Revised 02/01/2006

My first experiments with SO2R started in early 2000 when I decided to design and build an SO2R setup. After some experimenting I ended up with the following arrangement: First SO2R setup used in 2000-2001


The main SW I use for contesting is still CT and I also have Writelog. I use CT most of the time because after so many years I've really become used (or shall I say addicted?) to it and I managed to learn most of its tricks and nuances. Besides, as a potential candidate for RSI I'd like to minimize mouse usage and this keeps my ham directory as much rodent-free as possible.

There is no full joy with contest SW. CT can be a real PIA to get fully set up especially on modern PC's (hats off to Mark KD4D's enormous work to work out DOS boot options for different OSs). Writelog - despite its ad - is not supporting SO2R with Windows XP. The Radio A/B bit is only mapped to pin 14 on the LPT port. In order to get A/B switching third party LPT driver needs to be installed (see Writelog webpage for tutorial if you want to take this way - I don't).

There is a debate which regularly reoccurs on mailing lists about computer configuration. Both radios can have its own PC vs. both radios hooked up to the same PC's. Both options have their pro's and con's and I try to summarize them in the table below.


Both radios on a single computer  One radio per computer
Pro: less space is required on your desk Con: you not only need the space for two keyboards and mice but you need to coordinate which one to use at what time
Pro: no need to network the PCs - eliminates the risk of network failure  
Pro: lockout is usually implemented (1 signal at a time is guaranteed)  
  Pro: no external switching mechanism is required except the audio (No XP vs. A/B bit problem)

Having both radios on separate PC's is said to have the benefit of instant backup. However backup can easily be done by HDD mirroring even within the same PC (see IOmega's Automatic Backup SW but there are many free filesync utility on the internet to back up every change of your log onto an other physical drive like a pendrive)

I have chosen to have a single PC for controlling both radios and I find it very convenient. It can not be generalized though - everybody should choose what he/she finds the most convenient.

Until last year I used a Compaq E500 Pentium III notebook running at 660 MHz and having Windows 98SE software. It had only 1 built-in COM-port, the other 2 were provided by an Argosy PCMCIA serial port extender, which hooked up as COM5 and COM6. This year I got a HP (Compaq) NC 6000. The Argosy card works fine in this notebook, too.

First I used a separate PC for packet cluster connection which had a TNC and a VHF radio. Handling the frequent VHF link breaks and cluster breakdowns was easier on a separate PC. These days I use readily available internet connection either via LAN, WLAN or even GPRS or most lately via UMTS 3G mobile phone.

The SO2R-box was designed and built by myself. It switches the headphones, the keyer, the microphone, the PTT. The box combines the keyer output with external paddle as well as the footswitch with the PTT signal of the PC.

There are many excellent designs available either commercially or in public domain starting from the simplest but effective headphone switching (like that of N2NL) to the most complicated microcontroller-based units like that of SM3WMV's. As a radio engineer I always opted for simplicity and reliability and aimed to design a box, which

* is generic enough to be set up in different host environments (I do SO2R from guest opping)
* is RF-bulletproof
* easy to troubleshoot, even during a contest

That's why I used 12V 4PDT relays from Siemens or Matsushita. 12V is readily available everywhere, the relays easy to find and easy to measure (DVM or in extreme case a buzzer is enough to troubleshoot their circuitry)

SO2R audio handling either provides left-right separation of the two radios or TX-RX switching which selects the RX-active radio for both ears. The choice primarily depends on individual preference and capability. What is fact though that while the first method provides continuous monitoring of both radios the latter provides better S/I ratio. I wanted to have both option so on my box I can set both modes. The box has a flip switch on the frontplate to activate the A/B-bit controlled relay, which puts the audio channels of radio on RX when one of them is switched to transmit. When the pileups on the run radio gets too intense I temporarily disable the second radio.

I can also select left-right separation of the radios and the SO2R box also does audio mixing: With a 3 position switch I can select any of the 3 modes: active radio in both ears, one radio in each ear and non-active radio in both ears. When I use the two VFO's of the MP simultaneously, the switch is in the first position and the MP takes care of mixing. When I use the second radio, the second position is selected. The third (reverse) position is used when the S/N in the mixed position is not enough to get a good copy on the second radio and in this case I quickly turn the switch to get the call without changing the active radio (CQ does not have to be interrupted).

Separating the PTT-controlled audio swapping and the mixing function creates tremendous flexibility, which enables selecting the right combination for any operating situation.

To be honest, when I built my box I was simply not sure which method would suit me better so I implemented both. :)

I've also implemented voice keyer connections of the soundcard SSB contesting. The microphone is a Heil HC4 element mounted on flexible mike-boom (coming from a 4 euro PC headset) attached to a Sony MDR-V600 headphone. The microphone is plugged in the notebook's mic input and the output is fed to the radio via an isolation transformer.

