On Sat, 28 Apr 2018 10:43:31 +0530
"Ashhar Farhan" <
farhanbox@...> wrote:
> there are just a few challenges and many ways to meet them in
> transiting to 435 MHz, VHF is just a milestone along the way. The
> idea of making something on VHF/UHF is no longer economically
> justified if you are doing it just to save money. You can buy a
> baofeng for twenty dollars. Probably, it is a good idea to do that in
> anycase, you will have a ready rig to test your homebrew with.
>
> The local oscillator:
> The first challenge is to get a local oscillator going at around 400
> MHz. There are three ways to do it:
> - A crystal oscillator with a multiplier chain. This needs you to
> have a good way to sniff RF frequencies. A wavemeter of a lecher line
> would do the trick.
> - Just triple the Si5351. This means, you need to tune just one
> bandpass filter at 435 MHz
> - Use an Si589 or Si570, LVDS version. This costs as much as a
> Baofeng, you can order it from Mouser.
>
> Architecture: The options are:
> - Two diode mixers that directly mix down to audio, to make a
> phasing, direct conversion transceiver. This is simple, it involves
> cutting a phase line down by millimeters until you get the phase
> angle right. But you don't dabble with all the fun (really??) of a
> superhet.
> - Single conversion to 20-25 MHz IF with stripline filters to keep
> the image rejection high, it is a bitx from the other side
> - double conversion to 45 MHz, this throws the image to around 350
> MHz, easily suppressed by LC bandpass filters.
>
> Modulation/Demodulation:
> There are many ways to achieve it. You can build analog mod/demod
> with conventional technology as done in the bitx transceivers. Or...
> add an SDR back-end (if you are lazy).
>
> What do you guys think?
>
> - f
>
>
>
>
> On Saturday 28 April 2018 08:32 AM, Tim Gorman wrote:
> > Respectfully, as Allison points out, it's not just the PA active
> > element that will be the problem. When your frequency width is an
> > order of magnitude, e.g. 14Mhz to 144Mhz, you begin to run into all
> > kinds of issues with components. Lead lengths and circuit trace
> > lengths/widths at 2m cause many more problems than at 14Mhz. It
> > gets even worse at 432Mhz.
> >
> > I agree with others on here. It would be a lot more feasible to do
> > one band modules, e.g. one for 2m and another one for 432Mhz, that
> > are small enough they could be placed in one case along with a ubitx
> > being used as an IF amplifier.
> >
> > tim ab0wr
> >
> > On Sat, 28 Apr 2018 01:12:16 +0000
> > "Ashhar Farhan" <
farhanbox@...> wrote:
> >?
> >> Allison,
> >> For a power chain of about 5 watts that goes from 50 mhz to 500
> >> mhz, what would be your recommendations? The RD15HVF1 seems to be
> >> used frequently at 435 Mhz. Are there any broadband alternatives?
> >> What kind of cores can we use at UHF?
> >> - f
> >>
> >> On Sat, 28 Apr 2018, 06:37 ajparent1/KB1GMX, <
kb1gmx@...>
> >> wrote:
> >>> Several things, like others have repeatedly pointed out the uBITX
> >>> is very unsuited for FM or AM.
> >>> FM needs wider filter and far more gain to get the needed limiting
> >>> action.? Its not drop in its full
> >>> replacement.? A Baofeng UV5R goes for 30 bucks and does 2M and
> >>> 70CM.? ? AM there are
> >>> issues with drive level and sustained power out, that and its
> >>> sparsely used.? My opinion is
> >>> that if you want all that get a FT817, its a do all and has a
> >>> noise blanker.
> >>>
> >>> To get the front end to cover VHF the LO system deliver a VHF LO
> >>> (95mhz for 6M, about 99 or 189mhz for 2m)
> >>> and the input filter needs to pass the VHF band and not a low
> >>> pass.? IF memory sers the 5351 can go to 220Mhz
> >>> A LNA before the mixer would be required for reasonable
> >>> performance. For UHF if you had a version of the
> >>> 5351 or maybe used a si570 flavor to generate the LO and an
> >>> improved mixer 432 is possible but its more
> >>> effort and would likely need a board redesign.
> >>>
> >>> UHF is better done with a competent converter/transverter with a
> >>> 404mhz LO and run that into a uBitx at 28mhz.
> >>>
> >>> In all cases 6 though 70cm the tx power chain would need work as
> >>> the drivers are all 300mhz FT devices
> >>> just will not do it.? ?The IRF510 I've used at 50mhz as a monoband
> >>> linear and its respectable
> >>> (40+W for push pull @ 28V properly done for 6M only) but I think
> >>> maybe 70mhz is a stretch without
> >>> first trying.? In all cases the TX chain is mono band only as VHF
> >>> impedance matching from stage
> >>> to stage is required. Just dropping in higher FT devices will not
> >>> help its a across the board redesign
> >>> for a specific band.
> >>>
> >>> Receiving is easy enough, transmit above 50mhz is going to be
> >>> harder.
> >>>
> >>>
> >>> Allison
> >>>
> >>>
> >>>
> >>>
> >>>? ? ?
> >
> >
> >?
>
>
>
>
_Dave_ AD0B
Jay - WS4JM
K9HZ