In a world where increasing noise and QRM levels in residential areas are worse than ever, radio amateurs have to look for solutions. So, do, what the professionals do, and set up antennas on remote rural areas, and use the internet to distribute the received signals to the amateurs. Use WebSDR techniques.
- Offering an alternative for radio amateurs with high local man-made noise levels
- Supporting making QSO’s (short latency <0.5sec)
- Supporting ham bands only and including CW segments
- 24/7 available, reliable and predictable
- Antenna radiation pattern matching transmitting antennas common on residential locations
- Not intended to be a shortwave listening station or to provide the best possible reception
Why the choice for WebSDR?
- it offers a 400msec well controlled low latency
- supports a large number of users
Low consistent latency <500msec is essential for making QSO’s using a WebSDR!
This WebSDR uses a single broadband antenna for the 80m/60m/40m/30m/20m HAM radio bands. It is intended to give radio amateurs the possibility to receive a good signal on these band, in terms of QRM/Noise. It has not the intention to be the best receiving facility. Amateurs have to use their own transmitting antenna at their residential locations. It makes no sense receiving a lot of stations that are not able to hear you. So transmitting and receiving should be in balance.
A quick overview of the set up is given. The active small broadband receiving antenna is a 1.69 m2 small loop with a broadband amplifier. From there we use a 100m coax cable to the shack. In the shack we have a 5 and a 4 band passive filter which is feeding the receivers for the 9 bands. These receivers are connected to two computer. On the computers we run Debian, with WebSDR software of Pieter-Tjerk, PA3FWM, and specific intermediate software for the SDRplay receivers. Bas, ON5HB, helped us with the intermediate software (TNX Bas). More information about the WebSDR project of Pieter-Tjerk can be found on http://www.websdr.org.
Pieter-Tjerk (PA3FWM) is the developer of this WebSDR concept.
Initial development was for the bands 80m, 60m, 40, 30m and 20m. Later in 2020 we also started to work on a 2m websdr, which came to life end of 2020. Early June 2021 we splitted the 2m band in a lower band (horizontal Big Wheel) and a upper band (vertical Diamond). Most of the work for the 2m band was copy and past, but a separate chapter is written to discuss specific 2m issues. The 2m websdr runs on a PI4. April 2022 we added the higher HF amateur bands (17,15,12,10m).
A small broadband active loop antenna: Active broadband loop antenna
Broadband loop amplifier (update March 2022 of 2018 and of 2003 design)
The broadband loop amplifier design requirements
- Bandwidth starting from 1.8MHz or lower and up to 30MHz
- Noise contribution lower than the rural ambient noise level
- Best balancing and decoupling from the feeding coaxial cable (minimizing coupled man-made noise and for measurement applications)
- Very good large signal behavior (IM products <= noise level of the amplifier)
- Output level comparable to the half wave dipole
- Controlled gain (especially if using loops in matched pairs and for measurement applications)
- Overload protected (your own transmit signal e.g.)
- Receiver maximum input level limited to about 13dBm
- Filtering potentially overloading local out of band (VHF) signals
- Using regular components, not too complex circuit, no SMD’s (junk box)
- Low visibility of the loop for neighbors
Of course the result will be a compromise, on all aspects good enough.
(see for the principle of the amplification: Broadband amplification)
Design and specification bandwidth: 1MHz-30MHz
Note: balancing and visibility both are very relevant on a residential location. Especially balancing is most relevant because of the high man-made noise levels on residential locations.
The null of the loop is pointing east/west. The null is orthogonal to the surface of the loop.
Gain in the WebSDR is set for an equivalent antenna factor AF=0.35 on all bands.
PCB design by PA3CSG.
The PCB is available through the Maasbree WebSDR website.
More information is in Broadband_active_loop_PA0SIM.pdf
