PC for connecting to RTL-SDR

[Miguel Ríos Martín]

Hello.

I have the following setup:
Nooelec antenna -> Sawbird H1 -> RTL-SDR v4 -> 3m USB cable -> Laptop

The system works, but I'm detecting significant RFI interference (spikes). I've tried two different laptops, and the difference in interference is considerable.

I've also tried it with and without power (battery only), and this makes no difference.

I placed a metal plate in front of the device, and the interference was significantly reduced.

My question is, will using a low-power MiniPC significantly reduce the interference? Do MiniPCs generate less interference than laptops? Any experience with this?

[Alex P]

The only guaranteed solution is  DISTANCE   between the Antenna and Digital Electronics.

Shielding is effective, but it takes some 'creative engineering' to make it work well.

I keep my PC 15m from the antenna  .. &  still need to turn off the monitor on my 'internet' system.

Alex Pettit

[Andrew Thornett]

Monitor or laptop screens do produce lot of RFI so keeping those away from antenna helps, put LNA/filter as close to antenna fees as possoble makes big difference, keep PC whatever type few metres from antenna if possible, reduce spillover/ground noise onto dish using deep dishes and/or mesh extension around dish, do not aim dish at trees or neighbours house, ensure feed at focus point of dish.

Andy 

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Miguel Ríos Martín <mrio...@gmail.com>
Sent: Monday, 10 August 2026 17:09:54
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] PC for connecting to RTL-SDR

 

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[Miguel Ríos Martín]

I assume you have 15 meters of cable, LMR240 or similar, and between the Sawbird and the RTL-SDR, right?

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Miguel Ríos Martín

[Robert Hamers]

IN addition to the suggestions already made, two additional:

1.  you might also consider using a USB isolator  between your computer and your SDR.  It’s essentially a coupling transformer that helps to reduce noise from the your computer getting injected into the downstream electronics.  There are many of them available on Amazon for ~$20-$40.  

2. If your computer is injecting noise on the line, then you might also benefit by using a DC block between the Sawbird and the SDR, and powering the Sawbird from a low-noise linear amplifier via the USB-C cable.  

Good luck!

Bob

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From: 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Date: Monday, August 10, 2026 at 4:26 PM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] Re: PC for connecting to RTL-SDR

[b alex pettit jr]

15m-20m of LMR240  will work fine....

BTW, digital cables can also Radiate.

Alex

[Miguel Ríos Martín]

In my fight against RFI interference, I'm considering getting a fanless computer (MeLE Fanless Mini PC Quieter 4C, N150/N100 8GB RAM). Apparently, the fan is a major source of RFI, and since I can't place the computer more than 2 meters from the antenna...

Would this be a good idea?

Any ideas or experiences?

Thanks

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Miguel Ríos Martín

[b alex pettit jr]

Unless it is well shielded in a box. you are spending $$ and will not solve the issue.

I've been doing RA for 5+ years and have put a few Thousand manhours learning this highly complex 'hobby'.

Try 20m of KMR240 or RG6 Coax    Ant / LNA   <coax>    SDR / PC .

Alex Pettit

======================================

[Miguel Ríos Martín]

My problem is that, due to the dimensions of my balcony, I can't move the antenna more than 3.5 meters away from my PC unless I drill through the wall to run the cable, which I've ruled out for now.

My question is whether going from 2 meters to 3.5 meters would make a noticeable difference (I'm asking before buying the expensive KMR240 cable).

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Miguel Ríos Martín

[Robert Brown]

I dunno if it would've worked but when I was still with the local observatory we were looking at potentially using a fiber-optic USB extender (available on AMazon) to distance the (shielded) computer from the SDR.  But I've heard the latency/delay in these can be an issue with SDRs.  Any ideas or experience with this?

Rob

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[b alex pettit jr]

But, yes doubling the distance Might be useful. try RG6 it is quite Inexpensive

Try putting a screen / aluminum foil around the digital electronics, or put all in a metal box or

a combination of these  ideas. 

