Hallicrafters Dd1 Communication Receiver Instructions

							The A and B balance control consists, as Indicated by the schematic, of two controls on one 
shaft. In order to obtain most satisfactory diversity reception it has been determined that the 
gain of each receiver section should be relatively the same. 
Where the signal input to the two receivers is unequal as shown by a lower average reading on 
either A or B diversity meter it will be necessary to reduce the gain on the side getting the 
greater signal. This is accomplished by turning the A or B balance control until the average 
indications on the diversity meters are the. same. 
While electrical balance is no longer obtained the performance of the receivers in dual will be 
more satisfactory because the effective gain of each receiver will then be equal. The Master R. 
F. gain control simultaneously raises or lowers the gain of both receivers and is connected in 
series to ground with the Balance R. F. gain controls described above. 
The audio gain control adjusts the output of both receivers to the grid of the 6J5 audio 
frequency amplifier tube mounted in the receiver proper. The output of this tube is 
transformer coupled to the fone jack, the 500 ohm terminal strip mounted on the rear of the 
receiver cabinet and the input transformer mounted in the audio amplifier cabinet. When 
headphones are used, the fone plug will disconnect the audio amplifier and any load appearing 
across the 500 ohm terminals.  
The Diversity Action Meters show the incoming signal intensity for each of the receivers. It 
will be interesting to watch these meters as they show the fading of signals on each receiver. 
With the receiver operating in Dual position notice how seldom the Average carrier intensity 
meter shows a deep fade while the Diversity Action meters will alternately register fading of a 
serious value.  
Moving the Dual switch from Dual to either Receiver A or B will effectively demonstrate 
how handicapped you would be if you were relying on only one receiver. The Diversity 
Action meters, with the receiver operating in Dual, will dramatically show the benefits of 
Diversity Reception. 
These meters are adjusted similarly to the average carrier intensity meter described before. 
Disconnect both antennas. Set the Master R. F. gain control for maximum; adjust A and B R. 
balance control until each receiver is in balance electrically as indicated when the pointer on 
the meter reads O. Now adjust the control in back of each meter until each one reads 0. 
Upon re-connecting the antennas operate the receiver in the usual manner.  
						

							REJECTER THEORY AND OPERATION  
The Infinite Adjacent channel Rejecter enables the operator of the Model DD1 Receiver to 
cope with Interference more capably than ever before. The Frequency at which rejection 
occurs is indicated by the position of the pointer in reference to the calibrated scale. This 
control varies the amount of bucking capacitive coupling between the coils in the I.F. 
transformers from 3 KC to 18 KC. Rejection is accomplished by so arranging the Inductive 
and capacitive coupling in the I. F. transformers so that they will cancel each other at the 
undesired or interfering frequency. When this is done the signal to which you wish to Listen is 
in no way affected and is allowed to pass with negligible attenuation.  
Both of the I. F. rejection units are ganged to reject at Identical frequencies. The rejection 
slots (refer to the progressive drawings of rejection on the next page) are always equidistant 
from the I. F. frequency of 455 KC and appear on both sides of the signal carrier.  
Proper operation of the rejection control will not only enable the operator to attenuate the 
unwanted signal by 50 DB but also allows him to increase the nose selectivity of the 
receiver. 
The Hallicrafters Model DD1 receiver complete with audio amplifier and power supply draws 
210 watts at 117 volts 60 cycle current; 
GUARANTEE  
This receiver is guaranteed to be free from any defect in workmanship and material that may 
develop within a period of ninety (90) days from date of purchase, under the terms of the 
standard guarantee, as designated by the Radio Manufacturers Association, Any part or parts 
that prove defective within this period will be replaced without charge when subjected to 
examination at our factory, providing such defect, in our opinion, is due to faulty material or 
workmanship, and not caused by tampering, abuse or normal wear. All such adjustments to be 
made FOB the factory.  
Should this receiver require any adjustments, your dealer or distributor has complete technical 
service information, or the factory will be glad to assist you in any problem direct.  
Should it be necessary to return any part or parts to the factory, a Return Material Permit 
must be obtained in advance by first writing the Adjustment Department, who will issue due 
authorization under the terms of the guarantee.  
The Haillicrafters, Inc., reserve the right to make changes in design or add improvements to 
instruments manufactured by them, without incurring any obligation to install the same in any 
instrument previously purchased. 
All Hallicrafters receivers are built under patents of Radio Corporation of American and 
Hazeltine Corporation.