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- เผยแพร่เมื่อ 25 ต.ค. 2024
- In this video I show you how to tune some 75 Ohm coax for the 15m band. That is a 1/4 wave length of coax that will match 100 Ohm load to your 50 Ohm feeder.
This impedance matching method using coax cable is perfect for loop antennas.
NOTE: When within the Setup menu you can change the velocity factor of the coax that you are using.
The default is 0.66 which was the same as the RG6 used in the video. This is why it was not shown.
Velocity factor will vary with coax type and make. You will need to change this value to suit your own 75 Ohm coax used.
Cheers Billy, a good vid showing how simple things can be. All the best, 73
cheers
What would be the length for a 1/4 wave stub for 7.050 using 75ohm cable with a velocity factor of .86? I don’t have a rig expert 🙃 It’s for a 40m delta loop cut for Cw portion of the band.
instead cuting and meassuring a dozen time, just calculate the cable length and multiple it with the given velocity factor of your cable type......
That's correct. That is in the video however not always accurate use the analyser and it will be perfect.
@@GM6DX Of course you leave the stub a little longer. It can't be said often enough. Every HAM need a NanoVNA......
by law! if you don't own a vna, your license will become invalid immediately 🤪
I believe your rig expert would be more accurate if you calibrated it into a low wattage 50 ohm termination first before doing this. This is recommended and I have seen test that proves this true. Just a tidbit of information.
Great work brother 👍 KE2AUM
Thanks for showing how to measure the stub.
The Gainmaster antenna has also a matching stub, would the 1/4 wave of that stub be on 27mhz?
73 from Belgium.
I have no idea how that antenna is constructed
Is the velocity factor supposed to be figured when cutting the stub or argue just cutting a quarter wave and free space
No you are required to know the velocity factor of the coax you have purchased using this method (you make sure the analyser is set to this value before tuning). There is another method of tuning a quarter wave using the analyser without known the velocity factor but it is a bit more complex.
Music distraction. Rather someone explain the process