Beams for the magic band
The first steps on the magic band can be done surely with some very simple antennas. But for the very different situation here in DL and maybe a few other sites in the world we are forced to use our 25 W ERP very carefully and the most effective way possible. So using a directional antenna is a must especially when you are interested in DX-hunting. Due to the fact only CW/SSB is allowed (NO FM/Repeater/Packet...) horizontal is the polarization of choice.
Here is a list of different beam antennas starting at the very small and handsome end:
For a great variety of 6m yagis visit the the homepage of Martin, DK7ZB. He designed models of 0,6m up to 14m boom lenght.
Since there is still a restrictive licencing policy here in DL, I am not able to report about the actual transmitting performance, except some short on air testings, forced to use it in receive mode only. Somewhere in the future there will be a time...
The HB9CV - a two element 6m-beam
(construction details according to DK7ZB)
One of the smallest beams you can use is the HB9CV type. This concept is a dual driven antenna (no parasitic elements). That's also one of the reason why this type of antenna isn't considered by the amateur building his antennas himself. I found a rather simple and reliable method to solve this problem in an article published by DK7ZB.
He suggested to use for the phasingline the inner conductor of a RG-213 coaxial cable with the PE-Dielectric and it works great for me. This type of antenna is a rather handsome one, so you can use it for portable operation, add it to your existing antenna arrays with less supporting problems. The datas of 4,2 dBd gain and a front-to-rear-ratio of 20 dB are well worth to give it a try. The VSWR bandwith of 1:1,5 is ~ 1MHz. This small beam is a great solution for Es inside europe.
I built also a 10m HB9CV. The scheme is the same as for the 6m version. A report will follow.
Boom - the short boom is a 25 x 25 mm aluminium square tube
The elements are tapered: the middle section is a 16 x 1,5 mm aluminium tube through the boom prolonged with 12 mm alu tubes.The electrical junction is realized by hose clamps tighten the sliced 16 mm tube.
The distance of reflector to director is 750mm (center to center). The length of the reflector is 300cm the director is 277 cm. The inner part of the elements consists of 100cm of 16 x 1.5 mm aluminuim tubing mounted uninsulated through the boom and hold in place by phillips screws. At the ends the 16mm tube is sliced and the 12mm tubes are inserted and tightened with hose clamps.
The phasing line
The unshielded RG-213 has to be routed in a certain distance on the boom/element. So we need a 5mm-spacing (approximatelly) by means of isolating material (PVC, Plexglass, wood).
The feed point
Due to the remaining reactance you need a capacity to compensate the inductance. For this type of construction a 30pF capacitor is needed. I didn't have the exact value so i used a robust 33pf/6kV russian capacitor that resists the used power easily.
As you see above the rf-socket need to be grounded to the boom. I used the braid from the coaxial cable
If you are using the above mechanic the value of the capacitor of 30pf is just right to compensate the inductive components caused by the feedlines. For final tuning you just change all 4 elements for the same amount for the desired frequency. You can use a variable capacitor also and read out the exact value and replace it later
The above antenna was quick measured with a loaned MFJ-259 B SWR-Analyser. The result was a very broad impedance of 38 Ohms from 50 to 51 MHz. The reactance was unmeasurable.