----- Original Message -----
From: "Jim Shorney" <jshor...@inebraska.com>
On Mon, 16 Mar 2009 18:50:18 -0400, K8AC wrote:
The sensitivity of the TR7 is certainly lacking on the higher bands and a
good preamp is a great addition and doesn't require any metal work. I
bought one of the DF4NW preamps and you can turn it on/off by using one of
the TR7 front panel pushbuttons that's very rarely used for its original
purpose.
My sensitivity measurements don't bear this out. Sensitivity is
relatively flat across the HF spectrum, and I did all of my critical
measurements on 10 meters.
<<snip>>
Your one of the lucky ones then. Before the sunspots went away, I was using
my TR7 for daily DXing on the higher bands where the DX was often down at
the noise level. I inserted an external preamp (that used a low-noise cable
TV transistor) in the receive antenna chain and found that the S/N ratio was
improved enough to make a signal solid copy where it wasn't before. When I
acquired an R7, I found that indeed Drake had thought it necessary to
include a preamp in that unit and it also heard the weak ones better than my
TR7s. After installing the DF4NW preamp in the TR7, I was able to switch it
in and out using the STORE button and could easily hear the improvement in
S/N ratio on the weak ones. Does the preamp increase the IMD
susceptibility? I'm sure it does, but that isn't a factor when digging out
weak ones on 10 or 12 when there aren't strong signals nearby.
Whether or not the preamp makes a difference on 15 meters could be argued,
but at least in my case, the improvement on 12 and 10 meters was very
noticeable and worth the minor effort and cost. And, the external
appearance of the TR7 is unchanged by the mod.
73, K8AC
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