Jim Sheldon W0EB has now replaced all stock relays in one of his µBITx transceivers with Axicom D2n 12v relays.
This improved filtering by a wide margin on all bands except 40m. The results:
80 Meters 3.500 MHz
7.000 (2nd harmonic) – 65.7 dBC
14.000 (3rd harmonic) -76.4 dBC
40 Meters 7.000 MHz
14.000 (2nd) -58.0 dBC
21.000 (3rd) – 47.2 dBC
30 meters 10.000 MHz
20.000 (2nd) -76.9 dBC
30.000 (3rd) -75.8 dBC
20 meters 14.000 MHz
28.000 (2nd) -65.2 dBC
42.000 (3rd) -64.8 dBC
Jim didn’t test 17, 12 and 10 meters, but he suspects their harmonic suppression is in the same boat as the rest.
Graph showing results
The graph above provided by Gary AG5TX shows the resultant effects of using Axicom relays (using Jim’s data points).
“Your shared data maybe useful as you have shown the same board and relay with different measured results. For that particular board and the measurement data you gathered, I would say the results ARE encouraging from this viewpoint:
You have 4.5 dBc more margin to FCC spec on your worst case data point (40m 3rd harmonic) with the supplied data set.”
Sourcing Axicom relays
These relays can be obtained from a number of sources. If you live in the US they can be found at Arrow, Digikey and Mouser for less than US$3 each. They are also available from Aliexpress for under US$2 each in a set of 10 and from Component HK in Hong Kong for under US$1 each.
More details on using Axicom relays for RF switching
For those interested in the benefits of Axicom relays see this webpage for a switched Bandpass filter bank:
There are wealth of tips on this page for those building switched filter banks.
It appears that the Axicom relays are the answer, and Ashhar Farhan has already committed to replacing these relays in production µBITx, presumably when the current µBITx stocks have been depleted. Hopefully Raj’s mod for removing spurs will also feature in a v4 board upgrade shortly.