"birdies"... how to minimize them

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"birdies"... how to minimize them

Post by N4TKO » Tue May 31, 2016 3:56 am

i've been noticing that there are often "birdies" showing up on the display. for anyone who doesn't know what this is, it shows up as spikes on the display, and dead (or regularly pulsing) carriers at the frequency of the spike. this is not to be confused with external spikes from noise sources like SMPS bricks or TV hash. these spikes don't go away when you disconnect the antenna, and are caused by things going on internally to the SDR. a "birdy" gets it's name from the chirp as you tune past it. most radios have them, and some model radios used to have a chart in the owner's manual explaining what they were, and what frequencies they were at. because most of the parameters that were fixed in regular radios are variable in an SDR, there really isn't a good way to predict their frequencies or how many there are. most people have probably noticed spikes at multiples of the sampling frequency, and this is one source of them, as well as other things going on inside the radio. one thing i found that a)reveals them for what they are, and b) can help eliminate, or at least minimize them (or even just move them out of the way if they are on top of a wanted signal) is to bump the hardware center frequency by 10 or 100khz, (best to do this with the spectrum display unzoomed, so you can see where they are across the whole bandwidth), and watch which spikes disappear, and if any others appear. bumping the frequency a few times might get you no birdies, or one or two that aren't in your way... gqrx doesn't seem to have an IF shift option, so most of my experimenting so far has been zero IF.
Last edited by N4TKO on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Posts: 79
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Re: "birdies"... how to minimize them

Post by DK7OB » Wed Jun 01, 2016 7:12 am

On what frequencies do you see them? I am using SDRplay mostly on HF (up to 30 MHz) have no problems.

I read some people had a bit of success with a RF choke on the USB connection (some turns of the USB cable through a large ferrite core)

Wolf, DK7OB
Last edited by DK7OB on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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