Blog -- "Chinese Electronics Products Tested"

I was looking for information on my  FeelTech FY3200s Signal Generator.  I came across a very informative blog; it covers a variety of other Chinese gear and parts.  

Here is the Feeltech FY3200S article: 

https://chinese-electronics-products-tested.blogspot.com/p/fy3200s-function-generator-tested.html 

Here is the home page of the blog: 

https://chinese-electronics-products-tested.blogspot.com/

And here is backround information on the author: 

Thanks Jos! 

WB9IWT's Quarantine Mighty Mite and N3FJZ's "Hiram Percy Maxim Recognition Factor"

Leif WB9IWT has, during the emergency, been working on a Michigan Mighty Mite (See pictures above and below).  FB Leif.  

But also check out the very astute comment from Rick N3FJZ (below) .  I am, of course, all in favor of the HPMR Factor.  Almost all of my rigs would score quite high.    Others, I know, would seek a low score.  To each his own.  This is all for fun.  

Leif,

Great work.  If a ham from the 1920's were to see this rig, they
probably wouldn't recognize the actual components right away (but
knowing hams, they would no doubt figure it out), but the breadboard
layout circuit flow would be immediately recognizable; e.g. the plug-in
crystal, the coil, binding post.  The transistor and variable capacitor
may baffle them at first, but seeing there are three leads on the
transistor would start to give them clues.

That's the cool part about analog discrete component radio, no matter
how many years go by, and the appearance and size of the actual
components change, the physics of what's going on at the electron level
stays the same (SDR not withstanding).

I guess this could be a litmus test for us analog radio builders.  It
could be called the "Hiram Percy Maxim Recognition Factor" or "HPMR
Factor" with a range of 0 to 1.  After you  build your rig, take a look
at it and pretend that you could present it to Mr. Maxim and the more he
could understand the circuits, components and circuit flow on his own,
the closer to a factor of 1 your radio would achieve.  For example, an
SDR might only achieve a factor of .1 or even maybe 0, where as your rig
may achieve a factor of .8, and one of your crystal receivers would
definitely get a 1.

Someone could even workout a check list or formula where you would add
or subtract some fractional numeric values for each component you used;
e.g. you would subtract some value for every IC chip, microprocessor or
LCD display you use, and add some fractional value for each hand wound
coil, vacuum tube/valve or open air variable capacitor, et cetera.

Fun to think about.

Keep building.

Rick - N3FJZ

Quarantine Reading: Tribal Knowledge: Two Gems from Pete Juliano N6QW

WB9FLW recently reminded us of two very useful documents that have been kind of buried on one of Pete's web sites.   I think these documents are just the kind of thing we all need during these dark days of quarantine.  So just sit back, StayInTheShack,  and soak up tribal wisdom from the Wizard of Newbury Park.  

http://www.jessystems.com/Homebrewing%20for%20QRP%20SSB.pdf

http://www.jessystems.com/How%20To%20Stuff%20A%20Junk%20Box.pdf

Here is the message from WB9FLW that unearthed these gems:  

Morning Pete,

Three cheers for posting the Simple SSB Transceiver as a possible project during the pandemic lockdown.

Suggestion, folks that are new to your Website may not have seen some of your earlier posts especially on jesssystems.com. 

"Homebrewing For QRP SSB" is a gem and a great lead in to the simple SSB Transceiver project.

http://www.jessystems.com/Homebrewing%20for%20QRP%20SSB.pdf

There is a lot of wisdom in those pages, perhaps you can add a link for those interested in building the rig.

"How To Stuff A Junk Box" is good as well.

http://www.jessystems.com/How%20To%20Stuff%20A%20Junk%20Box.pdf

Hope you and the family are doing well.

Pete  WB9FLW

ZL2CTM Charlie Morris on "QSO Today" with Eric Guth 4Z1UG

Eric Guth 4Z1UG had a really nice interview with our friend Charlie Morris ZL2CTM.  Charlie shared with Eric a lot of wisdom about how to homebrew radio gear.  I especially liked Charlie's comments on keeping most of his rigs on the wooden prototype boards.  He said something important when he talked about the benefits of taking a break from a difficult problem, then coming back to it with a rested and refreshed mind. I noted, however,  that he said most of these frustrating problems have to do with software.  

