onsdag den 19. juni 2019

The GPSDO makes my LNB rock-stable

A consumer-type LNB for Ku-band can receive the QO-100 satellite transponder. A LNB with PLL-oscillator has an acceptable frequency stability after warm-up, but it still drifts. The reason is outdoor temperature changes and a simple oscillator using a cheap crystal.

Adding a GPSDO will greatly improve the frequency stability in the receive chain. The block diagram below shows how the GPSDO injects a clock signal into the LNB. The clock signal from the GPSDO has superior stability compared to the LNB oscillator. 

GPSDO generates a 25 MHz clock signal for the LNB.

I decided to buy a GPSDO developed by 4 danish radio amateurs. The project is named RFzero. The price of the RFzero board was less than 50% of the Leo Bodnar mini-GPSDO. Another advantage of the RFzero is the possibility of writing your own software using the Arduino IDE. The RFzero board is assembled, and only a few optional pins are soldered by the end-user.
The RFzero board.

I've mounted the RFzero board in an aluminium box. Power (5 V DC) is supplied via the USB interface. An external PSU can also power the board.

GPSDO front view.

GPSDO rear view.

GPSDO with lid removed.

Conclusion: Adding a GPSDO has greatly improved my receive chain. The Narrow-Band beacons are now rock-stable regardless of the LNB temperature. 

Vy 73 OZ1BXM Lars
My webpage: http://oz1bxm.dk/ 

onsdag den 1. maj 2019

Transmitting via Es'hail-2/QO-100 geostationary satellite

Transmitting via QO-100 was easier than I thought. The transmit chain is shown below.
TX chain for satellite QO-100.
A 70-cm transceiver was already in the shack. My trusty old Yaesu FT-847 is still doing well. The FT-847 output was reduced to 3 W on 432 MHz.

Yaesu FT-847 transceiver.
I needed a 13-cm transverter for the uplink. I choose to buy a ready-made one from SG Labs in Bulgaria. It was delivered assembled and tested from the factory. Time from order/payment to delivery was 6 weeks. The transverter provides 2 W output at 2400 MHz which is sufficient for making contacts on the satellite.

13-cm transverter from SG Labs.
The QO-100 uplink signal should be circularly polarized. 3 dB is lost if a linear signal is transmitted. I decided to employ my 10 year old helix antenna with 21 turns. I had to adjust the bracket so the antenna was elevated 24 degrees (this is the elevation of a geostationary satellite seen from central Denmark).

Helix antenna for 2400 MHz. Elevation is 24 degrees.
I was happy to learn that my transmit signal was visible (and audible) on the waterfall display. I had my first QSO via QO-100 on April 24th. 

The QO-100 narrow-band transponder can be monitored via this web-SDR: https://eshail.batc.org.uk/nb/

73 from OZ1BXM Lars
Homepage: http://oz1bxm.dk/

lørdag den 2. marts 2019

Receiving the Es'Hail-2/QO-100 geostationary satellite

Es'Hail-2 geostationary satellite (credit: Es'hailSat)

The main purpose of the new geostationary satellite Es'Hail-2 is to provide television services to the Middle East and North Africa. In addition to commercial services, Es'hail 2 includes two linear transponders for amateur radio; one with a bandwidth of 250 kHz and another one with 8 MHz. The uplink for both transponders is 2.4 GHz; and downlink is on 10.45 GHz.

Es'Hail-2 is called QO-100 in the radio amateur world (i.e. Qatar Oscar 100). Service for radio amateurs was opened on 14-February-2019. The linear narrow-band transponder has been busy since then. Two beacons indicate the upper and lower limit of the passband.
Es'Hail-2 Narrowband Linear transponder:
  •  2400.050 -  2400.300 MHz Uplink
  • 10489.550 - 10489.800 MHz Downlink

Es'hail-2 footprint.

The footprint of Es'Hail-2 covers half of the world. That huge pattern offers new opportunities for many hams: DX can now be worked without erecting big HF-antennas. A satellite dish on the balcony is all you need.

My RX set-up is shown below. It is simple and cheap while still providing a taste of satellite DX. The Win 10 computer runs SDR#

Receive chain at OZ1BXM

The satellite dish is Triax TD78 (offset, 70 cm wide, 78 cm high). The LNB is Maximum ST-11 (single port) with PLL and 25 MHz crystal oscillator.

Offset dish with LNB.

Bias T for 12 V DC.

RTL-SDR dongle V.3

The narrow-band transponder can be monitored via this web-SDR: https://eshail.batc.org.uk/nb/

73 from OZ1BXM Lars
Webpage: oz1bxm.dk

lørdag den 5. januar 2019

uBITX 10 W SSB-transceiver for 10-80 m

I've just acquired an uBITX. It is a 10 W SSB-transceiver operating from 10 meters down to 80 meters. The uBITX is made in India. The transceiver is not a kit - it is delivered as two assembled PCBs, an LCD-display, and wires.

The main board is the transceiver module and the smaller PCB contains the VFO. The user's task is to mount the circuit boards into an enclosure and fit terminals and controls.

The uBITX block diagram.

The block diagram above shows the RX-part which is a superheterodyn receiver with two IF stages at 45 MHz and 12 MHz. The TX-part is the same concept, but the transmit signal flows "backwards".

Main board and two digital PCBs mounted vertically. 

The main circuit board measures 15 cm x 14 cm and contains most of the components. There are no adjustments to make as they are set at the factory.

The VFO comprises an Arduino Nano and a programable oscillator Si5351. The oscillator frequencies are set with an encoder, and the operating frequency is displayed on an LCD. The factory delivered display is a 2 x 16 LCD; however, a larger color touch display can be added.

I found a cabinet at amateurradiokits.in. It has all holes punched and makes the transceiver look "factory made".

Support group for uBITX: groups.io/g/BITX20
Facebook group for uBITX: fb.com/groups/uBITX/

Vy 73 from OZ1BXM Lars
Homepage: oz1bxm.dk