[ICOM] [Fwd: Which Icom Radios are good for 60M?]

[Larry Benko]

John,

The following is part of an email that I posted here nearly a year ago 
concerning Icom radios and 60m.  Despite all the rumors you may here 
about someone using a particular radio or not the bottom line is whether 
the radio uses the 80m output filter or the 40m output filter when 
operating on 60m.  Listen to the relays in the radio when tuning from 
3.9MHz to 7.0 MHz and listen to where you hear the click.  The original 
email follows.

73,
Larry, W0QE

Much has been written about operating Icom radios on 60m (5.3-5.4MHz)
without damaging the radios.  Some of it appears to factual and some
appears not to be.  I have access to several Icom radios and have made
some meaurements.  Most of the problems with operating on 60m deal
with transmitting through the 80m low pass filter (which has signigicant 
loss
at 5MHz).  Measurements on where the radios switch the low pass filter
are shown below.

Icom 765:
 80m LPF (2.00MHz - 3.999MHz), 40m LPF(4.00MHz - 7.999MHz)
 Switch from 80m LPF to 40m LPF at 4.00MHz
Icom 746PRO:
 80m LPF (2.00MHz - 4.999MHz), 40m LPF(5.00MHz - 7.999MHz)
 Switch from 80m LPF to 40m LPF at 5.00MHz
Icom 756PRO:
 80m LPF (2.00MHz - 5.999MHz), 40m LPF(6.00MHz - 7.999MHz)
 Switch from 80m LPF to 40m LPF at 6.00MHz
Icom 756:
 Switch from 80m LPF to 40m LPF at 6.00MHz
Icom 756PRO2:
 Switch from 80m LPF to 40m LPF at 6.00MHz

>From the above table it would appear that the Icom 765 and the 746PRO
would work well on 60m (using the 40m LPF) while the 756, 756PRO,
and the 756PRO2 (using the 80m LPF) would not.  In fact measurements
on the 746PRO and the 756PRO show exactly this (with the radios
operated into a dummy load).

Icom 746PRO:
3.99MHz, 100w, DC current = 17A
4.99MHz, 100w, DC current = 22A
5.00MHz, 100w, DC current = 16.5A
5.36MHz, 100w, DC current = 16.5A
7.00MHz, 100w, DC current = 18.5A
Notice how the radio draws 13.6V*(22A-16.5A)=74.8W more at 4.99Mhz
than 5.00MHz.  This power is all HEAT!

Icom 756PRO:
3.99MHz, 100w, DC current = 17.5A
4.99MHz, 100w, DC current = 18A
5.36MHz, 50w, DC current = 20A (max. power 50w)
5.99MHz, 30w, DC current = 23A (max. power 30w)
6.00MHz, 100w, DC current = 15.5A
7.00MHz, 100w, DC current = 18.5A

Icom 765:
Could not easily measure DC current due to internal supply but would
produce 100w on 5.36MHz.

My conclusion is that the 765 and the 746PRO easily operate on 60m
while the 756, 756PRO, and 756PRO are not well suited to operation
on 60m.  Both my 746PRO and my 765 produce 100W at 5.36MHz
easily without heating up while my 756PRO can only muster 50W at
5.36MHz and does heat up significantly more than it does on the other
ham bands.

73,
Larry Benko, W0QE