I got got several chuckles out of Charlie's comments on the difficulty of building stable analog LC VFOs (here he seemed to be channeling our good friend Pete Juliano).  I chuckled because as I listened I was happily building the analog LC VFO for my Q-31 Quarantine receiver.  The centerpiece of this project is a variable capacitor that Pete gave me;   Pete took it out of an old  Galaxy V transceiver.   Believe me guys, no rotary encoder could possibly look as nice or have as much soul as that capacitor from Pete, with all its gears, reduction drives, and anti-backlash mechanisms.  It even smells of machine oil.  Call me a Luddite, but I will stick with the coils and capacitors.  

Listen to the interview here: 

https://www.qsotoday.com/podcasts/zl2ctm

Thanks to Charlie and Eric. 

The Low-Cost, Open Source COVID-19 Ventilator that Farhan is Helping to Build (Video)

While many of us are just trying to pass the time by building Quarantine ham radio rigs, our good friend Farhan VU2ESE has been hard at work on a really serious project:  He has been working out how to use an Arduino microcontroller as the electronic core of a simple ventilator that could save thousands of lives in the current crisis. See video above. 

Here is background info on the project (from ARRL): 

03/23/2020

Amateur radio volunteers from around the world have volunteered to assist University of Florida Professor Sam Lampotang and his engineering team in their quest to rapidly develop an open-source, low-cost patient ventilator that can be built anywhere from such commonly available components as PVC pipe and lawn-sprinkler valves. The amateur radio volunteers are developing Arduino-based control software that will set the respiratory rate and other key parameters in treating critically ill coronavirus victims.

Multiple volunteers responding to a call for help from Gordon Gibby, MD, KX4Z, included noted software developer Jack Purdum, W8TEE, and  uBITX transceiver maker Ashhar Farhan, VU2ESE. University of Florida physicians are working to address the critical legal aspects as the design moves closer to fruition.

The ventilator’s valves would precisely time compressed oxygen flow into patient breathing circuits under Arduino control, allowing exhausted patients with “stiff” lungs impacted by viral pneumonia to survive until their body can clear the infection. The software design team is also adding simple features such as an LCD display, encoders to choose parameters, and watchdog safety features. -- Thanks to Gordon Gibby, KX4Z

It is important realize that in countries around the world, many victims of COVID-19 will have no hope of getting anywhere near the kind of $50,000 ventilators found in U.S. or European hospitals.  That is one of the things that makes this low cost, open-source project so important. 

More details on the project here: 

https://github.com/afarhan/osventproto

Please pass the word on this project.  Please forward on Facebook, Re-tweet, etc. 

Quarantine Project: An AM Receiver for the 31 Meter Band. The Q-31.

During this StayInTheShack (SITS) emergency, it is good to have something to work on.  I decided it would be best to try to build something using only items currently in my parts collection.  I've been getting into shortwave listening again, and I've discovered that the 31 meter band (9.4 - 9.9 MHz) is my favorite. Thus the "Quarantine On-Hand 31 Meter AM Receiver."  A big part of the inspiration for this project comes from the AM receiver of Paul VK3HN. 

I propose that we all designate rigs built during quarantine as "Q" rigs.  This will be the Q-31. 

I had an old chassis on the shelf.  It held my WSPR DSB rig in Rome, and various other projects over the years.  It has so many holes in it that it looks like it has been used for target practice.  

A while back Pete N6QW sent me this really magnificent variable capacitor with at least two reduction dries and an anti-backlash gear.  I've been looking for a project that will allow me to use AND display this beautiful part.  It will be the main tuning cap for the Q-39. It will stay -- like the tubes in the rigs of days-gone-by --  above the chassis. 

While in London many years ago I picked up an old regen receiver at the Kempton Park rally.  The parts are still in my junk box.  A very nice 1.7 uH plug in coil (with socket) was there.  That will be the main coil in the Hartley Oscillator that will be the VFO.  I will add a few turns for the feedback coil (see circuit diagram below).  I wonder of that Eddystone coil was around for the Blitz? 

On the recommendation of our old friend Rogier (originally PA1ZZ), a few years ago Elisa got me a set of grey Altoids-sized metal boxes.  I will have three of these atop the target-practice chassis (they will provide shielding and will cover up the holes): 

-- One will hold the bandpass filter (designed with the Elsie program) and the mixer (probably diode ring, with transformers from Farhan). 

