Subject: Re:IC-706 Service Manuals are HERE!!!

From: gary




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

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