mandag den 18. maj 2020

Noisy PC Speakers - and a Solution

My PC-speakers are pretty standard: A pair of Creative A50 powered with 5 V DC from an USB-port.

I noticed noise coming from the speakers, when no audio signal was present. Changing USB-port did not help. I seemed like my USB ports were noise polluted! When I connected a power-bank (lithium-ion battery) to the speakers, the noise disappeared, but during pauses in the audio, the power-bank shut itself down!

I decided to build a noisefree 5 V DC PSU using a transformer with iron core and a 7805 which has 68 dB ripple rejection and low output noise. The 7805 is thermal overload protected and short-circuit protected. I had all parts laying around, so the building cost was nil.

Figur 1. The noisefree PSU.

Figure 2. Noisefree PSU with open lid.

Figure 3. AC Adaptor. 
Figure 3 shows the transformer which is an old AC adapter with iron core. It is heavier than modern AC adapters! The advantage: no switching technology is involved!

Figure 4. Circuit diagram.
The rectifier bridge is an integrated piece, but four discrete 1 A diodes can be used as well. I found C1, C2, and 7805 in the drawer. The circuit board has holes and solder islands, but no tracks. Figure 5 shows how the component wires are connected on the bottom side. The alu-cabinet is Hammond 1590A.

Figure 5. The circuit board seen from the bottom.
The PC speaker's power consumption is low. The noisefree PSU does not get warm at all.

Now I can enjoy music and speech without background noise - and a good feeling of having improved something!

73 from OZ1BXM
My homepage:


tirsdag den 24. marts 2020

Replacing Meinberg NTP with Network Time

I purchased a new PC last month with Windows 10 preinstalled. The Windows specs are shown in figure 1.

Figure 1. My new Windows 10.

I had problems after I installed Meinberg NTP. Whenever I booted the PC, the system clock was set by Meinberg, but then time discipline was lost. After some hours, the system clock could deviate as much as 1 sec. It seemed like Meinberg could not control the system time. I worked with this problem for a while, and then I decided to uninstall Meinberg NTP and try another piece of software for time control.

I need accurate time keeping because I'm using weak signal digital protocols in amateur radio. A time deviation of less than 100 ms is required with JT65. I use JT65 when I'm bouncing radio signals off the Moon and back to Earth (distance 800,000 km).

Figure 2. Network Time.

Network Time was easy to install, and it worked right away. Under "Settings" I set "Update Interval" to 20 minutes because I wanted frequent updates. Remaining options were left at the factory settings.

Before installing Network Time I opened UDP port 123 (inbound/outbound) in Windows Defender Firewall. This port is used by the NTP (Network Time Protocol). I named the rule "UDP-port-123-time1", see figure 3.

Figure 3 Windows Defender Firewall (Windows 10).

I changed "Set the time automatically" from On to Off as shown in figure 4. This tells Windows not to use W32time.

Figure 4. Date and Time (Windows 10).

You can check the accuracy of your computer clock by visiting this page.

Vy 73 from OZ1BXM Lars

onsdag den 12. februar 2020

2 GHz Spectrum Analyzer with SDRplay

SDRplay RSP1A can be used as a spectrum analyzer between 1 kHz and 2 GHz. "RSP Spectrum Analyser" is free Windows software developed for this purpose. "RSP Spectrum Analyser" can be downloaded from the SDRplay website.

Figure 1. SDRplay RSP1A with a 20 dB attenuator.
I wanted to test a Pierce crystal oscillator. The circuit diagram is shown in figure 2. I've built the oscillator on a piece of Veroboard using leaded components. The crystal frequency is 7.030 MHz.

Figure 2. Pierce crystal oscillator.

Figure 3. Measuring the crystal oscillator.

The different items are connected as shown in figure 3. A is the crystal oscillator. B is an active probe; it has no amplification but Zin is 10 Mohm and Cin is 0.5 pF. C is a 50 ohm coax cable. D is an 20 dB attenuator. E is SDRplay, and F is the USB-cable connecting SDRplay to a Windows PC.
Figure 4. Screen-dump from RSP Spectrum Analyzer.
The screen-dump in figure 4 shows a 5-25 MHz sweep. On the vertical axis, the reference level is 0 dBm and the lowest level is -80 dBm. Spike A is the fundamental frequency, C is the 2nd harmonic at 14 MHz and E is the 3rd harmonic at 21 MHz. The remaining spikes are B, which is a spurious signal, D is a real signal, and F is a spurious signal from the SDRplay clock at 24 MHz. Spike F can be removed be activating "clock spur removal".  

Another example is measuring a band-pass filter for 1090 MHz. I connected a noise generator in front of the filter in order to create an input signal. The RSPplay was connected to the filter's output, and no attenuator was used this time (the noise signal is weak and should not be attenuated). 

Figure 5. Measuring a band-pass filter.
The reference level in figure 5 is -40 dBm, and the lowest level is -120 dBm. The sweep is 1000-1200 MHz. The filter curve is clearly visible. 

I've had much fun running SDRplay as a spectrum analyzer. The RSP Spectrum Analyzer software works excellently. For the radio amateur and the hobbyist, SDRplay is an acceptable alternative to dedicated (and expensive) spectrum analyzers!

73 from OZ1BXM Lars

lørdag den 21. december 2019

Doublet multi-band antenna

For many years, I've used a lazy loop antenna for the HF-bands, and it has served me well. I've used it for working the difficult zones for WAZ. This antenna has - literally speaking - worked the world!

Now I've decided to return to an old favorite: The center-fed doublet antenna. From 1991 to 1996 this antenna helped me work many Carribbean stations on CW with 20 W output. In order to complete my QRP-DXCC award, I need QRP QSOs from that part of the world. That is the main reason for reverting to this antenna type. My present lazy-loop antenna is not strong into that part of the world.

