Is the (I) Max 2000 just a 5/8 like the A99 is just a 1/2 wave?

[RadioDaze]

When I go all out with my mobile set up I put a Sirio Gain Master on 6M-7.5M of pole but sometimes I want a quick set up for a 2-3 hour little spot when I am not out all day DXing from hill tops.

I have been looking into an IMAX (MAX 2000) as I often utilize a large metal gate for mounting antenna up a tall hill. I use this set up when I want a fast set up if for example it is cold in the winter etc. The gate is essentially about 8 Meters wide and I currently G Clamp a 1/2 wave basic vertical on the middle so I get 4M of heavy earthed steel each side (Sigma Eurocomm 1/2 wave Sigma Venom - UK built basic antenna)

http://www.sigmaeurocomm.co.uk/sigmasilverrodvenomhalfwave.html

The gate is a mere 1M off the ground. Yesterday I actually took 3M of aluminium tube as an experiment and clamped that to the gate, it added nearly no time to the overall set up. I may use that technique more in the future as a little height above ground might assist with ground losses. (If the large ground plane is not doing it's job.)

Anyway cutting to the chase.... is the MAX2000 electrically similar to any 5/8 wave or is it technically a different circuit (it ships with no ground planes). I found this... interesting but I do not believe it is strictly accurate. It suggests some kind of unusual coupling of RF from one section to another via a brass insert. Paid or free antenna review ? Who knows.

http://www.k3dav.com/solarconimax2000antenna.htm

After I read : "The I-MAX 2000 is known for blowing away all 5/8 wave antennas, and being equal to many small 3 element beams in gain towards the horizon." and "A few newer measurements have been made showing a 4.5 to 5dB gain over a dipole. " I lost some respect for the author I have to admit.

I also enjoyed this article which brought about some information regarding the MAX2000 (It will open a .pdf file in your browser) I was interested that this guy seemed to think the following : "Notice the very high angle of radiation. (54deg.)"

http://www.cvarc.org/new-wp/download/technical/antenna_myths.pdf

Again when the article suggested the Max2000 was a 1/2 wave (it clearly is not at 10/11M) I wondered how accurate the document was.

I gather that 5/8 waves need very long radials to be an actually technically specified 5/8 wave (i.e. 1/4 wave ground planes (x 4) otherwise any low angle radiation characteristics are lost and there is no gain over a 1/2 wave. I started to think the large ground plane of the gate might compensate for there being no radials somewhat and that on a gate the IMAX might be a very nicely performing antenna and work as a 5/8 should do and give me some more RF poke over the basic 1/2 wave.

So... for my gate is the £99.00 Max 2000 worth a shot for a little extra low angle performance directly G clamped on my gate or with the new 3M pole technique attached to gate? Or will it not likely have any gain over a basic coil loaded/coupled 1/2 wave. I know a little now but not expert as I know some on this board are so any input or advice very welcome.

I am extremely surprised the MAX2000 does not come with ground plane radials like all the Sirio 5/8 waves. Maco/Penetrator etc.

As an aside how does it negate the need for these radials in it's design ?

 

[wavrider]

The amount of $$ you spend on your antenna system is up to you.

I have an I2K in use and I like the performance.

I also have an A99 and I also like it's performance.

In comparisons of both antennas the I2K and A99 were both even on receive signal strength to test stations.

the I2K is a decent antenna for the $$ and is light weight and very portable.

It measures out at a .64 WL ( on 10 meters ) and is basically a 5/8 WL on 11 meters if my math is not mistaken.

 

[RadioDaze]

Sorry edited: I though your abbreviation was related to an Interceptor antenna. My mistake.

So in essence in your situation the A99 and IMAX are identical which may correlate with lack of adequate ground planes being no better than a basic 1/2 wave antenna.

I wonder if the steel large gate would possibly function as an adequate ground plane on the IMAX allowing the 5/8 wave low angle characteristics to be realized ?

 

[DainBramage]

... Paid or free antenna review ? Who knows.

http://www.k3dav.com/solarconimax2000antenna.htm

After I read : "The I-MAX 2000 is known for blowing away all 5/8 wave antennas, and being equal to many small 3 element beams in gain towards the horizon." and "A few newer measurements have been made showing a 4.5 to 5dB gain over a dipole. " I lost some respect for the author.