-- One will hold two IF amps with a 10 kHz 455 kHz IF filter between them (thanks to Bruce KK0S for the filters). 

-- One will hold the AM detector and the AF amplifiers. 

-- A fourth box will be under the chassis and will hold all the powered parts of the VFO circuitry.   I base my VFOs on this simple circuit from page 34 of Solid State Design for the Radio Amateur: 

This quarantine looks like it is going to last a long time, so it is best to take your time on projects like this.  I might work on the VFO today.  No need to rush... 

I am shooting videos as I go along and will at some point start putting them up on my YouTube channel.  

So, I suggest that any of you who are feeling bored and confined (that would be almost all of us) fight back by launching a Quarantine "Q-Rig"  project.   Send reports to me -- I will try to put them on the SolderSmoke blog. 

Remember:  StayInThe Shack!   #SITS!  #flattenthecurve. 

73  Bill 

SolderSmoke Podcast #220 -- S-38Es, AD9833s, Pete's Phasing Rig, FT-8

Java on the S-38E Tuning Dial

SolderSmoke Podcast #220 is available

http://soldersmoke.com/soldersmoke220.mp3

Hunkered Down.  StayInTheShack:  SITS!  Flatten the Curve!  It is working.

Teaching English again – via Zoom.  Kids completing the school year remotely.  

BILL'S BENCH

-- Finishing up on the S-38Es.

  

-- I wrote up my alignment, isolation and dial string experiences.

-- SWL  WRMI Radio Miami International on 39 meters 9.4-9.9 MHz.  Rock and Roll.

-- S-38E work is causing me some serious legal problems.  They are threatening to take down our sites and our podcast.   Google has put a CEASE AND DESIST ORDER on my blog:   Check it out http://soldersmoke.com/CEASEANDDESIST.JPG

--S-38E caused me to want to get my HRO dial receiver on the SW broadcast bands with a good AM detector.  

-- Next up: Hayseed Hamfest cap for my Drake 2-B.  And I have an idea on how to easily broaden it for AM:  Tap the 455 kc output on the Q multiplier jack.  455 AM detector to audio amp. 

SHAMELESS COMMERCE DIVISION

PETE’S BENCH

AD9833

Phasing Rig Project

.

DEAN’S PROJECT – Step by step.  Trouble shooting.  Understanding.  Receiver triumph.  FB.

MAILBAG

Jack 5B/AI4SV doing well in Cyprus

Daniel SA7DER listens during commute in Sweeden.

Peter VK2EMU building a 6 meter amp.  With Tubes

Jim WA8ZHN  says there are still 7751 Novices on the books.   FB.

Mike WB2BLJ modding his BITX – having a lot of fun.

Fred KC5RT – Great idea on isolation transformer in my S-38E.  

Jerry Palsson: S-38C's curves vs. S-38E's exotic places.  Java. 

Krakatoa East of Java

The Year of Living Dangerously

Anonymous mail:  FT-8 DX -- Are these contacts legitimate? See below. 

Dear Bill and Pete: 

I've been meaning to share with you something that has come to my attention by a rather circuitous route. 

As you guys know, I've been involved in the software/IT side of ham radio for many years. I've watched many digital modes come and go.  I've always enjoyed my work, but lately I've seen something that makes me uneasy. 

I'm sure you guys have heard of the fantastic DX that is being worked by many guys using FT-8.  It seems like all they need to work Jakarta is a couple of watts to a wet noodle. Shazam!  Contact! 

Well, I learned something that calls into some question the legitimacy of many of these contacts....  

As i understand it, certain manufacturers, in cahoots with a major American ham radio organization (that happens to be very dependent on ad revenue from that manufacturer), have secretly set up a system that combines the internet and ham radio. 

Here is how it works:  Suppose Joe Ham gets on FT-8 on 40 meters.  He puts out a call using his QRP transmitter and the aforementioned wet noodle.  No way that signal is going to Jakarta, right?  Well, it will with a bit of help.  

The system has SDR transceivers  and great antennas set up at strategic points around the world -- these are really great locations -- think mountain tops near the coastlines, always with high speed internet T5 connections. I think this is part of the whole “contest superstation for on-line lease” business model.  

