I'm sorry for the delay in responding. I'm traveling on business and
haven't had much time for email.
I measured the receiver MDS (500 Hz bandwidth) without the external preamp
at -126 dBm and with the preamp at -145 dBm. In both cases, the internal
preamp was also on. I used a calibrated HP signal source, but only measured
the signal strengths in dBm not microvolts.
I don't have time to do the measurement conversions. However, for
comparison, QST review of the 5000A measured the 500 Hz MDS at -128 dBm
which is 2 dB better than my measurement, but still corresponds to a 19 dB
noise figure. Their measured 10 db (S+N)/N, 1 kHz, 30% modulation
sensitivity was 3.7 uV, and for 12 dB SINAD it was 1.4 uV.
73,
Clay W7CE
----- Original Message -----
From: "Dan Eisenman" <k8...@allprophoto.net>
To: "Clay W7CE" <w...@curtiss.net>
Cc: <flexradio@flex-radio.biz>
Sent: Monday, June 22, 2009 7:10 AM
Subject: Re: [Flexradio] Why An Extra Pre Amp On Six Meters
Hi Clay;
Thanks for your observations , have you actually put a signal generator
on it ?
Just wondering what the microvolt sensitivity level is , then compared to
having the preamp on ?
73
Dan
K8ICB in Florida
On Jun 21, 2009, at 2:17 AM, Clay W7CE wrote:
Without a preamp, you haven't been hearing the weak ones. Assuming that
your local noise level isn't incredibly high, the stations that sound
weak without a preamp, won't sound weak with it. The stations that
sound weak with the preamp on, are non-existant without it. I've
measured the 6M noise figure and it is about 21 dB without the preamp
and 2 dB with it. My preamp has 26 dB of gain, which is more than I
really need. I've added an HP 0-12 dB step attenuator after the preamp
to reduce the gain when desired. I typically see my noise floor drop
8-9 dB when I turn on the preamp (more when local QRN is minimum). I'm
still experimenting with the best attenuator setting, but I'd say you
want at least 16-20 dB of gain.
I own five 6 Meter rigs, and the 5000A is the best by far since I added
the preamp.
73,
Clay W7CE
----- Original Message ----- From: "Dan Eisenman" <k8...@allprophoto.net
>
To: <flexradio@flex-radio.biz>
Sent: Saturday, June 20, 2009 10:52 PM
Subject: [Flexradio] Why An Extra Pre Amp On Six Meters
I have been using my 5000A on six meters , seems to work great as is ,
I have been
reading about the 3000 not needing a Pre Amp but adding one on the
5000A.
Just curious if any real lab test were run to confirm this data ? The
5000A seems fine to me , I don't seem to have any
trouble hearing and working the weak ones .
73
Dan
K8ICB in Florida
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