I went to the site and read some of his articles,........ many of his "facts" are pure B.S.


"The I-MAX 2000 antenna is made for these bands, and is widely known to out perform dipoles cut for the same bands. And it's the best ground plane antenna for 11 meters hands down."


"vertical polarization sends a greater amount of signal towards the horizon than a horizontal polarized antenna. And once the signal reaches the curve of the earth ... It becomes ... circular."


but, THIS shows that he really doesn't have a clue.............

"I have seen the many websites that tell you how to build a choke coil. They show charts of capacitance and inductance measurements and tell you the coil should be a specific length and size for different frequencies. They tell you where to mount the choke within the feedline.... blah blah blah blah blah...and so on....."



THANKS for the laugh

 

[RadioDaze]

Some of the info regarding IMAX2000 from the above .pdf

And here with an "optimized feed line and mast length"

 

[tba02]

It looks like the madel information was taken from W8JI, who paints a more detailed picture.
http://www.w8ji.com/end-fed_vertical.htm#IMAX

 

[RadioDaze]

Thanks for sharing that link. It would seem to suggest that a large ground plane (i.e. the large steel gate, if I mount antenna in the middle I have 3M each side.. with multiple heavy duty steel tubed piping right under the antenna) and a choke of the correct turns (according to the choke graph from G3TXQ - 5 turns of RG213 on a 4.25 inch pipe will assist in stopping common mode current down the coax)

It looks like a go-er to me. The fibreglass sections will be a little less cold to handle when it is 3C outside in the UK winter and it is a quick screw and go set up with a nice chunk of aluminium at the bottom for G Clamp fixing to gate or pole (pole would be coupled to the gate as well using G clamps).

I think I may invest in an IMAX2000 by the time winter arrives. I have been thinking about a beam but I am not a beam kind of guy. I like the "by chance" station working that an omni gives and like putting a signal out all around. You have to do 5/8th wave "ground plane" verticals right though and adhere to their technical quirks to get some serious performance out of them.

I love verticals, thanks for sharing the knowledge.

PS Gate is quite similar to this... (2 of them meeting in the middle) I hope this should be sufficient metal to lower the elevation a little, despite the low height above earth.

 

[wavrider]

good choke at the feed point of the antenna, with the metal on the gates acting as counterpoise or ground radials you should be fine.

Just have to try it and see how it works.

 

[RadioDaze]

Indeed wavrider, proof in the pudding so they say.

I might as well ask here as it is relevant.. what is an "optimized feed line" exactly. I was under the impression that making coax a specific length was a misnomer/CB'ers old wives tale.

What is and is not a good length for enhancement or attenuation of common mode currents in the coax?

I use a standard 10M run of RG-213 at the moment. Seems fine on the Gain Master (of course it is well choked by design) and no known issues on the 1/2 wave Silver Rod end fed.

Thanks

 

[wavrider]

Optimized feed line??

In coax it is the length required to reach from your antenna to your transceiver.

IF you are trying to tune your antenna then 1/2 wl with velocity factor figured in will allow you to tune the antenna with out any?? or very little interaction from the coax.

Once the antenna is tuned then any length of coax will not change the vswr drastically.

Sounds like something someone sells on Ebay, optimized coax

I use 200' of RG6 quad then another 60' of RG213 to my fan dipole, nothing on it is optimized but I sure can make some contacts with that old hunk of wire in the air.

 

[The DB]

What is and is not a good length for enhancement or attenuation of common mode currents in the coax?

Fair warning, this might get a little complex... You have been warned.

That isn't an easy question to answer. For example, a radial that ends (open circuit, no ground connection) near a 1/4 electrical wavelength from the antenna will attract current as it presents a low impedance for those currents to follow. This in comparison to the coax which will have some other, almost always higher, impedance helps keep the currents off the coax. The fact that there are multiple radials only adds to this effect, think parallel resistance in an electrical circuit.

Now lets look at a coax that is grounded an electrical 1/2 wavelength from the antenna presenting a short circuit to ground. In this case it will have the same effect as the 1/4 electrical wavelength radial, the coax shield will attract the currents just like the radials noted above.

