Metrocrest Amateur Radio Society
Archives
Updated September 14, 2021
August Play Day
August 21, 2021
MARS hams gathered again at the Carrollton Josey Ranch Library to play with Winlink, and VARA FM and VARA HF.
Evaluating RF Exposure
Amateur Radio is basically a safe activity. In recent years, however, there has been considerable discussion and concern about the possible hazards of electromagnetic radiation, including both RF energy and power-frequency (50-60 Hz) electromagnetic fields. To allay such concerns, the FCC set limits on the amount of RF energy people can be exposed to. Some stations should be evaluated to see if they comply with the rules.
At the August 12, 2021, meeting, Frank Krizan, KR5N, explained how amateur radio operators can perform these important safety evaluations to keep their neighbors and themselves safe. Please go here to find a video and additional information about RF exposure calculations.
Random QRM from the President’s Shack
August 2021
YouTube has become the go-to “Elmer” for a lot of folks—including me. If I need to repair a vehicle or an appliance, searching YouTube has become one of my early research steps. Over time YouTube learns your preferences and makes better suggestions of videos it thinks you will enjoy. YouTube has figured out I’m a Ham so I get ham-related video suggestions. So, thanks go to the YouTube algorithm for suggesting the videos that are the subject of today’s article.
The first video is from Jim Heath, W6LG. In this video Jim is trying to determine if a 100-foot section of gray RG-8X with molded connectors can handle the full legal limit of 1500 watts SSB. In his testing the coax showed signs of heating, which indicates loss, so he does not suggest using RG-8X with more than about 500 watts. Here’s the link: https://youtu.be/7-aD9eqtcb8
In a follow-up video Jim explains using that coax in a subsequent test. The results weren’t coming out right and his NanoVNA analyzer showed a short very close to one of the connectors. He explains that after the first video he was doing some additional testing (1500W into a dummy load) when his Ameritron linear amp “blew up.” At that time Jim did not determine what caused the amplifier to fail, but now he knows that the failure was because of the shorted coax. https://youtu.be/FOZncusW73I
In the third video Jim explains more about the amplifier failure and performs a post-mortem on the coax. Peeling back the plastic molding revealed some very poor construction. https://youtu.be/BvAo2SS2DKQ
These videos are a great reminder:
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Your amateur station is a system of components. The antenna and feedline are vitally important.
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RG-8X is fine for reasonable distances for HF at 100 watts
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If you plan to run 500 watts or more at HF frequencies, you should use heavier-duty coax
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Molded RG-8X short jumpers are probably fine for interconnecting tuners and SWR meters, but check them periodically for continuity or electrical shorts
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Quality coax assemblies from vendors like ABR Industries or DX Engineering are a worthwhile investment if you do not want to install connectors yourself.
That’s it. It’s still summer in North Texas, so stay cool inside and fire up a radio! 73 David K5GIL
Play Day Returns
July 17, 2021
MARS hams enjoyed their first Radio Play Day in over a year at the Carrollton Josey Ranch Library. Winlink Global Email® was the theme of the day as we got our rigs set up to send email to the world.
