Yesterday myself, Andrew, Graham, Rex, John and John spent the day at the Chantry renovating the club’s antenna systems.
Our plan for the day was to inspect the existing antenna systems, replace a section of coax between the attic and balun and to install and tune the new 40m dipole.
Condition of existing antenna systems
Existing 40m dipole balun
The overall condition of the existing HF antenna was good, but clearly the self-amalgamating tape has suffered from UV degradation. This doesn’t appear to be a major problem however the antenna has only been up roughly 4 years, so the problem would get worse over time.
Existing VHF Co-linear
While on the roof we also inspected the existing VHF antenna. It is clear that it is not ideally placed, being blocked by the chimney stack as well as the Chantry’s satellite dish.
Replacing the coaxial cable
One of the jobs for the day was to replace the RG-58 coax run between the attic space and the existing balun with some superior Westflex 103. In order to do this, Andrew and myself had to climb into the attic in order to cut the existing cable and solder new UHF connectors onto it. This allowed us to replace the cable between the attic and the antenna. On completion we measured the loss through the cable using a 50Ω dummy load and power meter.
New Westflex 103 cable run
We measured the loss at just under 3dB at 7mHz. We measured 60W at the end of the cable with a 100W input. Currently we plan to improve this loss further by replacing the rest of the cable to the shack
Andrew getting ready to test the loss through the new cable
Installing and tuning the new 40m dipole
With the new coax installed, we now set to work installing the new antenna. Before we could putt the new dipole in place we had to let down the existing antenna. As the two ends were attached to trees, I volunteered to put my tree-climbing skills to use and lower the existing elements
Rex giving us a hand getting up the trees
With the antenna on the ground we attached the new dipole and hoisted it into the air. Following some tests with Andrew’s MFJ antenna analyser we deduced that the elements were too long. Following several rounds of tuning we reached a state where everyone was happy with the performance of the antenna.
New balun installed
We sealed the connections with self amalgamating tape and headed to the shack to have a listen to the band.
Performance
| Frequency (mHz) | Resistance (Ω) | Reactance (Ω) | SWR |
| 7.0 | 60 | 8 | 1.2 |
| 7.1 | 78 | 0 | – |
| 7.2 | 112 | 0 | 1.5 |
We also tested the SWR in the shack and measured an SWR of 1.4 at 7.2mHz. A quick sweep of the band picked up some loud and clear Morse, although this may be due to a contest that was running at the time.
Conclusion
We hope that the new 40m dipole continues to deliver excellent results. There are still improvements that need to be made to the club’s antenna systems, including:
- Adding the two other elements (30m and 20m) to the fan dipole array
- Replacing the coax run between the attic and the shack with lower loss cable
- Deciding on an effective way to relocate and improve the VHF antenna system.
I’d like to thank Andrew G0RVM, Graham, Rex G4RAE, John M3EQQ and John M0HFH for giving up their time yesterday to help the club. I had a great day and learned a lot throughout the process.
Peter Barnes
2E0UAR
