Jack, I used an older Bearcat hand-held scanner as a signal generator for years. It has a 10.8 mHz IF and you can calculate the offset frequency that has to be entered in the scanner to give you the frequency you want. To prevent stray radiation and provide a means of attenuating it, I program it and then put it in a cake pan with an aluminum flashing cover that I fabricated, and put in-line attenuators on the feed through BNC on the cake pan. Just used the source as the normal receive input for the scanner, as it had plenty of radiated LO from the antenna connector.
That served me through the '70s and '80s until something better came along ( an analog Motorola signal generator ) I still use the Motorola to tune duplexers, as it has a better shielded generator than the service monitor I use. I use an Icom hand-held as the receiver for duplexer tuning, as it works quite well as long as there is zero radiation from the signal source. 73 - Jim W5ZIT -----Original Message----- From: [EMAIL PROTECTED] To: [email protected] Sent: Sat, 21 Apr 2007 9:20 PM Subject: Re: [Repeater-Builder] Service Monitors I suspect the accuracy of the deviation measurement depends on how the scope is calibrated. I too have for many years used a scanner as a pseudo service monitor. I have used both a calibrated FM signal generator and the local public service channels for reference. The DC coupling of the scope was adjusted to give a center line reference for frequency from the scanner's discriminator and the vertical gain controls were adjusted for a convenient deviation scale. Haven't measured it, but suspect the IF bandwidth on my scanner is fairly broad. Using a calibrated service monitor to compare this scheme indicated no difference in readings. Assuming we can get over that hurdle, the next one would be how to make an RF signal generator from the scanner. Could we use the scanner's image through a broad band amplifier block into a rudimentary attenuator? 73 de Jack - N7OO ________________________________________________________________________ Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.
