RS232 TRANSCEIVER INTERFACE
Although newer transceivers have an RS232 port to allow monitoring and control by PC based utilities, some older rigs need an interface to convert the radio's TTL RS232 to the PC's RS232 level. This simple circuit is intended for older Kenwood radios and was presented in chapter 22 of the ARRL Handbook.
Built around a MAX232 chip and using optocouplers for complete isolation, it permitted control of a TS-440 which I no longer have.
All my transceivers now have RS232 control as standard. However, before the widespread use of domestic PCs most radios were sold with this as an option. The Kenwood TS-440 is such a case. To have serial port capability with the 440 you needed to install two optional chips, one discrete IC and a UART, easily found and much cheaper than buying the serial port upgrade pack from Kenwood consisting of the same two ICs and some instructions. Even then, RS232 was only available at TTL levels. These needed to be converted with an interface box to 232 levels. More information about this is available on the many sites dealing with ham equipment mods.
Nowadays most new transceivers have some sort of monitor and control port. Kenwood use a basic RS232 set-up - just add a radio to PC serial cable. It's useful, when running the appropriate software, to facilitate logging. I use CT for working pile-ups when away from home and LOG-EQF for general logging, award-tracking and cluster 'eavesdropping'.
Linking a TNC and HF transceiver to a PC running LOG-EQF allows me to eavesdrop in on the local DX-cluster (I don't have to be connected) and when a spot appears the program filters it and warns me that there is a needed station on the bands. With a single keystroke I set-up the HF radio and listen to the station to see how he's working the pile-up. A lot of times, because this process is so quick, a large pile-up has not yet evolved and it's an easy, text book, 'clockwork' QSO - another one in the bag!
The DX-cluster - pros and cons
You don't need to be permanently scanning the band for needed countries. You can rely on the cluster and your fancy software to warn you of any needed entity. Great! Very efficient and it lets you occupy your time with other things. I use it often.
The bad news is that, after seeing the DX-spot, by the time you get to the DX-station's frequency he has been overwhelmed by other 'Cluster-DX Hunters' and the chances of you breaking this, now large, pile-up is slim. Things are often worsened when bad ops, who can't copy any morse apart from their own callsign, don't understand how the rare station is operating. They don't listen. They can't copy fast code. They don't know how to operate split. However, they can read from a PC screen! They've seen the DX-spot come up on the cluster, so it's a case of tuning, calling and waiting to see if they hear their call come back! No matter if the DX is calling only NA, only JA or working split although you would imagine that most ops would think it strange if a P5 station appeared and there was nobody answering back on his frequency!
Therefore, tuning around often to search for DX is probably not such a bad idea. You'll be surprised at how much DX you'll find and work in between the cluster generated pile-ups.
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