[INRAD] [Fwd: Re: IMPRESSIVE]

[Charlie Mazoch Jr.]

Thought I'd forward this e-mail to the group. George, W2VJN and I had 
modified my Icom Pro2 for an INRAD roofing filter. We started off 
putting the filter further downstream and ended up in it's present 
location. The after results are phenomenal and quite visible on the rigs 
pan adapter. Wide band noise is suppressed and signals are very visible. 
The modification is not that hard for a technically inclined person and 
is certainly worth the effort. The RF board does need a trace cut and a 
couple of miniature coaxial cables soldered onto it. George found a spot 
in the rig to mount the board and filter. It is activated by  "Dual 
watch" and rotating the balance control fully CCW. If both receivers are 
set to the same frequency and dual watch is activated the balance 
control can be rotated CCW for narrow band and CW for wide ban 
receiving. Recently I read an article about the Pro series of Icom rigs 
and how wonderful the DSP worked in relation to crystal filtering. I beg 
to disagree with the author of this article. DSP isn't the only cure for 
intermod. The IF strings still perform a lot better when the signal to 
be amplified is narrow.  73's
Charlie  W5VIN

-------- Original Message --------
Subject: 	Re: IMPRESSIVE
Date: 	Wed, 14 Mar 2007 19:55:18 -0700
From: 	George Cutsogeorge <w2vjn at rosenet.net>
To: 	Charlie Mazoch Jr. <w5vin at earthlink.net>
References: 	<45F8B1C5.2070008 at earthlink.net>



Charlie,

Thanks for the comments.  That wide band noise you see is intermod from all 
the strong signals.  I never measured the isolation.  The point I cut is a 
low impedance, so there is not much trouble there.  You can see from the 
curve that there is adequate isolation.

George
----- Original Message ----- 
From: "Charlie Mazoch Jr." <w5vin at earthlink.net>
To: "George Cutsogeorge" <w2vjn at rosenet.net>
Sent: Wednesday, March 14, 2007 7:39 PM
Subject: IMPRESSIVE


> Hi George:
>  I took some time this evening to listen to an extremely noisy band with 
> the Icom Pro2. One has to be in "Dual Watch" and the balance control CCW 
> to receive through the roofing filter. I set both VFO's to the same 
> frequency and rotated the balance control right or left while in dual 
> watch. On tonight's noisy 75 meter band the results of the INRAD roofing 
> filter were very impressive. Watching the pan adapter while rotating the 
> balance control from one receive path to the other I noticed the broad 
> band noise displayed between signals was much less with the roofing filter 
> inline. There is definitely a visual indication of the receivers 
> improvement. Very, very impressive. Putting the roofing filter right after 
> the 1st mixer certainly gets rid of a lot of broad band  noise being 
> amplified  and IMD generated in the RF amplifier after the receive 
> combiner. Smart thinking. Thanks and 73's
> Charlie  W5VIN
>
> PS:  What sort of isolation were you getting after cutting the circuit 
> trace where you tied in? According to the literature you didn't cut it in 
> two places and ground the center trace.
> 




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