I can't figure out what this is on 20M...or why it's happening


#21

Hi @Kc7noa and @M0GLO,

I know I’m reviving an old thread (1 year ago…), but I’ve two questions close to that topic about shielded case. If I put a lime in a pc case (a full pc, with motherboard, cpu, etc.), whether it is the USB or the PCI-E version:

  • Does the pc case makes a good shielding against external interferences?
  • But, on the opposite, should the cpu, the ram &co be considered as bad generators and should I protect/shield the lime from them? (which will be easier for the USB version than the PCI-E one).

I precise I am working on 433, 2400 and 5800 MHz bands mainly.

Thanks you for your advices!


#22

If you mount it inside the PC case you are mounting it in a box WITH half a dozen other oscillators, a switching power supply and sharing ground with it all.
That will create a ton of noise and various computer related lines moving and snaking across your waterfall and raise the noise floor a good 20db at least.

You CAN do this if you also put it in a shielded box of its own and float the ground out through the antenna shield and onto your outside ground rod without letting the radio box ground on the PC.

As for the PCIe version of this, great question. If it is used as designed for the purposes it was designed for (IoT, WiFi, Broadband and LTE development and relay use) then it doesn’t matter but if you are a SWL or HAM type then finding a way to shield it in socket is going to be a prime objective.


#23

Thank for the quick reply, to which I fully agree. A question though: why must the PC ground and the lime ground distinct?

In parallel, I’ll compare the noise level of the USB and the PCIe seating together, with no specific shielding. That will be an interesting test.


#24

Because the case is only electrically grounded and no RF grounded so it still transmits a lot of the noise.
One thing I did that helped a lot with a noisy laptop I had last year was to remove the USB shield at the radio side, this allowed the cable shield to remain working as a shield up to the case of the radio but not to transmit the horrid power supply noise to the radio. I still got some noise from the connections but it was a lot quieter overall and it really helped with the wandering wide band lines around 158Mhz that were coming from my screen.

I haven’t seen the PCIe boards traces but on the USB version there is a ground trace around the RF section, this allows the intrepid experimenter with soldering skills and a need for absolutely the best performance they can wring out of this thing to build a box shield where either there are connectors on the lid passing through or the wires themselves pass through for the case connectors.If there is a similar ground trace around the RF section that would be the way to isolate it from the noisy PC environment, you’d be stuck with any electrical noise on the power of course but you’d eliminate the stray RF in the cabinet from it.