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Re: Ensemble RX Filter Pads

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  • g8voip
    Hi Tim, No problem, feel free to drop me an email any time and I will try to help out if I can. Details are ok on QRZ.com or use the link besides the message.
    Message 1 of 13 , Apr 29 1:42 AM
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      Hi Tim,

      No problem, feel free to drop me an email any time and I will try to help out if I can.

      Details are ok on QRZ.com or use the link besides the message.

      73, Bob G8VOI

      --- In softrock40@yahoogroups.com, "KQ8M" <kq8m@...> wrote:
      >
      > Thank you for the excellent information Bob.
      >
      >
      >
      > I have an AM station a few miles away but I have not had any trouble with
      > it. Just for the heck of it, I am going to try this one without and compare
      > it with one of my other ones. I run them strictly as CWSkimmer receivers. I
      > do have an RXTX that I had messed up but got working again and will try that
      > normally but the Ensembles are all on 24/7 hi hi
      >
      >
      >
      > I do have a technical question for you that is totally off topic if we can
      > go off the reflector I would like to pick your brain when you have time.
      >
      >
      >
      > Tim Herrick, KQ8M
      >
      > Charter Member North Coast Contesters
      >
      > kq8m@...
      >
      >
      >
      > AR-Cluster V6 kq8m.no-ip.org
      >
      > User Ports: 23, 7373 with local skimmer, 7374 without local skimmer
      >
      > Server Ports: V6 3607, V4 Active 3605, V4 Passive 3606
      >
      >
      >
      > From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On
      > Behalf Of g8voip
      > Sent: Saturday, April 28, 2012 6:13 PM
      > To: softrock40@yahoogroups.com
      > Subject: [softrock40] Re: Ensemble RX Filter Pads
      >
      >
      >
      >
      >
      > Hi Tim,
      >
      > Apart from if you really want to have the S meter scaling correct when using
      > say PSDR on the two lower bands, there is likely to be more to be lost in
      > receiver performance than gained by not fitting the attenuators.
      >
      > Even with the 13dB attenuation in front of the filter there is still more
      > than enough gain on the lower bands, you will not hear anything more,
      > probably just have a higher noise floor level displayed depending on your
      > local conditions and an increased risk of problems being experienced when
      > strong AM broadcast stations are present at 3 x LO frequency.
      >
      > Perhaps you are lucky to live far away from high RF activity, but certainly
      > here in Europe the difference at night between fitting and not fitting the
      > attenuators is significant.
      >
      > Unless you really want to do anything requiring absolute calibration on the
      > lower bands, personally I would leave the attenuators in circuit.
      >
      > 73, Bob G8VOI
      >
      > --- In softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com> ,
      > "KQ8M" <kq8m@> wrote:
      > >
      > > Thanks Bob, I will remove/not install the correct resistors. Going to try
      > it
      > > on this ensemble and see how it sounds then maybe swap my other 4 around.
      > >
      > >
      > >
      > > 73,
      > >
      > > Tim Herrick, KQ8M
      > >
      > > Charter Member North Coast Contesters
      > >
      > > kq8m@
      > >
      > >
      > >
      > > AR-Cluster V6 kq8m.no-ip.org
      > >
      > > User Ports: 23, 7373 with local skimmer, 7374 without local skimmer
      > >
      > > Server Ports: V6 3607, V4 Active 3605, V4 Passive 3606
      > >
      > >
      > >
      > > From: softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > [mailto:softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com> ]
      > On
      > > Behalf Of g8voip
      > > Sent: Saturday, April 28, 2012 5:40 PM
      > > To: softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > > Subject: [softrock40] Re: Ensemble RX Filter Pads
      > >
      > >
      > >
      > >
      > >
      > > Hi Tim,
      > >
      > > As its a pi attenuator made up of 3 resistors, you need to remove all of
      > > them and fit links in place of R18 / R21 to connect the inputs to the
      > filter
      > > elements.
      > >
      > > If you did not remove the other resistors you would have the remaining
      > pairs
      > > of resistors in parallel across the inputs to the filters.
      > >
