CP Rail SD40-2 voice and Locotrol antenna placement by Manny Jacob - updated April 2016

Antenna placement on the roof of CP Rail SD40-2s is one of the most dynamic and difficult topics to understand. Placement changed through the years, especially on units that were involved in various Locotrol configurations. The purpose of this webpage is to try to establish some semblance of a pattern, so the antenna configuration on your chosen SD40-2 should equal FRED + Voice + Locotrol where applicable to era and chosen unit. I would still urge all modellers to refer to roof photos of the specific SD40-2 they are modelling, in the year, service and paint scheme they are modelling.


FRED antenna

Modellers of the cabooseless era (1990 to the present) should add a tiny antenna to the top of the numberboard assembly, slightly behind the bell and on the engineer's side. Here is a roof shot of 5714 to show typical placement, along with a photo of the required Miniatures by Eric (MBE) part #A12 shown on a sprue below. There was very little variation to the placement of this antenna, which receives signals from the rear end device that transmits brake line air pressure information to the cab of the lead locomotive. It also transmits information from the IDU/CLU. All SBU's on CP have the feature where the locomotive engineer can dump the air in the train's brake system from the tail end, and that feature is tested every time the SBU is initially applied (and armed from the head end) and/or things like a new leader is added to the train, IDU changed out, etc. (thanks to Ross Harrison) If you model the caboose era (prior to 1990) then you will want to omit this detail. It appears from many photos that these tiny antennas started appearing on newly-shopped units as early as 1988.


Voice antenna

All SD40-2s require at least one voice antenna, unless they are in a Locotrol receiver configuration. However, many of the Locotrol receiver units were once leaders and therefore kept their voice antenna even after being placed in dedicated receiver service.

Units 5565-5717 were delivered new with one voice antenna mounted roughly in the middle of the cab and slighly offset to the engineer's side as shown in the above photo of 5644. Around the late '80s it appears from looking at roof shots that the antenna was moved closer to the right edge of the cab roof and above the engineer's seat. For my era of 1989, I model the antenna closer to the edge as shown in the photo below of 5663. A general rule of thumb is the center-mount is more typically an early configuration (up to say 1988) while the edge mount is more typical of around 1988 to the present day.

Units 5718-99, 5800-05, 5836, 5837-64, 5900-6024 came delivered with a wedge shape VOICE antenna mount above the radiators on the engineer's side. Until the tiny FRED antennas were introduced, this resulted in a clean cab roofline as modelled on my 5928 and 5779 units. In the late '80s, the voice antenna was relocated to the cab roof on many of these units. In some cases the original voice antenna was removed from the rear wedge, and in other cases it was not. For example, the units 5950-6024 seemed to have the rear-mount voice antenna moved to the cab roof fairly early on, almost immediately after delivery (1981-82) in some cases. Check photos. The rear wedge can be modelled with MBE part #A6, shown here.

5806-35 were delivered with a rear voice antenna mount as above but with a different shape. Instead of a wedge it was a large box, and then it was later modified to a small rectangular platform. In addition, there was a rather thick external conduit pipe that lead from the rear mount to the cab roof. This is shown in the photo of 5818. Also note the different shape of the rear mount. In later years this conduit was removed from many units (but not all, 5814 still had it as late as 2001) and the voice antenna was relocated to the usual position on the cab roof. Modellers will need to scratchbuild the conduit with flexible .009 floral wire and make the rear mount with a piece of styrene plastic, then glue a regular antenna (MBE #A1) to the top. Be sure to have good photos of your chosen unit in the era you model before doing this!

5865-79 and 6025-69 came delivered with the voice antenna mounted to the cab roof in the usual location above the engineer's seat. None of these units have the rear mount found on most of the older units. Exception: 6051.

6070-80 were originally numbered in the 5837-59 group and all units have the wedge shaped rear mount above the rads on the engineer's side. The renumbering occured in 1989, at which time the Locotrol I sending equipment was replaced with Locotrol II receiving equipment. In 1991, most cab appurtenances were removed and windows were blanked over, affecting units 5702-15, 5758-72 and 6055-80.


Locotrol antennas

Units 5702-15 were delivered from GMD (as part of ordered group 5675-5717) with the voice antenna towards the middle of the cab roof as explained above. This changed in the early-1980s when these units were added to the pool of robot units for Locotrol 1 receiver operation. At the time, two antennas were installed on the cab roof for Locotrol communication, as well as sometimes a third voice antenna could be found mounted either towards the front or the rear center of the cab. No rear voice mount on these units.

Locotrol II receivers 5758-72 appeared to have an antennas configuration as modelled on my 5800. This is confirmed on page 34 of Fred Clark's excellent SD40-2 book (Canadian Diesel Pictorial: Volume One: Canadian Pacific SD40 & SD40-2s Acquired New) as well as in these photos.

5800 series units were always intented to be Locotrol master units and through the 1970s and '80s, units 5800-14 had three Locotrol antennas on the cab roof as shown here in this 1988 photo by Claude Prutton. The voice antenna was on the rear mount during this period.

Many units in the 5815-64 range, before they lost their Locotrol 1 leader status, had two Locotrol antennas on the cab roof and the voice antenna was on the rear mount, as shown in this 1977 Claude Prutton photo of 5836. Other units, like we see on the roof shot of 5841 had the voice antenna mounted towards the front center of the cab roof. Some of the units (like circa-2002 #5835 shown below) had their Locotrol antennas removed when these were placed in regular general freight service after 1989, and others (like 5822) did not. Another configuration is shown in the circa-2005 photo of 5818 below, changed from the circa-1981 photo shown farther above. Check your photos!

As mentioned above, 5837-59 were renumbered to 6070-80 in 1989 and there seems to have been little impact to antenna placement as a result. For example, most of the units 6070-80 had their voice antenna removed from the rear mount, but some units like 6077 shown here in 1993 still had it intact. Another roof shot of 6080 in Locotrol II receiver service shown here demonstrates the presense of three antennas, sufficient for Locotrol II operation. Keep in mind that the cabs in these units were not to be occupied, so the need for a radio antenna would be minimal. Note the purpose of locomotive renumbering was to signify the conversion of these units from Locotrol I masters to Locotrol 2 receivers.

Modellers of units 5693, 5696, 5865-79 and 6055-69 have it easy, since these have four antennas mounted to the cab roof in a diamond shape as shown on 5869. However, all SD40-2s were removed from Locotrol service by 1998 and many of the units were reconfigured to lead, causing further minor changes to antenna configuration on former-Locotrol units. An example is 6069 shown here from 2002 with one of the previously-installed antennas now missing.

Red Barns all have the same four antennas, mounted in the same manner for Locotrol operation until 1998. In addition, the FRED antenna is mounted right behind the bell as shown here. Post-1998 modellers should verify good quality roof photos taken around the year they are modelling in case placement changed in recent times.



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