Ask Michael, KB9VBR: How long of a coax cable is too long

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A viewer asks: what is a good length of coaxial cable for portable activities. He heard 50 feet was good while others say you should use 100 feet of cable. Dave and Michael talk about coax and what they feel the perfect length of cable is.
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Опубликовано:

19 авг 2023

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Комментарии : 15

@K3JRZOnTheAir 10 месяцев назад

Longer isn't always better. Check your antenna first, not the coax. Great answer! 73!

@norrinradd8952 9 месяцев назад

Good video with step by step instructions on making your own dummy load. Thumbs up, guys. Also, buy one (or three) of Michael's antennas. They work great and he needs haircut money. 73

@ac0gv 9 месяцев назад

I recall the instructions of a book I read in the 1970s that said in one chapter that length should be even multiples of a quarter wavelength and in another chapter said multiples of a half wave length. (don’t forget the velocity factor) I did it for my Mosley tri-band beam (yes, I found some multiple) and had GREAT reports from Europe.

@carlosroig5315 10 месяцев назад

Coax loss impacts both, forward and reflected power. If you use long lengths of cheap, lossy coax, the swr will be apparently lower on the meter because of the attenuation. Use the necessary length of good quality coax. Take Michael's advice on having coax of various lengths, for example 25' , 50' and 75'. That way you always have options depending on the installation when operating in the field. Also have some barrel connectors at hand( dual female ) if you need 100' or more.

@chrissewell1608 9 месяцев назад

When operating in the field!

@a2phil 9 месяцев назад

Funny, I've been told by people in the ham and Children's band to use odd half wave multiples of coax ( 1/2, 3/2, etc) after factoring in the coax's velocity factor...

@WeedyCreek 10 месяцев назад

Good question and good discussion. I also use a 50 foot length with my WRC and, generally, it works well. Also using the window screen and it also works well. I do carry a set of wire radials with me just in case! de W7PMR

@vk2lq 9 месяцев назад

Want to test the actual loss on your coax run before connecting to your antenna? lay it out on the ground connect a watt meter with a dummy load to your radio test the out power at the radio as reference then connect coax to the radio and SWR meter with dummy load at the end of the coax this way you see the actual amount of power reaching the dummy load (Antenna) EG 100 watts out and the end 80 watts you can use this to calculate the loos over the distance of coax used .

@bob-N4REE 9 месяцев назад

YES, coax length does make a significant difference. While not an EFHW, my WRC vertical is definitely affected by coax length. I use the smaller WRC coil base loading a 17' whip, sitting over a permanent radial field consisting of 16 each 33' radials. I work QRP and therefore want to use the best match possible. I tune the WRC using a NanoVNA to find resonance. When I tune it with the VNA measuring right at the antenna feed point, my 5W TR-45 (45 feet away) complains of high VSWR. When I tune it using the VNA at the transmitter end of 45' of LMR-400 coax, the TR-45 is happy, even to the extent of bypassing its built-in tuner. Yes, the coax shield becomes part of the radial field and affects SWR. When the antenna is well tuned (length shortened to be dead-on for 20M CW) the WRC performs VERY well. A few days ago, propagation was excellent and I found a late afternoon open tunnel from central Florida to a POTA activator in Northern Spain ... about 4300 miles.

@davewhite7679 9 месяцев назад

Out in the field I almost always put an RF choke or 1:1 isolator in the coax feed line, about 15 or 20 ft. from the antenna, to minimize the coax line shield length variables. KZ9V

@farmerwayne1404 Месяц назад

Q: I just purchased a Palomar 155ft antenna and it came with 100ft of coax with a choke 85ft from connection. I was told that I could run 200ft to the radio. Does this sound right???