This offset attenuator is used in transmitter hunting to shift the receiver frequency 2 MHz or 4 MHz up or down from the transmitted frequency. This solves the problem of leakage into the receiver that essentially renders a standard attenuator useless when getting close to the transmitter. It is good for getting close (within a foot) to perhaps a watt or two. If you will be hunting higher power transmitters, then a shielded box might be necessary and possibly a switched 20dB attenuator to keep the module from getting saturated with the unwanted signals. The offset is available in either 2Mhz or 4 MHz, and both seem to work just fine. The 4 MHz offset is probably preferable to reduce the possibility of inband interference. Generally, the 2 MHz is used for receivers that cannot tune out of band.
My experience is only using it on 2M but others have used it quite successfully on the 440 MHz band.
The offset attenuator modules are on a PC board 3/4" x 1 1/4". The kit consists of the circuit board with all the surface mount components soldered in place, and the other parts necessary to complete the unit (diode, potentiometer, crystal, socket, and 9V battery leads.) An enclosure is not included. When ordering, please specify either a 2 MHz or 4 MHz offset. Included with each kit is a one page schematic and parts list.
This kit is provided with permission from Joe Moell, K0OV. It was originally featured in the 73 Magazine Homing In column for May 1998, and more information is available on the HomingIn website.
| Qty | P/N |
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PCB w/ SMT components soldered in place |
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5K Potentiometer |
1 |
Oscillator (2 MHz or 4 MHz) |
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8-Pin DIP Socket |
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1N9148 Diode |
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9V Battery Lead |
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4" Tie Wrap |
| Assembled/Tested |
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| Assembled/Tested - 12 or more |
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| Kit |
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| Kit - 12 or more |
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To order, payment can be made by check, money order, or PayPal (my email address is my PayPal ID.) The total due will be the kit(s) prices plus $4.60 USPS (USPS raised their rates.) Priority mail including Delivery Confirmation. International Orders, please email for shipping. Please email me first to confirm what kits you are purchasing. My email address is: .
Note: This kit is provided with permission from Joe Moell, K0OV
This page updated on Tuesday, December 11, 2007 at 10:15 PDT