One of these stations picks up Joe Ham's FT-8 call. Sometimes it will just re-transmit it, sometimes is will send it to a counterpart station on the other side of the globe.  Bingo, Joe Ham's signal is suddenly in Jakarta.  A station there enthusiastically responds, and that signal goes back with the same kind of repeater/ internet assist.  This is all done out of the reach of the FCC.  They are usig overseas locations,  some of them in Mexico.

Of course they have to be careful not to "facilitate" these kinds of contacts during times in which the bands are obviously dead,  That's why 40 is so useful for this system.  Obviously they can't keep this kind of thing secret forever -- they just want to get guys hooked on FT-8, then they can reveal the system, selling it as nothing unusual, you know, sort of akin to Echolink.  

Of course, this hasn't been made public (for obvious reasons!) but I can tell you the name of the system:   They tried to make it sound like something familiar (in this case like APRS): They call it  "Automatic Private Radio Internet Link 1."  My understanding is that when they do their “roll out” they will offer the new service to those willing to pay a subscription.

Obviously as an old-school, traditional ham, I'm troubled by all this.  What do you guys think?  I wonder what your listeners would think. 

Please don't mention my name..  But here is a site that describes the new system: 

http://www.automaticprivateradiointernetlink1.com/

Thanks and 73... 

Please let us know if you have any information on this, or have observed any unusual and suspicious success with FT-8.

Quarantine Rig: VK3YE Resurrects an Old BITX Project

I think we should start calling these "Quarantine Rigs."  Many of us are pulling off the shelves rigs that we started a while back but then put aside.  Now, with the pandemic,  we have the time (and the need!) to work on them.  

I like Peter's BITX receiver video, especially the part in the beginning where he wipes the grime and oxidation off the long-neglected copper-clad board.  

Follow Peter's lead:   Pull those old projects off the shelf.  Get them going.  Now is the time.  SITS!  Melt solder and flatten the curve. 

Thanks Peter.     

Paul VK3HN's Portable Rig

Nice work Paul. 

Excellent Video on Maxwell's Equations

Really well-done.  He gets to the essence without getting bogged down in the math. Great graphics too. 

How They Make Chips That No One Can Understand

The December 21, 2019 edition of The Economist had an article about the Taiwan Semiconductor Manufacturing Company's plant known as Fab 18.  In just a few paragraphs  the article explains something that I have been wondering about:  We hear that some of the modern chips have millions, or even billions of transistors on them.   Who could possibly design at that level of complexity?  The article provides the answer:  humans don't do it.  These chips are really designed by other computers (see above).   

I don't like to use integrated circuits because they often seem like mysterious black boxes   I want to be able to understand how the rig I build really works.  Some ICs do allow for this kind of understanding -- you can get the internal wiring diagrams for an NE602, or an LM386, for example.  You can study them and gain an understanding.  Those little black boxes then become less mysterious.   But that kind of understanding is just impossible with the kind of modern microprocessors churned out by Fab 18. No one really knows how these chips work:    

"The circuitry is not as complex as, say, the human mind, but it is far more complex than any human mind could fathom."  

Sorry, but I prefer fathoming.  Please pass me some 2N3904s.   

Radio History Question: Why 455 kHz as the IF frequency?

My work on the S-38Es, on the HRO-dial receiver, on the Mate for the Mighty Midget,  and on various mechanical filters has caused me to think (once again) about why we ended up with 455 kHz as the  IF frequency for so many radios.  I've heard many explanations for this, but unfortunately I've forgotten the explanations and lost the sources.  I started digging into this again today.  I found the below e-mail from Al N3FRQ on the Boatanchors mailing list (2008). 

I contacted Al to find out if he had learned anything else on this topic.  He has not.  So if anyone out there has answers to Al's questions, or anyother info that would shed light on why they went with 455, please let us know. 

------------------------------- 

Every so often the question comes up: Why are all the IF’s 455 KHz? I’d 
like to get an article together that solves this riddle while the people 
who know are still with us. I know parts of the story, but I need help 
with a couple of issues.

