I've been using a Diamond CP-6S as my main shortwave antenna for quite a while now, and while it can hardly be considered ideal, it's been a decent performer given its relatively short size. Tuning can be a bit finicky especially on the lower bands, but that's to be expected. The system works on the 80 - 40 - 20 - 15 - 10 and 6 meter bands, and the secret that allows it to do that is of course the coils that are used, together with a matching network located in the base. Although a short antenna like this will never be able to compete with a full-size dipole or even a vertical, an afternoon of careful tuning (NanoVNA highly recommended!) results in an acceptable SWR on all 6 bands.
However, mechanical complexity unfortunately also increases the risk of failure, and I've had a couple of issues here and there. Below are some tips and tricks that may help you if your CP6 is misbehaving...
Broken coil leads and connections
The design of the coils in the radiator allows for a bit of internal movement, so the fact that the coils can be moved does not necessarily indicate a problem. If however one or more bands suddenly stop working or return a bad SWR reading (again, having a NanoVNA will help), it's time to have a look inside. Due to its position, the first radiator coil is the most likely cause of (sometimes intermittent) issues. In their infinite wisdom, the Diamond engineers have chosen to use rivets in stead of screws, so a bit of drilling is required to take the coil apart. If done carefully, the same holes and some RVS screws can later be used to put everything together again.
So what's inside?
Removing the outer shell reveals the coil inside, which looks like this:
Carefully inspect all solder joints, and reheat / repair any broken connections. Also make sure to check the rivets that connect the coil to the radiator:
Reassemble the coil and recheck SWR. With a bit of luck, repairing only the lower coil fixes the issue. If not, please proceed to the next coil and repeat :)
High SWR on all bands
Another issue to check for is the matching network in the base. As shown in the pictures below, the ground connection at the connector failed, which led to a high-SWR reading on all bands. Unfortunately removing the matching network also required some drilling:
The failed ground connection in closeup:
Repaired the broken connection and added a bit of flexibility:
These have been all issues I've encountered with this antenna so far. If you have any questions please leave a comment!
