LIstening post -update

VK3EB

Member
A few pix from todays work,
First impressions currently listening to 80m noise floor is excellent. My USB 5v supply, part of my battery box turned out to be a noise generator. Denys unit to the rescue. Tune to 3330kHz CHU time signal from Canada -very impressive!
Great location, thanks Bill.
modem rain protection_4370.JPG
Battery_4369.JPG
fly dog_4368.JPG
long wire terminate_4372.JPG
Modem on box_4365.JPG
door bond_4375.JPG
 

VK3ZYZ

Moderator
Staff member
I've been listening to the SDR this morning and have a couple of observations.
The background noise is higher than that on the Ironstone SDR. That may be my switch mode power supply producing noise. It may be worth while making a linear supply to see if that helps. VK3EB has a higher current reg I gave him a couple od fays ago, or I could put one together.
Also, the frequency seems to wander slightly as the SSB audio wanders up and down a bit.
 

Josh

Member
I don't know if it is relevant at all.
If I read right the SDR can have a GPS sync for precision control of the ADC clock, maybe just maybe its is trying to do that loop in the background without a gps sync which might, might cause the ADC clock to wander a little.
I did swap out ntpd for chronyd but i did not take the time to set it up for GPS PPS sync, as I was and am not sure if the open web rx software needs to control any of that.

This is ntp sync status:
Code:
210 Number of sources = 4
MS Name/IP address         Stratum Poll Reach LastRx Last sample              
===============================================================================
^+ 159-196-3-239.9fc403.mel>     2  10   377   180  +1231us[+1231us] +/-   34ms
^* time.cloudflare.com           3  10   377   775  -4621us[-6698us] +/-   14ms
^+ bitburger.simonrumble.com     1  10   277    14  -2577us[-2577us] +/-   21ms
^+ 14-202-65-230.tpgi.com.au     1  10   377   308  -3799us[-3799us] +/-   26ms

Reference ID    : A29FC87B (time.cloudflare.com)
Stratum         : 4
Ref time (UTC)  : Sat May 17 01:10:44 2025
System time     : 0.001697727 seconds slow of NTP time
Last offset     : -0.002077176 seconds
RMS offset      : 0.002063389 seconds
Frequency       : 6.657 ppm fast
Residual freq   : +0.001 ppm
Skew            : 0.111 ppm
Root delay      : 0.025742332 seconds
Root dispersion : 0.003906695 seconds
Update interval : 1040.1 seconds
Leap status     : Normal
As you can chrony picked the stratum 3 source not the 1's.



also a note on bandwidth. the water fall seems to an average take 100KiB/s / per user.

and to date we have used 1.13GiB upload and 159MiB download with respect to the modem.

here is a pic of the MW band last night. I didn't know that there were still that many stations. :) I've never heard 621 as good.

listening_post_MW.png
 
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VK3YNV

Administrator
Staff member
I have a spare LM1085ISX-5 Fixed 5V 3A linear regulator that could be used for experiments if you want to have a play.
 

BillC

Active member
Thanks Ray . The Listening Post noise :- There is a very strong spur, fundamental frequency about 268 khz the level as measured is S9 + 20 dbm. This generates harmonics all the way up the spectrum. The noise level is higher at the lower range of the spectrum. When listening with a sniffer probe in and outside of the cabinet there is a very strong "modulated (audio garbage) tone" at 268 khz. To get the best out of the low noise site we will investigate the power supplies. The noise floor seems to be about S5 in reality this site has about S1 normally. However as it stands the reception is quite good.The system might go off for short periods while we check out power supply noise etc. I might try a trap filter in the power leads could a kind person do the calculations for a trap on 268 khz.
 
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Josh

Member
Thanks Ray . The Listening Post noise :- There is a very strong spur, fundamental frequency about 268 khz the level as measured is S9 + 20 dbm. This generates harmonics all the way up the spectrum. The noise level is higher at the lower range of the spectrum. When listening with a sniffer probe in and outside of the cabinet there is a very strong "modulated (audio garbage) tone" at 268 khz. To get the best out of the low noise site we will investigate the power supplies. The noise floor seems to be about S5 in reality this site has about S1 normally. However as it stands the reception is quite good.The system might go off for short periods while we check out power supply noise etc. I might try a trap filter in the power leads could a kind person do the calculations for a trap on 268 khz.
That frequency is suspiciously in the range of the switch mode controller(225kHz-280kHz) that is inside Denys 5V power supply. It could be just a coincidence, but I agree it is definitely worth looking at. see attached page from datasheet. If its just conducted a linear post reg might give the best of both worlds.
 

