Why length matters when choosing coaxial feedline

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All about the maximum length you should use for your coaxial feedline to keep losses acceptable.

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[MIKROWAVE]

I switched from 500' of nitrogen hardline to a roll of radio shack RG58 from 1968, and my SWR improved. But nobody hears me?

[bill-]

i used this calculator too, Peter.
Everything I have is at the most 0.6dB for the frequencies and lengths of RG58. 60m inverted vee, attic dipoles for 20m to 10m and indoor collinear. I also bought and used a NANO VNA which makes it dead easy to see if they are too long or too short, unlike the days when I only had an SWR meter. Everything homebrew including my resistive QRP SWR meter.
73 G4GHB.

[notionocean]

When I saw the title I thought you were going to cover lengths to avoid (multiples/fractions of operating wavelength). But this was very good too.

[shanerorko]

One point not many hams are not aware of is noise rejection in coax,
The bigger the coax and the less loss generally the less noise there is.
I'm not an expert but I believe all coax acts like a leaky feeder to some degree meaning a small amount of signal will escape, but this means a small amount of noise will "leak" into the coax, this will add up over length.
I've seen tests where RG58 at 100m length has so much noise it's like 2 or 3 S points meaning you'll miss any signals at about 3 S points which is most of the contacts you want.
So many hams tell me I'm fine with RG58 for HF yet speak to me like I'm a fool for using M&P Hyperflex 10 on HF.
I'll use 2 inch heliax on HF for the noise reduction if I do a permanent setup.

But the best way to reduce noise is go POTA and run 10m of hyperflex 5 up a pole for a inverted V.

[QRPbyAdventure-VKMFX]

Great video Peter. Very informative. Keep them coming mate

[vkycj]

A very practical and helpful video Peter. 73, Jamie VK2YCJ

[MirlitronOne]

Many suburban aerials are roof-mounted wires and feed lines can be extremely short, e.g. there is only about 6 metres of feedline from my top-floor shack to my off-centre-fed dipole. Under these circumstances, RG-58 is fine up to the 6 m band.
It's also interesting to consider using satellite TV 75 ohm coax. Yes, it's an immediate mismatch but the stuff is low loss, high quality and dirt cheap compared with 50 ohm coax. It is also often available FREE in offcuts up to 25 m or so long from TV aerial installers who tend to take 50 m lengths to all installations and throw away the unused excess. It may also be a better match to your dipole aerial if not your transceiver!

[youtubeaccount]

I once bought online "5DFB" cable used but good condition. Its billed as LMR-300 equivalent. It had solid copper center with foil and copper braid shield. The company in Japan who made it doesn't exist anymore from what I can tell. I can't find much information about this kind of cable in general. The only other 5DFB cable i've seen is cheap stuff sold for consumer home cell phone repeaters. Shame as I really like the stuff. Its a bit stiff so I use RG8X for antenna experiments and portable etc.

[hobbyrob]

that was very interesting! 👍 but, I'm still missing pieces. ( Aircell 7 kabel 50 Ohm and Ecoflex 10 Plus kabel 50 Ohm ) It's too much, I understand!
for example: does the length of the coax also influence on a standing wave, for example, at certain frequencies?
Do I now also take lengths of 2 meters for the 2 meter band? so 2, 4, 6, 8, 10 meters or does that have no influence?
there are always questions! ;-)😉
.
I hope there will also be a video about types of antennas? (not just for the low frequencies!)
.
Healthy and Friendly Greetings from NL!👍👍👍
Rob

[ramjet]

Hi Peter, This video fails the consideration of hight and cost.
At 28 Mhz and higher frequencies, the longer the cable the "higher" you get to put your antenna. At 28 Mhz and higher you have to consider the DB Gained in an increase in height.
At lower heights you may have Zero signal to start with and the signal may not start till you hit 50 feet and another 10 feet might triple the signal.
The other factor is "cost", I've got around 3000 feet of RG58 lying around and while RG8 would be "nice to have" its not a need to have.

[indianna]

I use rg213 with my hombrew amp. 800 Watts generally is more than enough to upset Europe with my modulation full swing. Can't bloody stand the contest stations so I sit between working most dx stations. 😊😊

[vkwl]

Open Wire feeder is often the brst option.

[migalito]

I wonder if one of these days we see some manufacturer or hackster build a transceiver that's attached at the antenna's feedpoint with a remote control panel located in the shack? Sure would minimize one source of signal