New Technology for 2020 ~ A Direct Conversion Receiver You Can Build

Some Arduino Code as used with the Left Coast Loafer CW Transmitter.

//Turn ON:     si5351.clock_enable(SI5351_CLK1, 1);
//Turn OFF:   si5351.clock_enable(SI5351_CLK1, 0);

/*OK you missed it -- the "1" turns it on and the "0" turns it off.)

So my code senses if Pin 4 is LOW and if so then turn ON the CLK1. If it is not LOW then turn it OFF. This is the standard If Else regime. You also have to blank out the frequency in the else part of the code. Here is the code*/

 void CheckCW() {

                 if(digitalRead(4) == LOW){
                 si5351.clock_enable(SI5351_CLK1, 1);
                 si5351.set_freq( rx1 - 700, 0, SI5351_CLK1);
si5351.clock_enable(SI5351_CLK1, 0);

I plan on a MOX operation where you flip a switch and that turns on CLK1 and at the same time does the TR. There is embedded code to produce a pulsed 1kHz Tone for tune up. 

No reason with a little code rework that this 988Hz Tone would be the side tone. Since you have side tone the same code that turns on CLK1 could also turn OFF CLK0 which is the Rx LO. Lots of possibilities.

I have been having fun programming Nextion Screens and thought of screen where you would have a selection button  and if the button is engaged a text message would appear on the screen. This was FUN!

Press the button and the message says  "I have no responsibility". Don't you just love this technology?

Pete N6QW

Pre-Built Audio CW Filters for the DCR.

Thanks to a friend in the Mid-west the following are some links for audio active CW filters that could be used with the DCR

* 4 States QRP has the Hi-Per-Mite 200 Hz Bandwidth, 700 Hz Passband Kit.

* New England QRP NESCAF Filter Kit variable Bandwidth  90  - 1500 Hz, 700 Hz Center Frequency.

* SOTABEAMS Dual Bandwidth Filters (there are several models to choose from) CW 300-1300 Hz, 550 Hz-850 Bandwith

* Vectronics VEC-820K 80, 110,180 Hz Bandwidths 750 Hz Center Frequency

More helpful Amidon information. How many turns of what size wire will fit on a core?

Pete N6QW

Cracking the CW Nut...

After some lengthy discussions with N2CQR, I guess we've concluded the most applicable CW solution is to have one of the clocks generate (F-700hz) where F is the LO Frequency and tune to the upper signal so that on transmit you are Zero Beat with the opposite station. I like the 74AC08 idea from K1SWL so that a gating signal is supplied to one of the sections and the (F-700) is transmitted to the rest of the circuit. Although I would skip the three BS170's in favor of a 2N2219A driving the IRF510. Further study needed to finalize the circuitry; but we may have something in a week or so.

Pete N6QW

Trust But Verify...

A long time ago (read maybe 15 years ago) Amidon who makes/sell Ferrite and Iron Powder cores so often used in our projects, offered (for free) a handy guide that documented the parameters of the cores. There was even data on how many turns of various wire sizes would fit on a specific core. While I said it was a handy guide, it was actually like a folded Road Map that when opened fully is like about 2 feet square with printing on both sides. Mine gets frequent use.

I had always used an Al Value for the FT-37-43 core of 420 because that is what printed in the guide. Below is a sample of two of the pages from the guide. If you squint, then you can see the Al Value for the FT-37-43 is 420.

Fast forward to a couple of years ago and I was ordering some cores from Amidon and when I called up the catalog page I spotted that the Al Value was now 380 not 420. So I just filed that away in my brain and used that number when I calculated cores.

Just yesterday I had an email exchange with KK4DAS about some LT Spice simulations involving inductors and he and I had different values of inductance. I emailed Dean, and noted that the Al Value I used was 380 not the 420. He then emailed back and said the Amidon Website now shows 350 as the Al Value. 

So likely the formulation of the Ferrite Core material has changed and so the published 420 in the handy guide is now 350. Likely others have changed. So a word of caution to myself, check the Amidon specifications as likely others have changed too! Trust but Verify!

A superb source for any and all cores is W8DIZ as his pricing and shipping costs are far less than the original supplier. To wit a small batch of core (FT-37-43) from the supplier was about $10 but the shipping/handling was $14. I got the same batch of cores from W8DIZ for less cost and about 1/2 the shipping. Again: Trust and Verify.

