June 18,2023

For my VHF/UHF setup I am using a dual band Yagi antenna mounted with 20 deg elevation, beaming SSW (210 deg). The signal is fed to a dual band amplifier (DBA) from SSB electronics and split into the VHF and UHF path.

Fixed mounted VHF/UHF Yagi at 210 deg with 20 deg elevation

VHF goes to my Icom IC-9700. If not used otherwise, it is running on the 144.39 MHz APRS frequency. Signals are processed via LAN using the remote Wfview program on a Linux PC routing the AF signal to the Direwolf modem for digipeating.

The UHF signal is fed through a band pass filter to an Airspy Mini SDR. Signals are processed on a Raspberry Pi 4 running a SATNOGS client.




APRStt Gateway – Singapore

Use your analog handheld transceiver (HT) to report your position, status and receive frequency to the APRS network using DTMF touch tone!

Possible commands to the gateway are shown in the table below. Correct input will be replied with Morse code R for roger, or ? for errors. APRS frequency in Singapore is 144.390 MHz.

MEM 1ACxxxxxxxxxx#Your full 10 digit call sign (always transmit at first)
MEM 2C9*xxBzzzzz#Your home location xx (see below), status 9 (set to “APRStt user”) and your 5 digit abbreviated suffix zzzzz (see below)
KeypadxxBzzzzz# e.g. 20B15409#Set location to xx (zzzzz your suffix abbreviation)
KeypadxxxxxxCzzzzz# e.g. 145500C15409#Change QRG to xxxxxx (exactly 6 digits), zzzzz your suffix abbreviation.
KeypadxCzzzzz# e.g. 3C15409#Change status to x: 1 – off duty, 2 – en route, 3 – in service (check in), 4 – returning etc.
KeypadxxxAzzzzz# e.g. 223A15409#Change symbol. xxx = 159 Human/Person (HT), 229 APRStt (DTMF user), 153 Bus, 166 Bike.
Possible DTMF sequences. “*” = E, “#” = F

To check in to the gateway press MEM 1 for your full call and then MEM 2 to report your location. Afterwards you might change location, QRG, status or symbol using the keypad.

Example: FT-60

On the Yaesu FT-60 HT you have nine available DTMF memories with max. 16 chars each. Two DTMF modes can be selected: MEM and CODE. Press F/W DTMF to toggle between both.

In MEM mode you simply press the PTT and one of the keys 1 to 9 to transmit the predefined DTMF sequence of the respective DTMF memory.

In CODE mode you press PTT and each key 1 … 9 and A … D, *, # will send the corresponding DTMF tone.

Keypad FT-60

How to program the DTMF memories?
F/W SET sel 17 -> DT WRT F/W
sel d1 … d9 DTMF memory F/W
Press keys 1 … 9 or sel A … F followed by F/W for your DTMF tone sequence. E corresponds to “*” and F to “#”.
Press F/W > 1 sec to store.

Example: IC-9700

You can also send DTMF sequences from your home station. For example, the Icom IC-0700 has DTMF capabilities with 16 DTMF memories.

IC-9700 DTMF Menu

Select MENU, then 2 and DTMF. EDIT d0 (MEM 1) to enter ACmy10digitcallsign# and d1 (MEM 2) to enter C9*xxBmy5digitsuffix# – xx your home location.

Select Direct Input or d0 … d* to send manual input or predefined sequences.

Determine your 10 digit call sign number

Example: 9V1KG_ is the key sequence “981540“. The last “0” stands for space, as the call sign only has 5 characters. Next we need to add a check sum based on the position of individual letters. “9”: no letter = 0. “V”: 3rd letter of TUV = 3. “1”: no letter = 0. “K”: 2nd pos of JKL = 2. “G” 1st pos of GHI = 1. “Space” 1st pos of _ = 1. The resulting number is 030211. Taken as a base 4 number we need to convert it to a base 10 number:

0 * 1024 + 3 * 256 + 0 * 64 + 2 * 16 + 1 * 4 + 1 * 1 = 768 + 32 + 4 + 1 = 805

The resulting 10 digit number for 9V1KG is 9815400805.

Store ACyour10digitnumber# in your 1st DTMF memory.

