n3ajx radio experiments

 Since I enjoy the higher HF bands more 40m and below, I've found that using the dual D-type (74xxx74) flip flop method for generating a quadrature LO to be squirrely.  A 5351 can easily generate the 4x LO frequency signal needed, but 74AC74's seem marginal for 15m and 10m where they have to operate at 84 to 112 MHz - I've observed high current draw and low output.  No issues at 20m and down.  I even tried the notorious Potato Semiconductor version of the 7474 that's supposed to work well at high clock frequencies.  Results were mixed at best. In order to cover these two bands, I've used "set phase" capability of the 5351 to directly generate a quadrature LO.  Code to accomplish this abounds on-line.  I happened to use the ZL2CTM variant.  It's listed in one of my previous posts.  This method seemed to work pretty well on receive (phasing DCR), although I noticed that opposite sideband suppression was intermittently and variably lousy at time...

 I built this rig about 8 years ago in anticipation of improved conditions on 6m as the sunspot cycle picked up.  I had an old transverter for 6m that I built prior to 2000, but it never really worked all that well as a system, so it donated a number of its "innards" to a new TRX.  I saved the 25W M57735 amplifier and the existing TX, and RX mixer modules for use in the new rig.  The block diagram for this radio follows: I drew this by hand because (at the time) is was quicker than constructing it with one of the MS products or Open Office.   The only circuitry used for both receive and transmit was the 9 MHz crystal filter (KVF XF-9 S 44 USB filter) and the two associated MMIC amps.  I had plenty of TUF-2 and SBL-1 DBM's left from hamfest scrounging, as well as an abundance of 2N3904's and low noise op amps bought for other projects.  Using two essentially independent audio and RF chains greatly simplified T/R switching.  A list of modules used f...