A Bilateral IF Module for your next homebrew rig. Another element for you to build.
[Visit https://www.n6qw.com and feast your eyes on some interesting home brew SSB projects. Of Note: you can build a complete SSB transceiver using less than 10 common devices. That translates into low cost and ease of construction.]
Mistakenly there are many who think the Bilateral Circuit started with VU2ESE and the Bitx20. The first use predates the Bitx20 by some 40 to 50 years with the Cosmophone 35 based on a design from a California ham -- Butch Mason. Note you can have a quality Bilateral Circuit without using a Termination Insensitive Amplifier. So don't start down that path...
The above two photos contain an example of a bilateral IF Module which uses four transistors in the IF. Two each of the 2N3904 and two each of the 2N3906. The 2N3904/2N3906 combo is known as the Plessey circuit, and a direct lift from EMRFD.
The upper photo shows also the BPF and the Rx Tx Mixer. The lower photo details not only the Plessey but the Balanced Modulator / Product Detector and the BFO circuitry. This is like over 50% of the SSB Transceiver with just six devices.
In the Receive Mode the 2N3906 transistors are doing the heavy lifting and on Transmit the 2N3904's are in line. A couple of TUF-1's are used as the Rx/Tx Mixer with the other TUF-1 as either the Balanced Modulator or the Product Detector. Receive goes from left to right and transmit goes right to left. A couple of 2N3904's are the BFO.
Small 5VDC Board Mounted Relays apply either 6VDC (Receive) or Ground (Transmit) to the Plessey pair. So, it is Bias switching and not signal shifting. The other beauty is that the LO is connected to its TUF-1 in either Transmit or Receive and the same for the BFO being connected to its TUF-1 whether in Receive or Transmit. A single BPF is always in line and used for Rx or Tx. Those values in the BPF land you on 20M.
The Plessey circuit is good for about 17dB of gain (34dB total across the module) through 6 Meters and its Z in/out is 50 Ohms. There are matching transformers to match the 200 Ohm load of the Home Brew Crystal Filter to the 50 Ohm Plessey. For a commercial 500 Ohm filter use a 19:6 turns ratio as 19^2 = 361 and 6^2 = 36. Thusly, 361/36 = 10:1 which is the match from 50 Ohms to 500 Ohms.
This topology has been used in many of my designs but now days I have moved on from this approach. Today I use a single pass IF Module (one direction) that is relay steered to the various circuit elements as in the P3ST. I prefer this approach if only to be able to say: No Bitx, No EMRFD, No TIA and NO Facebook groups are involved with this design.
What a personal joy to be able to respond when asked: No this is not a Bitx but something of my own design. There is absolutely nothing short with the Bitx design except is not an original design from N6QW. BTW my P3ST only has 7 transistors and five of them are 2N2222A's.
The above topology would add about 6 or more transistors for the Rx RF amp and Tx Pre-driver plus add two more for the Driver / Final stage. You would need one in the Mic Amp and one in the Audio Pre-amp. The VXO would need a couple too. So, the device count would grow over what you can do with a P3ST.
Todd, K7TFC is selling a kit version of the P3ST.
With the 4.9152 MHz filter this could easily be put on 20 or 17 Meters. Our last posting on Crystal Switched VXO's could work easily with this module.
It is hoped that through the series of postings, that this would encourage some of you couch potatoes to heat up the iron.
Final Note: What you saw in the two photos is straight out of the Shirt Pocket SSB Transceiver.
73's
Pete N6QW