Ray,
In this case it was a pretty weak signal.
I cold not quite copy his call on the OII, I tried everything on the
OII to get it....RF gain, AGC threshhold, attenuator with/without
different RF gain, bandwidth, passband tuning, NR, etc.
Then, since I had the Halli SX-117 ad SX-115 on anyway..I switched the
anyenna to the SX-117 just for grins....I had just a slightly bit
better S/N or less high frequency sound...really don'y know why, then I
could copy his call. The best way I can describe it was that the band
noise was a very low sound...then his signal just rode above it,
pretty clear as well.
Anyway, I tried several times A/B OII to Halli...and wound up doing the
QSO the old way, mute the Halli RX when TX, then back to RCV.
It made me grin a little, thinking Bill Halligan may be watching me
from above and maybe he had a grin on his face as well.
If there would have been strong adjacent channel QSO nearby...it would
have not happened.
73,
Lee, KC9CDT
-----Original Message-----
From: Rsoifer <Rsoifer@aol.com>
To: geraldj <geraldj@weather.net>; tentec <tentec@contesting.com>
Sent: Sat, Feb 26, 2011 1:53 pm
Subject: Re: [TenTec] OII V2.044A
Jerry, Lee, and others,
It may be useful to draw a distinction between digging weak signals out
of
the noise and improving the SNR on stronger signals so they sound
better.
As we know, most of the intelligence in (male) human speech is below
about
2400 Hz. The human ear is very good at disregarding higher
frequencies, so
passing the signal through a low-pass filter will make it sound
better
but, for most good operators, won't make much of a difference in their
ability to dig it out of the noise.
73 Ray W2RS
In a message dated 2/26/2011 6:16:09 P.M. GMT Standard Time,
geraldj@weather.net writes:
That's where I find my passive speaker filter shines. It passes no
audio
section noise and no IF noise, an few DSP HF artifacts.
A fundamental of receiver design is that selectivity works best as
close
to the antenna as possible. Unfortunately that ignores the noise
contributions of all the stages after that. The typical product
detector
is double sideband so the IF noise of the image is there along with
the
signal and the RF noise that passed through the filter plus the same
sideband noise much wider than the filter that was up front. Receivers
would benefit from having a SSB filter at the product detector, but I
know of only one design that way, called the Hohentweil, a 2m
transverter kit. Then they would benefit from making the audio output
stage, often essentially a power op amp into an active low pass filter.
In tube receivers a simple capacitor from audio output tube plate to
ground combined with the tube and the audio output transformer to make
a
rudimentary low pass filter. In the 75S-3B, it was effective enough to
make using 2125/2975 tones for 850 shift RTTY (and for all recorded
history, the standard tones for 850 shift RTTY due to an AT&T
standard)
difficult until the capacitor was removed from the circuit.
73, Jerry, K0CQ
On 2/26/2011 11:57 AM, kc9cdt@aol.com wrote:
I think one of the reasons the Drake R-4B, Hallicrafters SX-117 and
many others are beter in a noisy condition is simply they do not have
all the high frequency respnse in the audio, or maybe it is the tube
amp??. I wish there was a HF cutoff on the OII, full EQ like Bob Heil
recommended day one to TT way back may have helped.
Interestng...last nght, on 40 I was working a really nice guy in St
Kitt. There was quite a lot of QRN, He was just above the noise floor
I found that if I used the old Hallicrafers SX-117 to receive
him...copy was more clear!!!!
OMG, Maybe we need to go back to the older stuff (I have both) Unless
of course it is contesting at a high level...where you need lot of
speed
I use the Collins S line& KWM-2
Drake C line (all Sherwood mods)
Halli SX-117/HT-44
Halli SX-115/HT-32B
Along with the OII of course.....
73,
Lee
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