Subject: Re: IC-706 Service Manuals are HERE!!! From: gary@ke4zv.atl.ga.us (Gary Coffman) Ok, here's the computer simulation info I promised. I modeled the 60 MHz to 200 MHz bandpass response. To say the least, it sucked rocks. There are two poles, one at about 136 MHz and the other at about 160.5 MHz. Response is nice and flat from 60 MHz to 120 MHz with less than 4 db of ripple, but it takes a dive from there. In the 130 MHz to 170 MHz range, the loss is at least 36 db, rising back to only 30 db at 200 MHz. Image rejection at 280 MHz is only 26 db. Now the ideal fix is to change the inductors so that L49 is 27nH, L40 is 22 nH, and change C152 to 30pF. That gives a lovely passband across 60 MHz to 200 MHz, and gives strong image rejection at 280 MHz and up, with one of the nulls falling right on that frequency. The factory ought to do that. Unfortunately, examination shows these coils aren't easy to modify. So there's another way that still gives a pretty good response. If you remove C53 and C153, you'll get full response, though with a dip of 4 db in the 160 MHz to 180 MHz range, and only 26 db of image rejection at 280 MHz. But if you increase the value of C152 to 32pF by tacking the removed C153 across it, response flattens and tightens in the upper VHF range, and image rejection improves to 31 db at 280 MHz. That's about as good as we're going to get without replacing L49 and L40 and C152 with the recomended values. Here's the ARRL Radio Designer file for the filter. ************************************************** *ARRL Radio Designer v1.0 *IC-706 60 MHz to 200 MHz bandpass filter * Gary Coffman KE4ZV 1/18/96 ************************************************** Blk **Component data inductors L22:1.2uH L49:82nH ;ideal 27nH L40:68nH ;ideal 22nH L25:0.15uH L26:0.18uH L27:1.2uH **Component data capacitors C51:.001uF C154:20pF C153:0pF ;was 12pF C152:32pF ;was 20pF C53:0pF ;was 20pF C151:24pF C52:18pF C54:220pF C55:22pF C56:82pF C57:27pF **Node list IND 1 0 L=L22 CAP 1 2 C=C51 CAP 2 0 C=C154 IND 2 3 L=L49 CAP 2 3 C=C153 CAP 3 0 C=C152 IND 3 4 L=L40 CAP 3 4 C=C53 CAP 4 0 C=C52 CAP 4 5 C=C151 CAP 5 6 C=C54 IND 6 0 L=L25 CAP 5 7 C=C55 CAP 7 8 C=C56 IND 8 0 L=L26 CAP 7 9 C=C57 IND 9 0 L=L27 BPF:2POR 1 9 END **Frequency block FREQ ESTP 50MHz 300MHz 511 END ********************** Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | |