attached, please find a picture that gives an impression of how much smaller the 5m DAM carbon pole is in comparison to the masts from lambdahalbe.de.
1. 6m lambdahalbe, 603 g
2. 5m lambdhalbe, 420 g
3. 5m DAM Pocket Pole, 213 g
Of course the open question is how well the carbon fiber masts will work with vertical wire antennas. Theory tells us that we might face a couple of problems, at least one of the following:
- The antenna wire might be coupled capacitively to the conductive mast, shifting the impedance and possible creating a shunt to ground if the mast is not properly insulated from ground.
- RF might be reflected from the mast and cancel out RF from the antenna wire (in the sense of an "image antenna").
Given the improvement in terms of weight and size, I am seriously interested in learning
a) how significant the effects are and
b) whether we can mitigate them.
For a), I plan to set up two identical wire antennas for 20m and attach them to two WSPRlite devices and measure the difference. I already did a few tests and got quite acceptable results. Without a systematic approach, however, they are not very useful.
On the Web, there is a wide range of opinions about carbon-fiber near antennas; many quadro-copter fans report problems with antennas behind or near carbon-fiber parts (but then again, they work at 2.4 GHz, and the materials used might be very different in terms of geometry and resin vs. carbon ratio etc.). Also, the rod elements are much thinner. Some hams report no problems except for a slight detuning.
Should the problems be significant, one could think of the following countermeasures:
1.Vary the distance between wire and mast, e.g. by attaching it close to the rod vs. using small spacers or sloping it slightly.
2. Insulating the lowest segment by adding a layer of shrink tube.
3. Connecting the rod to the wire electrically so that it becomes part of the radiator (but then again the question is how well the joints between the segments form an electric connection).
Any ideas and experiences will be very welcome!
73 de Martin, DK3IT