EMRFD Message Archive 3947
Message Date From Subject 3947 2010-01-04 16:34:22 Pete N6QW EMRFD
A quick thumb through the book leaves you with one very large conclusion: So many projects and so little time.
I am currently working on a MMIC based 20M/80M QRP SSB transceiver and wonder if any others have used MMIC's as a basic part of their designs. The Transceiver which has eight TriQuint AG303-86G's can be seen here:
http://www.youtube.com/watch?v=2ABvAgneIzA
Details of the design can be seen here: http://www.jessystems.com/20M_MMIC_XCVR.html
73's
Pete N6QW (ex W6JFR)3969 2010-01-12 03:04:10 drmail377 Re: EMRFD
Was just perusing your 20/80 MMIC Xcvr pages. Nice work!
I Was sniffing around the MCL site last week pondering a small (almost) all MMIC general-coverage receiver. You've taken it quite a bit farther with the nice implementation of the bi-lateral amps.
I don't have any ($$) 9MHz filters around. I do have some muRata 455kHz jobbies though. Also I intend to use an Si570 for the L.O. with PIC/LCD and shaft encoder kit I bought elsewhere.
I'm most interested in how you intend to implement AGC. MCL has a nice programmable attenuator that I could use with the micro-controller - but it's too expensive, overkill. Maybe a pin attenuator circuit. The nice thing about a low IF frequency is the opti3973 2010-01-12 09:30:12 Pete N6QW Re: EMRFD
Thanks for your posting on EMRFD about the 20M MMIC transceiver. I tried to respond twice via the yahoo reflector and both times my server went down and I lost the message So here it is one more time.
There is no reason why you can't use the Murata filters. Although for a single conversion I personally would not go much above 75M because of potential imaging problems. You could do a double conversion and that would work nicely.
Check out EMRFD figures 6-45 and 6-50. In the tri-band transceiver I built early in 2009 I used a circuit similar to 6-45 (both variants) but it was bi-lateral as designed by Ron Taylor G4GXO. See the GQRP SPRAT 128 for details. In fig 6-50 I sampled the output of the last transformer (6 turn winding) and used that circuit for the AGC. I also used an AGC circuit that you will find under the 17M transceiver on my website at www.jessystems.com. In the 20M MMIC XCVR I would need to replace one of the receive MMIC's with a circuit similar to 6-45. Or replace the complete bi-directional stage with the one designed by G4GXO. In such an application I used a DPST board mounted relay where on Rx AGC was applied to either the Dual Gate Mosfet or the J310's in Cascode. On Tx it switched to a fixed voltage to set the stage gain. EMRFD also has a circuit for using PIN Diodes with a MMIC stage --can't put my finger on it right now.
I have purchased the Analog Devices AD603 (two of them) for use in a double conversion all band transceiver that will predominantly use MMIC devices. That is for later this year. The AD603's are specifically designed with built in AGC capability.
I have reset the the carrier oscillator frequency and will run some tests. I am also looking at the value of the coupling cap out of the microphone amplifier. There just isn't room on the board for the SBL-1. But there may be a possibility for a mod to put the circuitry on a small vertical board. Going to the SBL-1 solves the tune up problem. There is also a possibility of using discrete components in place of an SBL-1 for the BM/PD and I have done that too. That is also on the 17M page.
This has been a fun project and for me has shown some real opportunities for using MMIC's. See also my MMIC based 40M CW Trans-receiver. That has worked nicely too with a homebrew filter that cost me all of $2.40 including the two carrier oscillator crystals.
Another possibility is to buy the Heathkit Filter and Crystals on the auction site-- that will cost about $25.
Good luck Dave with your project. Glad to answer any questions.
73's
Pete N6QW