RaDAR contest - Nov 2011

I have just returned from taking part in the RaDAR (Rapid Deployment Amateur Radio) event. The RaDAR event is a fun activity designed to test one’s ability to rapidly erect a small field station and to operate independently from normal power sources. Ideally the entire station must be transported by human power to the operating site.

I chose to use my homebuilt K2 transceiver a small 6AH SLA battery and a link dipole antenna. I operated both on CW and SSB. All the QSOs were made on 40M. For some reason most participants are hesitant to try the higher bands.

The event took place over 6 hours, but after 2 hours I had enough of sitting flat on the ground and decided to call it quits.

I did manage to make 34 QSOs, 28 SSB and 6 CW QSOs. There is something very special about working CW, whilst being outdoors.

I was hoping to make a few DX contacts on 10M, but my untested antenna seemingly had a high SWR and I did not want to subject the K2 to this. Pity, since the 10M band seemed to be alive with CW activity.

Had fun all the same….

      

Advantages of EFHWA over Dipole antenna

All the discussions pertaining to EFHWA and the ZS6U Mini Shack Special might create unrealistic expectations of the performance of one being better than the other.

A dipole antenna is a dipole antenna. It does not matter if the dipole or ½ wave length wire is fed at the center or at the end or anywhere in between. The only difference is the impedance at the feed point.

In the case of the traditional center fed dipole it has an impedance of around 70 Ohms and that normally suits us nicely with a reasonably good match between the antenna and the coaxial feed line and our transceivers without the need of an ATU.

When the same ½ wave length antenna is fed at the end as in the EFHWA then the impedance is very high in the order of 5000 Ohms. This in turn means we must use some form of antenna matching unit to transform the impedance to 50 Ohms.

What is the advantage of the end fed half wave antenna (EFHWA)??

An EFHWA cut for 40m is approximately 20.8 metres long and will work on the 40, 20, 15 and 10 metre bands and on 80 m at a push. The normal center fed dipole of the same length will work on 40m and on 15m at a push, and that is all.

The EFHWA does not require a feed line. In ultra light portable operation this is a big issue. The coaxial feed line is heavy and cumbersome.

Colin mentions that the capture area advantages and I tend to agree with that thinking as well.

When using the EFHWA we must still strive to place it as high above the ground and clear of surrounding objects as possible.

There is no free lunch !!