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Re: Possible ways to modify the Ensemble II VHF

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  • g8voip
    Oh dear, brain fade again, old age catching up. Just noticed: 108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz Should read: 108MHz LO (108 x 0.8 =
    Message 1 of 16 , Jun 2, 2012
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      Oh dear, brain fade again, old age catching up. Just noticed:

      108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz

      Should read:

      108MHz LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 21.6MHz

      Sorry for any confusion.

      73, Bob G8VOI

      --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@...> wrote:
      >
      > Hi Tom,
      >
      > No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :)
      >
      > The Ensemble VHF RX is fundamentally different to the HF version.
      >
      > The HF version has the 4 switched filters to cover the usable range from around 875kHz through to 30MHz. Everything operates directly at the received frequency range.
      >
      > The techniques used for the HF RX have an upper frequency limit between 30 and 50MHz, components like the current standard CMOS Si570 generates 160MHz maximum, so limits the frequency to 160/4 = 40MHz. Also the FET switches and divider chips limit the maximum working frequency.
      >
      > The Ensemble VHF RX is a completely different design. Its very much a throwback to VHF reception 30 or more years ago. Essentially it comprises two parts, a VHF down converter and a tunable IF.
      >
      > The traditional method for say the 2m band (144MHz) was to have a down converter with a fixed 116MHz local oscillator for the mixer. This gave an IF output of 144 - 116 = 28MHz. By using a conventional HF receiver and tuning 28 - 30MHz gave coverage of 144 - 146MHz.
      >
      > The Ensemble VHF RX works on the same principal, but with a clever twist by the designer Jan G0BBL. Instead of using a fixed local oscillator for the VHF converter section, by a clever choice of Si570 LO frequency it is possible for the one oscillator to provide both the LO for the converter plus when divided by 4 produce the quadrature clock needed for the following receiver operating at the IF frequency. The other major difference from the conventional VHF converter setup is that the LO is variable. This adds a slight complication to the understanding of its operation, but does work!
      >
      > When building the Ensemble VHF RX the constructor has the choice of 3 major VHF ham bands, 50, 70 and 144MHz. Each of these works over a large range of frequencies simply by retuning the frontend of the VHF converter section. The 144MHz version can use optimised for use anywhere between around 130 and 165MHz without any component changes.
      >
      > Originally there were just the two bands 50 and 144MHz.
      >
      > The 50MHz version uses a tunable IF in the region of 16.66 to 18MHz to cover 50 - 54MHz. Potentially it could be used over a much wider range given the IF frequency, the only limitations are the frontend filtering and a simple diplexer following the mixer output. The diplexer is designed to be transparent at the operating frequency, but provide the mixer with a stable termination impedance outside of that range. Both of these will limt the actual frequency range that can be used before changes are needed.
      >
      > Likewise the 144MHz version uses an IF out in the range 28.8 to 29.6MHz to cover 144 - 148MHz. Again the filtering and diplexer determine thefrequency range that can be covered without any modification. I have tested this version between 130 and 165MHz (IF between 26 and 33MHz)without any modification being needed.
      >
      > The 70MHz version is really a combination of the two other designs, the frontend components chosen for 70MHz, and the IF side for around 29MHz (i.e. the same as the 144MHz version).
      >
      > Playing around with the mix of designs, should be possible to build a version covering 88 - 108MHz quite easily. The front end filtering would need changing, but perhaps the 70MHz version might still be ok.
      >
      > By changing the LO divider ratio (normally 4/3 or 1.333) for the 50/70MHz version to the same as the 144MHz version (4/5 or 0.8) that would give you:
      >
      > 88MHz = LO (88 x 0.8 = 70.4MHz) and IF 70.4 / 4 = 17.6MHz
      > 108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz
      >
      > Using the AVR firmware configuration program CFGSR, these LO settings can be entered.
      >
      > As there are no switched filters to be controlled, the firmware settings on the ABPF page can be ignored.
      >
      > As an aside, I do have a set up consisting three SoftRock v9.0 receivers, fitted with 6m, 4m and 2m versions of the VHF converter. I make use of the ABPF filter outputs, and have set the crossover points to suit so that the three receivers are switched automatically when I change from 6m to 4m to 2m.
      >
      > There is plenty of scope for experimentation using the existing hardware, tweaking filters etc. The good thing is due to Fred PE0FKO's continuing great work in developing the AVR firmware from the original version, all possibilities are virtually already covered by the standard chip and have been extensively tested.
      >
      > My advice would be build and get your Ensemble HF up and running, get familiar with configuring and running the various SDR programs avaialable and find which suits your needs the best before thinking about tackling the Ensemble VHF RX.
      >
      > Sorry for the long posting, but hopefully might be of some interest to you and others, if not just bin it :)
      >
      > 73, Bob G8VOI
      >
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