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

Simpleceiver ~ Part 23

Revisions to the Simpleceiver Detector

 

We are delighted to see that there are homebrewer's out there who are building this project and that is most gratifying. This gives me a sense that all of the time I spend developing circuits and maintaining this blog is having some impact and benefit to the greater ham community.

 

In an exchange of emails with Bob, K6GGO, who built the product detector with the intent of having an 8.0 MHz IF, he reported that he physically built the circuit and ran some test to characterize the performance. His conclusion was that the circuit performed nicely but was seeing an output response capability that extended beyond 100 kHz and in fact had seen a peak response closer to 200 kHz.

 

My response to Bob was that I had seen the same thing but simply ignored anything beyond 20 kHz as this was AUDIO and anything beyond that would never be heard by humans --maybe your dog would hear it? So in the interest of those who would have sleepless nights knowing that the output from their product detector could support  a frequency response output beyond the audio range, I did some further evaluations.

 

Using LT Spice it was a simple matter of making some trial runs to see the effect of changes. Basically I used the Direct Conversion Receiver to test the part change but the same change is made in the Product Detector circuit in he Superhet version.

I am happy to report there will be no output or peak response beyond the audio range and thus those who may suffer a sleepless night will have a peaceful rest. One component value change did the trick. L1 which is in the output filter network is changed from 1000 uHy to 100000 uHy. (For the old school guys like me that s 1 Milli Henry to 100 Milli Henry). I am delighted to report that 100 Milli Henry chokes may be acquired from Mouser  100MHy Choke The cost is a staggering 38 Cents.

 

 

 

 

There is much good in collaboration and having an openness to making changes. One part value change = peaceful sleep!

 

73's

Pete N6QW

 

Simpletransreceiver ~ Part 22

Thoughts on the Control Circuitry

 

We have all heard that a long journey must start with the first step ( I guess 22 parts qualifies this as a long journey). With the Holidays my bench time has been somewhat limited but I did want to provide some of my thoughts on a control circuit for the transreceiver in the event there are those who want to forge ahead.

 

Perhaps one of the most critical items to make the receiver and transmitter play as a unit is how to control the transition from receive to transmit AND to accomplish that end without hiccups, burps, spurious artifacts, hot switching, "kerchunks" and on an on. Those who have followed my projects will find that I like to recycle circuits from prior projects chiefly so I am not continuously trying to reinvent the wheel and secondly since they are proven their performance is known.

 

The solid state control circuit that you will see shortly was a result of a project I did in 2009 where everything was switched with relays. At that time the frequency control in the dual conversion transceiver  (my solid state version of the Heathkit HW-100) was a PTO from a Ten Tec Triton IV. There was such a terrific back emf from all of the relays that the frequency would change by a few kHz every time there was a TR.

 

Below is the breadboard for that project. If you look in the upper portion of the photo near the center you can see a huge 4PDT Power Relay and somewhat obscured is the RF boards that had relay selected Band Pass Filters and another board that relay selected Low Pass Filters. There was also a TR relay to redirect the antenna to the right portion of the circuit. So after a week or so of trying to resolve this issue I came up with a solid state switching scheme which has been refined with several iterations and will most likely need work for the Simpletransreceiver BUT it is a place to start.

 

 

 

 

Next is the schematic of the baseline control circuit. STOP --I already see many of you sending me an email that since I have an Arduino why not use that to do all of the control. I am aware of that but that would require more development time. So why not use a proven hardware solution!

 

 (Some day I will share my Arduino Linear Amp control scheme that senses SWR, Power Source Voltage, Over Voltage, Over Temperature and sequenced step start of the power supply --so I do know how to do it --but an overkill for this application.)

 

For those who may have seen my JABOM transceiver (Just A Bunch Of Modules), this was the circuit used for that project. Essentially the PTT triggers the optoisolator (4N35) to toggle the 7400 IC wired as an Inverter. So OK use your favorite inverter chip --this is what I had in the Junk Box! With the wiring as shown the + 12 VDC R is always "On". BUT when you key the PTT this toggles the SN74LS00 to the other state and there is a transition from +12 VDC R to +12 VDC T. So long as the PTT is held in --you have + 12 VDC T.

 

The TIP32C PNP devices are good for a couple of amps --if you want to switch bigger loads then circuits with power MOSFET's would be the order of the day. So please no emails that "your circuit doesn't work or why did you do this or that?" This is a starting place and the circuit WORKS! You are welcome to make any changes.

 

There have been embellishments of this same circuit where I used a NE555 timer that was keyed and with the inclusion of one relay added a timed closure of the PTT such as you would have while sending CW or for a Tune function.  It was successfully used in my KWM-4 SSB/CW transceiver. There is no difference between using 1N914's or 1N4148's -- I am merely trying to head off a flood of inquiries! Also read the schematic and notes carefully -- I have received emails about what is the * after the SN74LS00 and what do you do with the unused pins -- the schematic is clear --GROUND THEM!

 

[Caution: This control circuit is a starting point to demonstrate a way to electronically switch most of the circuits from receive to transmit. It is envisioned that it will work pretty much as shown BUT not having  been tested with the receiver and transmit boards and other ancillary equipment such tests may result in some modifications. Thus the material is being presented now to show that there is plan being set forth to control the two major elements. Since this is a transreceiver and not a transceiver per se there may be other additions required. Bottom line "Heads Up".]

