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Maco 103c Beam Antenna
- Thread starter Troubleshooter
- Start date
Well my friend Danny who builds 123chicagobuilt amplifiers said to use rg213 and to use 12 foot jumpers, because of the veolicity factor of the rg213, depending on the coax used then the math would change.. So by using the rg213 it's in increments of 12, so 96ft, and 12 foot jumpers.. I corrected my post, because I just remember what he said after I wrote the original reply..
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Time to ditch Danny and find a friend that knows what he is talking about. I don't mean to sound harsh but I am getting fed up with people that think that you need a certain length of coax to make things work right. It is BS plain and simple. You will often see amp builders claim you need a certain length of cable to make things work but that is because they are taking a bandaid approach to curing a problem with poor design. I am a ham radio operator. Ask Danny what length of cable I should use on my Explorer-14 antenna. It covers the 10,15,20, and 40 meter bands. There goes that old special electrical wavelength of cable idea right out the window. The ONLY time you need a special length of cable is when you are making phasing lines to connect two antenna together or when using a coax cable as an impedance transformer which is what amp builders to to compensate for the poor input/output impedance of their design.
Again I don't mean to sound harsh but I am tired of some CB hack that insists on something that the rest of the engineering world knows to be false. In case you wonder just who I am to be commenting like that, in a former lifetime I spent 22 years in the engineering dept. of a commercial AM/FM broadcasting network installing and maintaining studios and transmitter sites. I want to strangle the living crap out of people that say you NEED a multiple of some given number of feet of cable. The best length of cable is enough to go from the radio to the antenna with enough left to be able to move things around a bit in the shack.
P.S. He says that because a half wavelength of cable is approximately 18 feet however that is a physical wavelength. An electrical wavelength of RG213 (or any cable) is the physical length multiplied by the cables velocity factor which in this case is about 66% IIRC so therefore 18x66%=12 feet.
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I totally understand what you are saying, and I do not take it as being harsh, it's all good.. I need at least 70+ feet to go from the antenna to my radio stuff which is in my basement. He was telling me just to make sure it's in 12 foot increments.. So 84, 96, 108, and that's based on the velocity factor of the rg213 coax. Again I am not an expert that's why I ask for opinions or advice here, and I was a little confused by the numbers with the velocity factor, or other numbers associated with the coax used. That's the coax I ordered and what I will be using to run to whatever antenna I will be using.. But Danny seems to know his stuff and I do not doubt him.. But again, I am no expert and do not claim to be.. I appreciate everyone's help here and enjoy reading and learning...
If you really want to test Danny ask him the question I stated in my post above. What length of coax is best used on my multiband antenna that covers several bands? It is impossible to have an exact multiple of half waves with that antenna or any other multiband antenna similar to it and since coax length does not matter the correct answer is whatever length reaches the radio. Even in commercial broadcasting where details are FAR FAR more important than on CB we NEVER used any special length of cable unless it had to do with antenna phasing where two or more antennas were connected together to act as a single antenna.
Personally, I'd keep the 103 and put it up at about 30 feet. Put the Imax on another pole on the other end of the house, and get it above the roof. Or, don't use the ground plane kit, and mount the Imax above the 3 element beam. If you're using the peak of the roof as a support, you shouldn't really have much trouble with the wind as long as you guy it.
It's really nice to have a directional antenna horizontally polarized, and a GP for the vertical. Propagation is strange, and sometimes you'll hear things on the beam that you can't on the GP, and other times it's the other way around. With the cycle being where it is now, you'll need every advantage you can get in order to make contacts.
73,
Brett
It's really nice to have a directional antenna horizontally polarized, and a GP for the vertical. Propagation is strange, and sometimes you'll hear things on the beam that you can't on the GP, and other times it's the other way around. With the cycle being where it is now, you'll need every advantage you can get in order to make contacts.
73,
Brett
Danny is full of crap or should that be Danny knows nothing about antennas.
I'll tell you how this whole nonsense came about. (This is simplistic).
Lets take a simple dipole antenna. First of all read this to get a basic understanding of how it works and keep in mind the following graphic. As we can see, current flows in both halves equally which is a good thing. Each leg is an adequate source and return path for the flow of electrons to and from the other leg. A dipole is effectively a perfect self contained antenna from an electrical point of view.
Your vertical is for all intents and purposes one half of a dipole and you need to make up the other half with a RF ground in order for electrons to flow. That is usually done by using radials.
Now here is how the myth gained traction. With antennas with effectively no or poor RF ground the antenna tries to use anything it can both as a source of electrons and giving them somewhere to go, in short to try to balance the antenna. The one thing it has it can use is your coax. On a dipole as you change the length of the legs it alters the tuning of the antenna. Because your coax has become part of the antenna and is effectively being used as the "missing leg", altering its length alters the tuning of the antenna.
CBers (and sadly too many amateurs) not having a requirement for much technical knowledge to put up an antenna didn't realise they had a crap installation with very little or no RF grounding. Some however did notice as they altered the length of the coax the SWR altered and that if they cut it to multiples of a quarter wave long that they got the lowest SWR and bingo, the myth of having to have coax that is 9ft, 18ft, 27ft, 36ft etc for CB was born. It then got regurgitated endlessly. And it was all bollocks but because of the sheer number of poorly installed CB antennas and the fact that this appeared to work it became regarded as fact.
