NAQP CW August 2015 – IF Shift “Magic” with the ICOM 703 and the FL-52A Optional Filter

The North American QSO Party CW was the main contest this weekend: 18:00z August 1 to 06:00z August 2, 2015. The 40 meter band was opened to much of North America and without much effort within a few minutes I had logged 15 stations in 11 states and provinces. However, my main interest was not to make many contacts, but to test the CW abilities of the ICOM 703 with the FL-52A 500 Hz filter in a busy band. A few moths ago, the Elecraft KX3, which for a couple of years had forced the ICOM 703+ into oblivion, suddenly was in need of repairs and had to be shipped back to its birthplace in California. I then decided to resurrect the ICOM 703+ by installing an “optional filter” and favoured the ICOM FL-52A. Here are pictures of the motherboard before and after the installation:



This filter is superb to cancel signals outside its 500 Hz window. However, in busy CW contests it is not infrequent to find CW signals calling in close proximity of each other, within the 250 Hz boundaries on either side of the filter bandwidwith. In the 703 these filters have a fixed passband. Also, contrary to the ICOM 706MKIIG, the 703 only accepts one single additional filter of fixed bandwidth to be installed in its mother board. However, the ICOM 703 has an additional interesting feature that together with the FL-52A does permit reducing the bandwidth to about one half the size of the passband of the filter. Using the IF Shift function ( it is possible to obliterate as much as close to one half of the bandwith on either (but not both) sides of the central frequency. Choosing different center frequencies and using the IF Shift function to cancel signals at either side of it it is possible to further hone on a specific signal and separate it from others near-by.  This can hardly compete with the roofing filters in the KX3, but it is a feature that still makes for quite an able QRP transceiver, particularly if cleverly combined with the CW/CW-R (Upper and Lower CW) function ( also available in the ICOM 703.


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