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3B7C and 80metres

 

Past FSDXA DXpeditions have allowed us to progressively develop our approach to 80 metres.

Firstly, for those who have never operated in the tropical zone, we should point out that the noise level from atmospheric static is awesome. S9 + 20dB and generally continuous ! This means that the operators are trying to hear YOUR callsign in the brief moments between the crashes of static.

We have tried all sorts of special receiving antennas to try to reduce the effects of the static and improve the signal:static ratio. Most have made little improvement, although for the 3B7C we will be trying sets of phased loops, as well as the K9AY and beverage antennas. In the end, the best filtering for static is the human brain.

On transmit we have come a long way. On 9M0C we started with a simple vertical - the Battle-Creek Special. Then for D68C we tried a full size four-square antenna. This was disappointing and suggested to us that large four-square arrays at 80 are difficult to set up at a new location without test equipment. Our antenna at D68C was clearly sub-optimal.

For 3B9C we tried a different approach. We designed a phased array based on 1/8 wave spacing of two quarter-wave verticals. With the right phase delay in this array, we can get a cardioid pattern which takes in everything from Japan to the US (short path). By simply switching the drive to the two antennas, we can reverse the pattern by 180 degrees, and beam long path. This worked well. On 3B9C we were also hoping to be able to operate on 80m SSB and CW at the same time. However, we were not able to get sufficient spacing between the two 80m arrays to do this.
 

The D68C 4-square

For 3B9C we tried a different approach. We designed a phased array based on 1/8 wave spacing of two quarter-wave verticals. With the right phase delay in this array, we can get a cardioid pattern which takes in everything from Japan to the US (short path). By simply switching the drive to the two antennas, we can reverse the pattern by 180 degrees, and beam long path. This worked well. On 3B9C we were also hoping to be able to operate on 80m SSB and CW at the same time. However, we were not able to get sufficient spacing between the two 80m arrays to do this.

Now on 3B7C we hope this will be possible. Our seaside location has a run of about 600metres of prime beach-side real estate, and we plan to position the two 80m arrays at opposite ends of this beach. With luck, we will get enough attenuation of the other 80m signal to be able to receive well.

We will have two dedicated stations on 80m, each with a linear.  Please look for us on 80, but most particularly, please listen for the operator to say where he is listening. We will generally only be able to identify a callsign fragment to begin with, so please only call if it is you we identify.