The meaning of "CM" in the Toyo CM-455 Filter

Photo by ZS1KE

A while back I picked up (from e-bay?) a 455 kc crystal filter for use in my Lew McCoy "Mate for the Mighty Midget" receiver.  I did a quick and dirty installation.  It kind of worked, but I had it in the back of my mind that I had to work on the impedance matching to ensure minimum passband ripple.  But when I learned what the P, B, E, and G pinout designations meant (plate, B+, earth and grid), I realized that this device had been designed with tube impedances in mind, so I probably didn't have to mess around with input and output networks (as I've done with the BITX rigs).  Last week I installed it as the manufacturer intended -- it sounds great.

Today I started wondering about the passband characteristics of the device.  What do the skirts look like?  So I started Googling.  There is not much out there, but I did come across a really interesting Epson site that describes the origins of this filter, and what the CM means.  CM is for "Crystal Mechanical."   Wow, this little box combines the characteristics of  a crystal filter AND a Collins Mechanical filter:

http://www5.epsondevice.com/en/information/technical_info/qmems/story2_5.html

An excerpt:  

"While at the Electrical Communication Laboratory of NTTPC, Mr. Nakazawa had had a flash of inspiration: ‘We could develop a crystal unit with a high Q factor by using the wire mount technology I'm studying now. Then, if we can achieve the idea of a mechanical filter that mechanically joins multiple units using quartz material, we should be able to develop a compact filter that achieves both excellent filter characteristics and thermal characteristics.’ Without a pause, he quickly tackled the next development issue, which resulted in the creation of the ‘crystal mechanical filter (‘CM filter’)*5). This CM filter was manufactured by processing the quartz substrate into an ‘H’-shaped filter element and functioned by using the long thin sections on the left and right sides as resonators (Figure 1). The middle portion connecting the two sides fulfilled the role of the coupler. This was precisely the ‘mechanical filter achieved using crystal (quartz)’ that Mr. Nakazawa had envisioned.

This filter was released on the market as a 455kHz intermediate frequency (IF) filter for single-sideband (SSB) modulation in radio communications. The use of quartz material meant that not only were good filter characteristics achieved, but thermal characteristics were also excellent. As this was the first filter to offer properties of this caliber, it sold extremely well throughout the world. Furthermore, this technology received the honor of being granted the Notable Invention Award from the Science and Technology Agency."

Does anyone have the specs on these filters, and perhaps a passband graph?

Three cheers for Mr. Nakazawa!

The Wizard of Wimbledon writes of Emperor Hadrian's QTH, HMS Belfast, JFK and QRP

Dear Bill

I write this to you from my shack in Wimbledon, south west London, with the crackle of the bands slowly waking up across Europe, having just devoured the final few pages of your excellent Soldersmoke book; an intriguing and entertaining tale to which many of us can relate, a highly-accessible technical primer which certainly helped me to clarify a few niggling “Yes, but why?” questions, and a compendium of handy tricks to try during future projects – thank you for sharing your story.

I was amused to read that GB2RN, on HMS Belfast in London, where I am now one of the “new boy” volunteers, was an inaugural contact for your Azorean 17m DSB rig. As it turns out, 12000 tonnes of British warship seems to play an crucial role in testing QRP radios:

Enjoying a peaceful hilltop picnic in December 2014 with my girlfriend, gazing out over the idyllic Italian countryside above Frascati, it occurred to me that what the situation really called for was a 40m QRP CW transceiver (I was possibly alone in this thought). Soon after returning home I set about researching small, reliable kits which could slip into my jacket pocket but still tune across the band.

The EGV-40 (in memory of Miguel EA3EGV, EA-QRP co-founder) seemed ideal: a “tutti frutti” architecture of well-proven designs, based around a VXO for high stability.

My construction schedule was leisurely, paced for enjoyment and attention to detail. At all times I looked to maximise reliability, crucial when operating from a hilltop, far from a workbench. To pre-harmonise the radio with an outdoor life, on sunnier occasions I often found myself soldering in the garden. For a personal touch, I made sure to instill plenty of “soul”, reminiscent of my electronics journey so far: my late grandfather's tools and solder were used throughout, alongside my own, together with reclaimed parts from old school projects and my elmer’s junk box; finally, in a shameless attempt at appeasement, my remarkably understanding girlfriend even helped to solder the final capacitor… and may be invited to recommend the paint colour!

