A Motorola Lapdock added to the RPi2 and Softrock V6.3

A new twist to Portable Rigs!

I have just added a Motorola Lapdock tothe Pi2/Softrock SDR Rig. Amazing technology! Portable operation is but a few keystrokes away. Pete N6QW 3/24/2016

Raspberry Pi2 and the SoftRock V6.3ng SDR SSB Transceiver

New Direction -- Using the Raspberry Pi2 with a SoftRock V6.3ng  as a SDR SSB Transceiver.

I have lost interest in continuing with the Simpletransmitter. Info has been provided to build the transmitter and I am not pursuing that project any further.

But I have successfully implemented  a Raspberry Pi2 with the V6.3 SoftRock using Quisk as the SDR Software in a 40M SSB Transceiver. See the video below

73's
Pete N6QW

Simpletransreceiver ~ Transmitter Stages Part 1

Heating Up the Iron ~ Transmitter Stages #1

After some six weeks of being off the air and tending to a family medical emergency, we are ready to start building the transmitter portion. While I was "noodling" over the transmitter stages I realized that many of the circuits used in the receiver stages are simply "ported over" for use in the transmitter. In the lower level stages the one new circuit board is that of the microphone amplifier. According to the LT Spice once again the "home built" Dual Gate MOSFET works quite nicely in that circuit element. So to be true to our initial design premise -- we will continue to use J310 DGM's in the transmitter blocks.

 

By way of review below is the transmitter block diagram with a special note that the stages with the red asterisk are a direct lift from the Simpleceiver. To that should be added the carrier oscillator. At one time I had thoughts of sharing that with the  in the Simpleceiver. It will now be either a separate oscillator similar to the receiver BFO. [I have already found 4 crystals that are a very close match to the BFO frequency] or it will be CLK2 out of a Si5351

 

 

 

 We'll start first with the microphone stage and once again using our template for the DGM  made from two J310's, is used. Frankly this stage is critical to a high quality sounding station and so we attempted to tailor the audio to the range of about 100 Hz to 4.5 kHz. Your signal should have presence without being "hissy".

Since the rig has been designed for use on 40 Meters the builder will undoubtedly encounter the Spectral Purity Police, many who have never homebrewed a rig, but are running high end SDR boxes with 52 inch LED Displays whose only goal in life seems to be to commenting on how bad your signal sounds. We wouldn't want that.

 We are reposting the schematics for the BFO (we'll now call that the carrier oscillator), the IF amplifier stages and the crystal filter. For the transmitter you must use the 4 Pole Crystal Filter. Please review the earlier post on the building of the crystal filter -- there is some art, science and pure black magic to building a successful filter. Do not believe those who tell you they built one in five minutes --5 hours is more like it.

The low level stages use packaged Double Balanced Mixers, the SBL-1 which are 7 dBm devices, meaning you need 1.414 Volts Peak to Peak to drive these DBM's. Some prefer the ADE1-l (both are from Mini-Circuits labs) which is a 4 dBm device that only needs 1 volt Peak to Peak of RF drive. Caution the ADE1-L is a surface mount device and is small. For the SBL-1 pins 2,5,6 and 7 are grounded. Pins 3&4 are connected together and this is where the audio is injected. Pin 1 is the output pin and Pin 8 is the LO injection Pin. Looking at the top of the SBL-1 package the letter M (as in MCL) is over Pin #2.

There are many purists who believe unless you make EVERYTHING then it is not true homebrew. You can make your own DBM -- I have three videos on youtube that show you how to do it. But you will never achieve the performance of something made under exacting factory conditions. You will also find that a homebrew DBM will need more drive like 2 Volts Peak to Peak. In several of my published articles I have used homebrew DBM's and will sometimes get emails like "Your homebrew DBM design doesn't work!" Well friends it does and often I hear back that the person having difficulty lost track of the windings and it was wired wrong. Save yourself grief and just buy the SBL-1 and get on with it!

