Surface Mount Part Bench Work -- it's a skill we'll likely need to hone

Greets!  Oi!

We get many views from Brazil -- a cheerful greeting to these readers.

We're busy at work on the main RF board for our hopeful 5 VDC Direct Conversion receiver.

The RF board is nothing special  -- but it does have a frequency doubler right on the piece
of copper clad board. 

 

Above — The 40 Meter band RF board. We''re evaluating a 5 volt op-amp for this receiver.
The LMV796 in single | LMV797 in dual. Only available in SMD and low-cost for pretty decent performance. This means we've got to up our game in surface mount technique.  We're assembling a small, reflow station -and- hope to show it off next month if all goes well.

Hybrid through-hole/surface mount works OK -- but soldering really tiny surface mount proves difficult and messy for us. Hence we hope to add a tiny reflow set-up to our arsenal.

Above — A LMV796 next to its prototype board. We hand soldered it -- but its getting tough for us old folks.

 

Above — The hand soldered board with flux spatter galore. The LMV796 datasheet says that with a 10K output load, we can take it to within 25 mL of the rail. Our + rail = 4.99 VDC, so we'll set it up as a simple, non-inverting amp on a scrap of copper clad board to briefly test this specification.

Above —Driven with a 1 KHz home-built signal source -and- pushing it nearly to the rails. 10K resistor load AC coupled to the output. 

Above — We rolled back the signal drive just until the sine wave cleaned up by eyeballing the sine wave in time domain. It's about 22 mV from the rail. 

 
Above — Changeover to FFT. All harmonic tones are under 60 dB down when driven pretty close to the rails -- wow, this seems good to us. The noise performance is similar to the NE5532 which we normally use for higher DC rail voltages. The NE5532 doesn't function well @ 5 VDC and less however.  We seek an inexpensive low-noise, low voltage SMD op-amp and this part might work for us --- can't wait to try it in a real, future receiver.

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In design work -- we're trying to sort out the buffer for the frequency doubler. We're currently testing out buffer amp options for the frequency doubler. 

Above — We adapted the Q1-Q2 stage of KO4BB, a full-wave rectifier that works like a charm.  Bias gets done with a standard voltage divider --- and VCC = 5 volts. The buffer is a bog-standard push-pull emitter follower.  Wideband matching it to 50 Ω was our goal -- however, first we felt a strong compulsion to first try a narrow match it with an L-network. We found the network values on the bench by just watching the response to different L values and peaking with a 6 - 450 pF variable capacitor. 

The output was connected to a return loss bridge , while the input was terminated with a 50 Ω resistor. Our tune-up frequency was 7.1 MHz. We found the perfect inductance, removed and measured this coil-- and then soldered it back in. We also removed & measured the perfectly peaked variable cap ( 341 pF ) -- a 330p plus 5-60 trimmer cap were substituted. The network was again re-peaked and the results lie in the table. We show the return loss from 7.00 to 7.40 MHz. Clearly, this is a 7.1 MHz L-match!

Terminating  the emitter follower for a wideband match to drive the LO part of a diode ring mixer proved vexxing. Some old tricks like a series resistor failed to give us good return loss results.

We'll keep working on it --- a new buffer was designed on paper tonight --and hopefully it might help move us us in the right direction. Stay tuned.

 Best!

 

New Bench Note resources added to our Resource Page

Greetings!

Readers like our bench notes & wanted more. We added 2 more Bench Notes categories this week to our Resources Page. We also added our new 40 meter band Direct Conversion receiver page to the main menu.

Thanks for making us a stop on your hobby radio knowledge journey!

Best to you !

 

40 Meter Amateur Band -- Direct Conversion Receiver page

Greetings!

Rather than wait until our 40 meter band DC receiver project is completed months from now, we decided to just post completed modules on a dedicated web page slowly over time. We’ve linked this new web page on the main menu.

Normally we work on several different experiments at once. Some never get posted, while others get abandoned (either temporarily or permanently) due to boredom on the topic, or getting stuck with a problem. While we try to take photos and curate notes, eventually we forget some of the details, or realize 3 years later we did not get a build photo or save a spreadsheet — or —something mindless like that.

It’s even tougher to remember, coherently name and edit video files. Sadly, this flight of fancy is 1 of our many flaws – as a hobbyist we juggle priorities, suffer time constraints, lose focus and go down a rabbit hole now and then.

For example, we recently found an essay we wrote in 2013 — and never quite completed. We forgot about it and it's actually quite an important historical work for homebrew radio enthusiasts. We hope to finally complete & publish it as a pdf file this Winter. 

Thus, going forward -- we plan to post some new topics in smaller bite-sized portions. This may seem random and chaotic – it might even really suck. We’ll figure it out with your help via emailed feedback.

Thanks -- & best to you !!!

 

 

We added --- Ferrite transformer + bead Bench Notes

Greetings! 

We're radio people -- and that means we must buy or build transformers - both
wideband and narrowband. Wide or broadband transformers seem more interesting and fun -- to us at least.  We added some new bench notes about ferrite transformers and beads to the main menu. 

Lately, we've made several baluns and other transformers for electrically small receiving loop antennas plus amplifiers.  Super fun to build -- & this continues in earnest.

  

Best to you -- many thanks for your support !