Center-feeding a wire antenna is a big advantage, because it can be forced to work on (nearly) any frequency. Even though the antenna is resonant in the 40 meter band (7.0 - 7.1 MHz), the 80 meter band (3.5-3.8 MHz) can be covered using an antenna tuner.

The antenna dimensions are those of a 40 meter dipole:
Doublet wire antenna (resonant in the 40 m band).

I'll let you know how this antenna works.

Merry Christmas and Happy new year!


torsdag den 5. september 2019

Connecting fldigi to a WebSDR

This post explains how I connected Fldigi to a WebSDR on a Windows 10 computer.

Fig. 1. Goonhilly logo.

Qatar-OSCAR 100 Narrowband WebSDR is an excellent receiver! It is located at Goonhilly Earth Station in Cornwall, England. This WebSDR offers different modes, variable bandwidth, fine tuning, waterfall display, spectrum display, zoom function, and so on. Why not use this WebSDR for receiving digital signals from the QO-100 satellite and decoding them in fldigi?

Fig. 2. Fldigi desktop icon.

Fldigi is the leading application in digimode. It offers a multitude of digital protocols, from CW and RTTY over PSK31 to DominoEX, Olivia, THOR, and many more. Fldigi was written by W1HJK and is maintained by him and his team. Fldigi is a digital swiss army knife!

Step 1. Enable Stereo Mix on your Windows 10 computer. This link explains how to do it:

Fig. 3. Sound window.

The Sound window is here: Control Panel > Hardware and Sound > Sound

Fig. 3 shows how Stereo Mix is enabled on my Windows 10 Home computer. A music video is playing in a browser window, and the audio moves the green bar up and down. The audio level is set to 100%.

Step 2. Select "Stereo Mix" as input source in the fldigi configuration window. The input source is called "Capture" in fldigi.  

Fig. 4. Configuration window in fldigi.

Fig. 4 shows how Stereo Mix is selected in the fldigi configuration window. The configuration window is opened by selecting Configure > Sound Card.

Fldigi can now receive audio from a webSDR or another sound source.You can test the function by playing a music video in a browser, and the fldigi waterfall will look like fig. 5!

Fig 5. Audio stream displayed in fldigi

Fig. 6. MFSK16 transmission from PA1SDB received by Fldigi.

Vy 73, OZ1BXM Lars

tirsdag den 3. september 2019

Help - fldigi won't start

Fldigi is the leading application in digimode. It offers a multitude of digital protocols, from CW and RTTY over PSK31 to DominoEX, Olivia, THOR, and many more. Fldigi was written by W1HJK and is maintained by him and his team. Fldigi is a digital swiss army knife!

Having installed fldigi on Windows 10 Home, I executed the setup wizard and typed call, QTH, locator, and other details.

Fig. 1. Short-cut on Windows desktop.

The next day, I double-clicked the fldigi short-cut on my desktop (Fig. 1). Nothing happened. I did it again, but still no response from fldigi. PC rebooted. Nothing. Cleaned the Windows registry with Glary Utilities. Nothing. Uninstalled fldigi, rebooted the PC, and installed fldigi again. Still no action.

The solution came from WO9B in this blog post. One or more files in folder fldigi.files are corrupt. Here is what to do:

  1. Rename c:\users\oz1bx\fldigi.files to c:\users\oz1bx\fldigi-old.files
  2. Restart fldigi. 
  3. Fldigi will discover, that fldigi.files is missing, and it creates a new one. 
Setup data must be typed again. Move important files from fldigi-old.files to fldigi.files

Vy 73, OZ1BXM

tirsdag den 27. august 2019

Lower SWR on Helix13 from Wimo

The QO-100 satellite uplink is in the 13-cm band. I'm using a 21-turns helix antenna (Helix13 from Wimo) for uplink antenna to the NB transponder. This RHCP helix antenna works fine except for bad SWR.

Fig. 1. Helix13 antenna from Wimo (picture from 2009).

Fig. 2. Remove this alu-tube.

First I removed the alu-tube from the antenne. This tube is intended for impedance matching. It is not needed any more, since I'll use a different matching method.

An N-connector is fitted where the alu-tube was before. You must drill holes in the helix reflector for the flange of the N-connector.

Fig. 3. Dimensions of the impedance matching plate.

I made an impedance matching plate for the antenna. The plate is cut from thin copper sheet. The length is 1/4 turn and it is mounted above the helix reflector (see figure 6). This matching plate converts the helix impedance to 50 ohms.
Fig. 4. Purpose of the holes.

The impedance matching plate extends the helix wire. The plate is soldered to the N-connector's center pin (green hole). The red hole is used for fastening the alu wire. You can use a short bolt for this. I soldered the helix wire to the matching plate using a short brass tube. Before soldering, the brass tube was pressed with a pipe wrench to make it fit the helix alu-wire.

Fig. 5. The new N connector.

Fig. 6. The impedance matching plate.

Fig. 7. Click picture to enlarge.  

Notes to fig. 7: Distance A is 3 mm above the reflector. Distance B is 7 mm above the reflector.

Fig. 8. Measuring SWR.

The graph in fig. 8 begins at 2.0 GHz and ends at 2.7 GHz. The marker (yellow triangle) is at 2.4 GHz.

The SWR at 2.4 GHz was measured to 1.08 which is an excellent value. All SWR values between 2.0 GHz and 2.55 GHz were below 1.2.

My antenna analyzer is a hand-held instrument N2201. It covers 137.5 MHz to 2.7 GHz. The N2201 has a smaller brother: N1201. The difference is that N2201 is equipped with an additional power meter. The less expensive N1201 would be sufficient for this SWR adjustment.

Vy 73 from OZ1BXM Lars