Random Wire Antennas

[@tmccusk1]

Another great video. Learn a lot every time.

[@CoffeeandHamRadios]

Thanks, glad you liked it!

[@BusDriverRFI]

You all know the one formula for finding the resistance of a pair of resistors in parallel. R1*R2/(R1+R2) but there is a variation of that formula to discover the resistance of the resistor needed to put in parallel to make it close to your desired resistance. R3+R4/(R3-R4) where R3 is the resistance of the closest value ABOVE the desired resistance, and R4 is the desired resistance. So R3 will be greater than R4. In this case you take the 470 being R3 and R4 is the desired 450 ohms. So we have 470*450/(470-450)=211,500/20=10,575. Then if you only have a 10k and not an 11k, we can calculate 470*10,000/(470+10000)=448.9 ohms. For better accuracy, take out your VOM and measure the actual resistances of your resistors. It's really easy with a calculator. Even an old school bus driver can do it.

[@BusDriverRFI]

The caveat is that the lower value resistor will be getting the brunt of the power dissipation. So if you have a pair of 1/2 watt resistors, in this case, the 470 ohm resistor will be dissipating the vast majority of the power and you should not go over 1/2 watt for any length of time. Use metal film resistors for repeatability (it looks like you do, SA) and for less inductance.

[@CoffeeandHamRadios]

Thanks BD, this is helpful

[@HOAHamRadio]

So much respect for all the work you all are putting into testing CaHR antennas!

[@CoffeeandHamRadios]

Thanks HOA

[@N1IA-4]

Great job on this. I love random wires, personally. I've put up a couple of these, the most recent using a Palmora 9:1 unun rated at 1500W. One was 71' and the other (currently in use) is a 203'. On both, my NanoVNA shows what one would expect: a higher SWR on 80, and gradually decreasing toward 10M. They are predictable if you use the stated lengths. I never trim mine either. I've found that counterpoise lengths don't matter much, as long as they are not too short. My 203' random wire sits atop of a 6' wooden privacy fence, and the counterpoise wire (100') sits just above the ground on the bottom of the fence. Trying to stay stealth. It's great for NVIS and most of North America but does struggle with DX in general due to the height above ground, especially below 20M, but my losses aren't terrible since my ground conductivity here in Florida is around an 8. By the way, ground conductivity is important with any antenna. It doesn't get talked about nearly as much as it should IMHO. 73 De Scott W1AL

[@CoffeeandHamRadios]

Hey Scott, that 203' sounds like a hack of an antenna. Thanks for the point about ground conductivity.

[@tomm899]

Watching next dsy, good information. Y'all explained so us non informed people can understand.lol Good stuff.

[@CoffeeandHamRadios]

Glad you liked it Tommy

[@jameski5oeb668]

Great Video Livestream!!

[@CoffeeandHamRadios]

Thanks James

[@haxwithaxe]

On one of those popular random wire charts they mislabeled 60m as 40m in the code. I rewrote it in python and made it more of a calculator. After I made a random wire antenna that doesn't need a tuner on multiples of 10 with a literal random wire.

[@CoffeeandHamRadios]

Didn't know about the error

[@charlesr9110]

Please elaborate. What length did you end up with, unun, etc?

[@haxwithaxe]

@@charlesr9110 the length is about 20m of unlabeled small diameter coax I inherited from an SK. I cut it long for a 40m EFHW and had trouble tuning it with just my radio's swr meter so I threw a 9:1 (made from a salvaged yellow iron powder core) on it and it either broke my radio or the swr is nearly 1:1 in the digital portions of 10, 20, 30, 40, 80. It does have a solder joint at about 5m away from the 9:1. I'm not ruling out the possibility that I have made a semiresonant dummy load yet. I can hit Toronto from DC on 40m with it in a nearly horizontal NVIS configuration using 20W so if it's soaking up RF it isn't too much. I use about 5m of the feed line shield for the counterpoise. After that I have a choke before continuing into the shack.

[@johnsonstechworld]

Yet to try my hand on winding RF transformers. Should to try to find where I can get those toroids from, in this part of the world! Will come back and view once again once I get hold of the toroids! 73 de Jon, VU2JO

[@CoffeeandHamRadios]

Thanks for watching Jon

[@MikeN2MAK]

Better late than never! Good stream fellas. #TeamReplay

[@CoffeeandHamRadios]

Thanks for watching Mike 👍

[@bassmanjr100]

With a transformer, if the voltage is increased by some multiple of x, the current is reduced by the same multiple x. This keeps the power (V times I) the same. So the impedance which is volts/amps is increased by x sqaured.

[@CoffeeandHamRadios]

Thank you Bassman

[@BryanDaniel42]

what choke would you recommend putting between the feed line and the antenna?

[@CoffeeandHamRadios]

I'd use a mix 31 👍