There are two major consideration is the choice of the intermediate 
frequency used in a superheterodyne receiver. The lower the frequency, 
the easier it is to attain high selectivity. Also, in the early days, 
before tetrode and pentode tubes, it was easier to achieve a high degree 
of amplification at lower frequencies. Conversely, a higher IF frequency 
results in better image rejection.

Early superhets had the IF at 100KHz or lower in order to get adequate 
gain from the available triode tubes. They suffer severely from 
“two-spot tuning” (images). By the early 1930’s, broadcast set had 
settled in at 175KHz, and automobile receivers would later adopt 262KHz 
as a standard.

The advent of the short-wave craze, and multi-band broadcast receivers 
dictated a higher IF frequency to achieve adequate image suppression on 
the short-wave bands. The broadcast band occupied 550-1500KHz at this 
time, and the designer encounters sever problems if his radio tunes 
across it’s own IF. Some shortwave sets used 1600-1700KHz for better 
image rejection, but one couldn’t go higher if the 160-meter ham band 
(1800-2000KHZ) was to be covered. Most multi-band receiver settled in 
near 450KHz, a comfortable distance from the first broadcast channel at 
550KHz.

Questions:

Odd multiples of 5KHz, 455, 465, etc., were usually chosen so that the 
image of the carrier of a broadcast-band station could be zero-beat with 
the carrier of the station being tuned to achieve minimal interference. 
(This assumes 10KHz channel spacing. Did the Europeans (9KHz) do 
something else?)

The Radiotron Designers Handbook, Third Edition, p. 159, states “A 
frequency of 455 Kc/s is receiving universal acceptance as a standard 
frequency, and efforts are being made to maintain this frequency free 
from radio interference.”

(1) Do FCC and international frequency allocations reflect this?

(2) I’ve heard the term “Clear-Channel IF.” Can anyone cite references?

(3) At lease one news group posting claims that broadcast frequencies in 
a particular market are assigned to prevent strong inter-modulation 
products from falling near 455KHz. Is this factual? Need reference.”

(4) Was this (3) at least part of the reason for “Radio Moving Day” in 
1941? See: http://www.dcmemories.com/RadioMovingDay/032341WINXFreqChange.jpg

(5) Many National Radio sets used a 456KHz IF’s and I think I remember a 
437 somewhere. Why? Are there different considerations for short-wave CW 
operation?

Further input, corrections, and elaborations are greatly appreciated. 
Scolarly reference will be looked upon with great favor.

Regards,
Al

-- 
Al Klase - N3FRQ 
Flemington, NJ 
http://www.skywaves.ar88.net/

Mr. Carlson Restores an All-American Five -- Tribal Knowledge! SITS! Flattening the Curve! (video)

It is always a pleasure to see a new video on Mr. Carlson's awesome YouTube channel, especially in these days of Staying-In-The-Shack (SITS).  Obviously Mr. Carlson is doing his bit in this area.  FLATTEN THE CURVE!   Thanks OM! 

My recent bout of S-38E madness has peaked my interest in the All American Five design, so this March 10, 2020 video was especially interesting to me.  Mr. Carlson puts out so much great tribal knowledge.  I didn't know about "rounder" resistors.  I didn't know that you have to be careful not to short out (to the IF can case!) the 455 kc transformers.  I really like his approach to dial cord restoration.  

Mr. Carlson's discussion of the adjustment of the front end tuner circuit on this broadcast band radio was very interesting.  Unlike the S-38 radios, there are no front end coils being switched in as you change bands. In fact, it appears that that big coil/antenna inside the back cardboard piece IS the front end coil.  This discussion has caused me to question my front end alignment technique for the S-38E.  Did I have an appropriate antenna or antenna substitute across the antenna terminal when I set the peak on the input LC circuit?   I will check on this.  Hooray!  One more thing to do during the COVID-19 SITS period.  

UPDATE:  I checked on this using the test set up described in an earlier post, but this time with my antennas connected.  First with a 40 meter dipole, then with my 130 foot doublet, then with a 50 ohm dummy load I was still able to see the resonance dips at exactly where I wanted them to be. 

My favorite bit of Carlsonian wisdom from this video?  Mr. C's confirmation that some hum in All American Five receivers IS NORMAL!  (This may be too much for the folks who find normal band noise to be offensive.)  

