This page describes how to connect a BC-1031 Panadapter to the SX-28, SX-28A or AN/GRR-2 receivers.  Click your Back Button to return to the SX-28 article.

photo above: The AN/GRR-2 receiver operating with the BC-1031-C Panoramic Adapter. The AN/GRR-2 is tuned to a Shortwave Broadcast station on approximately 9.980MC. It is represented by the center trace on the BC-1031-C. The smaller trace to the right is WWV at 10.0MC, or about 20kc away. WWV can't be heard in the audio output of the AN/GRR-2 but it can be seen on the BC-1031-C. The very small trace to the left of center is another SWBC station at about 9.950kc. The "jagged" slopes of the waveforms show the modulation of the carrier signal. A Panoramic Adaptor provides visual information about band activity outside the receiver's IF passband.

 The Panadapter is a spectrum analyzer that has a tuned input that is centered on the IF of the receiver. A sweep circuit allows the operator to look at various widths of the spectrum and the gain controls allow adjusting the sensitivity of the display. The Panadapter requires a 455kc IF signal from the SX-28 but it is very important from where in the IF circuit you extract the signal. Many receivers have "IF Output" connections provided but these are mainly to access a driving signal for RTTY demodulators or SSB converters. Full receiver selectivity was desired and usually necessary for these devices to function correctly

 If the Panadapter is connected to the typical IF output, it will only monitor the tuned signal and not allow seeing much of the spectrum surrounding the tuned signal. The Panadapter must be connected to the output of the Mixer stage of the receiver for maximum broadband IF that allows the operator visual information at the widest bandwidth. On the SX-28 and SX-28A, the Mixer plate is coupled directly to the first IF transformer. You will have to capacitively couple from the Mixer plate to a coaxial cable (RG-58U is fine for the cable) that is connected to either the accessory octal socket on the rear chassis or to an added SO-239 connector mounted to the rear of the chassis. Using an SO-239 was how most military receivers were connected to the Panadaptor but if your SX-28 is not military and/or doesn't already have holes drilled on the rear then utilize the accessory socket for your connections. There are two ways to couple the Mixer plate to the Panadapter. You can use a very small capacitor, less than 10pf is all that is required. Too much capacitance will load down the Mixer and result in decreased sensitivity in the receiver. Or, you can use a high value resistor of around 500K (470K was typical) to isolate the plate voltage from the panadapter input. The R-45/ARR-7 receiver uses a 100K resistor for isolation of the panadapter. Either way works fine. Trace the wiring to where the Mixer plate connects to the first IF transformer and select a good place to mount the capacitor or resistor and cable. The SX-28A provides a terminal strip on the Mixer section of the RF box. The SX-28 mixer plate is connected to a chassis mounted terminal strip. Route the coaxial cable towards the front of the chassis and around the RF box, down past the power supply to the octal accessory socket. If you choose to use an SO-239 connector, mount it near the accessory socket. Connect the shield to chassis at both ends of the cable. Connect to the Panadapter by using a coaxial cable from the receiver's accessory octal socket (or added SO-239) to the input of the Panadapter.

The BC-1031 series of military Panadapters are very nice units to use with the SX-28. They have a 3" CRT display and are built like tanks - they are also quite heavy. IF input is centered at 455kc but can be adjusted quite a bit either side of 455kc. Maximum slice of the spectrum is about 500kc either side of the tuned frequency. The standard Panadapter Corp. unit and its Hallicrafters version, the SP-44, are also excellent units. They use a 2" CRT. Any Panadapter will work with the SX-28 and SX-28A provided they are designed for a 455kc IF input.