Tuesday, January 28, 2020

Software Defined Radios for 2020

Some new technology to add to the new technology for 2020.

2-3-2020 Photos of the day..

First we have a photo of Virginia Hall (from Baltimore), a famous WWII Spy working for the Brits and later the OSS. Here we see her pounding brass on a Paraset.

That must be a British version of the GN82 hand crank generator. Notably she had a wooden leg, a result of a self inflicted gunshot wound. She passed in 1982.

Our next photo has a deep meaning...

Maybe this was about their voting for the emperor (with the small e)

After connecting power of the wrong polarity to a circuit how many have said what is on this T Shirt. 

I didn't do that but did put a Teensy 3.5 into a socket, one pin over, and did see a ball of flame come out of the top of the chip. Luckily I had two Teensy 3.5's (now only one). Even more lucky it was not the Teensy 4.0!


2-1-2020 TEENSY 3.5 ala ZL2CTM, Working Again; But needs further evaluation. 

[My plan is get a Teensy 3.5 working and then transition to the Teensy 4.0 MCU. Keep in mind the Teensy 3.5 build is modeled almost entirely after the work done by Charlie, ZL2CTM who has done all of the heavy lifting. My contribution is to routinely solder my fingers together --twice today.]

The Codec Board is the key interface tool.

The trick with this board is the interconnections to pins 11, 12, 13 and 14. These are the Line In / Line Out pins. I have terminated these connections into 3.5 mm stereo jacks one for Line In and the other for Line Out. Short jumpers connect from these two sets of jacks over the board to another set of similar jacks and an all important DPDT relay. 

(Notice I used a mailing envelope as a scratch pad to draw out the interconnections.)

This relay (as I found out in the RADIG V1) switches the I and Q channels on transmit. Yes friend this is also done on the Soft Rock V6.3 and the Ensemble. What I have yet to determine is the polarity ( I and Q) on my RADIG Board. So there may yet be some wire switching to be done.

I was listening to 40 Meters early this evening as the band was dying out --so must await more testing tomorrow when signals are bit stronger. I may call this the PlankSDR since it is mounted on a chunk of plank.

When you know stuff and have a junk box full of built modules, then you can do stuff in about a half a day!

Note the microphone (an electret) plugs into Pins 15 & 16. I may jury rig something so I can have a very low level transmitted signal to evaluate opposite sideband suppression and if I have all the wiring in the correct order.

Stay tuned.

Coronavirus may be a solution not a problem. Just saying!

Pete N6QW



If You Don't Want To Know Stuff, Then You Must Be A Republican U S Senator. But If You Know Stuff, You Can Do Stuff. 

Have started my Teensy 4.0 Trek by resurrecting my ZL2CTM Teensy 3.5 SDR using the RADIG V2 homebrew SDR Board. (http://n6qwradiogenius.us

This approach will enable me to get a working system wherein I can later swap in the Teensy 4.0 and Codec Board as I would know that the remainder of the circuitry is working properly. I have a couple of Teensy 3.5's and so if I smoke something, it won't be the newest Teensy 4.0.

I think I discovered a wiring error in my original ZL2CTM Teensy 3.5 / Codec Board. That might account for a couple of strange observations I had when I was putting it on the air.  Nothing like putting something away and then taking a look with a fresh pair of eyes.

Pete N6QW

1-30-2020 --- My Teensy 4.0 and Codec Boards arrived yesterday!

But I am resisting taking them out of the box and powering them "ON" until I better understand the interconnects and any special application considerations. 

I thought initially I might create a sketch just to drive a Si5351 as a single output. A friend has shared code with me to create the quadrature signals directly. I will get it to work first with a single output and fully understand its capabilities and short comings before heading off to quadrature outputs. Am really trying to avoid smoking my 1st Teensy 4.0.

Do know it has a smaller foot print than the 3.5 or 3.6 -- so that makes physical construction a bit easier. One of my first tasks will be to install Male pin headers on the Teensy 4.0 and then matching Female sockets on the Codec Board. I think they are 14 pins --I have 16 pin types so probably will get the proper size. 

