Coaxial Cable Impedence

[pkveazey]

What I'm going to say here is a little bit controversial until you really think about it. 52 Ohm coax feed line to a 75 Ohm antenna will work without a 1:1 balun but will usually show a slight standing wave which is a slight loss of power being radiated. The same thing with a 1:1 balun can bring that standing wave down to flat. Hmmmmm...... Then I must use a 1:1 balun. Nope. The amount of loss from the mismatch is equal to the loss in the balun. Now, on to to what I really want to talk about. You can find high quality, low loss 75 Ohm coax all over the place. I have 2 huge reels of it that I bought for $50. Just think about this for a moment. A 75 Ohm dipole fed with 50 Ohm coax or a 75 Ohm dipole fed with 75 Ohm coax. One is a mismatch the other is a match. The problem is at the 52 Ohm radio output. If you ignore the mismatch it will still work and have a slight power loss. If you match the radio to the 75 Ohm coax you will still have a slight power loss in the matching system. The point is, if you are in the field and you only have some 75 Ohm coax available, you should hook it up and use it because in the end it will work just fine. For 20 years, I used 75 Ohm Hardline to feed my antenna and it worked great. Last year, I decided that the extreme long run of hardline was just plain silly so I installed a shorter, more direct run of 9913, 52 Ohm coax. I can't tell the difference in receive or transmit. With all that said, I have used an antenna tuner on both coax systems so the radio is none the wiser. I used to use a manual tuner but for the last 5 years I've used an LDG autotuner. I know someone is going to mention Ladder line so I'll just say that I know it is absolutely the best way to feed an antenna but if its wet or if it has ice or snow on it then it becomes almost useless and it has to have a really good matching system to work. That makes ladder line a horrible choice when you are powering your radio with your car battery and you are out in the middle of the woods. I'm not thin skinned so any opposing comments will not hurt my feelings.

[JohnyMac]

Makes sense to me. 

Like everything in life there trad offs. 

[Kbop]

good points. 

one note- for DX only - impedance matching is less important receive power - the fewer breaks the better - that 3dB is a killer at a connection or splitter or impedance matching widget.   
when TX you want a good VSWR to get good resonance.  Your point is well taken that you can get 'good enough' with most antennas that are close.  don't let perfection be the enemy of good enough.

Oh and LMR240 and i are good friends - its a good midrange, tough, easy to get coax.  crimp and solder works fine with it. 

[pkveazey]

 After I wrote that extended thesis, I started thinking that I could have just said " If you are a newbie, you can use either 52 Ohm or 75 Ohm coax in a pinch to feed a dipole. Its just a matter of the mismatch being at the antenna connection or at the radio connection." But Noooooooo, I had to go off on a tirade with all the intricate details. Sometimes if you ask me what time it is, I'll tell you how to build a watch.

[patriotman]

After I wrote that extended thesis, I started thinking that I could have just said " If you are a newbie, you can use either 52 Ohm or 75 Ohm coax in a pinch to feed a dipole. Its just a matter of the mismatch being at the antenna connection or at the radio connection." But Noooooooo, I had to go off on a tirade with all the intricate details. Sometimes if you ask me what time it is, I'll tell you how to build a watch.

That certainly isn't the worst quality to have    and I found the write up interesting because I am new to this stuff and would have never known to use that if that is all I had