Back to looking at companion CW transmitter for the DCR... There are some technical issues to using the DCR and tracking the proper offset. I am sure there is a simple solution but just not readily evident. 

The simplest solution to get on the air quickly is to build a crystal controlled transmitter. I happen to have rocks for 7030, 7040 and 7058 kHz. So that gives a bit of frequency agility. Another solution is a second Arduino/Si5351 which adds a bit of cost; but you can transmit anywhere. 

I was made aware of a project from Dave Benson K1SWL called the Hill Topper which use a 74AC08 driving a pair of BS170's. It appears like the 74AC08 is "gated on" and driven by CLK1 to produce the CW waveform. 

Pete, N6QW

Thoughts on using the DCR as a CW Transceiver. 

I have heard and guess have seen as well the DSB transceiver trick although using DSB on 40M could well risk one's life. You know the SDR Police with their 72 inch screens would tell you that you are transmitting on two sidebands. Well Duh, that would be true; but there is no carrier present so you couldn't call it "faux" AM.

CW seems like a better course as most of the SDR Police wouldn't know how to do the binary form of communication. 

There is a bit of leverage here with the Arduino and the availability of three clocks. Several years ago I built the Left Coast Loafer which was a filter type CW transceiver. There was a trick to enabling a clock (with a hold time) thus you could program that clock to be off frequency by 700 Hertz and thus account for the offset and that clock would only be ON when you engaged the transmitter.

W7ZOI used a NE555 trick that when you hit the Key the NE555 would stay on for short periods of time providing power to downstream circuits even though the key was in the up state. There was a timing cap that held the NE555 on for enough time to form characters. The Arduino could simulate the NE555 and so that piece is taken care. The offset is just simple programming. 

Now the second trick would be to have the Si5351 CW clock in an ON state during the timing cycle and the trick from the old days when there were drifty VFO's was to have the VFO run continuously -- not keyed and a subsequent Buffer stage was keyed. This also enabled  one to shape the keying of the buffer so that it sounded crisp. 

I would not include an RIT but there circuits to do so. If the DCR would be a piece of a CW transceiver then audio filtering would be a welcomed addition. There are kits for sale or you could build one out of a couple of op-amps. Given my very negative view of op amp filters, I would probably not use one. That would be fine for me as I am not a CW person and my interest would be just to "kluge" something together to have a proof of concept.

Now as to power level. I would look to getting one of those $12 Linear amp boards from China that are good for 20 to 30 watts and then you could reliably make contacts. Keep in mind Heathkit sold DX-20's, DX-35's and DX-40's long before any HW-7's or HW-8's hit the market. the objective is to make contacts not cause angst! 

So I have been thinking about the "how to". But some may have already have such a transceiver in their shack. I am impressed by the sensitivity and the crisp signals being copied -- so I may just have to noodle a bit more on this

Be safe.

Pete N^QW


t "Listen to the Music" (Sound) of this Rig!

Pete N6QW

Northern California is On Fire... 

Terrible Fires and More on the way. But in the face of adversity there are always those who see the glass as half full. Take our dear friend Napoleon Dynamite. A friend sent this to me and I am not sure of the genesis of the poster; but aptly in the middle of a world wide pandemic, major fires burning millions of acres,  an inept emperor, and 178,000 deaths -- we need a bit of a lift. 

Notice he is wearing his Pocket Protector & ID Badge. That means he is employed--Nerds Rule!

WSPR & FT-8 Copied on the Cat-Around!

Now that we have your attention...

How about building a simple Direct Conversion Receiver? The parts cost is within the realm of reason and the most critical device costs $0.82 at Mouser in single lots. The use of single sided copper vector board facilitates construction and provides a superior ground plane to make all common connections. 

The MC1496 DCR on 20M --- Try this with your Drifty Analog VFO. Since it is a DCR the LO has to be on 20M. 

Part II of the 2nd 40M Listening Test below. I added a 100NF across the Volume control and that improved some of the background "hiss". This keeps getting better!

I made an adjustment so that the LCD will read the correct actual frequency. In a DCR the dial reads off by the audio value

The MC1496 can be bought at Mouser for $0.82 an SMD Version so you will need an adapter board. A DIP version is sold by Jameco Electronics for $1.95 and they have 200 pieces in stock.

