[Milsurplus] SC-901X questions

[Robert Nickels]

On 3/27/2018 3:34 AM, Nick England wrote:
>
> And commonality of modules for transceiver, receiver, and transmitter 
> was a big plus. Navy versions were RT-618, R-1051, and T-827. Amps for 
> 100w (AM-3007) and 1kw (AM-3924) output were used.

I'll reply here since this topic has become spammed across several 
reflectors.   I remember K9WT making that same point, Nick, and that the 
Minuteman Launch Control Center I toured in 1979 should have been 
equipped for receive-only on HF, although at one time each LCC (which 
directly controlled 10 missiles) would have been equipped with HF 
transmit capability as well.    Here is an undated photo of a Minuteman 
LCC,  and while the unit shown has the SC-901X control layout, it's 
possible General Dynamics made a receiver only with a similar 
appearance, or that the transmit capability of the SC-901X was just not 
used, depending on the timeframe when this photo was taken:

https://www.minutemanmissile.com/images/LCCInteriorViewB.jpg

These consoles underwent major changes over the years so it's likely the 
HF equipment would have been changed out as well. What I do know is that 
for the tour, several displays or pieces of equipment were obscured for 
security reasons, including a strip of opaque red tape placed across the 
frequency display area on the receiver so that the frequency it was  
tuned to could not be read.

Of course the reason for HF in the first place was as one of the 
redundant communications systems that would guarantee the ability to 
respond to a launch command, and thus a one-way system was all that was 
needed, since EAMs arriving by HF were authenticated in the same way as 
those arriving through the survivable LF system or others were.   
Multiple-redundant communications channels were provided to enable the 
crew to launch if ordered to do so by the national command authority.

The most interesting part of the HF system to me was the antenna system, 
which is described in the excerpt below from the National Park Service 
Minuteman National Historic Site in South Dakota . I'd spotted the 
"ports" in the concrete while we were being shown the UHF antennas above 
ground and it was explained that there were five redundant monopoles for 
HF reception that could be raised into position if one or more should be 
destroyed.     According to the NPS description of the Delta-01 LCF 
which is now a museum that is open for public tours daily, this HF 
receive system was deactivated 7-8 years after my visit:

*/Communication Antennae/*

"Delta-01 includes numerous antennae. A blast-hardened, HF transmit 
antenna, constructed in 1963 and deactivated in the early-1970s, stands 
near the east side of the compound, about 140 feet due south of the 
access road. This structure consists of an underground, 
reinforced-concrete cylinder, approximately twenty-one feet in diameter 
and fifty feet deep (outside dimensions). The well of the cylinder 
contains a telescoping, four-sided radio antenna originally capable of 
extending to a maximum height of 120 feet.

A hardened HF receive antenna is set into the ground about 160 feet 
south-southeast of the LCF support building. Built in 1963, this 
structure consists of a reinforced-concrete cylinder covered by a 
concrete cap and measuring approximately sixteen feet in diameter and 
thirty-seven feet deep (outside dimensions). Distributed evenly around 
the perimeter of the structure are five small ports. Each port contained 
a slender, ballistically actuated, steel, monopole antenna. This antenna 
system was deactivated c.1987-88. When it was still in use, one monopole 
extended from the cylinder at all times. If the exposed antenna were to 
have been damaged during an attack, a replacement could have been 
quickly deployed through the detonation of an explosive squib in an 
adjacent port."

---

I can always remember exactly when I toured the Lima-01 LCF near 
Kimball, Nebraska because it was the first of two tour dates that the 
USAF had set for landowners (and I had a friend who was one) whose 
cattle and wheatfields they co-existed with.  A month later in Jan. 1980 
President Carter announced the grain embargo against the Soviet Union in 
response to their invasion of Afghanistan and the elevated national 
defense status forced the cancellation of the second tour date.

73, Bob W9RAN