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Here is the r2pro:
The down converter is top left. Below it is the Audio Signal Processor. To the right of the ASP is a relay switched audio filter. To the right of the filters is the audio amp. The LNA is top right. I still have some small hum issues to work out but the receiver is very good even at this point. Actually, this receiver is excellent.



Tom, ak2b

How does a transformer generate a 90 degree phase split?  (It must be a frequency dependent delay).

I made another of the above circuits and carefully matched the capacitors. Wow, what a differnce! So long IQ-VFO. I now get about 40db or so of opposite side band suppression with the r2pro. I no longer need the IQ-VFO .

The T/R is from W7ZOI's Universal Transmitter QRP Transmitter with some mods. I shortened the key-up delay by changing C10 to 5 mfd from 22 because you could take a quick nap before you would hear receive audio again. It still is not breake-in but it does allow for an easy interface with any other receiver that I might want to try with my version of the universal transmitter. The T/R uses relay control for antenna changeover while switching audio output between the receiver input and the sidetone output. The side tone is horrible so I decided to use the square wave from the keyer - which isn't a whole lot better - but, slightly better. I have a twin T oscillator to solve that problem but want to square away the r2pro first before dealing with nuances of T/R control.

Tom, ak2b

Hi Diz,
I've never seen one with variable coils but on page 12.40 of EMRFD there is one using a phase trimmer cap. KK7B uses a LPF in that version as well as the Universal VFO on page 12.46 of EMRFD. I just wired the output of mine directly into the down converter.
I did not measure the one I just did other than to look at the I and Q signal with  my scope (almost a perfect circle using a lissajous plot). While listening to the opposite sideband of a very loud signal I could hear nothing. I was so pleased that I didn't bother to actually do a proper test .  I will, though...eventually.
Tom, ak2b

Here is what the R2pro looks like now.
Upper left is the down converter with the I/Q VFO input at the top.
upper right is the LNA with power and mute feedthru caps
below the down converter is the audio signal processer
to the right of the audio signal processor is the cw/ssb relay switched RC audio filters.
In the same box is the audio amplifier. On the left of that box are feedthru caps for DC to switch the relay and audio in. Power for the audio amp comes in via the feedthru on the top. There is another feedthrough for audio amp mute but it is not connectted at the moment.

I have found that the article most referenced for this circuit is  from Reed Fisher (W2CQH), "Twisted-Wire Quadrature Hybrid Directional Couplers", QST, January 1978. Unfortunatly, I could'nt find it anywhere other than the ARRL. If you are thinking about building this phasing network for a specific band then the QST article is a must read. Otherwise, I found it for 20 meters just in the course of Googling KK7B. You can also find a 40 meter version in the MicroR2.

It's been interesting, the more I get into this project to see other uses for some of KK7B's other receivers  like the one used by SETI.

Tom, ak2b


I modified the FCC-1/2/DIZ amplifier for more isolation of the VFO and phasing output (I/Q) from the rest of the circuits. I will upload pictures soon.

The yellow trace is from the mute line of the EZkeyer IC (RA1) and the other trace is connected to the keyed +12V output "T"of the W7ZOI T/R switch. The transmit line is delayed 7ms behind the mute and the mute is delayed 7ms after the transmit line goes low.

This is pretty much the final version of my R2pro.
The good:
The radio sounds fantastic.
The bad:
It is very susceptible to hum from power supplies or wall warts in close proximity. It also doesn’t like computer LCD's.

I think I went as far as I want to in terms of shielding. Frankly, I can’t think of much more to do. When used with one power supply that I have, you hardly hear any hum at all. Also, of course, if I use a battery, I just barely notice a tiny bit (you wouldn't notice in normal use unless you were really looking for it).
I finally got rid of the transmit thump by using the rest of the T/R circuitry in W7ZOI’s
Universal QRP Transmitter MK-II. I was using all of Figure 4 but later dropped the sidetone oscillator in favor of NT7S’s cpo (see above). It is relay switched between the audio jacks the same as the other oscillator was.
Today I finally read the whole article and realized that the top part of Figure 1 might contain some key components necessary in removing the key down thump. Mainly Q6, Q7, Q8 and Q4 - used to time the keying of the driver transistor Q2. I replaced R13 with R4 of Diz’s 5 Watt CW amp. It never ceases to amaze me, the good things that come from reading instructions .
I also use a thumbwheel type pot for R6 in the amplifier so I can easily turn the power up and down since I sometimes use it with an external amplifier that only need 2 watts of drive.
So, at this point, I have a complete transceiver (thumpless). The transmit part is pretty much the Universal TX, W7ZOI design, with a few substitutions.
Here is a short thumpless recording. There is some QRM, as you can hear and some recording artifacts on key-up....hmmm. The T/R is not QSK so the intial key-down is the important one. This is not perfect, but an improvement. Eventually I'd like to get QSK.