Re: Topband: Using CAT5 in place of coax (was video baluns)
I didnt say at the same feedpoint; each CAT5 pair is a seperate feed and then you seperate the actual antenna ends and ground rods the 30-40' as suggested. Thats what I do here and there is a minimum of 30' between each antenna and the relay box. Carl KM1H - Original Message - From: Mike Waters mikew...@gmail.com To: topband topband@contesting.com Sent: Monday, May 07, 2012 10:05 PM Subject: Re: Topband: Using CAT5 in place of coax (was video baluns) Multiple Beverages at the same feedpoint? When I put up my Beverages, I avoided doing that because I read at least one bad experience of someone who tried that. (My Beverage feed points are hundreds of feet apart.) I forget the details, but there was interaction and coupling and undesired consequences of having them all together like that. Maybe with some kinds of ground conditions, you can get away with doing that. 73, Mike On Mon, May 7, 2012 at 8:27 PM, ZR z...@jeremy.mv.com wrote: One application would to be to feed multiple Beverages at a hub ... ___ UR RST IS ... ... ..9 QSB QSB - hw? BK - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1424 / Virus Database: 2425/4985 - Release Date: 05/08/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Using CAT5 in place of coax (was video baluns)
On 5/7/2012 6:12 PM, GeorgeWallner wrote: The twisted pairs had #31 common mode chockes every 4 foot. While the twisted pairs worked, despite the balanced arrangement, there was more common mode (BC and noise) pick-up than the same runs using (non-balanced, but grounded) RG-179 cables. The RG-179 cables had the same #31 chokes as the twisted pairs. I attribute the performance difference to the fact that the shields of the coax cable were grounded, while the twisted pairs were floating. Hi George, Thanks for sharing your work on this. Your observations make sense, especially the comment about the coax shield being grounded minimizing common mode. We know that a multi-element common mode filter can be formed by a ferrite choke followed by tying the shield to ground at additional point, and even by a second choke. In private email, Herb raised the issue of common mode chokes on full size cores getting fairly expensive. One way I was thinking of using the CAT5 was to use one pair removed from the cable to wind chokes around smaller, less expensive cores, and inserting that choke into coax lines that are grounded as noted above. #31 material is still likely to be the best core material, and you still need a lot of turns. While one could certainly get anal about it and make a lot of measurements, for a choke intended for 80 and 160M, I'd start with 15-20 turns, and consider more is better a pretty good rule of thumb. One other point. While the loss in coax feeding a Beverage is no big deal, shielding is important, and shielding effectiveness is directly related to shield resistance at the frequency of interest. Coax designed for use in UHF CATV systems generally has foil shields with flimsy braid, and the resistance at 2 MHz is fairly high. Poor shielding effectiveness converts common mode current on the shield to differential voltage inside the coax. Thus, a better choice for feeding Beverages is RG58 or RG59 with a heavy copper braid shield. On the other hand, if we're effectively killing common mode current with chokes and additional ground rods, it may not matter. :) 73, Jim K9YC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: Using CAT5 in place of coax (was video baluns)
I did some careful measurements of CAT5 cable a few years ago using a 4 port network analyzer (NOT a 2 port VNA with baluns). On my random sample, the characteristic impedance was within 5% of 100 ohms. The cable is fairly lossy, which is no surprise given the tiny wires. There doesn't seem to be any compelling reason to use it in place of RG-6. Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Using CAT5 in place of coax (was video baluns)
That's why it's rated at 100 meters max distance when used for networking. Now before everybody breaks their fingers posting anecdotal evidence to the contrary I have done the same. It worked out great, till we starting loading that segment down. That 400' run was replaced with fiber inside a month. There's all sorts of stuff people do with CAT5/6 that isn't supposed to be done, like running it parallel to or in the same conduit as AC power. Using it for a transmission line has got to be right up there. Remember, I am only the messenger, the IEEE came up with these rules. On 05/07/2012 07:07 PM, Rick Karlquist wrote: I did some careful measurements of CAT5 cable a few years ago using a 4 port network analyzer (NOT a 2 port VNA with baluns). On my random sample, the characteristic impedance was within 5% of 100 ohms. The cable is fairly lossy, which is no surprise given the tiny wires. There doesn't seem to be any compelling reason to use it in place of RG-6. Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK -- R. Kevin Stover AC0H ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Using CAT5 in place of coax (was video baluns)
Loss can be mitigated by a preamp at the antenna end. One application would to be to feed multiple Beverages at a hub without a relay box with its isolation problems and intermittents. Carl KM1H - Original Message - From: Rick Karlquist rich...@karlquist.com To: Bill Wichers bi...@waveform.net Cc: TopBand List topband@contesting.com; Herb Schoenbohm he...@vitelcom.net Sent: Monday, May 07, 2012 8:07 PM Subject: Topband: Using CAT5 in place of coax (was video baluns) I did some careful measurements of CAT5 cable a few years ago using a 4 port network analyzer (NOT a 2 port VNA with baluns). On my random sample, the characteristic impedance was within 5% of 100 ohms. The cable is fairly lossy, which is no surprise given the tiny wires. There doesn't seem to be any compelling reason to use it in place of RG-6. Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1424 / Virus Database: 2411/4983 - Release Date: 05/07/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Using CAT5 in place of coax (was video baluns)
Shielded CAT5/6 is readily available. Carl KM1H - Original Message - From: GeorgeWallner aa...@atlanticbb.net To: topband topband@contesting.com Sent: Monday, May 07, 2012 9:12 PM Subject: Re: Topband: Using CAT5 in place of coax (was video baluns) On Mon, 7 May 2012 19:17:58 -0500 Mike Waters mikew...@gmail.com wrote: it would be interesting to experiment with some CAT5/6 sometime, just for the fun of it. :-) I did that. I was testing a small dual-feed DHDL loop (-50 dBi gain) using twisted pairs removed from a CAT 5 cable. On the bench the twisted pair showed 100 ohm of impedance and a loss of about 2.8 dB at 1.8 MHz on a 100' run. (I also tried CAT 6. The results were the same. The difference between CAT 5 and CAT 6 is that the CAT 6 pairs' twists are more precisely controlled, which results in a more uniform impedance and lower losses at the upper end of the spectrum.) I was running two 16 foot lenghts of twisted pairs, one from each element, into a phasing/combiner box, which had carefully designed balanced-transformer inputs. The twisted pairs had #31 common mode chockes every 4 foot. While the twisted pairs worked, despite the balanced arrangement, there was more common mode (BC and noise) pick-up than the same runs using (non-balanced, but grounded) RG-179 cables. The RG-179 cables had the same #31 chokes as the twisted pairs. I attribute the performance difference to the fact that the shields of the coax cable were grounded, while the twisted pairs were floating. I believe that if one wants to use a balanced arrangement, twinax may be the ultimate solution. Otherwise, just stick with good quality RG-6. 73, George ___ UR RST IS ... ... ..9 QSB QSB - hw? BK - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1424 / Virus Database: 2411/4983 - Release Date: 05/07/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Using CAT5 in place of coax (was video baluns)
GeorgeWallner wrote: I did that. I was testing a small dual-feed DHDL loop (-50 dBi gain) using twisted pairs removed from a CAT 5 cable. On the bench the twisted pair showed 100 ohm of impedance and a loss of about 2.8 dB at 1.8 MHz on a 100' run. (I also tried CAT 6. The results were the same. The I measured 1 dB per 100 feet at 1.8 MHz for my random sample of CAT5. Imagine the loss for 100 Mbit/s data! Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
