Another I-MAX 2000 question (s).

[Heavy Metal]

Ok am just curious, if according to K3DAV:


I-Max 2000
The bottom section is 80 inches, The middle section is 90 inches, The top section is 90 inches.
That is a total of 260 inches


OK that's 260 inches which comes out to @21.6666666667'

Which doing 640÷29.538 give or take point What ever lol.


Now if you add another section 90"( 7.5' ). Makes it @29.1666666667.


This brings it using 640÷ down to @22Mhz is correct.

Would it work and what's the trade offs of that and all.

 

[RatsoW8]

If your trying to make it into a half wave vertical for 15 meters then you would also have to remove the matching components in the base of the Imax. If memory serves me, 1/2 wave verticals are very high impedance at resonance and a nightmare to match. That's why we build 1/4 wave verticals.

 

[Captain Kilowatt]

I had a really bad day at work and my brain is fried so explain to me what 640÷29.538 is all about.

Also IIRC we have been down this road before. You cannot simply take an I2000 .64 wave (or half wave) or whatever that id tuned for the CB band and simply add length to make it a .64 (or half wave whatever) on another band. The antenna has a matching network in it that is tuned for the CB band. This tuning network will alter the tuning on the new band.

 

[Road Squawker]

I had a really bad day at work and my brain is fried so explain to me what 640÷29.538 is all about.

me too,....... I "think" he thinks thats how to compute a .64 wl long antenna.

 

[Heavy Metal]

me too,....... I "think" he thinks thats how to compute a .64 wl long antenna.

Okay how do you compute it.

 

[Heavy Metal]

So dump the matching network and just raise 33'-33.5' and @ 16'-18' radials?

 

[Captain Kilowatt]

Okay how do you compute it.

Standard formula for a full wavelength is 936 ÷ F where F is the frequency in MHz. Therefore to calculate a 0.64 wavelength antenna for 15m you would use (936÷21.225) x 0.64 which equals 28.22 feet for a 0.64 wavelength at 21.225 MHz in the 15m band.

 

[Captain Kilowatt]

So dump the matching network and just raise 33'-33.5' and @ 16'-18' radials?

Any end fed antenna other than a 1/4 wave or an exact odd multiple thereof such as 3/4 waves or 5/4 waves, WILL require a matching network at the base to transform the feedpoint impedance to something near 50 ohms.

 

[Heavy Metal]

Any end fed antenna other than a 1/4 wave or an exact odd multiple thereof such as 3/4 waves or 5/4 waves, WILL require a matching network at the base to transform the feedpoint impedance to something near 50 ohms.

So a balun 1:1 or 4:1 and why humor me.


I thought .64 was max and all else is over kill or is that 3/4 wave and all else is over kill. I am just trying to figure things out again been so long and use to have so much fun building antennas for the fun of it.

 

[Captain Kilowatt]

NO balun. You are going from an UNbalanced coax to an UNbalanced antenna. A balun is used when the antenna is balanced and the feedline not. You need a MATCHING NETWORK not a balun. BTW a 3/4 wave antenna or a 5/4 or such repeats 50 ohm impedance that is why it requires no such matching network at the feedpoint. The radiation pattern from them however is not great with mostly high angle radiation unless other things are taken into account such as phasing (NOT co-phasing) of 1/4 wave sections etc.

Get a good antenna book such as the ARRL Antenna Book and read some theory.

 

[DainBramage]

...unless other things are taken into account such as phasing (NOT co-phasing) of 1/4 wave sections etc....

tell me it ain't so,........ I got co-phased antennas fed with exactly 18 feet of coax........

 

[Heavy Metal]

Cpt Kilowatt


What I was trying was to use it to reach down to 20m for fun nothing more

 

[Captain Kilowatt]

Cpt Kilowatt


What I was trying was to use it to reach down to 20m for fun nothing more

Nothing wrong with that however you should realize that you can do anything for a receive antenna but for a transmitting antenna things must be different and a good SWR is required. A .64 wave antenna designed for CB is no more a .64 wave for 20m just because you extended it than an apple is an orange just because you wrapped in an orange peel. It's what's inside that makes it different. A physical length is one thing while an electrical lenght is another. Hers is something most do not know. The matching section of a .64 or a 5/8 wave actually tunes the antenna as if it were 3/4 waves. Remember back when I said that odd 1/4 waves repeated 50 ohms at the feedpoint? A .64 has crazy SWR however an electricak 3/4 wave antenna has 50 ohms.

 

[Heavy Metal]

Nothing wrong with that however you should realize that you can do anything for a receive antenna but for a transmitting antenna things must be different and a good SWR is required. A .64 wave antenna designed for CB is no more a .64 wave for 20m just because you extended it than an apple is an orange just because you wrapped in an orange peel. It's what's inside that makes it different. A physical length is one thing while an electrical lenght is another. Hers is something most do not know. The matching section of a .64 or a 5/8 wave actually tunes the antenna as if it were 3/4 waves. Remember back when I said that odd 1/4 waves repeated 50 ohms at the feedpoint? A .64 has crazy SWR however an electricak 3/4 wave antenna has 50 ohms.

Not wanting .64 wave at 20m 1/4 1/2 be fine just having fun with an extra one I have with an extra mid section. That's all and yup am wanting to get that book hardcovered. Be good to have.