There are some other preparations needed if the Teensy 4.0 is operated with a separate power supply other than being plugged into  USB all of the time. I thinks I saw some notes about adding a SD card. Lots to absorb before the first smoke test. Patience grasshopper!

Stay tuned!

Pete N6QW

1-29-2020 --- Some Noodling Thoughts about using the Teensy 4.0.

On the screen above is a prototype noodling exercise of how a 4X20 LCD might appear using the Teensy 4.0 in a Homebrew SDR Rig. The actual hardware  generating this is a Teensy 3.5 that was used with ZL2CTM's SDR project. I had to keep my hands busy with something, as I await a Teensy 4.0 to arrive from Oregon.

Typically if you use just a single output (versus the quadrature output of the Si5351) and then further run that through the 74AC74 -- you have two unused outputs of the Si5351. Assuming you use CLK0 as the LO (at 4X) to drive the dual flip flop, then CLK1 and CLK2 are idle. 

Thence in a flash of brilliance I said why not program fixed frequencies into these clocks. Therefore  by flipping a switch you could shift to the FT-8 frequency (or WSPR) and also make it shift to USB. A DPDT relay could easily switch the Clocks going into the 74AC74. With a bit more code work you could even make VFO B tunable versus fixed. 

So in the display above -- VFO A is tunable and VFO B is set to the FT-8 frequency using CLK2. Those wishing to really extend the envelope could make a VFO C that would boot up on WSPR. You could even have "enable code" so only when you selected the other VFO's would that clock be active. 

Lots of possibilities that come from a bit of noodling. Keep in mind I am a brute force homebrewer and those even mildly more proficient in software development than me would suggest writing code so that no switches were involved and it was simple menu selections using the encoder push button. So noted -- but when your are few cornflakes short of a bowl, like I am, then you resort to "kludge" approaches to achieve a desired end. Works for me!

Stay tuned for more misadventures from N6QW as he steers a Teensy 4.0 into a mushroom cloud of smoke.

Pete N6QW


Firstly, you all are encouraged to visit the N2CQR http://soldersmoke.blogspot.com Up on Bill's blog is a video of an LT SPICE simulation of a DSB signal. I didn't know you could do that with this program -- but I followed the video and was able to do it. 

This is a new capability for me and the bonus --you get to see a FFT display of the resultant output. This is more new technology to use in 2020!

The two spikes about mid-center of the photo below are the USB and LSB signals. If you add a DC Offset in the simulation factors you will see a third spike in the middle which is the Carrier. The stuff on the display toward the right hand side of the photo -- gives good cause for Filtering in our rigs! 
What I have not explored is how you look at the output of say a 1st stage audio amp to see the FFT spectrum. The video covers two voltage sources in a mixer stage. Some link must be made to see an output of say the audio amp as a voltage source. I just could not push enough buttons fast enough to do that so RTFM is in order.

New Technology for 2020

PJRC (up there in Oregon) has recently unveiled a new Teensy known as the Teensy 4.0. This is a smoking MCU board operating at 600 MHz and there is a matching CODEC Board so a homebrew SDR using something other than a Raspberry Pi is here!

Charlie Morris, ZL2CTM has done a lot of pioneering work with the Teensy series in a homebrew SDR transceiver and even the uBitix V6 can now be fitted with a  Teensy 4.0 in lieu of the Nano. That almost seems like shipping coal to Newcastle --true faster and more umphf -- but it still is a hardware defined analog radio. 

Hans Summers' QSX when it hits your mailbox I believe is using a Teensy. I suspect it won't be too long before Hans will be shipping product.

[A correction here. Hans is not using a Teensy but another processor so that was an inaccurate statement on my part (Thanks, Ben!). I also do not have any real knowledge about when the QSX is being released to production. I along with a lot of other hams are wishing and hoping  that it is soon.]

After a download of an ancillary program (from PJRC) you can program the Teensy 4.0 just like a standard Arduino using the Arduino IDE. The ancillary program has internal libraries that facilitate their use in SDR. 