In mid-December 2015 we once again flew out to Rome for our pre-Christmas break. Our first day was spent exploring the stunning Villa D'Este (stunning to behold, an ideal high radio QTH but far too beautiful for my wires to pollute the scenery without getting into trouble...) and Villa Adriana, near Tivoli. It was only right at the end of the afternoon, and annoyingly lower down towards the plains, when I stopped for a few minutes for an attempted sked with GB2RN.

Lesson 1: trees with lots of branches and twigs are a real pain for throwing wires through! I had guessed this already, but it truly is an exponential problem. 

After conquering a geometric puzzle, I had my EFHW strung so that the point of maximum radiation was about 4m in the air – not exactly ideal for DX but theoretically reasonable for a nice high angle of radiation, like I needed. The feed point (fortunately a current null) was at roughly half this… time to get on the air!

Lesson 2: when operating outdoors – beware of the locals!

Rather than a comfortable bench I resorted to operating whilst sitting cross-legged on the grass, balancing my ex-German military miniature key on my thigh as I tapped it with my finger and attempted to steady it with my left hand. 

The ambient sound of the 40m band seemed very different in I-land – that was the busiest I'd heard it outside of contests, riddled with deafening Eastern-bloc calls but not a single station from any of the British nations, which I presume must have largely been in the shade of the skip; apart from booming GB2RN beaconing to me high on the band :-)

The Villa closes at 1700 and from past experience the wardens come around at 1630 to chase stragglers out from the far corners. Annoyingly one such woman decided that my guy wire and its supporting tent peg looked highly out of place and must be interfered with. My Italian is woefully incompetent at the best of times, so I resorted to gesticulating at her wildly with my left hand as my right attempted to stay faithful to sending clear CW.

Perhaps it was for the best; had she understood that I was “Making a scheduled contact with a British warship via Morse code using home-built equipment which I had smuggled into the country by air last night", the tale might have taken an entirely different twist...

Cold hands, fading light and a dead leg from sitting in an awkward cross-legged position which is frankly impractical for anybody beyond the age of 8, but I was utterly thrilled to have enjoyed my first QSO from overseas, and particularly so since it was with my Elmer on the ship using a station which I had diligently put together myself over a number of months.

The first wisps of solder smoke have already left my iron this morning as I embark on the next stage of my QRP apprenticeship – to make the jump from a kit operator to a scratch-built home brew. All my life I have yearned to understand from first principles, and our remarkable hobby offers us a unique privilege to do so whilst sharing experience along the way.

Our objectives are decidedly more modest in scale, but I’m often reminded of President Kennedy’s famous quote: "We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard”.

72/3

Jonathan
M0JGH

PS Should you or any of the Soldersmoke brotherhood ever be in London and wish to operate from GB2RN, please don’t hesitate to contact me.

My Mate for the Mighty Midget Thermatron Receiver

A few days ago I received an e-mail from Jan PA3GSV -- Jan is working on a receiver similar to my old Mate for the Might Midget and had some questions about how I'd handled the filter portion of the circuit.  Then on Sunday, while listening to Eric's interview with Farhan on the QSO Today podcast, I got so enthused that I felt compelled to work on a homebrew receiver.   So out came the old Mate for the Mighty Midget.  I built this thing in 1997-1998.  It is described here:

http://soldersmoke.blogspot.com/search?q=Mighty+Midget

In the above  video  I was listening on 75 meters to a very congenial early morning roundtable featuring W4CH, K5KBZ and others.  I know, I know, this is the third or fourth video that I've made of this thing.   This is almost as bad as 2B-mania. Or the Michigan Mighty Mite thing.   I blame Jan.  And Eric.  And Farhan.  And Grayson.  And Lew McCoy!

Here is my e-mail exchange with Jan:

Bill:

I recently build the W1TS two tube xtal controlled transmitter, and am looking for a 80/40m companion for this that has a crystal filter.