Can you temporarily run a cable through a slightly opened window ?

What antenna are  you using ? ( post a photo of the setup )

What Software ?  

The real time spectral plotting of SDR# is useful for quickly evaluating changes,

and the latest version of IFavg V5 allows an ever more expanded spectral amplitude scale than SDR#

Unfortunately, no single solution fits all situations.

You need to Experiment ..

            Alex P

===================

====================

[b alex pettit jr]

Some work / some not so.

The one I selected limits the data rate to 3MSPS which is fits HLine without issue..

 This is a remote thermally stabilized SDR & FiberOptic Data Link which works GREAT ..

Takes some effort & cost, but this is the system I now use 100% for all configs.

Not recommended for someone not skilled in mechanical / electronics fab .

Alex Pettit

==============

=========================================================================

I dunno if it would've worked but when I was still with the local observatory we were looking at potentially using a fiber-optic USB extender (available on Amazon) to distance the (shielded) computer from the SDR.  But I've heard the latency/delay in these can be an issue with SDRs.  Any ideas or experience with this?

Rob

[Miguel Ríos Martín]

My setup is:
Nooelec antenna -> Sawbird H1 -> RTL-SDR v4 -> 3m USB cable -> Linux laptop. 

(Image attached)

I'm using ezRA, and I've attached a screenshot showing a lot of signal spikes.

What I've verified so far:
1) With an old laptop (which has since broken), the interference was much less than with my current one, and the H-line detection was quite good. In fact, the problems started when I had to switch laptops. Now, the interference ruins my graphs, even though the H-line is detected.

2) I have a 40x25cm metal plate that I place next to my current laptop, and the interference varies considerably depending on the plate's position.

Because of this, I've been thinking that perhaps a mini PC might emit much less interference than my current laptop and would solve the problem, at least significantly.

Another possibility would be to move the antenna up to 3.5 meters away from the digital equipment using LMR240 cable.

I'm afraid I'll have to experiment and see what works best.

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Miguel Ríos Martín

[b alex pettit jr]

Another Problem is your proximity to the other buildings..

Laptop radiation is in plane to the monitor .. Try rotating it 90 degrees = EdgeWise to the Antenna

The intent of this Endeavour IS to Experiment and Learn .. just plotting stuff without learning is not worth the effort.

                                          Alex P

================================================

==================================================

[Robert Hamers]

Maybe you could try making a faraday cage around your laptop, from aluminum window-screen?  If you used an external (wired) keyboard and mouse, you could have the laptop enclosed in aluminum screen and still be able to see the monitor…     Or perhaps have it inside a 5-sided cardboard box lined with aluminum foil, and the open end directed away from your antenna?

Bob

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Miguel Ríos Martín <mrio...@gmail.com>

Date: Wednesday, August 12, 2026 at 9:23 AM
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] Re: PC for connecting to RTL-SDR

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAFfVMO%2BhAKvG4mH4ns1Tph4xQR6zfriry1RyukudEqtNh721TA%40mail.gmail.com.

[b alex pettit jr]

To add a "wild card' to logical solutions, microwaves are halfway between 

radio & light frequencies .. 

meaning, to some degree they exhibit the properties of both:

They can be ( totally or partially ) :

Radiated

Absorbed

Reflected

Refracted

Diffracted

Focused

and have radiation wave-shape patterns across conductive materials

[Scott Elliott]