Let us start with a Block Diagram. I call it the Cat-Around and later on, that will become clear as to why it is called by that name..

We will test out the idea of a 2N3906 as a broad band RF amplifier stage. (This was described on the blog about a week ago). 

I happen to have a two section 40M Band Pass Filter that I will use for initial testing although later it likely will be shifted to a 3 section. I would think that the three most desirable bands would be 40, 30 and 20 Meters. I do have data on 3 section filters which I will subsequently post.

The MC1496 Detector is straight out of the Motorola Data Sheets 

Luckily the MC1496 is an active device so has some gain. But typically 100 dB of total system gain separates the toys from the boys. Thus we need some pretty healthy gain following the detection so the MC1496 will be followed by a really robust audio amp stage comprised of a 2N3904 driving the 8 pin LM-380-N audio IC. On a clear day with the planets aligned, the 8 Pin DIP version of the LM-380 could do about 1 watt. 

No Analog LO's (VFO) will be used for this project and that too will later become apparent (no drift or wobbly frequency stuff in my projects). One test objective will be to see how well this DCR copies WSPR and FT-8.

Thus our LO is supplied by the Si-5351 and an Arduino Uno R3. Yes the Uno is clunky and the new Seeduino Xiao would be cool; but I happen to have a few of these early space hog relics in the bin thus IUWIH. The readout is the 16X2 Cool Blue LCD.

If you had to purchase all new parts you would likely escape for around $40. Think of it as about 11 gallons of gas that you saved from not driving so much. Besides no bad emissions to pollute the air.

The beauty of the single sided copper vector board used for the project is that it is like regular perforated board but has a copper surface. This copper surface forms an excellent common ground plane with the bonus that in the event you need to add shielding around a circuit some scrap copper PC board can be simply soldered in place to form the shield. 

But there is some tribal knowledge to using this material such as preventing shorts to ground. To make for clean penetration holes, I use a 1/8 inch drill bit to remove material from around the hole for all connections that pass through the board as all wired connections are made on the underside (insulated side) of the board.

This is the board underside and the only cross over connections are the power wiring shown in Orange. The Connections form the Si5351 and the RF amp were just tacked to the anchor pins so they do not look very sanitary. These will be changed to more permanent and more cosmetic states. I was sort of in a hurry to get this thing fired up and the garage was >100F

For those connections that are grounded you simply solder the part right to the top ground pane. The SIP stock has machined pins. So for the socket installation, I first use the 1/8 inch bit to remove the copper from around the holes and then I drill through the holes with a 1/16 inch bit. The machined pin stock material simply drops into the hole and no pins are shorted to ground. For good measure I super glue the socket material to the top of the ground plane. Below shows the initial parts layout, the drilling and reaming of penetration holes and the final install of parts.

The board size is 4.5 inches long by about 1.75 inches wide.

On the right is the MC1496 followed by the 2N3904, about center and on the left is the LM380-N. The devices are socketed so if you smoke something -- easy parts replacement. all of the sockets were made from the SIP material. 

Above is the very healthy LM-380-N Audio Amp schematic.

A 40 pin breakable SIP strip cost about $1. A single strip (14 + 8 +3) yields enough pins plus some extras for the devices. I also use the pins as anchor points for like the audio pot, the audio output, at the LO in and Signal input and power. If you have been counting -- that is 40 pins with a few spares!

I have tested the audio amp and it is plenty robust but have not as yet tested the detector. With temperatures in may garage exceeding 100F -- you literally do not need a soldering iron to solder.

The Arduino is programmed and working and I do have a BPF. Tomorrow I hope to build the 2N3906 amp stage and so we will be able to test the whole system. Figure about 10 hours to build.

There is one critical piece here that I should mention. I do all of the parts arrangement using a standard piece of PC Board and then just move everything around until crossovers are minimized and we have a compact layout. I leave that intact while I build the final unit so that I have a reference where the parts go. It also tells me which are through holes versus ones soldered to the top ground plane.

But even then I often make some circuit twizzles while building the final board. But at least as I do the final build, I  know where to lay out the parts, which are grounded and which are through hole. That my friend is Tribal Knowledge!

Stay tuned for the excitement ahead. 

Pete N6QW

PSA: If you want to Dump Trump --Vote before November 3. He is doing everything he can to invalidate your vote. 

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