buy 3 or 4 lengths of LDF5 or LDF6 and use connectors to join them, you will run into big $ unless the connectors come very cheap. I have a ham friend who uses long runs of coax to his several towers. He is a big gun on 80 and 160 meters, so this mainly applies at m-f to h-f. He uses a lot of LDF5-50 that he obtains in shorter pieces. His technique, as he briefly described it to me, is to -not- use connectors but splice the lengths directly. The center conductor on these cables is hollow, so he inserts a short length of brass or copper into the ID and solders it in place. I don't know whether he adds any insulation next or not, but I would envision injecting some low-expansion spray foam later. He then wraps the outer conductor with brass or copper foil and solders this in place. (Here is where I would inject the foam.) This is then wrapped with tape for protection. I would use a double layer of #27 3M tape with an overwrap of plastic electrical tape. To strengthen the joint mechanically, he straps on a length of steel angle using stainless hose clamps. For lines on or in the ground this stays in place. For runs up the tower, after the line is in place, strapping to the tower is sufficient support. |
Coax recomendations
Owen Duffy wrote:
LMR400: 300' at 14.2MHz with VSWR=1.5, loss~=1.5dB Open-wire line: 300' at 14.2MHz with VSWR=1.5, loss~=0.225dB Costs about 16 cents/ft if one rolls one's own. -- 73, Cecil http://www.qsl.net/w5dxp |
Coax recomendations
Wes Stewart wrote:
I agree with Ian's comments, the larger sizes [of hardline] are often available here as they are less attractive to hams. But if you buy 3 or 4 lengths of LDF5 or LDF6 and use connectors to join them, you will run into big $ unless the connectors come very cheap. Generally the same applies to the connectors as to the cable itself - the surplus prices are much lower than the new prices, and larger sizes may even be cheaper. However, I do agree that you don't need connectors in order to make a splice in a static installation. This technique makes a solid splice, with a low SWR even at 432MHz: I have a ham friend who uses long runs of coax to his several towers. He is a big gun on 80 and 160 meters, so this mainly applies at m-f to h-f. He uses a lot of LDF5-50 that he obtains in shorter pieces. His technique, as he briefly described it to me, is to -not- use connectors but splice the lengths directly. The center conductor on these cables is hollow, so he inserts a short length of brass or copper into the ID and solders it in place. And for the smaller sizes with a solid center conductor, splice with a short length of hobby brass tuning over the outside. I don't know whether he adds any insulation next or not, but I would envision injecting some low-expansion spray foam later. The foam is mostly empty space anyway, so even at UHF an inch or so will hardly be missed. He then wraps the outer conductor with brass or copper foil and solders this in place. In some sizes, a slit length of copper water pipe can work too. This is then wrapped with tape for protection. I would use a double layer of #27 3M tape with an overwrap of plastic electrical tape. To strengthen the joint mechanically, he straps on a length of steel angle using stainless hose clamps. Yup, all of the above. It works fine. The overall conclusion is that - both physically and financially - large hardline is nowhere near as 'hard' as most people think. BTW, I do have one genuine Andrew splice for LDF5-50, which I'm hoarding for some undefined future need. It's truly a thing of wonder... especially the insert that connects the two hollow center conductors. One end screws in with a tapered variable-pitch thread, so the other end has to have a tapered variable-pitch *left-hand* thread. Only a CNC programmer with far too much time on his hands could have thought of that. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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