At first, I wanted to build the “Simplex Super” and finally got hold of the 1700 kc crystals, but then they got lost in the mail…

Only part of a two box shipment arrived, with 455 kc fundamental frequency FT-241 crystals, so now I am looking for a diagram using a 455 kc IF. Jan

Jan:   In this link you will find the schematic for the receiver I built. 

 http://jvgavila.com/mmrx_3.gif

 I was not able to build the filter with the two 455 kc crystals.  I could not obtain the needed crystals.  I used two 455 kc IF transformers as described in my article.   This resulted in a very broad frequency response but it was OK and quite good for AM. 

 Last year I put in a Toyo 455 kc SSB filter, but I did not match the impedances, so the results were not good.  Your e-mail makes me want to work on this again! 

 Let me know how your receiver turns out. 

 73  Bill  N2CQR

Thanks for your reply.

It is a neat looking little receiver.

And yes, I also have a cardboard box labeled “good junk” which is filled with stuff from ham fests J

Finally it will be put to good use!

I printed the article for some evening reading this week.

It will take me some time building this receiver, as there is some metalwork and mechanics involved.

I will let you know how the receiver turns out, and I am also curious what improvements you make on yours.

 Thanks again, and I will let you know.

 73  Jan PA3GSV

Wow, Jan has the Knack!   Check out his station:

That's the W1TS rig on the left.  More pictures from Jan on his QRZ.com site.  He too uses wood cabinets!  I'm not alone!  Here's Jan, PA3GSV

 

April 1 and WireWrapRap: How to Calculate Your Score

Let's make it official:

APRIL FOOL!

Even though "more involvement in contesting" was just another part of our WireWrapRap hoax, I thought it would be appropriate to offer a scoring scheme for those who participated in our little April 1 special event.  Just answer the following questions and keep track of how many points you earn for each:

When you read the WireWrapRap April 1 blog post, how many paragraphs did you read through before you knew it was an April Fool's Day joke? (Maximum 12 points.  If you knew it was a joke as soon as you read the title, award yourself ZERO points.)

When you read the WireWrapRap April 1 blog post,  were you at any point further convinced of its authenticity by the fact that the title of the blog had been changed?  If so, award yourself 2 points.

If after reading the WireWrapRap April 1 blog post you Googled "Wire Wrap," award yourself 5 points.  Award 15 more points if you even briefly thought that this might be a nice alternative to soldering.

When you read the section about the digital modes, did you at any point question the existence of the "new" SNICKR, Oreo, and Oregano modes?   If not, award yourself 5 points.

After reading the WireWrapRap April 1 blog post, did you  -- in an effort to confirm your suspicions -- go to  the comment section to see if others had declared it an April Fool's joke?  If so, award yourself 10 points.  (Be honest here guys.  We got 41 comments on this post, a new record for the SolderSmoke blog.  For some reason a lot of people were checking the comments section.  I'm just sayin...)  

If, after reading the WireWrapRap April 1 blog post you felt anger toward the author for the way he had so selfishly and greedily abandoned the cause of analog, discrete component, Hardware Defined, axial lead electronics, award yourself 5 points.

If, when you noticed that MANY  of the comments on the April 1 blog post had been "removed by the blog administrator," you assumed they were obscene, irate, or perhaps (justified?)  threats, award yourself 15 points. (In fact they all said "APRIL FOOL!" and were removed so that they wouldn't spoil the fun for late arrivals.)  

If one of your comments was among those "removed by the blog administrator"  award yourself NEGATIVE 5 points. 

If your anger about the changes being announced to the SolderSmoke podcast led you to send a complaining or threatening e-mail (or text or tweet!),  go ahead and award yourself 10 points (and please consider enrolling in an anger management program).

If,  on the other hand, after reading the WireWrapRap April 1 blog post you actually sent us an e-mail, comment, text, or tweet congratulating us or wishing us well on the new WireWrapRap podcast, award yourself a richly deserved 25 points. And thanks for the kind wishes.

If this scoring scheme is making you angry now, award yourself 5 points and seriously consider the anger management thing.

If, after reading the WireWrapRap April 1 blog post you actually tried to find out how to get the new podcast from Soundcloud,  award yourself 25 points.

Please send me your scores.  You can put them in the comments section (and I know you know how to do this).  Or you can e-mail them to soldersmoke@yahoo.com.   Or you can text them or tweet them to us or send them to the Soundcloud (just kidding).  Don't worry, we probably won't be announcing the winner.