Before you try to fix PC noise by throwing money at it, consider some dumb/simple fixes and diagnostics.  First turn off all WiFi/BT on your PC and your phone if you are near the ANT.  A simple and cheap first step if you can't increase distance is to add some ferrite EMI clamps at both ends of ALL your cables into AND out of your PC (including AC power).  You've probably seen a number of computer cords with these "tumors" on them.  Preferably add them at both ends.  Also consider turning off everything in your house including any LED/CFL lighting, WiFI, mice/game controllers, x box, monitors/TVs, etc.  As the EMI may be coming from an everyday device.  You can also do some caveman shielding tests: put a large metal trash can over your PC or put a large sheet of metal between your PC and your ANT.  Or the cheapest shielding test is to just put a large ugly bag of salty water between the PC and ANT (Just stand between them).  Such fooling around is probably not a sustainable solution, but if you see a reproducible change in EMI (e.g., trash can on/off or TV on/off)  then at least you know the source and you can attack it directly.  Fans mechanically attached to antenna structure can cause "microphoning" by vibrating the structure, cables, etc, but I've not heard of them being a major source of EMI at shorter lambda.  My experience in qualifying production products to pass FCC is that you often have to go on a long snipe hunt to find the root cause.  In the testing chamber you try a bit of copper tape here, a glob a solder there, sand the paint off between two metal parts between supposed grounded metal sheets elsewhere to find the issue.  

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[Adrian]

Some thought on RFI

Saying monitors are noisy emitters of RFI is like saying all snakes are poisonous and will kill you. You must specify what kind of monitors you are describing and there a variety of monitors technologies. Some are horrendous in terms of their EM emissions and some are totally silent.

Let’s start with the worst offenders first. The inexpensive external HDMI USB monitors, these combine every major EMI‑RFI producing subsystem imaginable: high‑speed TMDS clocks.  HDMI TMDS clock leakage, HDMI use Transition‑Minimized Differential Signaling at 742.5 MHz, 1.485 GHz, 2.97 GHz, and with harmonics of each along with poor PCB layout these radiate strongly though out the spectrums of interest.

Noisy LED PWM backlight drivers the LED backlight PWM drivers use frequencies typically 200 Hz–30 kHz, with harmonics extending into HF/VHF. Cheap monitors use unshielded boost converters resulting in broadband combs, the evenly spaced peaks observed in many observational spectra.

Emitting switching supplies, these Internal switching power supplies, flyback or forward converters running at 50–200 kHz with rich harmonics extending into HF/UHF. And combined with poorly designed internal power cabling that radiate much of this energy.

Low-Voltage Differential Signaling, LVDS panel interface noise, LVDS differential pairs run at hundreds of MHz, radiating through the panel’s FPC cable (Flexible Printed Circuit) the unshielded flat, ultra-thin ribbon cables made with printed copper traces on a flexible plastic film, they link parts like screens, The high-speed data, also rich in harmonic for digital communication standards, sends data through those unshielded cables.

And of course, the final blow is the plastic chassis with no Faraday shielding allowing emissions to escape freely.

They are the baseline rattlesnake bad “bad actors” avoid these at all costs.

Next In line which is likely the worst offenders we encounter are the High‑Refresh Displays Including those in the newer higher end gaming laptops. Besides most of what was discussed for the external displays above the increase in performance and even higher speed circuitry just compound the problem.

High‑Refresh Laptop Displays as Major RFI Emitters

High‑refresh laptop displays (120–360 Hz and now 480 Hz panels) are among the strongest unintentional RF radiators in consumer electronics. Their emissions come from multiple high‑speed digital and switching subsystems packed into a thin, poorly shielded chassis. The result is a device that leaks energy from tens of kilohertz through several gigahertz, contaminating any RF‑sensitive environment.

240–360 Hz Refresh Rates

Higher refresh rates require proportionally higher pixel clock frequencies. A 60 Hz 1080p panel uses a 148.5 MHz pixel clock; a 240 Hz panel pushes this into the 300–500 MHz range. These clocks generate dense harmonic structures that radiate through the panel’s flex cable and chassis, producing narrowband spikes across VHF, UHF, and sometimes up to microwave bands.

eDP Signaling at 1.6–8.1 Gbps

Modern laptops use embedded DisplayPort (eDP), with lane speeds of 1.62, 2.7, 5.4, and 8.1 Gbps. These multi‑gigabit differential pairs run through a thin, unshielded FPC cable routed through the hinge. The fast edges radiate strongly, creating emissions in the 1–9 GHz region. The hinge geometry often acts as a resonant radiator, making eDP one of the strongest single contributors to laptop RFI.