You should also visit Iowa Hills Software to get the free software that enables you to build Digital Low Pass, High Pass and Band Pass Filters. Data from the Iowa Hills Software filter output coefficients is simply embedded in your IDE sketch.

An interesting note here as the Teensy 4.0 can be had for less than a $20 (less than what the Teensy 3.5 and 3.6 cost)  and the matching CODEC Board is about $15 --so with shipping two $20's should get you both. I mention this in light of the abundance of new technology hitting us in 2020 that won't break the bank. Think if the Teensy 4.0 purchase is a light meal for two at McDonald's.

I am getting a strong urge to use the Teensy 4.0 in a SDR transceiver but a lot more noodling ahead before anything concrete would happen. Stay Tuned to this space.

Just so you don't think this project has died...

 73's (From the Left Coast Wonderland!)
Pete, N6QW

Thursday, January 23, 2020

Back to SDR Radios

A brief respite from the 1930's...

[1-26-2020 ~ Should we be worried? This morning as I pondered yet another project I was just about to hit the purchase button for several amazing technology products that were 'home ported" in Wuhan, China and Hong Kong. Then it hit me! Boom I cancelled! 

Can the coronavirus be hiding out in the packaging that would enclose these electronic jewels. That is a serious question and it needs an answer. Should we stop buying anything coming from China?

I even think about that when I pick up some bargain on eBay that has been lying in a barn for a couple of years. My standard process when I open that box is to use a mask and rubber gloves and I wipe over the gear using  Lysol spray before I start to work on it. More than once I have seem mouse droppings inside of a chassis. 

So why can't coronavirus be hanging out in that packaging coming from China. I just don't know --so those projects are now on hold!

If someone knows the answer email me at the above address.

Pete N6QW]

Some exciting things are happening in the world of SDR radio and especially homebrew radios. 

Charles Hill W5BAA, is a ham that I bought some soft rock SDR radios from over 10 years ago. But my first encounter with W5BAA was back in the 1970's when I built a copy of his all solid state 20M SSB transceiver that used a single IC, the LM373, to do all of the heavy lifting. If you go to http://www.n6qw.com you can see a second copy of that 1970's transceiver built about two years ago. Needless to say W5BAA is always pushing the envelope.

Now he has done it again! See ...

W5BAA has a working FT-8 transceiver using the STM769 MCU. Yes an MCU not a Raspberry Pi nor an ASUS Tinker Board -- an MCU. The STM769 Discovery Board comes with a display and W5BAA's rig mates with a variety of radios such as the hiQ-SDR and the Soft Rock radios using the si-570 and even ones using a Si5351. W5BAA shared via email this morning that it was even possible to supply a mono input from any SSB transceiver and it would decode. Below is the screen display of the rig.

So guys get a grip -- a shirt pocket sized FT-8 transceiver with a display that looks simply amazing.

So my 1st question to W5BAA, can this do regular SDR beyond FT-8. He explained that it was a climb to the top of Mt Everest just to do the FT-8. But I am sure the general purpose SDR aspect is being worked on somewhere in the world. 

In other related work that I read about this board -- one of the most critical factors was time synchronization for the 15 second scan. 

A quote from an email I got from Charley:

"The application does NOT required any WIFI or network connection to work.

I have a feature that allows the user to synchronize the unit with the rest of the FT8 world via a simple pushbutton.

And, in my current code I have added a Arduino RTC module that makes life even easier."

The STM769 Discovery board is sold here in the US by Avnet and the cost is about $55. They had about 65 in stock. The github link has some amazing documentation by W5BAA and is worth the read.

[Am taking a short "blog break" from the 1930's as I prepare the next round of excitement that will be shared here. Trust me it will be worth the wait!]

Pete, N6QW

I am not on the leading edge but usually a football field behind...  BUT "when you know stuff you can do stuff!"

Tuesday, January 21, 2020

You Saw where this was headed ~ A 1930's Style Station Part 5

The Pesky Power Supply Problem.

