[Linrad] SDR-IQ Birdies

[VK2KU <clearmail.com.au; vk2ku@xxxxxxxxxxxxxxxx>]

I spent some time today looking at various birdies on my Linrad
screen, in an attempt to identify the source of each. By far the worst
are a series of lines centred around 144.153MHz. Each line is actually
a triplet, and the centre lines of each triplet are spaced 1kHz apart.
The intensities fall off on either side of 144.153MHz, making the
whole spectrum from 144.145 up quite difficult to use. This
investigation was prompted by JT1UN operating on 144.150MHz,
fortunately midway beween two of the triplet lines, though Faraday one-
way propagation conspired to frustrate all my attempts to work Jeremy.

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.

Does any other SDR-IQ user experience this kind of interference, and
if so is there an effective cure?

73  Guy  VK2KU
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