The Collins manufactured PRC-47 covers 2-12 MHz, generating a USB signal. Unfortunately the only ham bands in this frequency range are the 75 and 40 meter bands, which are LSB.
The PRC-47 generates USB using a F500Z-5 LSB filter. Because of a frequency conversion in the signal generation, the LSB filter results in transmitting or receiving USB. The PRC-47 can be converted from USB to LSB operation by changing the mechanical filter to a 500 kHz carrier freq USB filter.
The perfect replacement USB filter is the 526-9377-00, F500Z-4. This was designed as a complement to the F500Z-5, with the same 2.7 kHz min @ 3 db bandwidth, 100 kohm impedance, and 105 pF shunt C.
To convert the PRC-47 to LSB only is a simple filter change, with realignment perhaps desirable. Some have added the USB filter as an extra one with relay switching, so that the set can operate on either sideband.
These filters can be purchased on this website or found in Collins 618T modules.
An alternative filter which has been found to work is the 526-9412-000, F500Z6. These are not as good an electrical match, with a 20 Kohm source and load resistance and 120 pF shunt C requirement, but have a 7 db max insertion loss where the F500Z-4 or -5 have a 24 db max loss.
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Copyright © 2004 John Kolb Last revised Jan. 8, 2004