I prefer Yaesu radios. Maybe because I always had Yaesu, maybe because I like ergonomics and their design. My first SO2R attempts were done with an FT1000MP and an FT990. The FT1000MP is the best radio I could afford and I use it for casual DXing, Dxpeditioning and contesting. I had my MP since 1996, operated it on 4 continents on dozens of expeditions of all kinds and it never let me down.

The FT990 was selected as second radio because:

- this radio combines simplicity and performance the best
- the connectors are the same as on the MP
- very well built and rugged
- available

The MP has all CW filters (Yaesu) including the CW filter for the 2nd VFO. This one will likely be replaced with an INRAD 400 Hz since its steeper skirts would better fit S&P. For SSB I had the 2.4k filters for years and I was perfectly happy with them - until last year I got a very good deal on 2kHz Yaesu SSB filters. First I lacked voice fidelity a bit but I go quickly used to it and nowadays I use the 2.0 kHz filters almost exclusively.

The MP's mod options are maxed out. The PIN diodes have been upgraded - there is an ongoing debate if this is a waste of money, however it was an improvement over the stock PIN diodes. Mine is a very early model and had 1SS83 diodes what even Yaesu suggested to replace (TB-9643). I measured IM2 (yes IM2 for M/M) and IM3 and noticed improvements. However the measurement was done very hastily so please take it as a subjective opinion at best. Now having the second MP I can do A/B testing and it stands high on my to-do list.

I also modified the ALC and NB circuitries and first took W2VJN's idea of an intermittent IF amplifier and use a broadband low-noise HP measurement preamplifier in the MP. This preamp was designed to provide maximum linearity and has three selectable amplification levels. These are set to 6, 8 and 10 dB. This provided very handy flexibility without the need of entering into the hidden menus. After obtaining an INRAD roofing filter for the 70 MHz first IF I removed this additional IF amp stage. INRAD opted to put the roofing filter behind (!) the IF amplifier for the sake of easy implementation instead of right behind the mixer where it belongs with proper impedance matching. An other long-term task is to redesign the circuitry around the narrow roofing filter and move it where it should be. For more about my ideas about how to modify this radio for better performance look here.

As an active user of the SUB-VFO I plan to replace the Murata CFJ455K13 (a good filter for its size and price though!) with a 2 kHz INRAD filter to improve the selectivity of the SUB-VFO. An other item for the to-do list: make a nicely photo-documented writeup of this mod.

During my last 2004, 2005 SO2R attempts in Russian DX Contest I used a TS-950SDX (courtesy of HG6N station) and I truly liked its sound on SSB. However its ergonomics or actually the complete lack of them (see SUB-VFO handling or the fact that you can not change RX parameters like tuning the sub VFO further while being on TX - when I actually have time and free hand to perform this) have not made me fall in love with it.

Having the second same plain vanilla MP (this one 98 vintage) helps me to use identical setups, giving me a big relief with connectors etc and offloads my brain a bit during contests.

In my setup the main radio has one amplifier connected, while the second radio has usually two connected. This comes very useful especially on dusk and dawn periods when quick sweeps always produce new mults on simultaneously dying bands. The benefits of this solution are:

- the two TX branches are completely isolated
- the tuning time is kept on minimal
- t he system reliability increases, since the outage of one amplifier does not influence the system performance significantly
- the switching is done at low power (beneficial for the future automation)
- even 3 manually tuned amplifier is cheaper than even one auto-tuned one (especially if the three are home-made)

When I have the chance to use Beverages, they are connected to a coax switch, where the appropriate direction can be selected, followed by a BC band filter and a two-position switch to select the Beverages to one of the radios.

This is the description of the SO2R setups I had so far. It was first tested in the IOTA 2000 (#2 in SO24/Mixed) and WAE CW 2000 (#3 in SO) contests. A year later my attempts in IOTA (#1 in SO24/Non-IOTA/Mixed with record) and WAE CW (#1 in SO) contests were more successful.

During the years it evolved a bit as some projects were completed (thanks to Peti HA1TNX who always patiently helps me !)

This is the current status:


Current SO2R setup


A few items from my to-do list:

- automate the amplifier PTT selection for 2nd radio
- build 3rd BP box to let the RF switching done by MP's internal A-B ant switching and get some redundancy on this element

SO contesting is always the secondary option for me since I always preferred team contesting. However there are some great contests like the Russian DX offering lots of opportunities to improve my skills while competing in the SO class. SO2R seems to be the most challenging and most competitive way of doing SO that's why I invested some time and effort to put this setup together. If you have any idea how to improve it further, please let me know. Your input would be gratefully appreciated.

You can get the schematics of the SO2R box via email for free provided you will not use it for commercial purposes and proper reference to this website will be given if it will be used in publications

No, I will not build one for you.

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