Coaxial cable is a pretty remarkable piece of every Ham's station. It is required to convey both transmitted and received signals efficiently, in all types of weather, and for (sometimes) years at a time.
But not all coaxial cables are the same.
Some are exceptionally capable of handling high power...or can be buried...or, as in the case of RG-174, aren't much better than a shielded jumper for a circuit board.
But how about coax for the VHF/UHF/SHF/satellite enthusiast?
To be totally honest, my first attempt this at modern satellite operation was less than ideal. It started with a dipole for 2-meters that I built on a rainy afternoon. That itself wasn't as much of the problem, as was the RG-58A/U cable that I used for the span...or the "solderless" BNC connector at the shack end. Never saw these? They are a BNC connector, all right. But, after straight-cutting the cable, you push the cable end into the connector...making sure that the center pin pierces the coax....then you use a screw to tighten against the shield, after it bites through the insulation.
It was horrible.
I am actually ashamed of myself for even TRYING such a slipshod method, given the fact that my FT-817ND is the first NEW rig I've lavished upon myself since 1991 when I was in college.
Funny thing is...it worked! Not only could I hit the local FM repeaters...but it could hear AO-51. This antenna was what gave me the inspiration to try for AO-51 and beyond.
This antenna's horrid characteristics were summed up in one word: LOSS. Not just any loss: dB loss.
At 7 MHz, RG-58A/U is pretty good. Not great, but good. In 1995, I built a dipole out of surplus RG-58A/U as my first HF antenna. In concert with an MFJ-941E antenna tuner, it was...OK. I made contacts, and at a whopping ONE WATT. I estimated the loss to be in the neighborhood of 2 dB...taking into consideration insertion loss for the PL-259 connector. 2 dB isn't Earth shattering at HF...but still lossy enough to make me switch to ladder-line. At 145.900 MHz, the loss is about 5 dB. What that means is that 33% of your signal is left. Pffft! Gone! Like the wind. 66% of your precious VHF signal is wasted as heat. At 435.2 MHz, 11.5 dB of loss are the order of the day. So, a theoretical 10-watt signal is now about 725 MILLIWATTS!
Clearly, better coax is a NECESSITY. But what to use?
I've always made life decisions based upon available finances. I grew up poor, so that logic was required. And when it came time to build a proper satellite antenna farm, the price of coax was an important determining factor. I would love to use Andrews Heliax...the 3 inch stuff that I used when I built Sprint PCS cell sites for Lucent Technologies. But, at several DOLLARS per foot, it would mean a divorce for sure. LMR-400 would be OK...but again...I have a 62 foot run. But, RG-6 and RG-6/U at $0.17 per foot make excellent alternatives. Even with a 75-ohm impedance, they can still fit the bill handsomely.
As for 50-ohm coax, RG-8 is a good, generic, common alternative. At 145.9 MHz, and 100-watts, a 100-foot run of RG-8 will give you approximately 70 watts at the antenna...given a "perfect 1:1" SWR. The line loss is in order of about 1.5 dB.
But...30 watts is gone due to line inefficiencies.
More examples are my Belden 9066 (RG-6/U) coax spans. I use 5 watts...so that is the base to work with. At 145.900 MHz, I have 1.6 dB of loss, leaving me with 3.40 watts at the Eggbeater. This translates into a 68% efficiency. On UHF, the numbers are even worse: 2.9 dB of loss, leaving me with 2.6 watts at the antenna. My 440 MHz setup is in the neighborhood of 52% efficient...and I can STILL work the birds without much difficulty. This possibly is due to the fact that an Eggbeater exhibits around 4 dB of gain, which would offset the -2.9, leaving me with about 1 dB. As you can clearly see, any coax upgrade to a higher quality will improve both my transmitted signal as well as my ability to hear.
If dB losses are plugged into an X-Y chart, the most drastic losses are actually within the first 6 dB. With as little as ONE dB of loss, you can expect to lose 20% of your signal. At 3 dB, 50% is gone.. And at 6 dB, a full 75% of your precious satellite signal is dissipated as heat and wasted.
It is because of these harsh realities that careful construction is so important.
But, as in my case with lossy spans that are 68% and 52% efficient, it proves that any antenna will still work better than no antenna at all...or so the old ARRL mini-book, "Operating an Amateur Radio Station" declared.
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