for all Dev board addicts -TI Sub-1 GHz RF Spectrum Analyzer Tool for $25

[tinhead]

Btw, about the antenna, although it looks & feels like those detachable wifi antenna, is it the same thing ? I mean can I replace it with bigger one from the wifi router/access point ?

RTFM

user guide, 2.4.1 "Antenna"


A center fed dipole antenna is supplied with the SA430 kit. This antenna works for most applications, but it
has some drawbacks. A dipole antenna is tuned to work best within a small frequency range. The antenna
that is supplied in the kit is a ?/2 antenna with a center frequency of 868 MHz and a recommended span
of 30 MHz. Using the antenna outside this range impacts the level reading.
For better accuracy outside of this frequency range, use a 50-? antenna designed for the intended
frequency range (915 MHz, 315 MHz, or 868 MHz).
However, it is difficult to determine the true level at the transmitter in an RF system, because the transmit
level and the received level depend on so many factors. In most cases, the effect of the antenna can be
neglected, especially during the prototyping phase.


so yes, you can use other 50Ohm antennas, as long they designed for the freq. range of interesst/covered by this SA

wifi router/access point ?

wifi however didn't looks like being in the frequency range, so no.

[Codemonkey]

Also, you might find that the antennas you already have are RPSMA (Reverse polarity SMA). They have the pin on the socket rather than the plug.

[tinhead]

it is interessting to see that the input balun have DC bias (pwm out from µC to OPA237, with ~23V supply from TPS61040) configurable over two varicaps (SOD523, marked P00, no idea what is the part number). From the source code of the DLL i can see that there is way to control that bias ( CMD_SETDAC =  26, // Set the DC value for the balun), however in the app (compiled and sources) itself TI simply haven't used this functionality. What a shame.

Wondering if the firmware itself is provding any DC bias, so if someone can measure it (TP6) please do so.

[BravoV]

it is interessting to see that the input balun have DC bias (pwm out from µC to OPA237, with ~23V supply from TPS61040) configurable over two varicaps (SOD523, marked P00, no idea what is the part number). From the source code of the DLL i can see that there is way to control that bias ( CMD_SETDAC =  26, // Set the DC value for the balun), however in the app (compiled and sources) itself TI simply haven't used this functionality. What a shame.

Wondering if the firmware itself is provding any DC bias, so if someone can measure it (TP6) please do so.

Using just DMM right ?

Curious whats is in your mind about this ? Honestly I've no idea. 

[tinhead]

The balun in front of the TI chip need/can be used e.g. to change frequency matching, which of course can improve accuracy. The circuit need then of course provide dc bias, whcih will be generated by the opamp/pwm combination, which will be controlled by the µC firmware itself. To check in detail it is necessary to compile own version of the UI (sources has been published), add a button or two to send various
CMD_SETDAC values. Then of course would be necessary to measure what CMD_SETDAC value is necessary to get 0 bias and what to get full ~23V.

I received today my TI toy, heh, and shot it immediately. Darwin awards for me, really. I don't work with MSP430, but have some launchpads here, so used one of them as SBW adapter to attached CC debugger to the SA µC. However in hurry i forgot to unselect "load program" and of course the flash got wiped :\ So i can't do any further testing, TI will for sure not provide the firmware file to me. Sure, i still can write own firmware but that was not my intention, the learn what the org. firmware is capable to do was more interessting.

Sure, TI could for sure provide some documenation or description of that CMD_SETDAC (and maybe as well the CMD_SETFREQ), but they didn't in first place so i doubt (i saw some replies from their support engineers on ti forum, ehm, yeah) they will do it now.

So yes, measure with DMM, but the best would be with as said above with an UI that have already extra button or two to send these CMD_SETDAC as well.

[Fraser]

You could send the SA back to the Ti supplier (The Netherlands?) and ask if they would be willing to exchange it as yours has crashed whilst being experimented with. They may be willing to help you at no cost ? It all depends how much effort you believe it is worth.

For other users, I have purchased band specific antennas for each of the bands that the SA covers, they cost very little from China. Users should also be careful what they feed into the SA in terms of RF level, as greater than 0dB will likely kill the RF front end. 0dB can be easily achieved when working close to a decent output power transmitter.

[tinhead]

You could send the SA back to the Ti supplier (The Netherlands?) and ask if they would be willing to exchange it as yours has crashed whilst being experimented with. They may be willing to help you at no cost ?

no, that would be not fair (unless TI ask me to do so). I've opened support case now and will wait their response.

[rf-loop]

I've tried the DVB-T dongle SDR's to see how well they work. Not bad but quite a lot of setting up, not great dynamic range and pretty deaf without pre-amplification. A cheap way to access 50MHz-2GHz though. A tool for the lab ? ....not until the messy configuration stages are conquered. Porr setup results in really poor performance.

Pretty deaf?   It depends...

But, here is data.

Some tiny detail samples from tests.

First need note that DVB-T dongle input impedance is not 50ohm. So, these levels are not exactly right. HDSDR software level scale is adjusted so that using -100dBm carrier level setting (for 50ohm load) on HP8657B also HDSDR software FFT show -100dBm. (true level may diffe due to mismatch. Dongle specs say 75ohm but who knows how it is in real and over whole band up to 2.2GHz.

Also not only single dongle. I have measured "lot" of same dongles -  not any markable differencies. Also I have tested of course other frequencies. (yes I have tested also other DVB-T dongles with different tuners etc but it is other story)

But it need also note that I have selected one of best dongle model (not cheapest possible what claims "E4000") on the market what have real genuine Elonics E4000 tuner (and of course Realtek RTL2832U for sampling tuner outputs etc.)

Software used in this part of test was HDSDR. (it have some advantages over SDR# hassle)

In RF FFT spectrum was used 1Hz resolution BW.

(note also small offset in tune. Becouse peak visibility is better when red line do not overlay it.)
50% Modulation depth was selected becouse sidebands levels are -12dBc. Most of pictures have 1kHz modulation freq.

In first picture modulation signals are 400Hz and 15Hz(!) for realize this 1Hz RBW.
HP8657B minimum output level is -143.5dBm.
Other pictures show also nicely how level scale is nearly perfect.