Most stations of the 1930's relied upon either battery power or the building of a power supply that plugged into the regular house mains. In either case you needed DC voltage to run either the transmitter or the receiver.

For most tubes used in the transmitter section this amounted to several hundred volts of DC. Receivers, however, often could get away with having say around 100 VDC on the plates. The All American Five Tube AM Table Radio did something clever. Here the radio designers figured out how to take the 110 VAC standard house power and to string the filaments so that the total filament draw = 110 VAC. 

This required the development of the 35W4 rectifier and the 50C5 audio power amp --yep the filaments for those two = 85 volts. Add in three 6 / 12 volt filament tubes (6BE6, 6BA6 and maybe a 12AU6) and thus the math = 85 + 24 = 109 Volts AC. A simple half wave rectifier like the 35W4 and you had about 120 VDC. Forget that the chassis was hot with AC and that you could get shocked -- but it worked.

There are a couple of ham receivers that used this principle (hallicrafters S-38 and the National SW-54). One ham transceiver the SBE-33 took the 115 VAC directly and voltage quadrupled it to produce 450 VDC. These were all shock hazards to say the least.

But there were another class of tubes that used DC voltage (only) on the filaments and a modest amount of plate voltage. These tubes were often used in battery operated portable receivers. Tubes like the 1T4, 1U4, 1S4, 1R5 and the 3S4, 3A4, 3Q4 and 3A5 are typical of those class of tubes. Many portable ham rigs were fashioned from these tubes. 

There were some tubes that could even develop 1 to 2 watts of RF at 7 MHz and so these too much like the IRF510 found their way into ham rigs. In several prior posts I covered the WesKit BN-1. It had a 3A5 used both for the transmitter and receiver and the filaments were battery operated and the typical plate supply was 90 VDC.

So now how would we get 90 VDC. This started an investigation by me of building a prototype power supply and from this test come up with a final design. Given "toob' and transistor CW transmitters can be prone to "chirp" one area of concern is a well regulated supply and of course a second area is cost. Power transformers today are costly and thus we need a bit of cleverness in our approach.

So I thought about using the old connect two filament transformers back to back approach. That is no longer a cheapo approach. Then I thought about a small VA rated isolation transformer. Better, as the secondary would be about 117 VAC and with a half wave rectifier and a good bleed -- about 120 VDC. Then the magic of how to make that a regulated 90 VDC.

Looking on the Internet and in my junk box I found the parts to build a prototype 70 VDC regulated supply operating with about 100 VDC input.

For the 90VDC supply there will need to be different values for the Zener Regulators and I have ordered some parts. For the 90 VDC I will use an 82V Zener for D2 and a 75V Zener for D1 and the LM7824 will be changed to a LM7812 netting about 87 VDC. BTW I used 5 watt Zener's. If I left the 7824 in there then the V out would be near 99 VDC. So I have some options. Below is an "ugly" prototype.

That still leaves the filament issue of somewhere between 1.5 to 3 VDC at possibly one amp. I bought one of the Buck Down power supply boards (about $4) and good for 3 amps. I need only supply 5 or 6 volts of DC for the input and I have several options for that. 

So it looks like a power supply is shaping up. Oh for a Rx -- that is the why of the PMR6A!

Pete N6QW

Monday, January 20, 2020

You Saw where this was headed ~ A 1930's Style Station Part 4

Dress for Success!

That sage advice typically was offered to those who were participating in a job interview. Showing up for a job interview for a position entitled Vice-President for Creativity with a three day beard, a somewhat soiled tank top and flip flops only works in Silicon Valley and only for Google positions. Elsewhere requires a very different "attire".

So it is with our hobby -- not the dress itself as what I described previously probably involved comments like what's wrong with that dress from many blog readers. The dress for success point goes to the heart of hams who have either very little or NO test equipment! Test Gear is the Dress For Success for our Hobby!

The recent re-incarnation of the PMR6A involved test equipment that is of old. Yes I do have a some really new and some really old test gear. One critical variable with the  PMR6A are the "toobs". Looking into the radio and seeing if all the tubes light is indeed a test; but they could all "light up" and it would not work. 