Possibly the Best Ham Radio Interview Ever: Farhan on "QSO Today"

Stop what you are doing.  Run -- don't walk -- to the "QSO Today" website of Eric Guth 4Z1UG.   There you will find his interview with Ashhar Farhan VU2ESE. 

There is so much great information, inspiration and wisdom in this interview.  I was so captivated by it that -- even with the availability of the pause button -- I was unable stop listening even for the time it would take to walk to the kitchen to refill my coffee cup.  But at the same time, listening to Farhan describe the joy of bringing a new receiver into operation compelled me to go over to the bench -- in mid-podcast -- to tweak a receiver that I am working on.

In this podcast you will hear about how Farhan got started in ham radio, about his Elmers about the origins of the BITX, about the Minima and the new HF-1 rig, about Farhan's spectrum analyzer project and about a new goodwill effort to send BITX circuitry to aspiring hams around the world, especially in developing countries.

Throughout you will hear Farhan speak of the importance of the book, Experimental Methods in RF Design. 

I really do think this is the best ham radio interview I have ever heard.  Congratulations and thanks to Eric and Farhan.

Here is the link:

http://www.qsotoday.com/podcasts/vu2ese

A Major Change For SolderSmoke: Introducing the WireWrapRap Podcast!

A New Direction for SolderSmoke

Introducing Our New Podcast:  “WireWrapRap”

Attentive listeners have probably noticed that for some time now the podcast has been drifting in a new direction.  Some have been concerned by this change.  I myself, as you know, have shared in many of these misgivings.   But I have become convinced that it is time for a major change in direction.  We've been doing this for more than ten years -- we are one of the oldest ham radio podcasts.  It is time for a change.

A number of people have encouraged me to make to this change.   My co-host Pete Juliano N6QW is clearly the main influence.  Pete has made me see the errors of my Ludite ways.  He taught me that it is time to put away the Dymo tape and get with it with glowing numerals.  Whenever I started getting enthused about VXOs or about Permeability Tuned Oscillators using brass screws moving through hand-wound coils, Pete was there to remind me of the beauty, simplicity, and efficiency of Arduino Microcontrollers and Si5351 chips.   Paul Darlington M0XPD contributed an element of old world legitimacy to this push for modernity. Tom Hall AK2B was another influence -- whenever I was on the verge of quitting, he’d Skype in from the Big Apple and get me back on the digital track.  And we can’t forget Farhan over in India – as soon as he started putting Arduinos and Si570s in his Minima, I knew this was really, as the kids say, “a thing.”

So anyway, it is time for a change.    I know many of you may find this shocking, so it is probably best for me to just go ahead and say it:  We are changing the name of the podcast and we are changing its focus.

n  Instead of SolderSmoke, the new name will be “WireWrapRap.”   Wire wrap is the solder-less wiring technique often used in computer circuitry.  We hope that the “Rap” thing will be especially helpful in attracting young people – especially those Maker Millennials -- to the show.  And, you know, soldering just seems so 20^th century.     

n  Instead of traditional homebrew radio, the show will be focused on Mini Computers (especially the Raspberry Pi), Software Defined Radio, Digital Signal Processing, Microcontrollers (especially the Arduino), and the use of smart phones in ham radio

n  Obviously this implies a move away from minimalist radio and QRP.  So yes, we are going maximalist and we are going QRO. And we are getting more involved in contesting (see below).  

Now I know what some of you are thinking – that this must be part of our long-standing quest for sponsorship and that this is all about money.  But that’s only part of it.  Yes, we have secured a lucrative sponsorship arrangement with a company involved in microcontrollers, small computers and smart phones that is focused on the millennial market.  But we’re really doing this for the good of our listeners. 

Don’t worry, you will find many of your favorite parts of SolderSmoke in the new show.  They will be the same, only different.   For example, instead of the “Bandsweep” segments that we used to do, now we are going to have “Codesweep”  (and it’s not about Morse).  Where we used to have SolderSmoke Mailbag, well, don’t worry -- we are going to continue to have a segment that will allow for listener input.  We going to call it “Pi Hole.”  We’ll only be accepting listener input via TEXT messages or Tweets – we are, after all, trying to be modern.  Along the same lines, we will be distributing the podcast exclusively via Soundcloud.  So get with it gentlemen! Get into the cloud!

