EMRFD Message Archive 424
Message Date From Subject 424 2007-02-01 18:48:36 Mike Scott 3 dB splitter I wish to split the outputs of the UVFO to drive two I-Q receivers
I am making a diversity receiver driven from two antennas.
The 3-dB hybrid splitter circuit in EMRFD that I see starts at 25 ohms
and drives two 50 ohm outputs at minus 3 dB.
With the UVFO I think I have single I and Q outputs at 50 ohms.
Help me get from single I and Q channels at 50 ohms (7 dBm) to two I
and Q channels at 50 ohms.
425 2007-02-02 07:29:03 Bill Noyce Re: 3 dB splitter Look at figure 9.38 -- the RF port has a splitter that is essentially
a pair of 70-ohm 1/4 wave transmission lines built from lumped
components. The two input 70-ohm capacitors are in parallel,
so the equations show a single 35-ohm capacitor instead.
To get 7 dBm at each output port, you'll need 10 dBm input...
-- Bill, AB1AV
On 2/1/07, Mike Scott <email@example.com> wrote:
> I wish to split the outputs of the UVFO to drive two I-Q receivers
> (both R2Pro).
> I am making a diversity receiver driven from two antennas.
> The 3-dB hybrid splitter circuit in EMRFD that I see starts at 25 ohms
> and drives two 50 ohm outputs at minus 3 dB.
> With the UVFO I think I have single I and Q outputs at 50 ohms.
> Help me get from single I and Q channels at 50 ohms (7 dBm) to two I
> and Q channels at 50 ohms.
> ..Mike AE6WA
440 2007-02-05 11:54:20 topossibilities Re: 3 dB splitter [I wish to split the outputs of the UVFO to drive two I-Q receivers
I built 75M SSB transceiver using R2 DC receiver and T2 transmitter
boards and had great success building a VFO and processing it's output
signal through a 'Johnson walking ring counter' to generate the two
pairs of needed quadrature signals (one for the Rx, one for the Tx).
Johnson counters are synchronous divide by 4 counters and provide very
accurate I/Q (90 degrees out of phase) square waves outputs for
driving diode ring mixers. They are very simple to build (e.g. a dual
D flip flop and a couple of resistors and capacitors). Using 74ACTxx
series D flip flops with a 100 ohm resistor in the output, the output
level was 7dBm into a 50 ohm load.
Although the oscillator runs at 4X the operating frequency, with care
15-28MHz oscillators can be made quite stable (any drift is also
divided by 4). For the higher operating bands, a heterodyning
oscillator is required.
I have the artwork and schedmatic (has VFO and two ring counters) and
would be happy to scan and email them.
477 2007-02-14 18:34:51 Mike Scott Re: 3 dB splitter Bill (AB1AV),
You pointed me toward a Wilkinson splitter a couple of weeks ago,
thanks. I had to learn a few things before I could write this email.
Now I have built and tested a UVFO system which has 7dBm I&Q outputs
driving a board which has a 6 dB feedback amplifier (my first design)
to two 3 dB (power) pi resistor attenuator networks. These drive two