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Category: 9V1KG

Weak Signal Digital Modes on HF-Bands

Many open source programs are available for Windows, OS-X and Linux, if you want to become active on the amateur radio HF bands using digital modes. Modern coding and modulation schemes allow for long distance contacts with low power.

Below you can  download my presentation about PSK 31 (Phase shift keying) and JT-65/JT9 modes as presented in our monthly SARTS meeting August 2016 in Singapore.

Presentation (pdf): WeakSignalModes

 

ICOM IC-7300 – SDR radio in a box

Finally the new IC-7300 arrived, and I am still in the process to get familiar with it. I could not resist, as my IC-718, though reliable, is quite “outdated” in its technology, developed more than a decade ago.

Unfortunately, the first IC-7300 unit I picked up from the retailer in Singapore, had a DOA (defect on arrival): the CW keyer always sending dashes. Luckily, there was a second unit available, and it was exchanged without any problems.

Now the new unit is in operation for a week and doing its job without any problems. Size and weight are the same as my IC-718, but the features are not comparable, and it is a real advance in technology. The menus are intuitive and signal reception is excellent, as I can adjust all parameters – gain, filter bandwidth and response, audio processing etc. – according to the actual band conditions.

IC-7300

Two days ago, I setup the configuration for digital modes, connecting my Apple MacBook via USB, using fldigi and the IC-7300 built-in USB sound interface and serial control. So there is no need for any additional interface box, just one USB connection between computer and radio. It works fine, and I was able to make my first contacts in PSK-31.

Minami-Tori-shima JD/M and Ogasawara JD/O

Minami-Tori-shima, also known as Marcus Island belong to the easternmost territory of Japan on the pacific plate past the Japan trench. It is an isolated Japanese coral atoll in the northwestern Pacific Ocean, located some 1,848 km southeast of Tokyo and 1,267 km east of the closest Japanese island, South Iwo Jima of the Ogasawara Islands, and nearly on a straight line between mainland Tokyo and the United States’ Wake Island, 1,415 km further to the east-southeast. (Source: Wikipedia)

Before my first radio contacts with JD1BOW and JG8NQJ/JD1, I even didn’t know that Japan has a couple of small island so remote from the main island.

MinamitoriDistance from Singapore approx 6000 km.

Linear loaded short dipole

For my amateur radio activities on the HF bands I only have a 3.6 m wide balcony available for antennas. After some study I decided to experiment with a shortened dipole for the 15 m band. The full size 21 MHz half wave dipole would require a span of approx 7 m, therefore I searched for a solution to shorten the full size length by 50 percent.

Finally I decided for a linear loaded dipole; the layout and resulting dimensions are shown below.

loaded-dipole

First measurements at the resonance frequency showed a low input impedance at the dipole’s feed point with values around 10 Ohm. The theoretical radiation resistance of a 2 x 1.6 m short dipole would be 10 Ohm, so it is an indication of low losses in the system. In order to match the antenna to the 50 Ohm of the transceiver, I use a quarter wave transmission line transformer consisting of two parallel connected 50 Ohm coaxial cables.

50ohms_12ohms

After fine tuning the length of the antenna wires, I achieved an SWR below 1.5 for the CW segment of the 15 m band.

2016-03-26-1

The antenna’s bandwidth is around 200 kHz; I could already work DX stations around the world.

dipole-feed balun-1-1

Dipole feed point and 1:1 balun

RUMLog, Macbook and IC-718

In Singapore you need to get approval from the authorities for your type of radio, you intend to buy, before you can actually buy it. So in order to avoid any problems, I selected the ICOM IC-718 HF transceiver, as I knew it was approved before and available from stock.

Now, setting up my station, I was looking for a good logging program, running under OS-X on my new Apple Macbook (early 2015). I decided for RUMLog, as it is free and offers all features I need for my casual operation.

To connect to the IC-718, I use a Icom CT-17 CI-V CAT Programming Cable with a Prolific chip set.  The drivers can be downloaded from their support webpage and work without problem under OS X El Captain (10.11.3). Now frequency and operation mode are automatically transferred to RUMLog.