I'm in need of some feedback regarding using the Smartee V5 SDR and the new cased H1 LNA

[Cathal O'Donghaile]

Good morning everyone

I've been troubleshooting a problem I'm having after replacing the barebones H1 with the cased version and I'm using the Nooelec Smartee V5 SDR. I use rtl_power to collect the data on a raspberry pi using the following command line:

rtl_power -f 1419.5M:1421.5M:1k  -T -g 42 -i 60 -e 2.5h radiotelescope.csv

After removing the -T switch (which appears to disable the BiasTee rather than enable it) leaving the manual gain switched on, I'm getting that spike in the centre of the ezCon317antByFreqMax.png and doppler. 

I know from using the barebones version that the -g setting is necessary as is the -T. I wonder has anyone else had this same problem with the Smartee v5? Do I need to look at the XTR instead which has hardware offset facility?

Would appreciate some feedback.

Cathal

[Marcus D. Leech]

The NooElec SmartTee series have ALWAYS-ON bias-T circuits as far as I know, but you should check with NooElec support on that.

When the two units are connected via coax, does the light on the LNA light up?  That indicates that it's getting power.

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sara-list/35498dbe-f575-4aed-b7a1-415a962be869n%40googlegroups.com.

[Cathal O'Donghaile]

Hi Marcus, thanks for your feedback. Yes the LNA light is lit up. The two units are connected via approx 8m of coax. I've attached some graphs here to highlight what's happening. So the EzCon317 with and without graphs and also 2 readouts I generate myself of us the frequency and time. Those two are quite different. When the gain parameter isn't set, the decibel level is actually higher than when it is set.

Cathal

[Marcus D. Leech]

On 2026-02-17 10:54, Cathal O'Donghaile wrote:

Hi Marcus, thanks for your feedback. Yes the LNA light is lit up. The two units are connected via approx 8m of coax. I've attached some graphs here to highlight what's happening. So the EzCon317 with and without graphs and also 2 readouts I generate myself of us the frequency and time. Those two are quite different. When the gain parameter isn't set, the decibel level is actually higher than when it is set.

Cathal

I don't know then.  I personally haven't used rtl_power in a decade, and then only to help the developer of it with some things.

Since you already have the "ezRA" suite available to you, you might consider using "ezCol", which I think can talk to an RTL-SDR directly.

But others on this list have more experience with it than I do, including Ted Cline, the author.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/060e80d3-4652-4994-99e1-754a7eb6d186n%40googlegroups.com.

[tedcl...@gmail.com]

Hi Cathal,

I think your new Nooelec Smartee V5 SDR should work well.

I think the Nooelec Smartee V5 SDR always provides biasTee voltage for the LNA ?

Long ago I made an ezColRtlP250526a.py to translate the   rtl_power.c   csv file data.


https://github.com/keenerd/rtl-sdr/blob/master/src/rtl_power.c
says in part,
      -g tuner_gain (default: automatic)
      -P enables peak hold (default: off/averaging)
      -T enables trough hold (default: off/averaging)


Your command,

      rtl_power -f 1419.5M:1421.5M:1k  -T -g 42 -i 60 -e 2.5h radiotelescope.csv

has   -g 42   to set the gain.

Apparently without it (tuner_gain = default: automatic), your power measurements are higher ?

I see the ezCon317 plots have different Y-axis multipliers in the top left of 1e-7 (without42gain) and 1e-8 (with42gain).

That agrees with your   hydrogen_line_2   plots ?

ezCol asks for a gain of 999 and usually gets only 49.6 .

Maybe   -P    for peak, records only the maximums ?
And   -T   for trough, records only the minimums ?
I can understand that with   -T   you see less noise.
I do not think the   -T   is necessary.



Why does the noiser ezCon317 plot bother you ?
I am not bothered by the center peak.  It is related to a DC voltage.

I do not think you need the XTR SDR.


---
Ted Cline
TedClineGit at gmail.com

For folks starting to explore radio astronomy,
      ezRA - Easy Radio Astronomy
      Free 1420 MHz Galactic hydrogen data collection and analysis
      Open source
      Windows and Linux
      https://github.com/tedcline/ezRA
        https://youtu.be/kHgwEbWKhzs    (13 minute Simple Overview)

[Cathal O'Donghaile]

Hi Ted. Thanks for your feedback. I ran EzCol last night to see the results and got no doppler and this huge spike in the 317 output. The reason I was bothered about it is because when it was working last year, the spike was absent. I've attached it here too for comparison and the EzCon67 output. 

[Ayushman Tripathi]

Hi Cathal,

As Ted pointed out, it seems something is affecting the gain or related settings of the NESDR Smartee. Here is the comparison on my NESDR Smartee V5, you can see that when the gain is near max, there is no "huge spike/DC spike."

But when the gain is lower (second image), you can see it appears similar to the DC spike response you're facing now.

You can try a simpler RTL command with minimal options and then see if the issue is fixed. Yes, the NESDR Smartee should have an always-on bias tee by default that does not need to be turned on, as per my understanding.

[Cathal O'Donghaile]

Thank you Ayushman. I have in mind a similar test using SDRSharp when the weather improves here. Hopefully I can narrow it down. 

Cathal

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---

You received this message because you are subscribed to a topic in the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/sara-list/wTeClrmSxzg/unsubscribe.
To unsubscribe from this group and all its topics, send an email to sara-list+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sara-list/bbddd747-30c7-4bc6-b0c5-9bb89dba0780n%40googlegroups.com.

[Cathal O'Donghaile]

Just to let everyone who helped me know, after doing a test using GPRX, I found the problem was with the cable run between the SDR and LNA. I'm now getting interference where I wasn't before and it still needs tweaking, but I'm nearly there. Thanks for all the feedback everyone.