[1000mp] INRAD IF Amp vs. Roofing Filter wrt rcvr noise

[Mike Schatzberg]

Hello John:

I measured a 50 microvolt signal on 10 meters, with the tuned preamp on, and
found that the Mark V read S9, before I installed the new roofing filter
modification.

After I finished the roofing filter mod, the same 50 microvolt signal read,
S9 plus 15db.

My IF gain, in hidden menu 9-1 was set at 11 from the factory.  If I reset
the gain lower to 8, the S meter again read approximately S9.

I then did some listening to very weak signals, and concluded that the best
signal to noise ratio seemed to be achieved at about IF gain setting number
9.

My receiver is much quieter after the mod, night and day difference, not
just because of the lower IF gain setting, but because of the more narrow
1st IF window.

It is a real pleasure to work very weak signals now, I can read an S0 to S1
signal Q5 easily, with the lower noise floor.

I understood that the IF mod results in the ability to lower the IF gain
also, but no mention of this fact was made with the roofing filter.  It made
a great improvement for me when I made the gain change, I would never go
back to the original configuration again.

Regards,

Mike Schatzberg
WB2AJI
----- Original Message ----- 
From: "John Becker" <johnb3030 at comcast.net>
To: <1000mp at mailman.qth.net>
Sent: Monday, November 29, 2004 3:34 PM
Subject: [1000mp] INRAD IF Amp vs. Roofing Filter wrt rcvr noise


> Lately I've been very active on 12M. There have been several very nice
> openings and many weak openings. Since 9/15 my 12M country count has
> gone from 50 to 125. Many of the stations I've been working are just
> barely out of the noise on CW, and I have the AF gain cranked all the
> way up and still need to really concentrate to copy them.
>
> I know the INRAD IF amp is intended to reduce the amount of white noise
> for improved readability of weak signals, but I know it also degrades
> the receiver in strong signal situations. How does the roofing filter
> mod compare to an unmodified radio where weak signals are concerned?
> Does it add any gain at all? The INRAD web page doesn't address this,
> and I didn't find anything about it on VA3CR's site either. I'm only
> using an inverted Vee for the WARC bands, so I need all the sensitivity
> I can get for these weak stations on 12M.
>
> 73,
>
> John, K9MM
>
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