Coax Length Question

Sorry, but you do not need to know string theory in 11 dimensions to be able to tune and match an antenna, any more than you need to know how to build an engine from parts to be able to change the oil.

I'm done with this "debate" before the thread gets locked.

 

I love how know-it-alls respond to simple questions with attacks hoping that everyone thinks they're cool and nobody notices they don't answer the question.

 

I CAN install an antenna on ANY kind of truck, car, or road tractor, and I won't use "coax length" to do it. I would simply select a proper mount, use non-resonant grounds to the frame, TUNE the ANTENNA, using a good quality antenna analyzer, match the feedpoint impedance as needed, and go from there. I have the equipment to do it, and have been constructing antennas since 1969. I've even made some "Big Coil" CB/10 Meter antennas that work excellently. It all has to do with an understanding of those impedances, reactances, and capacitances that affect the system. It's not about being king on the hill, or putting someone down. It's about doing it correctly so the antenna works up to specs.

I've never said you CAN'T do what you do (coax length), but I do assert that it is not the right way to do it. If you want to do it that way, it is fine with me. but it still not the right way, truck or no truck, and CB radio is the only place where this coax length thing is so prevalent. That's all.

GF

 

"and CB radio is the only place where this coax length thing is so prevalent. That's all"

Untrue. Every Ham operator on earth using an antenna tuner is doing exactly the same thing using lumped components. Introducing the proper reactance to achieve a match.

I fail to see in these 5 pages anything which would justify 'locking the thread'. I am an American and proud of it. We do things in freedom and have little use for excessive control of thought. Or speech within reason and decency. Nothing said thus far is outside of those parameters. While you can match antennas without knowing modern physics, you cannot claim to be an authority on field propagation when lacking this knowledge.

 

Well we agree!

You might want to check some of my other posts before you assume something.

Get locked! A spirited debate, but I hope nobody is mad about it!

Your first post on this set the tone of my response my friend....Looking back at it I wonder if it was meant in humor? I came back a little hard at you, sorry.

And I've always said the same thing............It is so prevalent because it is hard sometimes to get a match so you compromise. And when you slip seat, you are usually in a hurry and just want something that will work until you yank it back out at the end of the day/week.

By the way, hope everyone on here has a Happy and Safe New Year!

 

But my point is, no matter HOW the hams do it, you don't find all this obsession with coax. Hams use tuners, that's true, and when warranted. They also "match" impedances with capacitors, toroids, resistors, too. But you rarely hear this obsession with "coax length". The only place I EVER ran into it was on CB---after I had been into radio for at least 6 years. I never started in radio with CB, and it was years before somebody asserted that I simply MUST have a certain length of coax for the radio to work. And I was like.........."SAY WHAT??????" Well, that's funny: I've been working Europe and Australia for 5-6 years, and NOW they tell me I must have a certain length of coax or my radio won't work!!!!!!!

So you can see how it would be that I would call "horse hockey" to the coax length thing. With opologies to the board members, or course. And once again, if someone wants an antenna that works sub-standard, it's also fine with me. I just want mine to work right. That's all.

GF

 

Gadfly I agree with you. The real problem I have in the many length discussions over the years is never once has any of the 'experts' commented on the difference in length under two sets of conditions. One where reactance is not present, the other where it is. I have brought it up many times and as always it is ignored, the reply being length makes no difference. This is only true when the system has zero reactance at the feedpoint. By virtue of the fact this is never acknowledged, I can assume they really do not understand the theory in depth. There is a subset of theory proponents who are big on conjugate matching. We well know this should be renamed the 'theory of making the transmission line part of the antenna'. Or something like that. If one can get the reactance at the feedpoint to nearly zero then line length only relates to loss, given the dB/meter specs of whatever is being used. Obviously what we all hope to achieve. Then came the new trucks with less metal than a six pack of beer cans in the body. Been many problems since. If I did drive truck I would look for a 1973 Peterbuilt wood grained dash and all. I would go broke restoring it to perfection and when California said it was too old to cross their line I would say "good get your stuff on a slow boat from China". You could build a fleet of today's trucks with the metal in just one 73 Peterbuilt. Obviously the point being CB radios really worked great with all the metal providing an excellent ground.

I like the safety of real metal around me in whatever it is I drive. If only I had kept that old 56 Olds. However I doubt with the low quality of gas today it is possible to get that much mass moving.

Not kidding, I would never drive a truck anywhere they said perfection is not allowed my truck is too old. Someone else can haul their freight. They have no problem with rolling disasters, bald recaps and all coming in from Mexico, how dare they ditz me over the age of my beautiful Peterbuilt.

Buts that just me.

 

But this is also where I get the thing about the screwdriver antenna. Now I don't have to mess with too many "plastic" vehicles and mine is an S-10 truck. But I have a lot of fun with the people that believe that one MUST have "so many feet of coax, etc, etc", or the radio won't work. They also believe it even if they have a 1958 Cadillac! Ya GOTS to have "18 feet of coax". Now if that were true, hams, military, and commercial mobile HF operators would be out of business because they would be physically unable to store all that coax needed to cover all those bands and frequencies! Hams typically cover 10 or more, bands with the screwdriver antenna I described several times, and if the coax length thing were true, then it have to be true for ALL bands and frequencies. It could require 10 difference coaxes cut to a different length, ranging from 120 feet to 17 feet. WHERE would I store all those lengths of coax in a small pickup truck???????? But the monkey wrench in the "CB bible" is, I have ONE coax, of no particular length (about 7 feet from the bumper to the radio), and I work from 3.7 MHZ to 28 MHZ with ONE coax with an SWR (not "swr'zzzzzzzzzzzzzzzzzz") of 1.2: 1 from top to bottom. I have presented this problem many times to CB forums, and not even the best CB guru has been able to answer this: HOW can a multi-band antenna cover the entire HF spectrum with ONE coax of 7 feet?????? To me, it proves that, minus all the hocus-pocus, stripped of all the hoopla and CB legend, coax length is simply a bunch of horse manure! A placebo that satifies an inaccurate meter, and makes people think, "OH! I'm a-gittin' out sooooo good, an' my 'swr'zzzzzzzzzzzzzz' are flat!" If folks want to live with a mis-tuned antenna and WASTE wattage thru an inefficient radiatior, then by all means....................

 

SWR ZZZZZZZ nice, CB shop in West Memphis on channel 5 advertises that they will check your swr's ha ha