Steve
I always wondered what people do in the dead of winter in VE6 land. Mystery
solved!
Regards,
Mark, K1RX
> On Jan 21, 2020, at 7:16 PM, VE6WZ_Steve <ve6wz@shaw.ca> wrote:
>
> A few days ago I posted a video explaining some experiments I did adding
> short radials to my feed and termination grounds on the Beverage.
> During that week temperatures went as low as -41 C at the station.
>
> The mystery has been solved.
>
> I wondered if the frozen ground was limiting conductivity and upsetting the
> ground resistance part of the impedance. The experiments showed that adding
> radials to stabilize the frozen ground had no effect.
>
> In the video I show how the real resistance of the 920 foot galvanized steel
> wire might drop 10-20 Ohms when the temperature drops 50 deg C from the
> summertime. This would mean that I need a LOWER termination resistor to
> match the surge impedance.
> However, I also show that the ceramic termination resistor I use has a very
> high negative temperature coefficient (-1300 C). This results in an INCREASE
> of 30 to 40 ohms in my 470 Ohm termination resistor. Therefore, the
> termination could be 40 to 60 Ohms too low!! I show in the video that the
> resistor does indeed increase by 40 Ohms when I chucked it out my back door
> at -30C for an hour.
>
> Today I was at the remote and it has warmed up to -1C (35 deg C warmer) and
> the analyzer sweep of the wire has mostly returned to it summer time reading.
>
> This seems to indicate that the main cause of the Beverage miss match is the
> temperature coefficient of the wire and the termination resistor. Obviously
> the ground is still just as frozen today as it was last week at the feed and
> termination and under the wire length! Perhaps I will look into changing the
> term resistor with a metal foil unit that has a positive temperature
> coefficient. Carbon composition units also have a negative TC, but not as
> severe as the ceramic units. Those ceramic units are almost like
> thermistors! (well….not really)
>
> However, as I said in the video, this is like a “solution looking for a
> problem” because few Hams experience these extreme temperature changes, and
> even when we do, it's just for a short time. Also, Beverage modelling shows
> that the termination resistor can effect the F/B, but it has limited effect
> on the RDF which is what really matters. This exercise was done mostly out
> of interest and to try and solve the puzzle.
>
> I made a new video showing the sweeps I made today if interested. The video
> includes the original content so if you've seem that just jump to the end.
>
> YouTube video here: https://youtu.be/3Oft826Q8tA
> <https://youtu.be/3Oft826Q8tA>
>
>
>
> 73, de steve ve6wz
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