Kategorier
Övrigt

Lars Thunberg

This is the homepage of Lars Thunberg in Sollentuna, Sweden

Domänen larsthunberg.se ägs av Lars Thunberg, Sollentuna

Kategorier
Amateur Radio

Active SAW Filter LNA 435 MHz

This is my measurement of the low cost filtered LNA with SAW filter for 435 MHz. It got it from AliExpress (link).

I used 20dB + 10dB (=30 dB) attenuators and calibrated my NanoVNA for 380 MHz to 510 MHz.

As you can see below the LNA performance well. Gain is aprox 23 dB (exact acoording to specification) and the bandwidth is aprox 15 MHz (a little bit more then the specification of 10 MHz BW).

Kategorier
Amateur Radio

RTL-SDR v4 vs IC-705 one hour FT8 RX

I was curious how the RTL-SDR v4 would perform against the IC-705 during one hour of FT8 receiving so I set up and did a little test. The setup:

  • One hour RX on the 20 meter HF band FT8 section
  • Antenna tuned random longwire
  • HF signal was split according to the image below, but I did not use the first stage ”AMP” and no LNA from the RXout from the SDRSwitch.
  • SDR software = SDR Console
  • Same bandwidth was used in the IC-705 and SDR Console
  • Two (2) instances of WSJT-X Improved running on the same PC, calibrated to the same RX dB level
  • Both instances reporting to PskReporter

Result after one hour RX

Transmitters reported in PskReporter:
– IC-705: 323 transmitters
– RTL-SDR v4: 323 transmitters

Top distance IC-705:

Top distance RTL-SDR v4:

Distance chart IC-705:

Distance chart RTL-SDR v4:

WSJT-X view IC-705:

WSJT-X view RTL-SDR v4:

Kategorier
Amateur Radio

UNUN for HF longwire

After my 80 meter HF loop antenna (SkyLoop) broke during high winds in 2025, aprox 30 meters of the loop antenna still is up and can be used as a random long wire antenna.

In Januari 2026 I connected an UNUN (DIY – maybe a 1:49, not sure…) to be able to tune the wire on all HF bands with my remote auto tuner RT-100.

I also added two counterpoise wires about 8 meters long to help reduce some common mode current on the coax and add better tuning possibility.

This is the NanoVNA SWR plot before the RT-100 tuner. The overall impedance is low so it should be better to use a different UNUN winding. But that will be some other time…

Kategorier
Amateur Radio

UHF LNA for SatNOGS

Oktober 2025

Time to upgrade my UHF SatNOGS station with 435 MHz bandpass filter and LNA. These are the items I use from AliExpress:

Also read this interesting post about low cost LNAs.

Installation and testing

Some pictures from the installation and measuring:

LNA and BFP measured with VNA
LNA and BPF in a waterproof box

Some more installation images

Roof mounting

Kategorier
Amateur Radio

DC Distribution board

Made a very simple DC switch and distribution board for all the stuff that need 13.5 V DC.

DC distribution board can be found on Aliexpress.

If the link does not work, search for ”12V 24V Car Accessories 6 Gang Toggle Switch”

Kategorier
Amateur Radio

RTL-SDR v3 vs IC-705 FT8 RX

With an antenna RX splitter I did some fast compare between a simple RTL-SDR v3 SDR dongle and my IC-705 on 21 MHz and 14 MHz FT8. The RTL-SDR v3 is not original designed to run on HF, but with HF Quadrature mode it is possible to use it on HF.

And I was very surprised that this very cheap SDR could decode a lot of the stations that the far more expensive IC-705 did. The spectrum was cleaner from the IC-705 and more stations was decoded, but the results from the SDR was impressive because it is such a cheap and simple device.

Used equipment:

Cable mess
Cable mess during testing

All images below:

  • Left – RTL-SDR v3
  • Right – IC-705

PSKReporter map compare – 15 minutes RX on 14 MHz.

14 MHz

WSJT-X window. Cleaner spectrum from the IC-705.

WSJT-X screendump

Logbook from PSKReporter.

PSKReporter

Signals in dB from WSJT-X. The yellow reports are from the same station. I could notices some difference and RTL-SDR via SDR Console would often give higher dB values, but I have no idea why.

dB
Kategorier
Amateur Radio

New installation 50 MHz Oblong Januari 2025

New installation of the 50 MHz Oblong in Januari 2025.