On 12/12/2014 10:51 AM, Joe Rocci wrote: > Rev 1.1 of the previously referenced paper is attached, showing Rx/Tx > switching using a bus-switch. > > ----- Original Message ----- > *From:* Joe Rocci <mailto:joe@xxxxxxxxxx> > *To:* minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx> > *Sent:* Friday, December 12, 2014 8:47 AM > *Subject:* [minima] Re: A New Approach > > For anyone who might like to try out my Buffered HyCas IF > amplifier (B-CAS), I wrote the attached paper that describes > background, theory and construction notes. I intend to post > something additional describing the switching to make it BiDi. > > Joe > Joe, That is great work and documentation. Add a suggestion. For those wishing higher gains the use of two packages and paralleling the switches gets one clear of the substrate coupling issue. It might even make for a cleaner board layout and is not cost prohibitive. Relays can be used as well but the coil current are often a battery penalty. Some history and useful info attached. An interesting detail on the Hayward/Damm HyCas is they documented it and presented it for a very useful and flexible IF. Their work characterizing it was valuable as the circuit was forgotten save for a few oldsters like me. made for interesting Emails. I'd been using it for the front end of my Allied/RadioShack AX190 for two decades by then and in 2001 build of frankenradio my first 6M SSB design (bidirectional IF, 8pole filter, fet/bipolar RF, agc and alc). That radio is still in use now mobile with Le Junque Box brick (uses MRF247 for 60W with 4W drive on 6M). They had speculated on its origins and at the time I recognized it as a variant of the circuit published in the early 70s National (and Siliconix) in ap-notes. I'd used it in differential form (two stacks coupled) as the solution for the video amps in my first solid state O'scope. The solution was twofold Miller reduction and getting past the modest voltage limits of then current FETs. The Miller reduction gets both more stable gain and bandwidth and at that time saved a FET as at that time they were not as cheap or common in my parts supply. I've attached the ap-note the reference circuit is on page 7 top but there are other useful ones. Note the circuit on bottom right page 8 used with a buffer into a diode doubler circuit makes a fair AGC detector rectifier for either RF or Audio AGC. If the same circuit is used again after the diodes and RC time constant it can provide level shifting without opamps with a few value adjustments. Everything old is new again. ;) That and a lot of old ap-note are being scanned and return to the 'net with a lot of valuable info. Allison/KB1GMX
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