#ICOM IC 7100 MODS SOFTWARE#
is a nice program for designing filters, and the price is right for hobbyists! I did have a few hiccups with the software while using the diplexer design, but I eventually got it to work. That way the transmitter is presented with a 50 ohm load at all frequencies, instead of a highly reactive load for the harmonics and 50 ohms for the fundamental. The idea is to route just the harmonic energy to a 50 ohm dummy load, and the fundamental to the antenna. I decided to use a diplexer filter design to try to tame the transmitter and internal SWR meter. I didn’t want to find out the hard way (like with a puff of smoke out of the radio). It’s possible it might also cause some other problems (poor efficiency or oscillations). That page doesn’t say if a filter was inserted between the rig and an antenna or not (I guess not), but it’s the author’s opinion that the energy in the harmonics plays havoc with the internal SWR meter. shows that the transmitter has severe distortion when the load is the typical short vertical used on the band.
In researching a suitable filter, I found mention of a possible problem using a low pass filter. A filter is required to keep the radio legal. The 2nd through 4th harmonics are passed right through. This modification will indeed make it transmit on 472 kHz, but the problem is that the radio’s final amplifier filtering is ineffective since the 160 meter low pass filter in the radio is used.
The North American version of the Icom IC-7100 can be easily modified to transmit in the 630 meter band by removing a couple of diodes on the bottom circuit board.
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