The IF amplifier schematic is presented below and much like in the receiver the output has a resistive pad ahead of the crystal filter. Once again we must match the in/out impedances to this this stage. The output of the SBL-1 (pin 1) is at 50 ohms and the input to the DGM is set a 2.2 K thus we have a 1:44 match (2200/50 = 44). Using a FT-37-43 (it must be a ferrite core) a 3 turn primary (50 Ohm side) will match  with a 20 turn secondary to the input --remember turns ratio squared 3^2 = 9 and 20^2 = 400 ---- 400/9 = 44.44444 --so really close! The output side must match 50 Ohms to 150 Ohms which is the input to the crystal filter so we need a 50:150 Ohm match which is 1:3 which is easily done with an 4 to 7 turn match. 4^2 = 16 and 7^2 = 49 --- 49/16 ~ 3. So close enough.

For the second IF amp stage you must match the 150 Ohm out of the crystal filter into the 2200 Ohms input. You can do it with one or two transformers. In the two transformer case it is 150:50 (7 to 4 Turns) and then 50:2200 (3 to 20 Turns). I recommend doing this since you clearly understand the impedance match. Or you could do it with a single transformer where you match 150 to 2200 Ohms which is a 1:14.666 and thus 6 Turns to 23 Turns would get you close 6^2 = 36 and 23^2 =529 ---529/36 = 1:14.7. The resistive pad is not used on the output of the 2nd IF stage.

Following the 2nd IF stage the signal is fed into Pins 3&4 of another SBL-1 which is used as a frequency translator. The LO signal supplied either by an AD9850 or an Si5351 is fed into Pin 8 and the output is taken from Pin 1. The signal out of the frequency translator includes the sum and difference frequencies and so we need to run that through a Band Pass Filter to select the difference frequency ( 12.096 MHz - 5.0 MHz = 7.096 MHz).

Repeated here is the 40 Meter Band Pass Filter that is 50 Ohms in and out. So it simply connects to the output port of the SBL-I which is at 50 Ohms (Pin 1).

Finally is the circuit board layout that can be built with the W1REX MePads. You will note there is space on the board for the SBL-1 Frequency Translator and the 40M Band Pass Filter.

Lot to swallow here but this should keep everyone (so OK probably at this point maybe 3 or 4 of you) busy building the hardware.

Thanks to all who inquired about the XYL -- she is home and returning to her usual old self. The metric here regarding her return is how much she complains that I am a ham radio operator. She has always hated the hobby and now that is going on 49 years!

73's
Pete N6QW

Simpleceiver ~ Part 27

Some light at the end of the Tunnel!

 

My XYL has been steadily improving and hopefully we expect her release from the nursing facility in about a week or two. That means I can get back to heating up the iron and continuing with this project. I have not had any comments regarding those who forged ahead and started work on the transmitter stage and so that either means there is a complete loss of interest or the project is dead. I sure hope not as I think given what I have observed from the receiver performance this project could rival some of the currently popular homebrew radios.

 

The basic transmitter board had 4 elements including the microphone amplifier, the carrier oscillator, the SBL-1 and the IF Amp/Filter block. The output is of course at 12.096 MHz which is the filter frequency and just so we all are on the same page the Zout is 50 Ohms. The block which will follow the basic transmitter board is the frequency translation board which performs some very specific functions. The 12.096 MHz SSB signal must be mixed with the local oscillator so that one of the resultant frequencies is on the band of choice. From our earlier discussions the mixing process results in sum and difference frequencies and a second effect is depending whether the Local Oscillator is above or below the filter frequency there may be a sideband inversion. We certainly do not want the case where we have the receiver on LSB and the transmitter is on USB.

 

The Simpleceiver receiver used an LO at 5.0 MHz so that the one of the resultant frequencies is in the 7 MHz range. Here it is the IF- the LO result we want (12.096 - 5.096 = 7.0). But there also is a component where you have 12.096 + 5.096 = 17.192 MHz which must be filtered from the output. So following our frequency translation we must have another Band Pass Filter centered on 7.150 MHz so that only the subtractive mix is in the output.  Given that we will also be using an SBL-1 for the frequency translation there will be a need for several amplifier stages to boost that signal to something directly usable on 40 Meters. A J310 based Dual Gate MOSFET would serve this purpose nicely for the 1st stage of amplification. Thus we can actually use the Simpleceiver RF amplifier stage as a circuit block following the Band Pass Filter. Again we stated that many of the circuit blocks built for the receiver could be simply reused for the transmitter and so this is what we will do.