For Inspiration and Education: Dean's Radio Blog (with video)

Be sure to check out the blog of Dean KK4DAS.   He is a new homebrewer who is having great success with one of Pete Juliano's ingenious SSB designs. Dean has a video of his receiver working -- AL FRESCO -- as construction on the full transceiver proceeds.   

This is amazing.   Just a short time ago Dean was taking his first steps as a homebrewer with his version of the Michigan Mighty Mite.  He has followed the advice of the Tribal Wizards and has proceeded slowly, step by step, stage by stage, gaining the experience that has allowed him to actually build a superhet receiver and be on the verge of completing a full SSB transceiver. 

Lots of inspiration to be found on Dean's blog.   Check it out: 

https://kk4das.blogspot.com/2020/03/dean-kk4dass-furlough-40-ssb-rig.html

Technical Manual 11-455 -- Radio Fundamentals -- July 17, 1941

This is an illuminating little book.  It was published by the U.S. War Department on July 17, 1941, less than five months before Pearl Harbor.   Far from being dated, this book contains a lot of  great explanations of -- as the title indicates -- the fundamentals of radio.   I turned to it this morning for a little refresher on the physics of regenerative feedback.  

You can get your own paper copy here:  

https://www.amazon.com/Technical-Manual-Radio-Fundamentals-11-455/dp/B000HI6306

Or here: 

https://www.ebay.com/itm/War-Department-TM-11-455-Radio-Fundamentals-WWII-1941-/141763081079

Or you can read a slightly more recent edition (1944!) online (free) here: 

https://archive.org/details/Tm11-455/mode/2up

Please let me know if you find this book useful. 

These Variable Capacitors Work -- Ether or No Ether!

Amazing that the arguments about the presence or absence of a luminiferous ether made its way into parts advertisements in a radio magazine.  This is from Radio for January 1923.  (About 18 months before my dad was born.) 

BTW that capacitor looks very nice, and would almost certainly still work.  I have caps like that in my junk box.   The shape of the blades helps address one of Pete Juliano's complaints about analog oscillators -- the inconsistent spacing of frequencies on the dial. 

Thanks to the K9YA Telegram for posting this.  

COVID-19 -- StayInTheShack ("SITS") -- Our Contribution to Flattening the Curve

Early in the COVID-19 Emergency, I saw this inspiring picture of Dick Dillman W6AWO.  Dick had placed a caption under the picture:  "I've moved to the command bunker and will be staying here for the duration." That's the spirit OM!  That is what we as radio amateurs should be trying to do at this point.  That is how we can help flatten the curve and slow the transmission of the virus. 

I guess we could call this  #SITS:  Stay-In-The-Shack.   For many of us this is really not much of a sacrifice -- this is what we mostly wanted to do anyway.  And we have people to talk to (on the air).

So... Follow OM Dillman's lead.  FLATTEN THE CURVE!  STAY IN THE SHACK!  

73 and take care. 

AM Diode Detector + 41 and 49 meter Shortwave Bands for HRO-dial Receiver (videos)

The COVID-19 emergency is a good time to look around the shack for projects you have been meaning to take on but didn't have the time for.  We have the time for them now! 

When I first built my HRO-dial receiver (using an HRO dial given to me by Armand WA1UQO and an enclosure from Tim KI6BGE)  my hope was to have the 40 meter ham band and some shortwave broadcast bands.  But it didn't work out that way.  I had trouble getting an AM detector to work properly, and I had a hard time getting a sufficiently broad filter to work right.  I ended up adjusting the VFO so that the receiver would cover only the 40 meter ham band.  

My recent S-38E adventures and a video from VK3HN have alerted me to the nice programming that is now on the shortwave broadcast bands (I really like WRMI's afternoon rock music program).  So I decided to take another shot at getting this receiver to cover SW BC frequencies. 

When I built this receiver, I made the front-end bandpass filter tune-able. There is a two section variable cap behind that "Pre-selector" control you see on the front panel.  That lets me tune two loosely coupled LC circuits from about 5.5 to about 8 MHz.  So without any mods to the front end, I could cover the 49 meter band (5.9 -- 6.2 MHz) our 40 meter band, and the 41 meter band (7.2-7.5 MHz)

Here is how I do it: 

For 49 meters:  I now have the VFO set to run from 6.34 MHz to 7.120 MHz.  The IF is .455 Mhz.  So to get down to the lowest frequency in the 49 meter band, I tune that front end preselector down to that frequency (variable cap in filter almost fully meshed).  Then I take the VFO down to 6.355 Mhz.  I take the difference frequency out of the mixer -- .455 MHz.  

