Archive for the ‘HF’ Category.

Multiband SDR with remote receivers

In past I assembled small SDR receiver based on Raspberry Pi and SDR USB dongle based on software developed by PA3FWM. The problem was with limited usability by multiple clients connected to the Raspberry pi at the same time. The old SDR was retired and put aside for few years.

Then András Retzler ha7ilm developed (and stopped developing) OpenWebRx, which was the base for now regulry maintained and further developed

I recently built homelab server based on “proper” server infrastructure with plenty of RAM and lots of processing cores. I decided to setup OpenWebRx in one linux virtual machine with raspberry pi only as remote receivers serving single user (server itself).

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Yaesu FT-991A Frontend has nasty hidden fault. It is not normal from €1000 radio to stop working just because you use it in a pileup situation or when your close OM is beaming toward you with QRO.

New, out-of-the box radio receive performance of the FT-991(A) was normal, but after other station(s) had transmitted at a higher power levels, the FT-991(A) receiver failed. The failure mode was as follows:

  • Receiver operation is normal when the Attenuator feature is disabled.
  • Receiver operation fails (no receive and a very quiet noise-floor) when the Attenuator feature is enabled.
  • IPO operation enables the Attenuator and results in the same receiver failure mentioned immediately above.

Same issues are reported elsewhere:

Patient with exactly the same simptoms got to the operation table in my lab today. The owner is OM S52W, very successfull contester and member of the famous contest club.

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6×1 antenna switch

This is complete project for 1×6 antenna switch. It was bult in more than 50 pieces around the world and performs really good. Even big guns use it for their systems. The project was designed with help from other OMs (S55O, S59MA, S50LD, S51CT, S51ZJ, SM2WMV/SJ2W and others).

6×1 antenna switch

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Adjustable gain LNA

Low noise amplifiers are very useful. I built one with single BFG425W transistor with adjustable bias current. The schematic diagram is very simple:

LNA schematic diagram

and the PCB is 20x24mm:


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Simple HF amplifier for QRSS beacon

This is 5 minutes soldering project. There is no schematic, just simple circuit, something between “dead bug” and conventional PCB design. I did this in two steps. First attempt was complete failure. Local OM told me that any power mosfet can operate as power amplifier for HF. Ok, maybe not just any. I tested with couple of them including IRFZ24N. Finaly I took “proper”  MOSFET for higher frequency and the circuit worked pretty good:

Simple output stage for QRSS beacon assembled in "mixed" technology

Simple output stage for QRSS beacon assembled in “mixed” technology

I will briefly describe this quick and simple project and I hope readers would enjoy it.

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Mini CW Keyer / QRSS beacon V1.1

I designed dedicated PCB for the CW keyer. The project is very similar to the version made on prototyping board.

keyer pcb

Here are the updates:

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Programmable CW Morse Keyer / beacon

Mini USB dongle with STM32F0xx is suitable many for simple, mini projects. I attached speaker to Timer14 PWM output (Pin PA6) and LED (or optocoupler connected to PTT) to GPIO pin PA0:


The provided software is based on USB Virtual Com Port (VCP) device. The setup is done with command line interface using terminal from any PC. The setup is stored in the internal flash and PC is not required for normal operation. The mini beacon keyer can be used when powered with 5V.

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Simple small QRO for HF

I followed the ARRL Homberw challenge 50 watt aplifier entry. It is low cost, simple HF linear amplifier designed and built by the author as an entry in the ARRL’s 2009 Homebrew Challenge contest.  The requirements of the amplifier were: 40 meter band 50 watt output amplifier intended for use with a QRP transmitter as driver (less than 5W), constructed at a total material cost of not  over $125.00.

I redesigned author original design an put it on the double sided PCB with additional output banpass filters. I started with first prototype:


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