Skip to main content

A New Line of Transceivers ~ DifX

Transceiver Architecture ~ 2.17


[For more info on the LM373 SSB Transceiver see http://www.n6qw.com/LM373.html)



Reworked Color Display for the Dual Conversion DifX
 

The Crystal Filter Build Out

 
5/25/2017 ~ Where "Noodling" pays big dividends.
 
Yesterday I made a "linear layout" of the six pole crystal filter and the result was a series of 11 pads where the crystals and caps would be installed and that assembly was about 6 inches long. This is an unwieldy dimension to handle inside of a compact radio. Then I spotted a photo of an 8 pole filter as used in the Elecraft rigs and saw how they had compacted the build. So that led me to think a smaller footprint. I now have come up with a compact version that get the footprint down to something like 2 (or 3)" X 4" inches --much more accommodating. I also had concerns about signal leakage between the sections of the compact layout and think that can be fixed by the addition of a shield between the sections. See my "noodling" sketch below. (I are not an artist and barely an engineer!)
 

 
I have already created the design for the compact board in G Simple and have the dxf file ready to cut a board on my CNC Mill. I will add a photo of the cut board when I am done.
 

 
Noteworthy I have received an email about my capacitor selection process and a link to a video about polarity of capacitors and the stability of capacitors. Hopefully the extra $$$ I spent for the 1% caps and the NPO criteria will abate some of these well founded concerns. I will also exercise caution in NOT applying too much heat to the caps during the soldering process.
 
73's
Pete N6QW
 
 
5/24/2017
 
The caps arrived today and I also measured the 150 PF NPO caps I had in stock. One of values needed (4 places) was 151.2 PF. Using my AADE LC meter, I measured 13 caps and here are the results.
 

The results of this test shows that of the 9 caps we have nailed down 5 of them. The two 115.4 PF I think will be asy to achieve with the 100 PF NPO I bought and the 15 PF trimmer. The 430 PF that were to be the basis of the 437.1 PF are so small I can hardly see them so I may have to invoke a work around.
 
I also designed the PC board and it is about 5 inches long and 3 inches wide. There may be a way to compact this but for this 1st run it will be linear. Hope to cut the board tomorrow and start soldering in crystals and caps.
 
73's
Pete N6QW
 
I have been awaiting the delivery of some 1% caps and they will be arriving in the next couple of days so in the meantime I will flesh out the circuit board for the crystal filter. So let us examine what is required. My Dishal filter for the 6 Crystal Filter has a total of nine capacitors and they are as follows: 
 
  • 2 X 151.2 PF
  • 2 X 437.1 PF
  • 2 X 115.4 PF
  • 2 X 151.2 PF
  • 1 X 156.8 PF
Noteworthy is that we really only have 4 values of capacitors including 4 caps of the same value. The precision caps I ordered are 100 PF, and 430 PF and these are 1% and NPO AND Surface Mount. I have a bag of 150 PF NPO caps which I will measure to find values all below 150 PF. (Hopefully finding four that are all below 150 PF but close in value. I have an AADE LC meter and that is my measurement tool.
 
The PC Board will require a total of 11 Pads to accommodate the crystals and the caps. To get me exactly on the values needed I will make the pads large so that there room for the 15PF  air variable trimmer caps in addition to the fixed value ones and the crystals. Playing with these parts before I cut any pads is critical to the final assembly. Thus 437.1PF = 430 PF + 0-15 PF Trimmer
 
I will add to this posting with the layout of the crystal board after I get it laid out.
 
73's
Pete N6QW


Popular posts from this blog

January 26, 2024. A simple CW Transceiver/Transmitter

Cruise through the lower part of the ham bands bands and what do you hear? Well, FT-8 and CW. Often you will not hear any SSB stations yet go to the lower part of the bands, and it is a cacophony (I love that word) of bad sounding signals and some high-speed keying. Fast is not so much of the issue as is bad, run together and jerky keying. But none the less our hobby started there.    So, you could crank down your ICOM 7300 and watch the waterfall on CW or you could homebrew a radio. Actually, to do CW right you need more thought up front than you do with a SSB transceiver. Often, I will state that a CW Transceiver is much more difficult to build than a simple SSB rig. I published two articles in QRP Quarterly on CW transceivers and all I got was a yawn so maybe history will repeat itself.  Yawn!   30M CW Transceiver with RIT!   Of interest is that the LO is a Varactor tuned LC oscillator using a NE602. Look closely at the RIT circuit which is only activated on ...
Read more

March 31, 2024. Happy Easter to those who celebrate this day.

What a great day to Binge on Chocolate and experience the pain of that filling that has been leaking.  I would be in that category with the leaking filling(s) had I not just spent an amount equivalent to one of the fancy new uptown appliance box transceivers on two filling repairs. Well at least I can binge on the Chocolate bunnies without fear of pain. Regrettably everything appears to have jumped in price including the price of parts. Well not so much the parts as the shipping costs.  That notably is seen in the eBay treasures. I spotted a nice heathkit DX-20 for about $50 and the shipping was $65. Likely it is a twofer with part being a way to in effect charge a higher price by inflating the shipping and in part by increased shipping costs. Shipping with insurance across the US was about $150 for this jewel and that was three years ago. 6AM on the Left Coast ~ 20M Easter Sunday! My only hope is the cost of Chocolate Bunnies remains steady although a pound of See's Candies f...
Read more

August 30, 2024. A PNP 20M SSB Transceiver

Shown below is the Block Diagram for the 20M PNP SSB Transceiver steered in the  Transmit Mode . The components shown in the dotted block are relay steered so that the block module is single pass and amplifies in a single direction. The Block diagram show steered in Transmit.  Essentially the steering process works so that the IF Module input follows the Balanced Modulator on Transmit and then the input side follows the Receive Mixer on Receive. All done with some relays and a bit of RG174U coax. For those who count things in detail, this block diagram is not unlike what was used for the PSSST Transceiver which can be found on my website . Yes, a warmed over P3ST only using PNP devices. TYGNYBNT. 73's Pete N6QW
Read more