Here are some extracts from a February 1976 doc that I found that may help define the 718U series Collins radio systems

Here are some extracts from a February 1976 doc that I found that may help define the 718U series Collins radio systems.

718U-1/9:

Consists of 671U-1A and 548S-1 PA coupler (100 watt).

U-1 version was a "manpack" config uses a PRC-47 antenna and BB-451/U battery.

U-9 is Transportable/Vehicular/Base system with 990X-2 mount and 981G-1 load coil. Uses AT-1011 antenna.

The 671U-1A is a panel mount radio. The synthesizer boards are similar to the 671U-4, but the others are somewhat different.

Marine AN/TRC-169. Local guy had a 671U-1A working, but couldn't talk him out of it.

718U-2B:

400-watt system that used 313V-8 or 514N-1 FSK control.

Consisted of 718F-8A Receiver-Transmitter Group and 490B-6 antenna coupler group. Powered by 28 VDC. AC power supply was 639G-1B.

718F-8 contained 671U-4D/4E RT, 635U-1/2 preselector, 548T-1A PA and 636X-2A power supply.

490B-6 contained 490T-2A antenna coupler.

Netherlands Army used many of these systems in the back end of light trucks. I have one of these working.

718U-4A/AN:

400 watt system that used modulo two controls such as the 514A-3/4/7

Similar to the U-2 system, but generally did not include the preselector. 400 Hz version used the 636W-1A power supply. I have one of these systems, but have not hooked it up yet.

718U-4B/BN:

Same as the U-4A system but was configured as a 618T-2/5 retrofit system. Used 636W-1A 400Hz supply.

718U-5:

100-Watt system used modulo two control.

Consists of 671U-4A/AN and 548S-3 non-pressurized PA/Coupler or 548S-5 pressurized PA/Coupler. May also include the 641D-1 Auxiliary variable cap.

I have one of these working, but with 548S-1 PA/Coupler. The 548S-1 and S-3 use the same connector; the S-5 uses a different connector.

The 718U-5N (671U-4N narrow filter RT) is still in use on a lot of business jets and does have TSO certification. (Don't know if the 671U-4A version maintained certification or not.)

HF-117:

Dual 100 watt systems that used FSK controls.

Rack system that had a 499R-21 shelf that mounted two 671U-4Es and two 635U-2 pre-selectors.

Used separate 514N-1 controls (19-inch rack panel). Used dual 990X-2 mounts for the 548S-1 PA's and 981G-1 load coils. Generally used AT-1011 antennas.

HF-120:

400-watt system that used the same components as the 718U-2 system except used the 499R-19 equipment rack (19-inch rack mount) instead of the 718F-8 box. Could use either 636X-2 DC power supply or 636W-1 3 phase 400Hz supply. I have two of these, but have never been able to get either to work completely.

There are other 718U variants but I don't have info. The 671U-4 (no letter) used the 6 wire CCCS serial control (514A-1A or data processor) that was used with the URG-II systems and may have been used as an auxiliary radio in some URG-II installations.