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Dave

I suggest keeping this surgery within your comfort zone.? Nothing sacred about surface mount parts, but at 45 MHz keep connections short.? I am not yet considering this particular mod - but you could consider using a small daughter board connected with leads to main board.? At the moment with lower bands doing the best - I suggest the LPF filter relay issue is a bigger deal.? Here in our club build we are adding 3 relays on a daughter board.?

I have been trying the approach of using an added xtal filter at C22 - while it corrects spurious we find it inhibits CW transmit power on 40m.?

I suggest insuring your work can be reversed if correction is found not to work well enough - been there, doing that.?

73 Curt

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.

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.

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.

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

>From my personal experience the RF Explorer seems to be good at the
harmonics.? I have measured the 3rd harmonic at the same levels as reported by others (between 35 and 40 DB down), which gives me confidence on that front.? I have not been able to measure the reported spurs on bands above 20 meters.? Makes me question the usefulness for that measurement.
The minimum bandwidth setting is 112khz, which is broken into 112 segments so that each segment is 1khz wide.? That is then measuring only 112khz of the spectrum.? If you open the bandwidth to cover more, the resolution goes down.? So that for a 1.12mhz bandwidth, the resolution is 10khz, and so on.? What ever is displayed can only be divided into 112 discrete measurement intervals.? Based on that spec, it should work.? I just have not been able to see the spur.? More likely an error on the operators part.
Overall I am not disappointed with the device, it is 1/8 to 1/10 the cost of a Siglent or Rigol.? It is also portable (the main selling point) so that you can use it in the field.? However, If you are going to get really serious on RF measurements, then it may not be enough.
Above is my opinion/experience.? Yours may vary.
73
Evan
AC9TU

I too looked at that Rigol.? My perspective is if I am going to spend that much, I might as well go all in and get the units that include the tracking generator.? Depends on how you will be using it.? Just to check for spurious emissions, or want to look at filter responses, detailed design analysis, etc....? There is a reason for the tracking generators.
The unit you listed would handle the uBitx emissions testing.
More on the RF Explorer:
If you connect to a computer and use the software, it is really easy to shift scanned start and stop frequencies.? I will look again later this week (I am traveling on business and will not be able to "play") and let you know if I learn any more.? Will also try to take some pictures of the software to show you how it works.
Maybe we need to take this off of the reflector and do it with private emails.
My opinions only
73
Evan
AC9TU

If you want to pursue this, what you really need next is a step attenuator:
Kees is on the forum, he has a nice one here, kit #13 for $15:
And a whole bunch of other stuff you could spend that $165 on.
The RTL-SDR will be fine to learn with, a much better choice if you plan to
burn out the front end with that transmitter.? (I assume you also have an up-converter,
since those DVB-T dongles only down to around 30mhz.)
If you wind up with a $2000 spectrum analyzer someday, you will still need the step attenuator.
Yup, red flag that they say nothing about dynamic range on the RF Explorer, that's pretty basic info.
Manual is under Documents here, describes a bunch of different versions of the RF Explorer:

Page 46 of the manual has a table showing "Measurable Input Range" when using various
external attenuators, the figures they give are consistent with an 8 bit ADC (a 40dB dynamic range).
??
Get the vague impression elsewhere that it can see stuff between roughly -115dBm and 0dBm,
but that could be done with an 8 bit ADC and a variable gain amp.
So a very red flag.
But I could be wrong in this, look forward to hearing further from those that have one.
Jerry, KE7ER

I read something in an ARRL publication about getting around that 40 dB dynamic range problem. Maybe by W7ZOI or W1FB. But it almost wants a spectrum analyzer to set it up. So it's a circular solution. Circular means chasing your own tail :) If you have a spectrum analyzer to set it up why do you need the toy analyzer?

It might be doable without a second SA.

If anybody can remember more about this 40dB dynamic range get around, I'd be very curious.
Can't imagine how you would set up an 8bit ADC to get around the dynamic range problem.
Seems the only path is to somehow filter out the strong signal(s).
Would be interesting to tear apart an RF Explorer.
I'd half expect to find a DVB-T dongle buried in there somewhere.
An RTL SDR plus upconverter and step attenuator can be a very useful "toy".
Even if it only has a 40dB dynamic range.
Verifying that spurs and harmonics from a uBitx are at least 40dB down
is about good enough for a 10W rig.? Much better than just hoping.
Educational too.
Jerry
On Mon, Jan 21, 2019 at 08:17 AM, Bill Cromwell wrote:
I read something in an ARRL publication about getting around that 40
dB dynamic range problem. Maybe by W7ZOI or W1FB. But it almost
wants a spectrum analyzer to set it up. So it's a circular solution.
Circular means chasing your own tail :) If you have a spectrum
analyzer to set it up why do you need the toy analyzer?
It might be doable without a second SA.

The work-around I saw was using a notch filter to reduce the carrier a specified or known amount. The idea being the carrier is reduced going into the SA but the harmonics are not. Obviously close-in spurs are attenuated too. So it's not good for measuring those unless they are really gross. Nothing is done to the ADC.

The trick is to assure we reduce the carrier without reducing any other part of the spectrum. A good spectrum analyzer with a tracking generator could do that. It would be needed each time the 'trick' was used and adjusted. We might be able to do that but it seems like more of a headache than it's worth. I would have trouble trusting the notch.