The thing you have to remember about a coax is it acts like an impedance transformer. I know you have heard about the half electrical wavelength multiple feedline length and how it repeats the impedance seen at the other end of the feedline. That is also explaining why this grounded electrical half wavelength will attract said currents as you can't get any lower impedance than a short to ground.

Taking this a step further, the odd electrical quarter wavelength multiples actually transforms the impedance from a low impedance to a high impedance, or a high impedance to a low impedance. In essence, the high impedance point, namely the open circuit at the end of the radial in the example above, looks like a short circuit to the antenna because of the transformer like function of the rf signal on the radial. In essence you have an appearance of a short circuit where in fact there is actually an open circuit.

Now lets reverse the examples above and use an electrical half wavelength radial and a coax that is shorted to the ground an electrical quarter wavelength from the antenna. In the case of the radials, you now have a repeat of the impedance at the tip instead of a transformation of the impedance, and the antenna sees the high impedance of the tip of the radials. As this is a high impedance, it is resistant to currents flowing on the radials, which is in this case a bad thing. The feedline now has a low impedance ground connection, but an impedance transformation to high impedance at the antenna, again resisting the flow of currents, although this time that resistance is desirable as we don't want currents flowing on the feedline.

So the easy answer to your question is to use a feedline that is an odd electrical quarter wavelength multiple to help resist common mode currents. Unfortunately om the real world there is more to it that that...

One problem you have is an unknown velocity factor for the currents flowing on the outside of the feedline. This velocity factor is not the same as the one listed on the coax jacket or specifications, and is closer to .95 to .98. Further, anything conductive that the coax passes nearby will affect both the electrical length and the velocity factor in the immediate area of the outside of the coax. Also any turn in the coax will also affect the outer shielding's electrical length.

Next we look at the radio. The radio acts like a short to ground, but in many (if not most) radios the circuit to ground doesn't end there, and continues up the negative power lead to the power supply. Further complicating things the radio can also modify the impedance in other ways as there is a matching circuit inside the radio itself the the feedline is directly connected to.

Long story short, yes, this "magic" common mode current resistant length(s) exists, but in the real world, it is nearly impossible to calculate to any degree of accuracy...


The DB

 

[wavrider]

DB that was a mouthful, and well said.

 

[222DBFL]

Wavrider and CK gave it to you on a silver platter there man!! No more to be said about coax length!! What reaches from point a to b is what should be used. Either cut excess or use large coils. Mind you, don't go using rg58 for a 100ft run and not expect some losses. But that is just about another topic in itself!
Add some ground radials like mentioned. Might help. Best way to know is to just try it. You would be suprised how well a tuned antenna will work even 10ft off the ground. Sure it's not optimal, but everyone doesn't sport that luxury at times. Get the antenna up and get to talking! JMHO.

 

[RadioDaze]

Thanks for all explanation especially the complex one The DB. I will have to read that many time to absorb it but it is there for people to see so it is appreciated.

Hmm... in short maybe I should be using the Gain Master whenever it is possible as opposed to getting an IMAX.

My concern is the GM will not be a happy bunny bolted to a gate given it's design as a centre fed dipole. I would be very surprised to see a good SWR on a gate (though I guess there is only 1 way to really find out !) But I anticipate problems given that the lower radial part of the balanced design would be close to the gate. I will have to try that but suspect it might not SWR in happily. That is one to experiment with before spending money on the IMAX I think.

I will test and report back on the GM SWR directly ona gate and also test to see how it fairs on a single (1.5M) and 2 poles (3M) attached to the gate with G-Clamps.

The Gain Master is fairly quick to install of late due to me rethinking the way it assembles using the factory supplied heavy duty fibre glass tubes. (Instead I use a 7M fibre glass margin pole for fishing cable tied to the lower section of the GM to make it lightweight for portable use and just run the GM coax/capacitor/wire up this pole) but obviously not quite as fast to erect as an IMAX would be. I have made it easier to erect as time has progressed.

 

[222DBFL]

I'm sorry DB!! I thought that was CK giving the poster help lol!! It's early!! Gots to get me coffee!!