In the new and improved podcast we want to explore the new and exciting digital modes.  We plan segments on all the new ones: PSK-99, Opera, WSPR, SNICKR, Throb, Thor, Piccolo, Oreo, Oregano,  you know, all those weird sounds you’ve been hearing near what used to be considered the CW portion of the band.  It will be such fun!  I can’t wait to decode some Oregano!

Smart phones, are, of course, the future of ham radio, and we intend to be fully into those little magic boxes.  I don’t know if you guys realize it, but all of that ugly dusty junk in your shack can be replaced by a few lines of code from the App Store.  That room you used to call “the shack” can be converted into the Yoga studio or knitting room that your wife has been longing for!  Now you can carry your station with you wherever you go and autonomously participate in contests from stations around the world.  Imagine the thrill of learning that while you were playing golf or bowling, you were also WINNING a major DX contest from a “station” in Ulan Bator. And that ALL of your reports were 59!   It’s like owning your own ham radio drone!  Congrats old man.  YOU WON! Welcome to the 21^st century! That’s the kind of operation we are going to explore on WireWrapRap!

For those of you who are worrying that we might be abandoning our microphones, have no fear my friends, Pete and I remain committed phone operators. Only now, it will be DIGITAL VOICE.   We’ll be squeezing our dulcet tones into a mere 800 Hz of bandwidth.  This way we both sound exactly the same.  Heck with this new technology everybody will sounds the same.  How cool is that!   We’ll all sound like a mix of Stephen Hawking’s synthesizer, Apple’s Siri, and MTV's Max Headroom.   The AM guys and the Enhanced SSB crew may need some time to get used to this, but c’mon fellas, it is time to get with it!  There will be no more need to tweak all those menus for “presence” and “brightness” and “mid-range.”   Heck no, we’ll all sound the same!  Progress my friends, PROGRESS!

As I said, I had my doubts about this.  But over the weekend I walked into the TV room and Elisa happened to be watching one of those “inspirational self-help” speakers on Direct TV, and you know what?  He made a lot of sense. Change IS good!  We have to EMBRACE the future!  Impossible = “I’m possible!”  Yea!  So thank you Deepak Chopra!  Thank you Pete Juliano!  And welcome --  all of you -- to the WireWrapRap!

From Wayne and Garth in San Diego: EMRFD Joy of Oscillation Part 2

Oh great and mighty masters of the SolderSmoke:

We've continued on with this project and it has been a lot of fun.

Sure, there's

THE JOY OF OSCILLATION

but we've progressed to

THE JOY OF MODULATION (added a keyed buffer)

THE JOY OF AMPLIFICATION (added driver and PA, not threatening QRO, yet)

THE JOY OF RADIATION (perhaps my favorite)
THE JOY OF RECEPTION (picked up by RBN, yeah!)
last on the list is to experience
THE JOY OF COMMUNICATION

for that, we'll try out a number of different receivers.  Cheap SW
portable.  Softrock Lite.  websdr.org.

Does one try to count all the joys?  :-)

Here's a few snaps:

0.jpg - RBN evidence
1.jpg - lashup on the lid of a tupperware container
This worked great for throwing the work in progress in a backback for
our build session meetups.
2.jpg - Fig 1.34 less output LPF.
3.jpg - The missing LPF.  THE JOY OF FILTRATION  (OK, that's taking it too far.)


4.jpg - Fig 1.35 amp with BD139 transistor.
5.jpg - "breadboard" and a front panel to hold the T/R switch.  Key
and cheap SW portable for RX.  Waiting for DX contest to end, so I
have a chance.  :-)

6.jpg - simple breadboard chassis

Our fun has certainly been cheap.  The parts cost, including PCB and 1
BNC jack, was about $13 in low quantity from Mouser (and Diz) for all
but the amp.  The amp portion was $4 in low quantity from Mouser (and
Diz), and most of that was the expensive heatsink.  The "chassis" was
just a piece of cheap 3/4" hardwood and lexan from home depot.  I
drilled and tapped the holes in the wood for the #4 screws.  (Seems to
hold quite nicely.  I thought I might have to harden the threads with
CA adhesive as is done sometimes with balsa.)