Overdrive Switching

High‑refresh panels rely on overdrive circuits to accelerate pixel transitions. These circuits use rapid voltage slewing and local charge pumps switching in the tens of kHz to several hundred kHz range. Their harmonics extend into HF and VHF, adding broadband noise whenever the display shows motion.

RGB Lighting PWM

Gaming laptops frequently include RGB keyboard and chassis lighting. These LEDs are driven by PWM controllers operating around 200 Hz–2 kHz, with harmonics extending well into HF/VHF. Multiple lighting zones produce overlapping PWM combs that are easily visible on SDR waterfalls.

VRMs and Power Conversion

Laptop voltage regulator modules (CPU, GPU, RAM, display backlight, battery charging) switch at 200 kHz–1 MHz, with harmonics spreading upward into HF, VHF, and at least UHF. Because VRMs sit only centimeters from the display cable and other sensitive wiring, their noise couples readily into conductors USB outlets and radiates throughout the chassis.

Thin Chassis and Minimal Shielding

Laptops lack the metal enclosures and ferrite‑loaded cabling found in commercial monitors. Their thin plastic or aluminum shells provide little RF containment. With no EMI gaskets or isolated power compartments, internal noise escapes freely, raising the ambient noise floor across multiple bands.

Hinge Cable as an Antenna

The hinge region bundles eDP lanes, backlight power, touchscreen lines, webcam wiring, and sometimes USB or I²C. Bending the cable disrupts differential balance, and the exposed geometry allows it to behave as a multi‑band antenna. This region often radiates the strongest emissions, including to GHz‑bands eDP leakage and include broadband noise from backlight power lines.

 

These two are some of the worst offenders besides cell towers, your neighbor’s solar panel inverters and yours and your neighbor’s large screen TV set including possibly the whole neighborhood’s wireless LAN systems and all sit close to being also the worst besides the laptops you are likely to be using. These are all the king cobras of the deadliest RFI dangers that you might encounter in the radio astronomy wilderness.

So unless you are fortunate enough to have a few acres in a countryside estate or even just a home with a good sized back yard were a 50, 30 or even 20 foot run of coax cable separating your antenna and LNB and even your SDR from the offending laptop or the multiscreen system you also use for your day trading side hustle with, what  can you do if you live in a multifamily dwelling structure or live in an apartment or penthouse with limited space available and have possibly only a balcony for outdoor access.

 

Low‑RFI Display Choices

Once you accept that laptops and cheap HDMI LCDs are the worst RFI offenders, the next step is figuring out how to maximize a system for as quiet a setup as possible, E‑ink is great but slow and color‑limited. So, we need a realistic ranking of consumer‑grade displays that won’t trash the spectrum.

Below is the practical hierarchy.

 (Quietest Practical Consumer Option): E‑Ink / E‑Paper Monitors

These are the closest thing to “RF‑silent” displays you can buy without entering exotic territory.

Why they’re quiet:

No LED backlight → no PWM comb

No high‑speed pixel clock → no TMDS harmonics

No LVDS/eDP noise

No overdrive circuits

Minimal switching electronics

They refresh slowly and color is limited, but for spectrum watching, IF monitoring, waterfall displays, and control interfaces, they’re excellent.

Examples:

Dasung Paperlike

Onyx Boox Mira / Mira Pro

These are the top choice for low‑RFI computing.

 

 (Second‑Best Practical Consumer Option): OLED Displays

OLED is not perfect, but it’s far quieter than cheap LCDs and high‑refresh laptop panels. It’s the best “normal” consumer display technology for RF‑sensitive work.

