Re: [amsat-bb] Icom IC 910 ( again)!!

[Wayne Estes W9AE <w9ae@xxxxxxxxxxxxx>]

Dave Guimont wrote:

I compared my ICOM 821 to several of the newer Yaesu's, side by side, switching
the same antennas for an immediate comparison.  My neighbor had the 
Yaesu's, and when he heard the difference between them and my 821 he sold 
the Yaesu's and purchased the 910H.  The 910 was a tad better than the 821, 
and I now use the 910  with a TEKSHARP 1.2 meter dish.  I can now peak my 
antenna position using the noise floor.

Wayne replies:

I just looked up the receiver specifications of the IC-910H and FT-847.  The Icom does indeed have better IF filtering.

IC-910H:
-6 dB bandwidth of 2.8 kHz
-60 dB bandwidth of 4.2 kHz
this is a shape factor of 1.5 (good)

FT-847:
-6 dB bandwidth of 2.2 kHz
-60 dB bandwidth of 4.5 kHz
this is a shape factor of 2.05 (not good)

Compared to the FT-847, I would expect the IC-910H to have:
1. Better audio fidelity because of the wider -6 dB bandwidth.
2. Better rejection of strong adjacent channel signals (almost never an issue on satellites).
3. The wider -6dB bandwidth probably degrades the signal to noise ratio more than the narrower -60dB bandwidth improves it.  But the difference is probably small.

I "fixed" my FT-847 by adding an INRAD crystal filter:
-6 dB bandwidth of 2.175 kHz
-60 dB bandwidth of 3.35 kHz
shape factor of 1.5 (good) and narrow -6dB bandwidth for QRN and QRM rejection

The fidelity of my "INRAD" FT-847 isn't as good as your IC-910H because I chose a narrower -6dB bandwidth.  But I have better signal to noise ratio and better immunity to strong adjacent channel signals.    I use my FT-847 on the HF bands where that selectivity is essential (the stock FT-847 is unsuitable for most HF operation because of the awful receiver selectivity).  With satellites, you never have an adjacent channel signal 40 dB stronger than the station you are trying to hear.  But you can benefit from the reduced noise of a steep IF filter.

Overall, I agree with your conclusion about the "stock" radios.  The specs show that the IC-910H should have better audio quality.  The signal to noise ratio is probably similar.  But the FT-847 can be made the same or better by adding an accessory IF filter, and you can choose among several bandwidths.

Wayne Estes W9AE
Mundelein, IL, USA
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