If there are any of those air variable caps left that you are meting
out to the worthy, well, like Wayne and Garth, "we are not worthy."
If you do have between 1 and 4 and find it in your heart, we'd be very
grateful.

Best regards,

Drew
kb9fko
San Diego

Renewed Hope for Divide by 2 I and Q

An anonymous reader posted this interesting message in the comments section yesterday.  Very interesting.   A potentially important tip that may help in the quest for 90 degree phase shift with divide by 2 Flip Flop circuits.  What do you guys think?   And who is that masked man?

I wanted to make a comment regarding your Frankenstein R2 Clock divider, but did not come around to do it until now and fear if I were to put it below the appropriate post, it would be so many pages away nobody sees it. Please forgive me for posting this here if my assumption is wrong. I had a play with two edge-triggered JK - Flip Flops (74HC109 & HC107) and tied the J and K to the appropriate rails to use them as T- Flip Flops. Because of one being positive, the other one being negative edge triggered, this behaves as a divide by 2 IQ clock generator. The HC107 has an inverting clock input, so as with the other design, some kind of inverter is involved. And as Bill has reported, I initially measured the Phase shift on the scope to be off. But while playing around, I realized this was a function of the signal level. I could tune the phase shift by adjusting the signal level of the driving clock! When the clock and power supply levels were almost equal, the phase shift was very close to 90° and pretty stable with frequency (tested with 1-10Mhz). Later I thought about it some more and suspect it might have to do with the exact time the inverter "flips" on different signal levels in relation to supply voltage level. Aside from the exact cause, I believe one could vary the supply voltage of the gates with the same effect on the phase shift as with varying the signal level. I hope my observation helps to somewhat make the advantages of divide by 2 IQ clock generators more accessible.  

Grayson Evans TA2ZGE on "QSO Today"

Eric 4Z1UG has a really great interview with Grayson Evans TA2ZGE.  I'm writing this as I listen.

My reactions:

I sympathized completely with his reaction to EE professors who insisted that current flows from positive to negative.  Indeed.  Let's turn those arrows in the diode and transistor symbols around!

I too stripped down a Heathkit VFO and rebuilt it from scratch.

I share Grayson's aversion to metal work.  Viva Manhattan!  

Here is the interview:

http://www.qsotoday.com/podcasts/ta2zge

Switching to a Resistive Splitter on the Frankenstein R2

I did a little work on the Frankenstein R2 phasing receiver.  I noticed that I had a lot more noise and hum on 30 meters and above than I did on 40 and below.  I don't think it was common mode hum -- switching to a battery supply didn't help much.  But when I took a look at what happened to RF signals between the antenna connector and the input to the DC receiver mixers,  I noticed that the signal level seemed to vary quite a bit with frequency. 

There were only two circuits in there:  a 1.7 MHz high pass filter (to knock down AM broadcast interference) followed by a simple bifilar toroidal transformer signal splitter.   My guess is that the 1.7 MHz high pass filter's response was being messed up by the bifilar toroid transformer that I was using as a signal splitter. There might have been some unplanned-for resonances between them. This might have had the effect of knocking down the higher freq signals, making any noise in the receiver (probably from the digital VFO) more apparent.  Also, I noticed that I had this toroid too close to the digital VFO box and to the DC power plug for the Arduino/Si5351 combo -- that might have been sending some noise into the DC receiver input. 

To make a long story short, I took out the toroidal signal splitter and went with a resistive splitter like the one above.  This seems to have helped quite a bit.   I know it adds some additional loss -- about 3 db over the toroidal transformer, right? 

Another possibility:  While rummaging around I found a little 3-terminal TV signal splitter.  It is marked "5-900 MHz" but I'm guessing it would be fine down to 1.8 MHz.  Any thoughts on trying that?  

KK7B's Thoughts on Notebooks, Experiments, and Building

From the r2pro yahoo mailing list:

Hi All,

Some interesting posts lately, with notes or links on "to build or not to build," new H-Mode mixers for HF, and front-end filter intermod.  A recurring thought is that I do lots of projects and each of my projects is a separate design, starting with a bunch of sketches.  I didn't invent this approach--think of DaVinci, for example.  I don't count my sketches, but probably make ten or twenty for every one that progresses to a design of something that would actually work, and maybe only one in ten of those makes it to prototype hardware.  I do a lot of sketches--hundreds for every working radio, and maybe finish a dozen working radios for every one that I write up, either as a good or bad example.