Why LED is quieter:

No PWM backlight

No LED boost converter

No LCD overdrive artifacts

No backlight switching noise

What OLED still emits:

HDMI TMDS at 742.5 MHz, 1.485 GHz, 2.97 GHz + harmonics

DisplayPort/eDP lanes at 1.62–8.1 Gbps

TCON switching at 100 kHz–1 MHz

VRM noise from the monitor’s power board

OLED is not silent, but it’s cleaner than any consumer LCD and dramatically cleaner than high‑refresh laptop displays.

Best OLED choices:

Standard 60 Hz OLED monitors

Metal‑chassis OLED TVs (rare but exist)

Avoid:

OLED gaming monitors (120–240 Hz → high pixel clock harmonics)

OLED laptops (eDP through hinge → GHz radiation)

OLED is the best “normal” display” for RF‑quiet setups.

 (Third‑Best Practical Consumer Option): Low‑Refresh, Metal‑Chassis LCDs

If OLED is too expensive or unavailable, the next best option is a basic 60 Hz LCD with a metal chassis and no gaming features.

What to look for:

60 Hz refresh

No RGB lighting

No HDR (extra power circuitry)

Metal back shell

External power brick (less internal switching noise)

Short, shielded HDMI or DisplayPort cable

These are not silent, but they’re much quieter than:

cheap plastic LCDs

high‑refresh gaming monitors

laptop displays

This is the “budget‑friendly but not terrible” category.

 

System Architecture: Mini‑PC + Shielding + Quiet Display

The quietest consumer‑grade setup looks like this:

Mini‑PC (not a laptop)

No internal display, no hinge cable, no battery system, no RGB lighting. Already 10× quieter than a laptop.

Mini‑PC inside a grounded metal enclosure

Ammo can, aluminum project box, steel junction box — all work. Copper tape on seams. Ferrite‑loaded cable apertures.

Short, shielded HDMI/DP cables with ferrites

HDMI TMDS is a radiator; choke it hard. DisplayPort is slightly cleaner.

Quiet external display

E‑ink monitor (quietest)

OLED monitor (second‑quietest practical option)

60 Hz metal‑chassis LCD (third‑quietest)

Wired keyboard/mouse with ferrites

Avoid RGB keyboards and “gaming” mice.

Physical separation

2–3 ft minimum for LCD/OLED. E‑ink can sit right next to the RF gear.

Optional: headless operation yields zero display noise.

Adrian

[Wende Waters]

Hi Miguel, 

I am wondering, if you disconnect the fan in your existing PC, how much your RFI drops. Some people have tried hanging Faraday cloth around or over or between things, blocking a monitor with a laptop (or vice versa) but the thing is, power supplies can be noisy too. Some brands of PCs are inherently noisier than others. But it sounds like a lot of people sent you good ideas to try. 

Wende 

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[Adrian]

Disconnecting the fan in your laptop during the current heat waves across the US  is guaranteed to solve your RFI problems once your CPU overheats and gives up all its magic smoke.

Adrian 

[Miguel Ríos Martín]

Thank you so much for all the suggestions.

So far, I've managed to significantly reduce the interference by doing two things:
1) orienting the front of the laptop (closed) away from the antenna.

2) placing a piece of cardboard and a metal plate, approximately the same size as the laptop (but without the metal in direct contact), under the laptop.

I'll continue investigating your suggestions and try them with a mini PC.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/506b25fd-3020-410c-8ece-5dca7f75ccd3n%40googlegroups.com.

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Miguel Ríos Martín

[b alex pettit jr]

Can Someone Please Explain :

How can 'Lowering the RFI' result in an overall Increase in the "Relative RMS Level" ?

How can one condition be compared to another if each data set is not consistently scaled ?

These area Miguel's  Before ( Red ) and After ( Blue ) plots

Plots were shifted such that the Y-Axis Relative RMS Power Scale Values of each overlay.

