We still have a small supply of MHz crystals available at $12 postpaid contact us for details. If you try this, remember to solder a third ground wire to the crystal, then ground it to the radio chassis.
PACE SIDETALK 1000M SMOKY INSTALL
Install it in place of the correct IF coupling capacitor.
PACE SIDETALK 1000M SMOKY SERIES
You can order an MHz crystal (specify series or 10 pf Load Capacitance) to really sharpen up the bleedover rejection. The CHANNEL GUARD won t work with these models. SPECIAL NOTE: AM-only Models Many older AM CBs used an MHz IF. The last two pages show the specific capacitor to remove for all the most popular CB chassis types, along with the correct INPUT and OUTPUT holes. Then the middle bare wire is grounded, and the 12" stranded wire is run to the +DC voltage source. This normally involves nothing more than removing an interstage coupling capacitor and installing the CHANNEL GUARD s INPUT and OUTPUT wires into the correct empty capacitor holes. TEL & FAX: I-FIX-CBs ( ) Local: (520) Internet:Ģ INSTALLATION & APPLICATION NOTES For proper performance, the filter must be correctly installed in the radio s IF strip. The extra selectivity will reduce extremely strong signals which might otherwise desensitize the receiver IF strip. In most installations the best placement is early on, immediately following the First Mixer stage. It s a cheap way of using two crystals in one can, instead of two individual crystals (which are sharper) like our filters use. Monolithic means that it has two quartz elements that share the same physical ground, in a single crystal holder. The second filter (if present) is a simple monolithic device which looks like a regular crystal, with three wires instead of two. For the SSB TX mode, it filters out one of the two sidebands. For RX, it provides basic IF selectivity. This filter is the large metal can about 2" x 1" that you see on the main chassis. All AM/SSB rigs use a multipole crystal filter, which is switched to operate on both RX and TX. A few of the better base rigs already use two IF filters. Noise is broadbanded in nature and the less noise that gets through to the Detector, the better the Signal-to-Noise Ratio of the receiver. This results in improved sensitivity as well as selectivity. If the filter is placed further down the IF strip toward the Detector end, such noise can be reduced. Noise is normally generated within the IF amplifiers themselves. So placing the filter early in the IF strip means that it will work in all modes. Or they convert down a second time for AM and FM later in the circuit. Many CB rigs only use a single conversion process for both SSB and AM. Placing the filter very early in the IF strip, such as immediately following the first mixer, will help establish the overall receiver selectivity. There are two schools of thought about its location in the circuit path: 1. FILTER PLACEMENT The exact placement of any filter in the receiver IF chain is very important, and can make a difference in receiver performance. The result is a dramatic drop in adjacentchannel interference. The skirts are very narrow, and at ☘ KHz, the attenuation can be 60 db or better. Compare this broad curve to that of the crystal filter. Strong adjacent channel signals can easily cause bleedover interference to the desired signal. Even at ☘ KHz away from center, the attenuation is still minimum, about - 18 db. But the typical IF transformer is much more broadbanded.
Both curves at the insertion point are about 8 KHz wide. However the Q (the Selectivity Factor) of such transformers isn t nearly as high as that of a crystal.
All CBs have tuned transformers between the IF amplifier stages to help produce the receiver s overall selectivity. Our filter uses two very high-q quartz crystals and a compensating amplifier to achieve this result. They work by narrowing the skirt selectivity around the center of the radio s IF passband. 1 INSTALLATION INSTRUCTIONS CHANNEL GUARD High-Frequency Crystal IF Filters These crystal filters for 7.8 MHz and MHz CB receiver IF circuits are designed to reduce bleedover interference.
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