Antennas info

On these pages i would like to share with you some info about  ham radio in general but mostly homebrewing antennas,which is still after all these years my greatest passion.

In the photogallery you will find some of my antenna projects in the past and antennas i use untill today.

Latest antenna project : summer 2015

PHASED DELTA LOOPS 3.5 - 3.8 Mhz (see picture above)

This summer i took down the four square ( the tilt over towers all still on place) for 80 meters ,because i just wanted to try something else and see how well this would work.

I played around a bit with Eznec and decided to put up an two element delta loop ( beaming South-Nord).

After reading in Low band dxing (ON4UN) i was convinced.

I use a simplified version of the ON4UN feed for my 80 meter delta loops, which are ideally equilateral triangles that have their apices up at 70 feet and base legs about 10 feet off the ground. The apices are spaced 25 feet apart, with the bases spread to a distance of about 55 feet. The feedpoint impedance of a loop is close to 100 ohms. Each feedpoint runs to a central switch. There are baluns at each loop feedpoint to isolate each antenna from it's feedline. Standard feeding calls for a 1⁄4 wave matching section of 75 ohm line before connection to 50 ohm coax leading to the rig. The non driven element is loaded with ~110 ohms inductive reactance to make it act as a reflector. The pattern is switchable in two directions broadside to the loops. Each loop is fed 1/4 wavelength from the top, which works out to about 10 feet up from one corner.

After some google work i found a nice article from K1KP.

New stub method for tuning down to 3505 for CW. 

I did add at each loop a stub of wire (spaced just 45 mm attached at middle of base, supported parallel to ground by cord towards the main tower. Other end is closed. This lowers resonant frequency nicely for CW. Stubs are about 5 m long. Stub can be switch in or out with small relais, so switching between CW and SSB is done in the shack.

The K1KP Feed Method

Uses the length of coax from the feedpoint to the relay box for inductive loading of the reflector.

Coax sections from feedpoints to the relays are lengths of RG-11/U foam (with a higher velocity factor than non- foam coax) coax, (10,92m or 36 feet) long. The switch is a relay that selects one feed as the driven element. 4,85m or 16 more feet of RG- 11/U foam coax after the relays adds to the 10,92 m or 36 feet on the driven element to form a quarter wave matching section, yielding a 50-ohm impedance for the coax to the shack

The relay also shorts out the end of the other 10,92m or 36 foot feedline forming the reflector. The shorted 10,92 m or 36 foot coax line functions as a loading inductance to lengthen the electrical size of the loop in use as a reflector. Current implementation uses Dow-Key relays for switching. 

I can reports reasonable flat SWR and detectable gain over the single loop with this system, which is fairly close spaced (average distance = about 1/8 wl) as parasitical systems go. It represents an ingenious way to switch beam directions and simplify feedline requirements without sacrificing performance from the wire array.

F/B is always 15db or better, can approach 25 db at best point. 

In summer its always difficult to evaluate antennas for the lowband,but i have been working quite easy into ZS,VK,ZL (and even JA in the first week of august).

I just know that this system will give me a lot of fun in the next winter.

 

Thanks for reading 

OT4A Theo