 

 

I have not detailed the interconnection to the receiver or transmitter circuits --remember this is a starting place. But basically the plan is to identify modules that would always remain powered regardless of Transmit or Receive such as the Arduino/AD9850 and probably the Audio amp stage. What will be switched are circuits such as the Rx RF AMP and Rx IF AMP & Product Detector and a maybe on the BFO. On the transmit side the Microphone Amp and the transmitter specific circuits and final the antenna change over. In work is a block diagram of the control circuits but some of that will be refined after hookup.

 

This information is being provided now so that those who want to start the control circuits have most of the information needed. Below is the Low Pass Filter Information. The inductors have been wound using a standard number of turns and the cutoff made slightly  beyond 8 MHz and the second harmonic suppression is almost unbelievable. In/Out is 50 Ohms.

 

 

Many are endeared to the BITX IRF510 Final amplifier --I am not and a future post will include a "real RF Device" final amplifier as used in the JABOM, ZIA and KWM-4 transceivers.

 

Happy Holidays,

 

Pete N6QW

 





 





SimpleTransReceiver ~ Part 21

The J310 Companion Transmitter ~ The Journey Continues!

Addendum: 12/16/2015 Simple Transmitter Board Layout
Addendum: 12/18/2015 NEWS FLASH 9A3XZ, has a working Simpleceiver! Bravo Mikele.

If it hasn't hit you right between the eyes, by now, then turn off your soldering iron. So far we have built what I consider a pretty decent receiver for not a lot of money. There is ongoing development work on that part of the project inclusive of the incorporation for the W7ZOI Hycas AGC. That addition is not quite ready for prime time; but we are close.

 

The building of that receiver involved what I call a common template, the J310's configured as a Dual Gate MOSFET. That has worked very well and you only need to listen to the you tube videos and you can adjudge for yourself. We also introduced the use of LT Spice as a simulation tool. Most of the time is spent at the computer and when we are ready to solder up a circuit it is pretty much the final configuration so there is minimum time wasted rebuilding hardware.

 

Now we are ready to proceed with the building of the transmitter portion of the transceiver. For those who tuned in late, the project involves building a separate receiver (done) and a separate transmitter with a sharing of the LO and BFO that commonly links the two to form a transceiver. Some would argue hey I can build a BITX and be done. Well for those so inclined have at it. But if you want the ability to fine tune the receiver and transmitter for optimum performance, including features not normally found in the BITX like AGC and maybe ultimately a color display then this project is for you.

There is much flexibility in my design --yes I can really say it is my design wherein you can employ different filters (both homebrew and commercial) as well as different IF frequencies. We have provide information for IF's such as 12.096, 9.0 and 8.0 MHz. The use of the LT Spice makes for short work in being able to do that. Below is the block diagram for the low level circuits for the companion transmitter. You will note that the very same circuits employed in the receiver are now used in the transmitter. So if you have built the receiver all you will have to do is to duplicate several of the circuit blocks and you are there. The one new block is the microphone amplifier which will be covered shortly.

This is our starting point and be advised there may be some alteration but it is a the first step. One possible change is to take the 2nd SBL-1 which is used between the IF amplifier and the Band Pass Filter and put another DGM stage in there wherein the J310's are configured as a mixer stage. That very likely will be the case but for now we have a placeholder with the 2nd SBL-1

 The one block on the above diagram we have not seen before is the microphone amplifier and we will next provide that schematic --any similarity to the Product Detector template is not accidental!

WE have added the filter on the output so we have a very nice audio spectrum being presented to the Balanced Modulator. R3 is a 10K Trim Pot and the center wiper has a 10 NF capacitor (called C3) connected to it and the other end of the capacitor is connected to the Pins 3 & 4 on the SBL-1.

The audio generator used for the LT Spice simulation presumed a 600 Ohm series impedance and thus the amp is predicated being used with a 600 Ohm low impedance microphone which seems to be the norm today. While not included in the simulation this would be a great opportunity to test one of those inexpensive electret microphone cartridges. A bit of bias for the microphone and it would simply connect into the input.

Below is the output plot for the microphone amplifier as above. See the note about where to connect the 10 NF capacitor referred to as C3. This plot shows a very nice output curve. Thank You Pete and Thank You LT Spice.

We decided to publish this schematic since some of the experimenter's wanted to get a head start on the build of the transmitter.

Addendum: For those who are itching to build the transmitter below is the board layout that will enable you to get most of the modules on a single board. The squares are 2/10 of an inch so you can count the number of squares and figure the size ( about 4 X 6 inches). I have decided to build a specific BFO carrier oscillator for the transmitter stage. There is a good reason for this -- loading on the BFO when you shift between Tx and Rx most  likely would result in a frequency change. I have  stock of about 30 pieces of the 12.096 MHz crystals . I ran all 30 through the Simpleceiver and found 4 that are "dead on" with the crystal in the receiver --so we now have BFO crystals for the transmitter. Look at the arrows as that will be the signal flow. Virtually all interfaces are at 50 OHms so there will be many matching transformer --- get a large stock of FT-37-43's (Toroid King is a good  place to find these. The BFO layout will be the same as is the IF amp block. The microphone amp block will be similar to the product detector.

I will cover the control systems/switching/TR early in 2016.

73's
Pete N6QW