Jim W0EB has finally received his >500 mW Axicom relays, after they got misrouted in the mail.
H plugged these into his V4 test bed built up on an aluminium open chassis. Sockets are mica filled 2mm thick with silver plated flat contacts. This leaves the relays 2mm above the PC board.
With the >500mW coils (i.e. with coils that have fewer turns on them) the hope was that this would lessen the extent of inductive coupling between the switched portion of the circuit and the relay coils. Unfortunately this does not appear to be the case. Jim got almost exactly the same results as with the 400 mW relays mounted the same way.
40 meters is still just barely in spec with the 3rd harmonic being -43.8 dBC. The others are also in spec but not much better with 3rd harmonic varying from -46 dBC on 10 meters, -44.5 dBC on 12 & 15 meters , -44.7 dBC on 20 meters and -57.3 dBC on 80 meters. 60 meters wasn’t tested.
Raj VU2ZAP notes that it makes quite a difference between socketed an unsocketed replacements. It is best not to use sockets for the relays, in order to get the relays as close as possible to the PCB.
Before and after shots of relay replacement as observed by Raj follow:
Raj and Jim both note that there is variation between boards in terms of improvement in performance. The reasons for this are not known.
The conclusions are:
- relays help, and ubitx.net recommends them, but replacing relays with AXICOM relays may not always be sufficient to reduce “blow by” on some bands or modes
- there is no point in spending more on Axicom relays with a higher coil current
- the best option would be to replace the filter section altogether, and there are a number of ways of doing this.