==============================================================

Alex Pettit

===============================================================

[Miguel Ríos Martín]

Two things need to be considered:
- The data corresponds to different times.
- As time passes from when the ezCol application is launched, the data stabilizes at slightly lower values. I've attached the graph taken two hours later.

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[b alex pettit jr]

For system performance comparison and  adjustments,  1/10ths of a dB are significant.

On Thursday, August 13, 2026 at 06:18:23 AM EDT, Miguel Ríos Martín <mrio...@gmail.com> wrote:

Two things need to be considered:
- The data corresponds to different times.
- As time passes from when the ezCol application is launched, the data stabilizes at slightly lower values. I've attached the graph taken two hours later.

===============================================================

[Miguel Ríos Martín]

And it continues to descend slowly; this is half an hour later. The Milky Way's arm is starting to appear!

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[b alex pettit jr]

Miguel,

These are the  3 overlaid with Y levels shifted so 1419.5 - 1419.7 MHz is the same for each ( below HLine data )

[Adrian]

Too bad the limitations of the available small antenna apertures make the Hi signal so difficult to observe.  If one was able to just increase the proportions of our antennas by a factor of 400 then this kind of spectra would be possible in seconds. Oh well, we can only wish.

 

[b alex pettit jr]

This is from an antenna with an 'aperture' of 150mm.

[Scott Elliott]

Adrian, Great detailed and professional discussion.  To expand on a few of your points:  

"Mini‑PC inside a grounded metal enclosure - check for heat build-up"   <--.  Bare Stainless and Aluminium act like solar ovens and trap heat.  Oddly, painting the outside of stainless/Al  (white) will greatly help it dump heat.  Also, heep the box shaded to prevent solar gain. An enclosure's ability to dump heat is proportional to the surface area, the bigger the better.

"Ammo can, aluminum project box, steel junction box — all work. Copper tape on seams. Ferrite‑loaded cable apertures."  <-- besure to remove any paint at metal to metal or metal to copper tape mating areas.  The copper tape must have conductive adhesive (Amazon will have it).  It must be metal to metal intamate contact and a thin coating of NoOx (Autoparts or Electrical department at building supply) at the metal interfaces prevents corrosion (no NoOx under the copper tape).  All metal paint cans care great and have snugg metal joins to prevent RF leakage (a slot in a shield acts as an antenna).  I've been able to find free used  industrial "electrical enclosures" on crags list, but they need a bit of work to seal their door openings (flexible EMI gaskets).

To view this discussion visit https://groups.google.com/d/msgid/sara-list/3d39b308-518a-429b-a5dc-e358b652aa9cn%40googlegroups.com.

[Stephen Arbogast]

Verification of what has been said above, attached are two screen shots.  The one with Dell in the title is GQRX  tuned to HI running on my mini-pc with a Dell 27 inch LCD display about six meters from my Discovery Dish pointed straight up, showing a spur at approx 1420 Mhz.  The other is GQRX tuned to HI running on my Raspbery Pi-4  with a small cheap 7 inch display  but about 12 meters from my Discovery Dish and does not show  the spur at approx 1420 Mhz.  Both are using AirSpy R2 at 10 Meg samples/sec.

I know this not strictly Scientific, I kept the settings on GQRX the same.

Enjoy,

Stephen

[Miguel Ríos Martín]

I think I've made some progress in my fight against RFI. With the current position and placement of the laptop, I can now see the H signal decently.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/5d7afa96-d165-4a96-831c-a3be17ca2e56n%40googlegroups.com.

--

Miguel Ríos Martín

[b alex pettit jr]

Yes .     Good Improvement

[b alex pettit jr]

FYI :

HLine3D provides Automated RFI removal tools 

Info Here

https://github.com/AP-HLine-3D/HLine3D/blob/main/Info_HL3D_processing_RFI%20Eraser01.pdf

The software will reduce or eliminate RFI noise Without altering H Line Data.

Alex Pettit

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