The utility of Elecraft's CP1 bi-directional coupler with the tinySA

Set-up for measuring spectral output of 100W rig. Note the 100W dummy load behind the tinySA

This is an example of where the availability of a new item adds value to something that's been around a while. The new item is the tinySA - many hams now have one of these small spectrum analyzers/signal generators - and the old item is Elecraft's CP1 bidirectional coupler.

Questions I get whenever I post something related to the tinySA are:

• Can I use it with non-QRP equipment?, and
• How do I measure a transmitter's output to make sure I don't exceed the tinySA's 6dBm (4mW) max input?

I decided to use my tinySA ULTRA to measure the spectral output of my Yaesu FT-891 when operated at full power: 100 watts.

tinySA ULTRA in Spectrum Analyzer mode, with Index QRP+

I'm really liking the new ULTRA and am finally using it as a spectrum analyzer instead of just a sig-gen.

The new Index QRP+ has been daring me to measure its spectral output - and the ULTRA's latest firmware supports storage of the displayed traces as a bitmap file, saved to an included 32GB MicroSD card.

A combination of Elecraft's bi-directional coupler and my step attenuator knocked its 10W output down by 40dB, to 1mW.

For some reason, I saw no harmonics on 160, 80 or 40 meters so I brought out the big (comparatively) Rigol. Same thing - and something I need to investigate. Surely, there are harmonics being generated on these bands...

Incidentally, I looked at the other bands on the Rigol as well - the displayed traces were practically identical to those of the tinySA ULTRA.

So why buy a Rigol instead of the tinySA?

Video: Checking (and comparing) receiver sensitivity with tinySA ULTRA

Soon after the original tinySA was offered, I made a video showing how to make an MDS measurement of a receiver by using the tinySA in 'Signal Generator' mode. But with the tinySA's minimum output being -76dBm (almost S9), a lot of external attenuation was required to get the signal within range of typical MDS values.

The new tinySA ULTRA has a minimum output of -123dBm, making it much easier and less expensive to make the same test. And with less clutter since less external attenuation is needed - actually, none, other than the step attenuator you'll need anyway.

You can see the original video here.

A former co-worker of mine verified the output level accuracy of my tinySA ULTRA with an HP power meter and found it to be within 1dB of its indicated value on HF down to -100dBm. After that, inaccuracy increases to 3dB at -123dBm.

So, with the output set to -100dBm, and a 0-62dB step attenuator, I did a quick by-ear comparison of my new Index Labs QRP+ to my IC-705.

Tale of two spectrum analyzers: tinySA vs. Rigol DSA-815, looking at IC-705 IMD

After yesterday's IMD measurements of the (tr)uSDX, I decided to have a look at the IC-705's IMD characteristics with two spectrum analyzers: a Rigol DSA-815 and the tinySA.

More than anything else, this comparison seems to help justify the purchase of the upcoming tinySA ULTRA - not that I need much help in that department.

As expected, third order IMD of the IC-705 was about 30dB down from the injected frequencies on both SA's, but...

...with the lowest resolution BW of the tinySA being only 3 kHz, it was unable to distinguish the RF representation of the two audio frequencies, seeing them only as one signal rather than two signals 1200 Hz apart (700 & 1900 Hz).

Measuring MDS with TinySA, RMS multimeter and attenuators

The popularity and low price of the nanoVNA and TinySA devices allow hams and other radio hobbyists to make measurements that were out of reach just a few years ago due to the expensive equipment required.

For those who have a TinySA, you not only have a spectrum analyzer - you also have a surprisingly accurate signal generator.

With a series of attenuators, a TinySA, RMS multimeter and some cabling, I had all I needed to make an uncalibrated MDS measurement of my radios. Maybe you do too. Here's how to do it.