 

I hope in the next week to post an amplified block diagram of the transmitter circuits that will include the follow on boards to the basic transmitter.

 

 

73's

Pete N6QW

Simpleceiver ~ Part 26

 N6QW Back on the Blog (at least part time)!

A family medical emergency had caused me to stop blogging but that situation is somewhat improving and so I am now back on the keyboard. After three weeks of being turned off, I can see where my soldering iron actually has rust on the tip --that is not good and I soon hope to be soldering some parts on island squares. I might also have to recalibrate the CNC Mill.

 

Our plan is to now focus on the building the transmitter and then take the next step of configuring the blocks (receiver, transmitter, control and LPF + TR) into a working transceiver. During the last three weeks KK6FUT has built the DCR version and has a you tube video -- it sounds really good as does the superhet Simpleceiver  built by Mikele, 9A3XZ. I do know that others are building portions of the project so if anyone has built either the DCR or superhet variant please let us know.

 

In moving on the transmitter, it would be well to review the final configuration. Essentially the design intent was to build completely separate receiver and transmitter boards and to share a common VFO and BFO and thus one would have a transreceiver. There are benefits as well as potential problems in this approach. The chief benefit is that you can optimize the receiver for best performance while not impacting the transmitted signal.

 

[Many older technology transceivers had this problem and frequently the alignment instructions would strongly suggest that the final alignment was a compromise between that which could be achieved with separate circuits. Today that is not so much a problem and it is probably for the second reason that separates were chosen and that is experimentation. With the separate approach it would be possible to test variants individually without compromising overall performance. For instance one change might be to put a 6 pole filter in the receiver and only use a 4 pole for the transmitter. Or to even have switchable filters, SSB/CW, in the receiver. You get the idea.]

 

One other problem rears its head especially in the older technology transceivers and that was circuit loading that caused frequency shifts when going from transmit to receive. Imagine my surprise when I was working with the Ten Tec Model 150A SSB/CW transceiver to find there was a compensating circuit in the BFO circuit so that the BFO was calibrated in receive and then using circuitry that was only switched into play on transmit was calibrated on transmit.

 

Being on the same frequency in both transmit and receive is critical! Typically where there are crystal oscillators involved, variable circuit loading can cause a shift in the fundamental frequency. A shift of 100 Hz can be picked off with some of the new crop SDR radios --and if you are on 40 Meters many times the newly minted Extra's running those $10 K SDR radio using a 37 inch flat screen for a waterfall display will tell you that you are 100 Hz low (or high) followed quickly by a command to get on frequency --you are on frequency it is just the BFO shifted.

 

My original thoughts were to share a common BFO and VFO for the receiver and transmitter. Because of what was just described I am now leaning to separate BFO's and a common VFO. The VFO if you use the AD9850 or the Si5351 is fairly immune to frequency shifts caused by circuit loading since the frequency being generated is a result of mathematics and not an inductor / capacitor. Thus the plan is to have separate BFO's that can be individually "netted" (an old term for being on the same output frequency). If the Si5351 is used it may be even a lesser problem as the BFO like wise could be generated mathematically and not subject to loading. But with the AD9850 (or LC VFO or VXO) you will have to supply a BFO signal. In my current build I am using the AD9850.

 

So Ok how do you get two BFO's on the same frequency and how do you switch them on and off. Having two BFO's running continuously is more of a problem on the receive side than the transmit side. If the transmit BFO was only 20 Hz off (not enough for the SDR guy to scream at you) but is sufficient to be heard in the receiver. So the plan is to leave the receive BFO run all of the time and to only run the transmit BFO when in transmit. In our earlier post on control circuits which uses a NE555 that will work nicely to power on the transmit BFO. So that part of the problem may be minimized.

