Re: Spurs/Harmonics fixes for v4 based on v5 board design?

Bill Cromwell <wrcromwell@...>
 

Hi,

I agree with Jerry. I have an RTL-SDR here. It's a fun toy. Signals from off the air overload it regularly. Never mind about being in the same room with a transmitter. It is not good for that kind of work.

Sorry to say but you are fooling yourself.

73,

Bill KU8H

On 1/21/19 12:11 AM, Dave Space wrote:
Possibly.  I'm using a -40db attenuation.  Think it needs more attenuation than that for RTL-SDR?
On Sun, Jan 20, 2019 at 08:43 PM, Jerry Gaffke wrote:
Agreed, spurs on 80m-20m are not a big issue with a stock uBitx.
Harmonics on a stock rig are 30dB down or more, so down in power by
a factor of 1000.
Should be better, but I doubt anybody will ever get into trouble
using a stock rig on the air.
But do avoid the use of an external linear amp.
Avoid using any scheme to goose the mike gain unless you can take
some measurements of spurs,
since increasing mike audio above that given with the stock mike
will disproportionately increase the spurs.
I would tend to question what that RTL-SDR was telling you.
For one, it's only got an 8 bit ADC, so dynamic range is limited to
40dB or so (theoretical max of 48dB).
You would have to carefully adjust the power into the RTL-SDR using
a step attenuator such that your
carrier uses up most but not all of those 8 bits if you want to see
spurs or harmonics that are 40dB down.
My guess is that you overloaded the RTL-SDR.
Jerry, KE7ER
On Sun, Jan 20, 2019 at 07:40 PM, Curt wrote:
Most spurs below 18 MHz haven't been that horrific,  no not 0 dB
down. I can share measurements on my rig later this week, but
several examples are around. Many of us are using the rig on
lower bands while a solution emerges. I would stay barefoot with
the rig, and avoid operating above 20m. The types of antennas
you use also impacts degree of caution. These spurs were be
addressed with affordable solutions in time.
--
bark less - wag more

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