      > > Pretty sure Robby's build instructions are pretty clear regarding fitting
      > > the attenuators or not.
      > >
      > > 73, Bob G8VOI
      > >
      > > --- In softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > <mailto:softrock40%40yahoogroups.com> ,
      > > "KQ8M" <kq8m@> wrote:
      > > >
      > > > I have a question about bypassing the attenuators in the Ensemble RX.
      > Can
      > > I
      > > > just short across R18 and R21 to bypass or do I also need to lift
      > R17/19,
      > > > R20/22 in order to do it correctly?
      > > >
      > > >
      > > >
      > > > Tim Herrick, KQ8M
      > > >
      > > > Charter Member North Coast Contesters
      > > >
      > > > kq8m@
      > > >
      > > >
      > > >
      > > > AR-Cluster V6 kq8m.no-ip.org
      > > >
      > > > User Ports: 23, 7373 with local skimmer, 7374 without local skimmer
      > > >
      > > > Server Ports: V6 3607, V4 Active 3605, V4 Passive 3606
      > > >
      > > >
      > > >
      > > > From: softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > <mailto:softrock40%40yahoogroups.com>
      > > [mailto:softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > <mailto:softrock40%40yahoogroups.com> ]
      > > On
      > > > Behalf Of g8voip
      > > > Sent: Saturday, April 28, 2012 2:40 AM
      > > > To: softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > <mailto:softrock40%40yahoogroups.com>
      > > > Subject: [softrock40] Re: Ensemble RX Filter Pads
      > > >
      > > >
      > > >
      > > >
      > > >
      > > > Hi Warren,
      > > >
      > > > The optional attenuators (approx 13dB) were added to the Ensemble RX
      > > design
      > > > on the two lower bands as there can be problems with strong AM broadcast
      > > > stations on higher frequencies.
      > > >
      > > > The QSD mixer is still very sensitive to signals at 3 x LO frequency and
      > > the
      > > > simple BPF filters used do not reject these adequately when the receiver
      > > is
      > > > used with a large antenna.
      > > >
      > > > The 3 x LO response is used to good effect on the simple crystal
      > > controlled
      > > > receivers where the LO is run at 1/3rd the RX frequency (sub-harmonic
      > > > sampling).
      > > >
      > > > The Ensemble RX has more than adequate sensitivity on the lower bands
      > even
      > > > when the attenuators are included, so as you point out the only minor
      > > > downside is the S meter scaling no longer holds true.
      > > >
      > > > In practice few SDR programs actually allow you to perform a real S
      > meter
      > > > calibration, even then I wonder how many people have the required
      > > calibrated
      > > > signal source available and actually do this?
      > > >
      > > > p.s. I did make a similar reply yesterday morning in response to another
      > > > question but it seems few messages were actually posted by Yahoo.
      > > >
      > > > 73, Bob G8VOI
      > > >
      > > > --- In softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
      > <mailto:softrock40%40yahoogroups.com>
      > > <mailto:softrock40%40yahoogroups.com> ,
      > > > "warrenallgyer" <allgyer@> wrote:
      > > > >
      > > > > Just completed my fifth Softrocks project (THANK YOU Tony!). This one
      > is
      > > > the Ensemble RX in a KM5H case. What a sweet little radio to throw into
      > my
      > > > travel bag.
      > > > >
      > > > > In doing a proof of performance on the rig I noted 10-15 dB lower
      > > received
      > > > signal levels when using filters 0 and 1. Checked the schematic and,
      > sure
      > > > enough, a 10 dB pad in line with these bandpass filters. Does anyone
      > know
      > > > the purpose? I assume it is to prevent overloading?
      > > > >
      > > > > In any event I bypassed the pads and now S meter calibration holds
      > > within
      > > > a couple of dB across the four filters. I did a quick search and read
      > all
      > > > the builder's notes but I cannot find the rationale for these pads.
      > > > >
      > > > > In any event I am going to try it without them for a while and enjoy
      > my
      > > > consistent S meter indications. I would be interested in anyone else's
      > > > observations.
      > > > >
      > > > > Thanks!
      > > > >
      > > > > Warren Allgyer
      > > > > W8TOD/BG1
      > > > > Stealth Amateur Radio in Beijing
      > > > >
      > > >
      > >
      >
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