[ICOM] PBT Mod and questions

[Adam Farson]

Hi John,

Well...the IC-735 was an amazingly full-featured radio for its size. It had
a built-in keyer, VOX (if I am not mistaken), and even an excellent IF notch
filter. By comparison, the 728 was an upgrade in base technology but a
downgrade in features. The 728 used the same DDS chipset as the 725/726; its
synthesiser was much quieter than the 735's "classic" PLL, even though its
composite noise at 2 kHz offset on 14 MHz was as high as -85 dBc/Hz. 

Current DDS implementations are significantly cleaner than those of the late
1980's and early 1990's. One of the better Icom DDS designs at the time was
probably that used in the IC-781 and the IC-x75 series. Still, the IC-781
composite noise on 14 MHz was only -105 dBc/Hz at 2 kHz offset, as compared
to -110 dBc/Hz for the IC-728 and -125 dBc/Hz for the IC-756Pro2 (per ARRL
Lab tests.)

The first Icom HF/6m rig with 100W output on 6m was the IC-736 (1995). It
had 30V MOSFET PA devices. The IC-756 (1997), with BJT PA devices, was the
first "12V" Icom HF/6m radio with 100W output on 6m.

My first Icom HF transceiver was an IC-725 (1989-90). Apart from its
complete lack of QRM-fighting tools except for a narrow CW filter, it was a
pretty decent little entry-level rig in my estimation. Thanks to the DDS,
the receiver was very quiet. I have never owned an IC-707, but the ARRL
tests show its receiver performance as significantly superior to that of the
IC-725.

For an entry-level Icom HF radio nowadays, I would choose the IC-718 over
the IC-707. The 718 is excellent value for money.

It is interesting to browse through all the ARRL Lab test reports on these
radios; this is a good way to arrive at a comparison.

Cheers for now, 73,
Adam VA7OJ/AB4OJ




Scanned for viruses by Blue Coat
http://www.WinProxy.com/