Re: Harmonics and Relay Replacement
toggle quoted message. . .
I've just finished the tests up through 20 meters and it's only 40 that I have any issues with.
Test parameters - since the power output gets lower the higher in frequency you go, on each band I set the SA so that the carrier was on 0 dB each time I changed bands. My rf pickup is from a 50 ohm dummy load through a voltage divider to the SA to keep input below +30 dBM.
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
I didn't test 17, 12 and 10 meters at this time but I suspect their harmonic suppression is in the same boat as the rest.
I did do a quick test on 20 meters with 1KHz tone into the mic jack (I'm a CW op and don't keep a microphone in the shack), power out about 7 watts, SA set so carrier was 0 (top) of screen and got basically the same results - 2nd harmonic @ 28 MHz was -65.0 dBC and 3rd @ 42 MHz was -63.9 dBC, very close to the same as I got for CW. There were a few spurs that showed up on the 20 meter test, but they were all -80 dBC or better (I do have the 2nd 45 MHz filter in place).
It appears that the Axicom relays DO provide a significant harmonic reduction over the originals used. ( Except for 40 meters on MY uBITX board. I suspect there is something else in play there that I need to track down). I still need to swap relays on the 2nd board and check it but as I said earlier that will be most likely tomorrow.
Jim Sheldon, W0EB
From: "Gordon Gibby" <ggibby@...>
To: "BITX20@groups.io" <BITX20@groups.io>
Sent: 10/10/2018 2:37:30 PM
Subject: Re: [BITX20] Harmonics and Relay Replacement