Archive for the ‘Ham’ Category.

Quick and dirty 868MHz antenna in 5 minutes

This is simple antenna for 868MHz built in 5…10 minutes. Take about 10cm of RG214, a plate of PCB with the copper at one (or both) sides. Remove the coax shield and inner dielectric on one side in length of about 85mm. You will cut this to proper length during SWR measurements.

Simple antenna made with piece of coax and piece of old PCB.

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Collinear antenna for 868MHz Lorawan Gateway

This is description of coaxial collinear antenna for 868MHz applications. I designed this for Lorawan gateway.

Antenna tested with lorawan gateway

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Tiny, isolated USB to Xcvr interface (PTT, Audio, CAT, …)

I will descvribe here the USB interface between the redio station and the computer which I recently developed and tested. This post is a continuation of the first part, where I described a simple interface for controlling two digital lines using the USB / Serial Converter, where I presented simple interface to control two digital signals (e.g. PTT and CW). This time I will describe an interface that combines more functions:

  • Controlling several digital (switching) inputs and outputs,
  • Interface for controlling the station via the serial interface
  • Audio input and output interface (sound card)

I had some implementation issues with the microcontrollers and USB virtual com ports, which I have described in detail in the previous contribution, I decided it’s better using the tested solutions. The block diagram of the interface is swhown in following picture:

Block diagram of the interface

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Small USB to PTT/CW adapter

In this post, I will first introduce some of the basic technical background of the control of the transmit signal (PTT) and other signals (eg CW or linear activation). The second part will describe the  interface development and the final product.

Standard DB9 male connector

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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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Cheap sh*t magnetic pickup

Do you ever wondered how much magnetic field garbage is around you? This is cheap and easy build to measure magnetic noise or to compare which switching supply is more sh*tty.

Near field probes are nothing new. It’s easy to find one via web search. Here is one good reference for H and E field probes which I found via google image search:

EMC near field probes for H and E field

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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 Rh, T and p sensor with UART communication

The Pressure, temperature and humidity sensor based on MS5637 HDC1080 originally (Rev. 2) operates via RS485 interface and multidrop HDLC-like protocol.  I decided to simplify this for use with Raspberry Pi, arduion or any other mass platforms. First, I took away the RS485 transceiver and second, I simplified the communication.

First adaptation was easy:

Remove RS485 driver and connect Rx/Tx to A/B

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Pressure, temperature and humidity sensor based on MS5637 HDC1080 Rev.2

Gal ordered some PCBs from PCB-Way a while ago. It was multiproject panel with several PCBs. One of the modules was double sided revision of the Pressure, temperature and humidity sensor based on MS5637 HDC1080 which was posted while ago.

Pressure, temperature and humidity sensor based on MS5637 HDC1080

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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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