Re: [TowerTalk] 2 element 40m steppir yagi

[Jim Lux <jimlux@earthlink.net>]

At 07:26 PM 10/7/2004 -0400, Larry Phipps wrote:
> 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

Very nifty...

Very clever how you separated the receive and transmit functions. 

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