There are several factors with tubes that determine if they really are working  such as internal shorts, emission quality and grid leakage. A negative showing for any of these factors (even though the tube lights up) will render the radio inoperative.

Abut 10 years ago when I was working on some "toob" boat anchors I purchased a Tube Tester. Now there are some really expensive tube testers such as the military TV-7 and some really inexpensive ones that only test if the filament lights up.

I settled on a gently used Sencore Mighty Mite II which cost me about $40. That said the tester itself is worthless unless you have the tube data tables. Before buying the Sencore, I checked the Boat Anchor Manual Archive (Edebris) and found the tube data for this tester. We were now on a roll.

My tester has about 9 sockets so you can test all kinds of tubes although the 9 Pin socket has been used so much that the contacts are a bit flaky. I keep saying I will change the socket (easy to do) but for the last 6 years I haven't tested one tube. So now maybe it is time.

In the Sencore Mighty Mite II shown below is a 6CL6 tube and you can see the emission is in the middle of the Green range. Below that is my hp Netbook with the Tube Data for the 6CL6 and that data tells me where to set the four controls and what socket to use. Some tubes have multiple entries and so you can test variability for many parameters. 

Now not only was this tester used for the PMR6A; but also another project that was acquired for a really low price because it would not receive or transmit. 

Based on my experience I thought I had a pretty fair shot of getting this transceiver project to work since it had tubes and components could actually be seen by the naked eye nor were there circuit boards involved.

As it turned out it had three bad tubes which I had replacements for in my tube stash. (6U8A and 2 X 6AZ8's were the bad tubes.) The receiver is working but the transmitter only puts out about 60% of power on 40 Meters (but less on other bands). 

[Now transmitting 100 watts out on 80-20M (haven't tested 15 or 10) and this was a result of two things. Initially I started the KWM-2 using a Variac on the 516F2. The actual variac ( a homebrew one at that) was set for about 108 VAC. When I moved it up to 117 VAC, boom more fire in the wire. Before finding the low input voltage I had cleaned up all of the band switch contacts and relay contacts with De-Oxit. So with these two actions 100 Watts! Boom receive seems better too.]

The transmit signal quality is quite good as heard on an external receiver and I had one on the air signal report (20 Meters) that complemented the nice sounding audio. 

I did carefully apply De-Oxit to the band switch turret wafers sing a very small brush. DO NOT SPRAY De-Oxit  directly on the switch wafers! I opened the Final RF Amplifier cage and applied some De-Oxit to the final tank band switch and to the three relays (one in the cage and two on the underside). Dirty relay contacts can be an issue with flaky receive and transmit signals. NOTE: Power totally disconnected when you open that cage!!!!!

But having a $40 used piece of test gear enabled me to find three bad tubes and quite possibly reincarnating another "real jewel" of the past. Having a Tube Tester is absolutely mandatory when working on this older tube equipment --Dress For Success!

Pete, N6QW

Thursday, January 16, 2020

You Saw where this was headed ~ A 1930's Style Station Part 3

The PMR6A Receiver itself will now undergo the re-incarnation process.

1-18-2020 ~ when you know stuff, you can do stuff! Not a uBitx v.6; but a trip back 67 years!

Pete N6QW

1-17-2020 ~ It is Alive! 

More Space Filler.

Ham Safety while working with Thermatrons (vacuum tubes). 

Most of our homebrewing taking place today uses 12 VDC and that is not high voltage. Although I do know of a case where a constructor had his hand on a 5 VDC 30 amp power supply output -- seems like his ring got shorted across the supply and the ring nearly melted around his finger, which subsequently I think required amputation. So any voltage can be dangerous.

The voltages in the PMR6A under load show 260 VDC on the lead to Pin #3 on the power connector. [There is a clue here for those who read every word...] The problem with the HV is that it can start your heart (defibrillator) or stop your heart if applied too long.