For 40 and 41 meters:  I just tune the pre-selector to this range (variable cap about mid-range) and tune the VFO accordingly.   For a signal at 7.5 MHz, for example, I put the VFO at 7.045 MHz.  7.5 - 7.045 = .455 Mhz.  Note:  There is no sideband inversion in this case -- this is important because 40 meter SSB is lower sideband.  The Kokusai mechanical filter that Pete N6QW gave me is a lower sideband filter.  I have my BFO set at the right spot relative to the filter passband for LSB.

As you can see, I just tune to the "image frequencies" with the preselector.  This gives me double the frequency coverage.   

As for the filters, well Pete's Kokusai filter works great on 40 SSB.  My problem was,  ironically, getting a filter that was broad enough to let AM sound good.  I concocted a filter using old 455 kc IF cans, but I wasn't happy with it.  Paul VK3HN used a ceramic .455 MHz filter that was 6 kHz wide at 6 db down. I ordered some from Australia.  That should have been wide enough for AM, but I had gotten spoiled by the very WIDE bandwidth of my S-38Es (no real filters at all, just the two 455 kc IF cans).  At this point The Radio Gods interceded. Bruce KK0S heard me talking about this on the podcast and kindly sent me some 10 kHz .455 kHz filters.  Now we're talking!  I put one of them in this receiver and AM started sounding as good as it does in my S-38E.  BTW -- a look at NA5B's WebSDR receiver shows that most of the SW broadcast stations are running at 10 kHz wide.  See video below: 




Finally,  I had to get a decent AM detector going.   The SBL-1 product detector I have in there works great, but I had tried several AM detectors and none of them worked well for me.  This was puzzling -- it should be so simple, right?  Just a diode.  But I would get weak and/or distorted audio.  I realized that I really needed was something that looked to the rest of the circuitry like an SBL-1, but with just a diode and an RC filter section instead of the SBL-1's diode ring.  I ended up using a small 455 kc IF transformer that Michael Rainey (AA1TJ) had sent me a long time ago.  My detector looks like this: 

It works great.  During the day I can hear the Toronto CFRX talk-radio station that simulcasts with 1 kW on 6.07 MHz. In the evening I her WBCQ and many other stations on 41 meters (see videos).  And of course I am ready to use it for amateur AM signals on the high end of the 40 meter phone band.   

There is a lot of soul and friendship in this receiver: 

-- HRO dial from Armand WA1UQO

-- Aluminum box from Tim Sutton KI6BGE

-- Mechanical Filter from Pete N6QW

-- IF transformer from Michael AA1TJ

-- Ceramic filter from Bruce KK0S

-- 10k pot in the detector from Thomas KK6AHT

-- Inspiration and ideas from Paul VK3HN

-- Many parts from Jim... 

But you know, I find myself thinking that there are many stations I like on the 39 meter band.  I think it might be best to build a separate receiver for those frequencies.  Maybe throw in 30 meters.  Hmm, let me see what's in the junk box... 
 

Will, KF4IZE's Beautiful Boatanchors

Wow, check out the paint job on that SP-600.  Nice work Will.  Hammarlund should have done it that way.  And I should have kept the one I had years ago.  I would have painted mine that way.  

And my DX-100 (given to me by John K2ZA) has similar vernier reduction drives. 

I run into Will KF4FZE fairly often on 40 meters.  He and I were in the same (very cool) part of the U.S. Army (in different times).  Will is retired but he still works at Ft. Bragg. 

I heard Will on 40 SSB yesterday afternoon.  I was listening with my HRO dial receiver (that I am now working on).  I shot quick video: 

Will was on a Swan Cygnet 270 that he had recently picked up on e-bay.  

More on Will KF4IZE here: https://www.qrz.com/lookup/d/kf4ize

Vernal Equinox Today -- Earliest in 124 Years

https://www.space.com/vernal-equinox-2020-earliest-spring-124-years.html