SDRplay Community Forum

Hi All,

Have homed in now, entirely, on (trying to) learning to use SDRUno, rather than the other SDR programs
that are available.
Do listening only, which i enjoy a lot, but have lots of fairly basic questions.

Great Forum(s), and truly appreciate all the help I've received.

Have a RSP-2, and a Scantenna up in the attic for >30 MHz.
A long wire antenna, and a coax feed from into the house, and then that NooElec B1:9 Balun for the <30 MJz items.

Regarding the noise floors I see on the specrum waterfall:

When using the Scanner (what a terrific addition), or looking at sw items >30 MHz, my noise
floor, and it varies quite a bit of course, seems to be typically around -120 db using ANT A and the attic Scantenna.
Is this a "reasonable" noise floor ?

And for the outside long wire antenna ending up in the the HiZ input, it seems to vary
between -80 and perhaps -110 db
Again, is this "reasonable" ?

Have ordered a bunch of clip-on Ferrite Chokes, and when i receive them, I'll play around
with them on various wires.
My understanding is that they can/should go on most wires, but "primarily"
they are for the wires that are apparently actually radiating the noise.
True ?

Thanks for the help. Lots to learn,
Bob

Hi Bob and welcome.
I'd say your noise levels are fairly typical. Long wires are very prone to local noise, and with every one having their homes crammed with digital electronics these days things are getting worse. One major source of noise which has appeared more recently is VDSL, which appears in certain bands. One of the bands starts at 8.5 MHz and here I can see a step upwards in noise of about 20 dB at this frequency. There's nothing I can do about it as it seems to come from all directions, including our own home (we are on VDSL from the local BT cabinet).
Clip-on ferrites can help on USB cables (put one at each end) and sometimes on antenna coax feeders, but you'll need more than one ferrite to get enough effect at the lower frequencies. Large ferrite rings with the coax wound through several times are better for the lower bands.

Hi,,
Much thanks for info.

Glad to hear that my noise floor(s) are "typical".

Will try out the ferrites as soon as they arrive.

Followup Question:

I have a very cheap USB 2 cable that I got from Amazon, and that is what I am
presently using from the RSP-2 to the pc.

But was wondering:

Is this cable likely "shielded" ?

And, do you know of a really good one that is single or double shielded, for sure ? (USB A to B)

Amazon does not do a good job is describing whether these USB cables they offer are shielded or not.

BTW: If you are not using CSVUserListBrowser with SDRUno, do take a look.
It works very well with.
Terrific, free, program.

Regards,
Bob

Re the usb lead, I've heard the Trip-Lite ones are quite good:

https://www.amazon.co.uk/Tripp-Lite-U02 ... B003MQ29B2

They have a ferrite at each end so they radiate less hash.

It's also worth experimenting with your earth (ground) system, as ground loops can cause terrible noise injection.

It's also worth experimenting with your earth (ground) system, as ground loops can cause terrible noise injection.

Through experimentation I have found that antenna grounds that are also used as equipment grounds can inject a lot of noise into a receiver. As a result I keep the grounds separated and use an RF isolation transformer. If one does not install an isolation transformer the antenna ground becomes an equipment ground and is in parallel with any other equipment grounding conductors creating a ground loop.

A very good tutorial on dealing with noise, ground loops and ferrites:

Chokes and Isolation Transformers For Receiving Antennas http://k9yc.com/RXChokesTransformers.pdf

Above Red Line: RF Isolation transformer in circuit:
Below Red line:Ground loop created by bypassing ground around RF isolation transformer:
The horizontal streaks are due to distant thunderstorm activity. Primary noise source, among others, is the PC's SMPS

Mike2459 wrote:

It's also worth experimenting with your earth (ground) system, as ground loops can cause terrible noise injection.

Through experimentation I have found that antenna grounds that are also used as equipment grounds can inject a lot of noise into a receiver. As a result I keep the grounds separated and use an RF isolation transformer. If one does not install an isolation transformer the antenna ground becomes an equipment ground and is in parallel with any other equipment grounding conductors creating a ground loop.

I've done the same. All my receivers (I have a few as you can never have too many...) are fed via homebrew isolating transformers wound on binocular ferrites. This got the noise down by 10 to 15 dB, especially at LF, which is one of my interests.