In this post, I'll give information about the initial testing results of the Serial No. 141 V2 sBitx as received.
The testing setup was very similar to that used in the validation tests with the Icom 718? ? The coaxial cable to the radio was a BNC double-shielded cable with appropriate adapter to allow it to connect to the Radio Shack ancient SWR/power meter.? ? The MFJ power supply was set to approximately 12.9 VDC based on its front-panel meter, which has been generally accurate when compared to a digital VOM.? ? Morse code was generated using an external key.? ?
without any further adjustment of the received unit, here were the values recorded:
MHz? ? ? ? Fundamental? ? ? ? ? ? ?Any notable Spurs? ? ? ? ? ? ? ? ? ?2nd harmonic? ? ? ? ? ? ? ? ? ? ? ? ? ?3rd Harmonic
3.510? ? ? 20W 75% -20.9dBm? 5.48MHz -69 dBm? -48dBC? ? ?7MHz -63.5dBm -43dBc? ? ? ? ? 10.5MHz -77 dBm? ?-56 dBc
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?among others?
7.010? ? ? 20W? 72% -21.5dBm? appx -66 dBm or less? ? ? ? ? ? 14MHz =59dBm? -37.5 dBc? ? ? ?-65 dBm? -43.5 dBc
14.01? ? ? 20W? 78%? ?-21.3dBm 8.9MHz? -63 dBm? ? ? ? ? ? ? ? ?28MHz -48 dBm? -27 dBc? ? ? ? ? 42MHz -53dBm? -32 dBc
21.01? ? ? 15W? ?86%? ?-22 dBm? ? ?approx --56dBm or less? ? ?42MHz -43 dBm? ?-21 dBc? ? ? ? ?63 MHz? -52dBm? ?-30 dBc
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? (uncorrected measurement)
28.01? ? ? 12W? ? 40%? ? -23 dBm? ?around -66 dBm? ? ? ? ? ? ? ? 56 MHz -60 dBm? ?-37 dBc? ? ? ? ?84 MHz? -73 dBm? ?-50 dBc
(any higher and non linear)? ? ? ? ? ? (uncorrected measurement)
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ??
These data were obvious of considerable concern.? ?Particularly the existence of a fairly strong SECOND harmonic.? ?Balanced push pull circuits are supposed to null out a second harmonic.? ?This suggess the amplifiers of one or more stages at not well balanced.? ? ?The Third harmonics of some bands are above spec.
Here is a photograph of the testing situation:
And here is one spectrum observed :
Here are the uncorrected results from the Siglent:?
Based on these results, I decided a change was needed to the radio, to be detailed in the next post.
Gordon L. Gibby KX4Z
