|Subject:||Re: [TowerTalk] 2 element 40m steppir yagi|
|From:||Larry Phipps <firstname.lastname@example.org>|
|Date:||Thu, 07 Oct 2004 19:26:02 -0400|
I use a novel approach to tuning my E-Beam minibeam prototype from 14-30
MHz with fixed length elements. The same approach could be used for
3.5-7 MHz. My elements are fan shaped, so they are inherently more
broadband than the SteppIR elements, so that helps with reactance swings.|
I use 3 very hi-Q coils that uses relays to rough-tune the inductance in 8 steps. Only one coil would be needed for 80/40. The coil Q is well over 500, putting the loss at less than 1 ohm on all bands. In series with the coils is a variable transmitting cap that allows fine tuning of the inductance. The variable cap uses a split-stator design, so there are no moving contacts. Even though the coil combo has to be a little larger than it would be without the cap, the ability to use large fixed coils more than offsets the minimal extra loss that would otherwise be associated with smaller, or toroidal coils.
It also allows for very fast tuning. The combination of the relays and the stepper driven cap allows me to tune from 14 to 30 MHz in <200 msec using a PIC microcontroller. On receive I use a broadband active phasing technique to acheive 3-el yagi performance down to at least 7 MHz, and useable F/B down to 3.5 MHz. The idea is to provide excellent all-band rotatable receive performance, as well as decent 14-30 MHz transmit performance. Scaling the design to cover 3.5 -7 MHz would result in 60' elements, and would provide very good receive performance down to 160m as well.
I will tentatively be publishing an article in QEX on the entire project. They already have the article in hand on the mechanical design and receive circuitry, and are awaiting the final section on the transmit controller.
More info on all this on my website at www.telepostinc.com/n8lp.html
73, Larry N8LP
Mirko Sibilja wrote:
_______________________________________________As for 80m yagis, as far as I recall Titanex sells (among new products) so called "motor driven" 80m and 40m 2 el yagis. I think they use the same approach as SteppIr, but don't know any details except I saw pics and prices at their web site.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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