Attachments

VK3YNV

Administrator
Staff member
I might try a trap filter in the power leads could a kind person do the calculations for a trap on 268 khz.
Hi Bill, you want minimal DC resistance in line, so just a ferrite in series and a low esr cap in parallel might help.
Denys just told me there is no filtering on the input, so clamp on ferrites on both on the input DC and output DC cables since the 268 kHz could be radiated as well as directly conducted.
 

BillC

Active member
Hi Bill, you want minimal DC resistance in line, so just a ferrite in series and a low esr cap in parallel might help.
Denys just told me there is no filtering on the input, so clamp on ferrites on both on the input DC and output DC cables since the 268 kHz could be radiated as well as directly conducted.
Thanks for the help Ray and Josh. I will try a few ferrite clip on,s and see how that works, but we might change the power supply. By the way the battery voltage "dived" overnight / 24 hrs dropped by .29 of a volt. I think we can handle that discharge rate easily.
 

BillC

Active member
I've been listening to the SDR this morning and have a couple of observations.
The background noise is higher than that on the Ironstone SDR. That may be my switch mode power supply producing noise. It may be worth while making a linear supply to see if that helps. VK3EB has a higher current reg I gave him a couple od fays ago, or I could put one together.
Also, the frequency seems to wander slightly as the SSB audio wanders up and down a bit.
Hi Denys .Thanks for the report. The noise could be from the power supply. I will try to check it out soon. Thanks for the use of the power supply it certainly got the system up and running quickly, plug and play etc.
 

BillC

Active member
The Listening post battery is now sitting at 12.15 volts. I will now run a lead out from the house for a "quiet charge" 2.30 pm 18/5.
 
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BillC

Active member
I have just checked out the 5 volt power supply with the scope . The pictures tell the story, the square wave image shows waveform across the input terminals and the spiked waveform is across the output terminals. I will build up a linear type 5 volt regulator and we will see how that works, hopefully no noise.
IMG_4514.JPG
IMG_4513.JPG
 

BillC

Active member
Cheers .Thanks for the replies. Ray and Josh. I am constructing a regulator using an LM 338k, it is taking some time to organize the hardware. At this stage I intend to use fixed resistors to set the output voltage to about 5.05 volts, we will see how it holds up under load and wiring loom and contact resistance. More to follow.
 

BillC

Active member
Changed the regulator at 5 pm no spur now. Also I will build a 31 meg low pass filter for the antenna input as there is a bit of FM breakthrough around 30 megs. I hope we have obtained a lower noise result.
 
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VK3YNV

Administrator
Staff member
I listened a bit on FT8 earlier, lots of US and European Stations on 40M, this is about 30 minutes of signals on the PSK reporter map.
Screenshot at 2025-05-19 17-02-01.png

Looking pretty good Bill, I think the noise is lower with the linear regulator, but it was already pretty good anyway.
 

VK3ZYZ

Moderator
Staff member
I think I'll make another regulator but this time, use the correct input electros. The original (2019) has a couple of 47uf caps but I only found 18uf as used on the o/p. Also I do not remember if the switcher chip was insulated from the case or not. It is in this current build. A large electro added to the i/p terminals will not hurt.
The linear reg is definitely better noise wise. Maybe the switcher can be used as a pre regulator and mount it right at the battery.
And thanks Bill, for finding a loose terminal so it is working well again :)
 
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BillC

Active member
It looks to be playing up this AM (8:30 Tues 20th)
Thanks Denys. I have been out and tightened all the power wires on the linear regulator connector strips and the Rcvr seems to be working. I think that long term we will use your regulator with a bit more filtering. It is of course much more efficient in terms of power consumption.Cheers.
 
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