[hpsdr] MDS
k3bu at optonline.net
k3bu at optonline.net
Sun Aug 13 18:01:42 PDT 2006
Amen to that!
Another important requirement for superior RF preamp is continuous gain control and AGC control with possible programmable levels for various antenna selections.
Continuous gain control is very important for top notch RX performance, the gain of the preamp should be set just at the treshold of band noise, so you know that there is enough gain to hear the weak one, but not more than needed. For systems with switchable antennas of various gain (beverages, verticals, beams) it would be desirable to preset, preprogram gain for each antenna configuration, so one does not have to ride the RF gain with antenna switching. For serious DXing/contesting setups this is a big plus. Option to select band filters or good old Q-multiplier is icing on RF cake.
AGC should be fed to RF preamp for the situations where great signal levels are experienced, nothing new here.
Let me give an example of my still unbeatable R4B modification I had done. I replaced preselector tube with EH7 (EF183), inserted RF gain control pot in the cathode, left the AGC controlling the grid. This gave me more gain for beverages on 160 and beam pointed North on 10 m. RF gain would be set, so I just heard a bit of band noise. R4B decent preselector tuned input/output filters provided needed front end selectivity. That "boat anchor" is still superb performer, with one narrow roofing filter and LC IF it is the lowest ringing RX.
Yuri Blanarovich, K3BU, VE3BMV
----- Original Message -----
From: Robert McGwier <rwmcgwier at comcast.net>
Date: Friday, August 11, 2006 4:25 pm
Subject: Re: [hpsdr] MDS
> ***** High Performance Software Defined Radio Discussion List *****
>
> It is my personal design preference to have an extremely well
> design
> preamplifier capable of delivering whatever minimum noise figure
> we want
> on HF. We then raise the noise figure to accommodate different
> antenna, QTH, etc. noise environments with the use of
> attenuators. If
> we use an excellent Output IP3 design, we can get increased input
> IP3
> with these attenuators that allow the noise floor of the receive
> system
> to more nearly match the ambient temperature. I see no reason to
> change
> my opinion at this time.
>
> My experiences at FN20rg vary from exactly what Ulrich sees on 17
> meters
> to occassionally as bad or worse than John has seen on the 10
> meter
> band. Versatility would be the key since I think it is easy
> enough for
> us to be versatile.
>
> 73's
> Bob
> N4HY
>
>
> John B. Stephensen wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> >
> >
> > -----------------------------------------------------------------
> -------
> >
> > Since the CCIR measurements were made with an omnidirectional
> > antenna,they would have to be an average. However, when I had a
> > 5-element 10 meter beam in the Los Angeles area, I never saw
> anything
> > below 20 dB even with the band closed. If there is a switchable
> RF
> > preamplifier, most conditons should be able to be accomodated.
> >
> > 73,
> >
> > John
> > KD6OZH
> >
> >
> > ----- Original Message -----
> > *From:* KA2WEU at aol.com <mailto:KA2WEU at aol.com>
> > *To:* grant at ghengineering.co.uk
> <mailto:grant at ghengineering.co.uk>> ; hpsdr at hpsdr.org
> <mailto:hpsdr at hpsdr.org>> *Sent:* Friday, August 11, 2006
> 15:44 UTC
> > *Subject:* Re: [hpsdr] MDS
> >
> > ***** High Performance Software Defined Radio Discussion
> List *****
> >
> > -------------------------------------------------------------
> -----------
> > This is somewhat inconsistent with my measurements with a
> beam on
> > 17 to 10 m. I would loook for a sensitivity of a NF of 6Dm...
> >
> > 73 de Ulrich, N1UL
> >
> >
> >
> > In a message dated 11.08.2006 14:23:27 Westeuropäische
> Normalzeit,> grant at ghengineering.co.uk
> <mailto:grant at ghengineering.co.uk> writes:
> >
> > ***** High Performance Software Defined Radio Discussion
> List> *****
> >
> > John
> >
> > Many thanks for posting this - I've never seen it
> before.
> > Please could you
> > post the data for 160m and 6m as well if you have it, to
> > complete the list?
> >
> > regards
> >
> > Grant G8UBN
> >
> > >Minimum atmospheric noise levels (above thermal noise) for
> > the HF bands in
> > the quietest locations at the quietest time of the year are:
> >
> > >80 m 38 dB
> > >40 m 33 dB
> > >20 m 28 dB
> > >15 m 23 dB
> > >10 m 18 dB
> >
> > >This is according to CCIR surveys. The receiver NF
> should be
> > 6-10 dB lower.
> >
> >
> >
> > -------------------------------------------------------------
> -----------
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> --
> AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
> NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
> "An expert is a man who has made all the mistakes which can be
> made in a very narrow field." Niels Bohr
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