 

The real nut to crack is the netting. Assuming you have the receiver working properly and on the correct frequency then it is a matter of a little cut and try. In my receiver build I used a socket for the BFO crystal (three pins of a SIP socket) and this functionality will provide a means of finding two crystals that will be very close in frequency. Before I started this project I had a batch of 12.096 MHz crystals and then purchased another batch of Series type crystals. My process for finding two close crystals was to tune in say a net on 40M with the normally used BFO crystal and then to simply cycle through a batch of crystals that I had. It is a pretty simple mater to find ones that are higher or lower in frequency as the pitch of the voices will change. There will be a grouping that then seems to produce the same pitched sound. Run this group through a second time and "listen" for the closest ones. The ear is quite good at this process. The ones that pass this test are candidates for the transmitter carrier oscillator.

 

What is significant here is that the crystals are tested in a circuit that is used in the receiver and that same circuit will be used in the transmitter. The feature of this circuit is a small trimmer cap to put the crystal on the exact frequency needed. The same value trimmer is used in the carrier oscillator. Thus it will be possible later (just like the Ten Tec Model 150A) to calibrate the transmitter carrier oscillator on the same frequency thereby bypassing the wrath of the 40M SDR Frequency Police!

 

I will stop here and pick up next time with more discussion of the transmitter circuits.

 

73's

Pete N6QW

Simpleceiver~ Part 25

Temporarily QRT @ N6QW

 

 

Due a family medical emergency there will not be much coming out of the pipeline from N6QW for a short period of time. However there has been enough information presented to proceed with the transmitter portion. You would only need to add a pre-driver and driver stage plus the final amp and the low pass filter and you are there.

 

Here are some circuits to consider for the final pieces of the transmitter portion. These are proven circuits having been used in the 2009 Tri-bander, the JABOM and the KWM-4. I strongly recommend NOT using the IRF510 as is the favorite of the BITX crowd but instead put a real RF device in the final amp. For those who want to pick apart the pre-driver/driver check EMRFD for an explanation and specifications of the circuit. The RF Final is my own design and the LPF you can simulate in LT Spice. You will need to fit in a TR Relay and the final integration wiring. If  at this point you are not capable of doing that then I suggest you do some Internet research on how this is done. I just do not have the time right now to provide that information.

 

 

 

Good Luck and I hope this temporary cessation is in fact temporary. That said  the objective has been to share my experience and knowledge of how to scratch build a radio. The over documentation in this project was so that the project didn't end up like so many kits --solder all the resistors first and then .. Hopefully I have provided information on the functions of the circuits and how with tools like LT Spice it is possible for you the homebrewer to make changes. I know how to do it -- the important point is that you know how.

 

 

73's

Pete N6QW



 



Simpleceiver ~ Part 24

A Single Schematic for the Simpleceiver!

 

Quite honestly I bristled a bit when I received several requests for a single overall schematic for the Simpleceiver project. Many of the inputs were if I had a single schematic I could better understand the project. Friends that is why we have the block diagram.

 

Well I guess my bent is if you don't understand the circuit blocks having the whole schematic may not lead to a "Level 5 Enlightenment". Another goal of the Simpleceiver was to encourage experimentation and the modules have been designed for the most part to enable matching to 50 Ohms. You can simply replace a Simpleceiver module with a different module and have a go at it so long as you look at the impedance match. An overall schematic may make that task more difficult.

 

But one kind soul  DuWayne, KV4QB has taken on the chore to create such a schematic which is in a pdf format (Sorry guys no GIF's or jpg --so don't send me an email about the quality coming from a pdf) It is only through the generosity of KV4QB that you have the singular pdf. Also please no emails can you break the circuit up into pdf blocks!

 

I have repeatedly stated the use of LT Spice in developing and working with such a project. A serious homebrewer needs to adopt and adapt to that tool. If you want to make circuit changes the first thing you should not do is send Pete and email asking me to do the analysis. You have the tools and examples, so you the homebrewer need  to ask the question of yourself about substitutions.

 

Click on this "LINK" and it will take you to the Simpleceiver Software link which is hosted on my website http://www.n6qw.com. There you will find the Simpleceiver Single Schematic in .pdf document.

 

Happy New Year to all of you.

 

73's

Pete N6QW