One of the additional steps I will be undertaking is to provide shield covers over the power supply so one does not experience an unwanted jolt! HV kills!

Pete N6QW

That process will entail a clean up, tube testing, circuit integrity checks and a lot of getting to know the innards of the PMR6A. But that will not happen in one day. So stay tuned.

To have a space filler for this blog since I will be working in the background on the PMR6A Receiver I would like to share a little more about simple rigs that are now nearing over 70 years old!

Enter the WesKit BN-1 Novice Transceiver. You might think of this kit much like the $3.50 Pixie CW Transceivers that are currently on eBay direct from China. Here is a BN-1 in all of its glory!

There are some notable points to observe here and firstly is that it could be operated over the range of 3 to 8 MHz --shades of a Paraset. It was battery operated (a plus for portability) and you could have as high as 180 volts on the plate and as low as 45 volts. Most likely the power output with say 90 VDC on the plate in the less than one watt range. The plate dissipation was one watt and when the two halves are operated in Push Pull the Pout is 2 watts! So definitely QRP. 

Yes a CW transceiver was all done with a single tube, a 3A5 which is a dual triode intended as a power output stage in a battery operated receiver. I did see one variant where a 6SN7 was used in lieu of the 3A5 which opens the door to a bit more power output. But the 6sN7 needs more filament voltage (6.3 Volts)

One slick advertising photo shows the BN-1 with a loaded coil whip antenna on the box but was never produced or sold that way. I can just imagine the number of hams who were getting postal money orders (the plastic card of the 1950's) and sending off to purchase a BN-1. With that whip antenna it was now a complete rig in a box on 80M CW!

With a large tip of the cap to my friend Bill, N2CQR who recently built and operated a homebrew ET-2 that was not unlike the BN-1 in that it had a one transistor regen and an a one transistor 100 milliwatt oscillator. Bill made two dozen contacts in multiple states. So the BN-1 could likely do the same. Most BN-1 field reviews were not so kind attesting to a poor receiver and low power. But others had remarkable records using the BN-1.

Circuit Forensics

I guess one could argue was this a true transceiver as we think of transceivers today? What we have is a tunable regenerative receiver (1/2 the tube) covering the range of 3 to 8 Megahertz and a crystal controlled modified Pierce Oscillator (the other half) covering the same range. So the true transceiver is only when the receiver is near the Crystal operating frequency. But I guess you could operate cross band with the receiver on one band and the transmitter on another. Unlike the Pixie which forces a received frequency near the transmit frequency.

So lets us look a little more closely at the schematics in our tour of the circuit forensics. Although the two schematics are drawn a bit differently they are the same. 

The first thing that catches my eye is the DPDT toggle switch which is the TR switch (on a small metal box). You had to really be deft when you engaged that switch. You guys with 500 pound gorilla hands, if you pounced on that switch you probably would move the received signal location. There are no vernier drives on those tuning capacitors and with a range of 5 Megahertz over the arc of the capacitor --a velvet touch is mandatory. So that could be an issue. 

The only items being switched is filament power between the two separate filaments. However on receive the crystal is grounded but on transmit connected to the plate of the transmit half.; but there is no filament voltage supplied to the transmit half of the 3A5. I have no explanation about why it would be grounded on receive.

However as mentioned on transmit, the crystal is connected to the plate circuit to form a critical function in the kB=1 criteria. The Pierce oscillator uses this topology. BUT normally one sees a blocking capacitor in series with the crystal on the plate side. 

There are many concerns about crystals used for frequency control. Two concerns with the use of quartz crystals are voltage and current. If say you were running 250 VDC on a plate of the 6SN7 variant, then one side of the crystal would be hot with 250  volts without the cap. The other issue is that huge currents can be developed in crystal oscillator circuits and an excessive amount will shatter your one and only rock. 

Perhaps the cap was left out because of cost --a penny here and a penny there. I have no crisp explanation as to why it wasn't installed. 

