[TowerTalk] 2 element 40m steppir yagi

[Larry Phipps]

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.
>
>Mirko, S57AD
>----- Original Message -----
>From: Michael Tope <W4EF at dellroy.com>
>To: Al Williams <alwilliams at olywa.net>; towertalk <towertalk at contesting.com>
>Sent: Thursday, October 07, 2004 7:39 PM
>Subject: Re: [TowerTalk] 2 element 40m steppir yagi
>