But my sketches all seem to have something in common--they are sketched to do one particular thing well.  They tend to be for one band, one mode, and are designed with particular power supply limitations and the antenna I'm going to use known ahead of time.  They often include at least one but no more than two experiments--something new and risky enough that it might not work.  More than two experiments almost always end up interacting in some unpredicted and dysfunctional way, so I try to limit risky new brilliant ideas to no more than one or two per project.  The key is to do lots of projects, and lots and lots of sketches.

I don't normally operate in brutally strong signal environments, so my dynamic range/IIP requirement is already satisfied with techniques that have been standard since all the excellent work by Wes Hayward, Ulrich Rohde et al. in the 1970s and 80s.  The problem has been solved, like the appropriate number of wheels on a bicycle.  Sure, there are extreme enthusiasts who limit themselves to one wheel and play the bagpipes while riding...  My risky new front-end sketches are often aimed at meeting those acceptable prior benchmarks in some clever and different way, rather than adding a few dB on top of already good dynamic range.  ...Yes, that works well, but I think I'll try doing it this way instead...

Similarly, my input filters aren't the limitation on my intermod performance.  PIM is a big deal in some contexts, and the latest research is fascinating.  Do a google search on Passive Intermodulation PIM to get started on some interesting reading on that topic.

Regarding the question "to build or not to build," I believe that comes down to something very basic: are you a builder?  If yes, then you have no choice.  I can look around my radio room and see a hundred different radios that I've designed and built, and a few more in progress.  If you do the math in my first paragraph above, that's around ten thousand sketches.  My lab notebooks have 200 pages, and I've filled up 140 notebooks since 1975, so that figure is reasonable.  It's just something I do, like some guys go fishing.  Sketches don't take long.  I can do two or three on a half-hour train ride on the way to work.  A complete design to where I start cutting metal and gathering parts might be a few hours a day for a week.  Then another month, maybe a few hours at a time on weekends to finish up a nice project.  There have been more than 2000 weekends since 1975, so even 100 completed radios has left most of my time for other things.

I am very close to folks who are the same way writing code.  They've been filling notebooks with it since grade school, and doing Software Defined Radio since long before they ever encountered the abbreviation "SDR."

If your personal sketches are full of code or CMOS logic, I expect your radios to look and work differently from mine.  If you operate 6m weak signal modes a half mile from a hilltop kilowatt contest station, you have a fascinating set of dynamic range problems to solve.  Years ago, my 11 year old daughter and her best friend thought the absolute best radio ever was the morse code transmitter that Wes Hayward and Bob Culter worked across town using a couple pieces of metal stuck in a lemon for power.  Neither Wes nor Bob would embrace the limitations of that rig for all their amateur radio contacts, but at the time it was a really cool project.

These are just some rambling, Saturday night thoughts, but if you read between the lines you can maybe understand a bit more of why I tend to do things some interesting way that might not apply to your particular application.  One time I accidentally left one of my notebooks at a close friend's house, and he took the liberty of making copies of a bunch of the pages.  I'm not sure it did him any good, but he sure found it entertaining.  There is great freedom in sketching things that have a small probability of actually having to work well in practice.

Enjoy the experiments, and if you have self-identified as a builder, as have many of the denizens of this site, then enjoy making sketches, developing designs, and taking risks that either pay off or end up as learning experiences.

Best Regards,

Rick

Be afraid! Be VERY afraid! Digital Audio on 20 Meters (video)

Here is a very interesting comparison between digital audio, and plain old SSB audio (from a Collins rig!).

I don't know.  I may be prejudiced here, but that digi audio just doesn't sound too good to me.  And I ask myself: "How could it?"  They are restricting the transmit bandwidth to 1.2 kHz.  Can the error correcting elements of the software help them get around the bandwidth limits of Shannon's communications theory?  

The digi audio sounds quite robotic to me. Even Siri sounds better.  Is this because -- as the receiving station noted -- they were only getting "80 percent decode"?   Would the digi audio have sounded better if signal strength had been better? 

Again, I don't know.  But remember. I am a Ludite (with a single d -- the ORIGINAL spelling!).