Hot-Rod Your ICOM IC-725-Series Transceiver by Jukka Vermasvuori
Hot-Rod Your ICOM IC-725-Series Transceiver Part 1 by Jukka Vermasvuori OH2GF Receiver Issues The receiver in my IC-725 exhibited these drawbacks: Its audio frequency response was too narrow, dropping 6 dB from its maximum by about 2 kHz. High-end rolloff that is this profound filters out speech energy necessary for good SSB intelligibility and severely muffles AM broadcast signals, which carry audio up to at least 4.5 kHz. 4 The AM-mode audio had a “mega bass” quality. The level of in-band intermodulation products seemed to be quite high. 5 On CW, I could hear weak phantom beat notes from out-of-passband signals. The pitch change of these spurs was the opposite of that of desired signals during tuning. In effect, a strong signal would come back into the receiver passband if I tuned in the right direction. Although these spurious signals were weak, they sometimes disrupted communication as I worked weak DX stations in crowded bands. During CW rec...