Now a big caution about Crystal currents. I see there are many FT-243 style crystals being sold on eBay today that are essentially smaller HC-25 or HC-49 crystals stuffed inside a FT-243 holder and re-labeled with a new frequency. Read the fine print... It says these crystals are only good for QRP rigs where the current is low. I suspect you put one of those crystals in a 6AG7 oscillator circuit you will see a mushroom cloud of smoke in your shack

The transmitter tuning involved the old light bulb trick to show when the antenna was taking  juice -- brighter = more fire in the wire! BUT given the link coupling -- this might be an issue with harmonics when operating say on 3706 kHz ( Novice CW frequency in 1950) and the second harmonic would be 7412 kHz. That might get you a post card from an OO. 

So using that rig today might not meet the current FCC spectral purity issues on transmit. A Band Pass filter, should you build this transmitter, is much in order. Today around $7 will get you a tube and socket from Antique Electronic Supply in Phoenix, AZ

Because the regen receiver is in fact an oscillator even in receive it too is radiating a signal. Think about those hams running 10 milliwatts on WSPR and being heard hundreds and even thousands of miles away.

A couple of issues with the receiver! Your Sony Walkman 32 Ohm earbuds will not work as the phones must be high impedance "magnetic" earphones and they are an active element in the receiver plate supply circuit! Also the headphone interconnects are insulated "pin type" connections so another issue. Typically the 3.5 mm stereo jacks have a common ground. Ditto for the Key and Crystal using the same type pin jacks.

Let us now look at the back side of the BN-1 box and again at the schematic.

Since this is the back side the receiver portion is along the left side where clearly we can see Coil L1 and L2. On the right side we see L3 and L4 as well as the connections to the pilot bulb (antenna current indicator) and the two wing nut antenna posts. Pretty clear.

BUT and a BIG BUT ... The schematic does not show any connections from the antenna to the receiver! The antenna is always connected to the transmitter coil L3.

So how does the received get from the antenna to the receiver. Often in a regen receiver you would have a third coil winding that essentially link couples the off the air RF to the tank circuit of the regen. I thought initially if that if coils L3/L4 were close enough to coils L2/L1 then we would have mutual inductance link coupling. But it is clear that they are too far apart for that to happen.

Here is where we can get fooled. I keep looking at that circuit diagram as two tubes. Like Bills ET-2, where there were two separate FET devices, the 3A5 is two triode tubes in a single tube shell. Not two separate tubes!

I am theorizing that in the signal path from the antenna to the regen receiver is the inter-electrode capacitance of the 3A5. Thus within the 3A5 itself the antenna on receive is connected to the receive half through a small capacitance internal to the tube. 

From the NJ7P Tube Data Base we have data for each triode so we can assume there likewise is a small interelectrode capacitance between the two triodes. That value in the 1 to 2 PF range would give "light coupling" between the antenna and the regen. The light coupling is probably good for a smoother regeneration and with moderate band condition some signals would be heard!

Each Triode
Source ........................................ RCA RC-29 - 1975
Input ......................................... 0.9 pf
Output ........................................ 1.0 pf
Grid to Plate ................................. 3.2 pf

[One of our very astute blog reader's emailed me after this was initially posted and made me aware that there was perhaps even a bit more sophistication to this circuit... lurking there in the bushes. If we think of L3 / L4 as the front half of a Band Pass Filter coupled with a very small capacitance (internal to the tube) and in turn that L1 / L2 is the other half of the BPF. This then  would indeed add some front end selectivity. So having the transmitter tank tuned close to the receiver operating frequency makes for a nice way of achieving a BPF and keeping crud out of the receiver circuits. Bravo WesKit!]

Thus today's filler has covered the WesKit BN-1 Novice two band CW Transceiver that likely does work but in itself might not bring thrills but real challenges. 

(The WesKit BN-1 was sold through Western Radio in Kearney, Nebraska and if you mated that rig with a Gotham Vertical --you could work the world!)

Pete N6QW

New Technology for 2020 ~ Improvise, Adapt and Overcome

What to do during the Pandemic? This is a chance to get back on the air or to take up an interest in homebrewing your own rig. You can bui...