Hallicrafters SR-150, Operation And Maintenance Manual

By Walter Cates WD0GOF (UPDATE 10/30/2013)  

25  

3-4-2. CW RIT OPERATION & THE SR-150.  

I have received these questions many times. “Why is it that the only way I can get satisfactory operation in CW mode is 

when the RIT is turned on?” Also “I don’t seem to have enough tuning range on the RIT” or “I have to turn the RIT 
CONTROL almost to its limit to copy code”. 

First

, why is the RIT necessary for CW operation? In short that is the way the rigs were designed. In CW mode the RIT 

functions as the BFO. These rigs were primarily designed for SSB phone operation. It would appear that the rig was 
designed for SSB operation and then they looked at it and said “how will we make it work on CW”. 

When you switch to cw mode, regardless of the band you are operating, you are in USB mode (Therefore once again I 

stress the carrier oscillators must be 

on freq

). In the cw mode the balanced modulator is biased to a full unbalanced 

condition and the USB carrier osc signal is passed thru with no sidebands. If the USB oscillator is as little as 400 HZ off 
the system operation will be degraded. The transmitter and receiver are locked dead on. With the RIT off you are 
receiving and transmitting on exactly the same freq and there is no “BFO”. The RIT/ON function allows you to shift the 

receiver

 off the zero beat to a comfortable tone to copy code without moving the transmitter freq. In order to get proper 

operation in the cw mode you need to 

calibrate

 in the 

CW

 mode 

Assuming the rig is functioning properly and the VOX is set up properly: 

Set up with your keying device plugged in, VOX, CW, RIT-ON/OFF is 

off

 and RIT CONTROL is in the 

center

 of its 

rotation. The CAL control is in the 

center

 of its rotation. 

(Check the knob position. The knob index line or dot should 

rotate an equal distance in each direction.)

 Turn the CAL on and set the main tuning to the nearest cal point to where 

you intend to operate. Adjust the CAL control for a zero beat. Switch the RIT-ON/OFF switch to 

on

. From this point on 

the RIT ON/OFF switch remains on. The zero beat will have a weak side and a strong side. Now ease the RIT CONTROL 
to the strong side for let’s say a 500 Hz tone (or whatever tone is comfortable for you to copy). Now when you tune the 
Main Tuning to a station and get the same 500HZ tone (or your comfort tone) your transmitter carrier should be centered 
on the other station. Now you are calibrated and ready to tune up the transmitter and operate. You should not have to 
touch the RIT CONTROL again unless you wish to change “BFO tone”. 

Second

, “not enough range” or “I have to use almost all of the RIT CONTROL to get good copy”. This is a definite 

indication of a failure or need for alignment. The RIT CONTROL should provide for a 4 KHZ shift in the receiver and 
that should be seen as + and – 2 KHZ from the center of the mechanical rotation of the RIT CONTROL. To check this, go 
to the center of the 80 or 20 meter band in the STBY mode. With the RIT-0N/0FF control in the off position adjust the 
CAL and the RIT CONTROL for the center of their rotation. Turn on the CAL and adjust the main tuning for a zero beat... 
If the dial reads within 2 KHZ of a 100 KHZ tuning point it is in spec. Now switch the RIT-0N/0FF to on, and adjust the 
RIT CONTROL for a zero beat. If you need to rotate the RIT CONTROL more than 45 degrees off mechanical center 
then repair or alignment is indicated. To further check VFO alignment, with RIT off and cal on, tune the main tuning knob 
across the band taking note of the position of the zero beat at each cal point. If the error at any cal point is more than 2 
KHZ then repair, alignment or tracking of the VFO is needed. 

Bottom line is if your CAL and RIT CONTROL are top dead center on each band you have an 

exceptional

 rig 

and all your heterodyne xtals are dead on. If they are not, you have a 

normal

 rig.  

IMPORTANT FINAL NOTE

: Any time you are aligning and tuning the VFO you 

must

 insure that the RIT is 

turned 

off

 and the CAL ADJ pot is in the 

center 

of its rotation.