Treetop Circuits
Owner’s Manual for SB-51 SSB adapter
Version 4
3
Preparing the Radio
The radio should be in good operating condition and properly aligned. If this is not the case,
it is recommended that a performance check and alignment be performed before
proceeding.
Complete documentation for the R-388A/51J-4 can be downloaded from the Collins
Collectors Association website at www.collinsradio.org at no charge; this organization is
authorized by Collins to disseminate Collins documentation. Membership is not required in
order to access the website, the reflector, or other services. However, Collins enthusiasts
are encouraged to join.
The BFO alignment instructions in parts 5.3.5 (g) and 5.3.6 of the Collins document ensure
that the BFO is centered at 500 kilocycles. This is adequate for CW because it generally
does not matter whether the BFO is above or below the IF passband. With an SSB signal,
best performance requires that the BFO be placed on the correct side of the passband, and
ideally just outside it. Correct settings can be found by trial and error, but these will vary in
a complex manner from band to band.
The situation arises because these receivers use different conversion schemes on different
bands, so the signal in the second IF is sometimes inverted and sometimes not. Also, by
convention, the lower sideband is almost always used below 10 MHz and the upper
sideband above 10 MHz.
To help resolve this situation, stickers are provided with the unit. These are applied to the
skirt of the BFO PITCH knob
(Fig. 3, 5, and 6)
. You can use either the ham band sticker
(yellow highlights) or the general coverage sticker (blue highlights), or both. The extra
stickers provided are spares -- do not use two stickers of the same type together.
Fig. 3 – The BFO PITCH knob with stickers.
You can safely ignore the band designations on the stickers at this point. A detailed
explanation is given in the section on Operation.
