[Linrad] Re: SDR-IQ Birdies

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Guy,

> Pickup is through the antenna from something radiated inside the
> shack. It appears that the SDR-IQ is the source of this interference,
> which can be reduced somewhat by several clip-on ferrites on the USB
> lead close to the SDR-IQ. The USB plug is too large to pass through
> any of the ferrite rings I happen to have on hand, though I could
> obviously buy some larger ones.

I suggest you wrap your SDR-IQ carefully in aluminium foil and
remove the outer plastic from the two cables entering the unit.
They are both screened and you should make a good connection
between each screen and the aluminium foil.

This way you will eliminate any voltage difference between the
two cables leaving the wrapped unit and you will also eliminate
any voltage between different points on the foil. All currents
will flow inside the enclosure and you should easily reach 60 dB
attenuation. More aluminium will improve until the limit that
is set by the leakage through ths screen of the USB cable.

Make a small wire loop and connect to the 144 MHz input. It
could be one turn with 20 mm diameter. When you place that loop 
against the various conductors in your setup you will easily see
where currents of the interference frequencies flow. Once you know
where the currents are it will be reasonably easy to do something 
about them (as long as they are inside your own house...)

73

Leif / SM5BSZ


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