Glad to hear you're home and recovering.

The question of how to interface ladderline with coax can be as simple as just hooking the coax up to the ladderline but this depends on the antenna and the length of the ladderline. All this require a bit of math and the use of a Smith Chart. This can be a challenge since most of us don't use Smith Charts everyday. The original G5RV antennas didn't use a balun and they were connected directly to the ladderline or twin lead.

That's just an example and may not be right for your purposes. Most connections like that are now done with a 1:1 current balun. Some folks report good results with the 4:1 balun. In both cases you would need the assistance of an antenna tuner to obtain multi-band operation.

For a single band operation refer to the G5RV and follow the dimensions carefully. Do not deviate from the type of feedline coming from the antenna. The G5RV is just like any other antenna in that it's scalable. Just take the usual frequency a G5RV would be tuned for, this is usually 20 meters, and find the dividing ratio for the frequency you desire. As an example the G5RV is tuned for about 14.150Mhz and you want to build one for 40 meters at 7.150Mhz. Right away you can see there is about a 2:1 ratio but it's not exactly that, so it comes out to about 1.97 times the 14.15Mhz dimensions. There you have it just multiply by 1.97 on the length of the antenna and the lenght of the feedline to the coax junction. Multiply by 2 would probably make for a workable antenna as well. Just remember to use the ratios between the dimensions. If the frequncy is higher then your multiplying ratio would always be less than 1 and if it is lower in frequency then the multiplier would always be greater than 1.

Now you could also use the length of the antenna feedline as a method of matching to your coax. A simple dipole has about 70-75 ohms of radiation resistance it can be lower if your mounted closer to the ground. If you feed the center of the dipole with 450 ohm ladderline then for every 1/2 wave lenght the radiation resistance of the antenna will be the same as at the center of the dipole and that is the norminal 70-75 ohms which is a good match for 50 ohm coax. The length of the 450 ohm line is determined by the following formula; length =246/Mhz*VF. This is where you divide the frequency in Mhz into 246 and then multiply that value by the velocity factor of the feedline and that will be your length.

If you can look at W5DXP's website and you will see multi-band antennas with a tuning capability by just varying the feedline length. Look here for details;

http://www.w5dxp.com/notuner.htm.

There is also a short section on the G5RV;

http://www.w5dxp.com/G5RV.HTM.

If you want some reading material here's a complete book on antennas;

www.eagle3.net/n4ywn/docs/PracticalAntennaHandbook-vol4.pdf.

It's 625 pages long so you're not going to read it in one sitting. Save it to your computer and refer to it whenever you need some information on antennas and feedlines.

Hope this helps and it's not TMI.

73

Gary