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Re: [TowerTalk] [Bulk] Coax cable economics. (was Mosley Antenna Questio

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Subject: Re: [TowerTalk] [Bulk] Coax cable economics. (was Mosley Antenna Question)
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Thu, 19 Feb 2015 13:26:01 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Addressing both Jim's and Ed's comments

Agreed, and it was 220 feet to the top antennas here.

The average, and /I have to emphasize "average" ham does not normally run much more than a 100 feet of coax to an antenna(s) at 40 to 60 feet, nor are they in the best of locations.

That describes my station for the first 10 years although the 3L tribander was only at 30 feet. Then I did add three big monobanders after moving to Breckenridge MI They up another 10 feet to 40 feet, they were KLM monobanders for 20 & 15 and a 7L Yagi on 10. For a bit over a year or so. When in Farwell MI, I did have a long run to the antennas on a 40' tower on top of a hill. 30 years ago, I moved here and installed a 90' tower with a 4L tribander. The coax run increased to about 130-140 feet. In none of those installations would the coax make a detectable difference.

When it gets to 2 or 3 db, an "experienced" ham with a lot of operating time can start noticing differences. I had thousands of hours and many thousands of QSOs. My CW speed was close to 40 WPM copying in my head. I could type 70 WPM, but never mastered copying on the mill<:-))

I never had any incentive to work for any awards and I've not had any QSL cards since moving here for which I apologize to many hams. When I get some it'll take months to catch up .

With that background, I "think" and I emphasize "I think" I notice a difference in the the number of answers between 100 and 200 watts. I have an Icom 756 Pro (100 watts) and the Yaesu 5000 MP @ 200 Watts. A "blind", A/B comparison is much like the "I think I can". Few stations could sense a difference and then a few noticed from barely copy to clear Q5. There is a huge difference between 200 and 1500 watts and the signal reports are all out of proportion to the difference in power as in the receiving stations often report going from S7, or S8 to 20 over or even more. Even going from S7 to S9 at 200 watts would indicate 2000 watts, let alone 20 over. I should add that the A/B comparison is not just the simple switch as I couldn't mute the "other" receiver, but had to remember to manually turn the RF gain to zero. The Alpha Delta switch has good isolation, but not good enough.

The big antenna system went operational July 29 2001. The tribander (TH-5) was a bit high but it sure played good. Band conditions were like the stock market, mot anything worked. 20 through 6 were fantastic. 160 through 40, not so much. Pretty much dead in the daytime. 6-meters, with 7L @ 115' was much like working 10. I worked a ham in central America who was testing a 6-meter rig on the bench with a "test lead" for an antenna. I don't know which of us was more surprised.

I sure miss those days<:-))

The upshot is that few hams will notice the difference in coax and few have the experience to notice it and fewer still will run A/B comparisons or adjust the power as Ed did.

I seriously doubt that the hams on TT are representative of the average ham's skill, or station. That's not meant as a slight, I think it's just a fact of life that hams on here "typically" have bigger and/or more elaborate stations and spend more time on the air.

73

Roger (K8RI)
On 2/19/2015 3:00 AM, Jim Brown wrote:


Those fractional dB numbers, which are for 100 ft of cable, add up when the coax gets long. The run to my SteppIR is 350 ft, and I use it on 6M. That's why I scrounged the used 7/8-in hard line to feed it.

I'm using Belden 8213 on my high (135 ft) 80/40 dipoles. The closer match of 75 ohm cable to those antennas (approximately 85 ohms feedpoint Z) through 160 ft of coax saves me fractional dB, and more at the band edges.

The important point here is that every engineering problem is DIFFERENT. One size does not fit all. I'm using Commscope 3227 (#14 solid copper center, shield like LMR400) for the 200 ft lines to my 160M slopers.

73, Jim K9YC

On Wed,2/18/2015 10:47 PM, Roger (K8RI) on TT wrote:
How often can the difference between the following even be detected? It is after all, only o.5 db. 1 db can just barely be detected under ideal conditions. If this is the standard 9913, I either gave away, or threw out nearly 1500 feet of nearly new 9913.

LMR400  0.7 dB
RG213   1.2 dB
9913 0.7 dB

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73

Roger (K8RI)


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