You do not want the coax to be part of the antenna. It means more noise on received signals, it can mean noise on your transmitted audio, you can get RF burns and in a vehicle it can interfere with the ECU, you'll set off neighbours burglar alarms, you'll cause TV interference to you and your neighbours, you'll pick up your transmitted audio on your hifi speakers because we have stray RF going where we don't want it to go. Simple truth is that if altering the length of your coax alters the SWR then you've an inadequate RF ground and you need to be addressing that at the antenna.
So does the myth work? Yes it does but only because there is a fault in your antenna system and this allows it to "work" the same as any botch you can do on a car or an appliance in your home to keep it running for example. The SWR will be low, you'll be able to make contacts but you'll experience the issues I highlighted above and it doesn't fix the problem.
If anyone ever comes out with the "you want to be cutting your coax to X, Y or Z length", it is literally the best indication that they actually don't know what they're talking about and it is advisable to pretty much ignore anything that comes out of their mouths when it comes to antennas and to treat other information with caution. As has been said there are times when you do need coax to be a specific length such as phasing or when using it as filtering in a repeater but for a typical home base or mobile antenna install, no you don't.
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And if it alters the values of R and X as well, you have issues or have used an incorrect method to tune the antenna!! Once tuned correctly, you should be able to use whatever reaches from antenna to radio or meter. All good posts gents! So tired of hearing people argue with me about coax length and that you need this length or that length for antenna to work. If that is the case, guess I F'ed up royally using the coax I did LOL!! I had to see the light myself to believe it. All it took was to have an antennna analyzer and some help from some members here to open my !! Once you understand this you will too say that the coax length myth is BS as well! JMO's!!
Can you imagine following that rule on 80 or 160m? I can see it now. So my antenna is 100 feet from my radio but that is more than an electrical half wave so I need to use two half waves of cable. What do I do with the extra 67 feet of cable? LOL Also something to consider is that once you get into multiple half waves long there is a cumulative error you have to deal with and that is caused by the end effect and measuring errors as well as variations in the cable along its length. These errors add significantly over several half wavelengths and simply measuring will not work. Tuning the length with an analyzer is the way to go with that. Been there done that while playing around to demonstrate that to people.
He did not say I need a specific length, he just said its 12 ft length do to the velocity factor of the rg213.. If I was using lmr-400 then I think it would be 15 ft.. So when I ordered the 96ft of rg213 I thought I was going to get the antenna up 40 feet in the air, and then routing it through my garage into the basement where my equipment is, its another 40 feet or so, so I got a little extra in case I want to move the stuff.. I just made it x12 because of what he said.. Listen guys, I have no idea, like I said, back in the day I had a antron 99 on my chimney with gpk and I was able to talk wherever I wanted. I had no idea how high the antenna was, nor how long my coax was, or even what kind if coax it was.. It did not matter because I was able to talk locally and shoot skip without any problems, AM, SSB, it did not matter.. So I am not sitting hear claiming that I know about the coax, velocity, this or that, I have no idea... I am sure you guys know a lot more then me, thats why I am here asking for opinions and any help I can get.. I listened to a few different people already, I changed the coax and the length I had twice, and I have a maco 103c in the box along with a IMAX 2000 w/gpk.. So thats what I have right now, I have 96 feet of rg213 coax and the 2 antennas. I really wanted to use the beam, but I do not want to put a tower in my yard so I then made up my mind I was going to put the imax up, 40 feet, then everyone chimed in and it made a lot of sense, putting it 40 feet with the way I wanted to do it was not a solid choice.. Now I have another friend mentioning I should go with the Mr coily excalibur base antenna, he says it is much better then the IMAX.. So I asked about that in this same thread.. This is getting crazy already.. I am confused now..
For coax, I buy just like you did... determine how much you need and hook it up. You can beat yourself to death with velocity factors, lowest SWR, and jumper lengths. Put your antenna together properly, tune it, and get on the air. Done!
The 103 is not such a heavy antenna that it requires a tower. A good strong pole will handle it just fine. Lots of guys in my area use oil field sucker rods, which are quite thick and strong. And they put antennas as large as a Moonraker IV on them. With a mount to the eve of the house, you've increased the stability of the pole by a considerable amount. If you're only going up 30 feet with it, you really should be fine with the eve bracket and some guy wires. Throw the Imax on top of it with a 6' pole, and that puts the tip of it at 54', That's not bad at all. You should only need a medium duty rotor to turn it, too.
As far as the Mr. Coily ground plane goes, I don't have any experience with them. The Imax takes some harsh criticism, but it has proven to be a solid performer for many years.
73,
Brett
Thanks Brett.. That's what I wanted to do in the first place is use the Maco 103c and run it vertical to shoot dx.. But everyone kept telling me you need a tower etc, etc.. So I am going to put the Maco up if I can and use the method as I described in the middle of this thread.. With my idea 40 feet would not be a smart idea as someone had mentioned, sorry forgot who
, but the person mentioned he would have no problems at 30 feet.. So I am going to use 10 feet 3 1/2" pipe buried 3-4 feet as base into concrete, put a 3" pipe inside to make it an even stronger footprint, then take another 3" pipe into that pipe and cross bolt it, attach brackets at the peak of the garage to help secure it, then attach 2 1/2" pipe to that, and maybe a shorter 2" pipe to get it a little higher and throw the beam or the IMAX up.. I guess when my friend is ready we will decide which antenna or antennas to put up.. Hopefully all will go as planned.,
If you want the beam for dx then mount it horizontal not vertical. You gain an extra 5-8 dB from wbat is called ground reflection gain. Vertical antennas do not have this. Mount the Imax above it. You can space it only a foot or less and it will see the beam as a groundplane for it
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