n3ajx radio experiments

Weather is too nice (but hot, humid, and buggy) to justify a lot of inside time for electronics.  Thought I post a gallery of recent HF (broadband) amps.  No tube amps, here.   Left to right:  2-stage 2N5109/RD15HVF1 - 6W out for 1mW in;  push-pull RD15HVF1's - 16W out (KK4DAS's design);  push-pull RD30HVF1's - 35W out; push-pull RD70HVF1's - 85 to 100W out; single-ended MRF101 (WA2EUJ design) - >100W output with 50 volt supply.  (All the other amps are designed for 12 - 14 volt supply.)   I tend to use the HVF devices, even at HF, for higher gain.  No power oscillators, yet!  I plan to evaluate/optimize IMD behavior for each of these (probably during the winter).  One of them will get packaged with a switchable LPF for day-to-day use. Haven't delved into any => VHF amps, recently.  I have a selection of these left over from the past, ranging from 25W to 1000W out.   Don't need to build any more. ...

Some time ago (just before Linear Tech & Analog Devices merged), I requested a few samples of LT's 5517 quadrature demodulator and 5598 quadrature modulator.   They happily supplied a few samples of each, but the local LT rep also called me at work and asked if I'd also like to have a dc678a evaluation board ( https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards-kits/dc678a.html#eb-overview ).  Of course, I said, "Hell yes!" and it appeared in the mail soon after (no charge).  But then it sat unloved and unused for years until I recently decided to see how well it worked at HF. The 5517 board is the green one in the upper left corner.  A 2-channel baseband preamp is the Manhattan-style board next to it.  The board below the 5517 board is a split supply boost converter that powers a 100x gain, 2-channel baseband preamp using THAT1510 instrumentation amps.  These devices are very similar to the widely used INA217....

In a previous post, I briefly described issues I had preserving quadrature output from an Si5351 board.  Allegedly, once a 5351 is programmed to provide a fixed phase offset on a second output,  it should maintain that phase shift across frequency excursions, provided the "even divisor" remained unchanged - No PLL reset needed until the a large enough frequency excursion requires a change in the "even divisor".  PLL resets caused annoying "pops" in the output of direct conversion front ends that I typically use for phasing-type receivers.  I was loathe to include a PLL reset on every frequency change because of that.  So, I (and many others) only do a PLL reset when the required integer "even divisor" was changed.  Many fewer "pops", but semi-random loss of LO quadrature within a relatively small frequency range.  I added a polled front-panel switch to my hardware that I use to manually reset the  PLL when my "ear detector" de...

Some folks have built HF gear using MMIC's (gain blocks) as either IF amps, receive preamps or pre-drivers.  I've used AG303-86's, MAV-11's, MAR-0685's and even a some hamfest SGA-6486's with few problems and with excellent repeatability.  50 ohm input and output, low external component count, relatively low noise figure and low distortion up to about 20dbm output at 1 db gain compression - what's not to like!  The issue I have with these devices is that they're a bit anemic for use use a QRP final amp or as drivers for 5+ watt PA's.  Recently, I bought a couple of SV1AFN's (SV1AFN) 1 watt driver, PHA-202+ boards to fill the need for 1 watt (approx.) gain blocks in a few projects.  This device/board can , indeed, deliver close to 30 dbm (at 1 db gain compression) output for 10 - 13 dbm input.  The down side:  the PHA-202+ is relatively expensive (Digikey's single unit price is around $16.64 (US)),  current consumption is rather high compared ...

 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...