Shortcut: For Singapore hams (9V1) with a 2 letter suffix just add the position of the first suffix letter (1…3) multiplied by 16 to the second suffix letter (1…3) multiplied by 4 to 769.

Example: 9V1LH_ = 981540, checksum 769 + 48 + 8 = 825 (L: pos 3*16 + H: pos 2*4 ), the result is 9815400825.

Abbreviated 5 digit call sign

Once your full call sign is known to the gateway, it can be abbreviated to the 3 character suffix only. For 9V1KG the suffix is 1KG. Calculation is analogue to the 10 digit call sign. Key sequence for 1KG is “154“. “1” no letter = 0, “5” 2nd letter = 2, “4” 1st letter = 1, i.e. resulting in 021. Converting to a base 10 number:

0 * 16 + 2 * 4 + 1 * 1 = 8 + 1 = 09

The resulting abbreviated 5 digit call sign number is 15409. My full call sign can be abbreviated with 15409 or even shorter 154.

Shortcut: For Singapore hams (9V1) with a 2 letter suffix just add the position of the first suffix letter (1…3) multiplied by 4 to the position of the second suffix letter (1…3).

Example: 1LH = 154, checksum 12+ 2 = 14 (L: pos 3*4 + H: pos 2 ), the result is 15414.

Terminate any tone sequence with ACzzzzz# – in my case AC15409# – the gateway will complement it to your full call sign. You just need to remember a 5 digit number.

After check in with your call sign ACtttttttttt# (MEM1) and home location C9*xxBzzzzz# (MEM2), you can change to a new location by entering the DTMF sequence xxByyyyy# with xx your location number – as shown in the tables below – and yyyyy your abbreviated call sign (see above). Example: Pressing 30B15409# on the keypad in CODE mode will set my location to Bedok.

Stored Singapore Locations

xxLocations in the North of Singapore
10Lim Chu Kang
14Sungei Kadut
xxLocations in the North East of Singapore
20Ang Mo Kio
xxLocations in the East of Singapore
32Changi Business Park
33Pasir Ris
34Paya Lebar
36Changi Village
37Changi Bay
xxLocations in central area
42Bukit Timah
43Central Area
45Marine Parade
49Toa Payoh
60Bukit Merah
xxLocations in the West of Singapore
50Boon Lay
51Bukit Batok
52Bukit Panjang
53Choa Chu Kang
55Jurong East
56Jurong West
xxOther locations in Singapore
70Western Water Catchment
71Central Water Catchment
81Sentosa Island
82Jurong Island
83Pulau Ubin
84Pulau Tekong

Link to Direwolf configuration file

APRS Map Singapore


j XahHx

SDR with Active Antennas for HF

A couple of weeks ago I started to gather my first experiences with software defined radios (SDR) and active antennas. I started with low investment, using the RTL SDR dongle, but I quickly realized that using the direct sampling mode for HF is not an ideal solution and added the Spyverter HF up-converter.

For my first trials I used a Mini Whip from RA0SMS as antenna, but the results were quite disappointing.


Finally, I ended up with an active loop antenna (see featured image), using the Cross-country Wireless Loop antenna pre-amplifier (10 kHz to 30 MHz version). The pre-amplifier is powered with 13.8 V via a bias-tee. Common mode chokes on the antenna line and all power lines helped to reduce noise, especially on the low bands. This is final hardware setup setup:

The setup is now running 24/7 on a Raspberry Pi 3B+ using GQRX and WSJT-X. I was surprised, how many stations and countries can be decoded down to 80 and 160 m.


Further Information

Talk given during SARTS monthly meeting

PSK reporter link to stations currently received by 9V1KG

CQWW DX Contest SSB 2019

Last weekend I participated in the CQWW DX contest SSB part under the call sign 4E1A. Propagation was miserable on 40 m and 80 m; with my 100 W low power I was seldom heard by DX stations in EU or NA. On 20 m and 15 m propagation was acceptable, and I got even some openings on 10 m. Finally, I could exceed my points from 2018 and made 852 contacts with 62 DXCC entities and in 30 zones.

Contacts per band. Total 2287 QSO points and 191 Multipliers.

Raw score: 2287 QSOs x 191 multipliers = 436817 points.