Hacking the Ten Tec Model 150A ~ Final Chapter

The Final Round Up ~ Hacking the Ten Tec Model 150A

This is the last in the series on the "hack" of the Ten Tec Model 150A. In a few words -- highly successful and worth the effort. This same approach possibly could be applied to other commercial radios such as the Kachina 102/103 or the Heathkit CAP transceivers.

 

Many of the blog readers have most likely been bored with this subject and want me to get back to the Simpleceiver -- Believe it or not, what I learned here will end up in parts of the Simple Transreceiver.

 

I could not find the LSB Filter which was an option; but was apprised by the filter manufacturer, Network Sciences,  that by adjusting the BFO frequency it would be possible to make the USB Filter work on LSB. That was in fact a reality. The secret was the use of the Si5351 to generate the VFO (operating frequency + 12.7 MHz) with Clock 0 and a switchable BFO on Clock 2.

 

Based on some work I did nearly a year ago my Arduino Pro-mini has been connected to a keypad so that band selection are Keys 1 through 6 (160M, 80M, 60M, 40M, 30M and 20M). Two Keys (0 and 8) enable up/down tuning of the radio from the keypad based on the step rate chosen. Keys 7 and 9 introduce non-standard tuning steps not normally chosen by the encoder switch ( 10 Hz and 100 kHz). That leaves two unassigned Keys. Selection of USB/LSB is done from the front panel of the Model 150A. The LCD Display shows the frequency, the band, USB/LSB and the step tuning rate. If the color TFT display were to be used then you would need more IO pins such as the Mega.

 

In summary the work that was done was to:

 

Change the Band Pass and Low Pass Filters to extend the range to 15 MHz. The channel selector switch was programmed so that Channel 5 = 1.8 -3 MHz, Channel 6 = 3 - 5 MHz, Channel 7 = 5 - 8 MHz and Channel 8 = 13-15 MHz.  All filter networks to expand the coverage to 15 MHz were simulated in LT Spice before any changes were made. All original inductances were retained and only the capacitance was changed.

 

Program the Arduino Pro-Mini and Si5351 to cover the ham bands based on the keypad selection

 

Create the USB/LSB functionality. [A separate Arduino + AD9850 was used to find the correct LSB BFO Frequency and then that frequency was included in the Si5351 sketch for Clock 2.]

 

Wire the radio using jacks on the back panel so that the LO, BFO, USB/LSB Selection and Power for the Arduino/Si5351 are plug ins to the radio.

 

The radio has been tested on 60, 40 and 20 meters with all excellent signal reports. Not bad for about a $120 investment.

 

 

 



In the photo above the two boards shows the low pass/band pass filters that were changed. In the upper board (low level amp) the filter is located in the very upper right hand corner and in the lower board which is the RxTx mixer board that filter is also located in the upper right hand corner. The Ten Tec construction methodology made the task one of simply unplugging cables and removing four screws and then  removing the boards The traces are very large and a simple task to remove components --try that trick with your FLEX 6300.

Thanks for your patience whilst I dabbled with this project. You can find the manual for the Model 150A at the Ten Tec website under the Obsolete Manual Tab.

 

Back to the Simpleceiver in the next post. Final comment to the naysayers of the Si5351: Here is one more example of its versatility to modify (hack) commercial radios for use on the ham bands. I am having a lot of fun with this "hacked" radio.

 

Funny comment: While I was having a QSO with a friend whom I asked to listen to the signal since he knows what I sound like -- suddenly a phantom operator (no call sign just a voice) saying he was using his FLEX 6300 said I was over 100 Hz low (since corrected) and that he saw an energy spectrum of about 3 KHz. Thank you for your input.

 

73's

Pete N6QW

 

PS I used jpg. and not GIF's this time --sorry!



Hacking the Ten Tec Model 150A to extend its frequency range to 15 MHz

Be Amazed at the Wizardry of N6QW

Hacking the Ten Tec 150A SSB/CW transceiver to extend its range to 15 MHz

Three actions:

1. Modify the Final Amp Low Pass Filter
2. Modify the RxTx Mixer Band Pass Filter
3. Modify the Low Level Driver Low Pass Filter

All filter changes were simulated in LT Spice and I think it worked.

Pete N6QW

Errata ~ Part 4 Simpleceiver

Errata in the Part 4 Discrete Audio Amplifier

 

One of the blog readers, W4JED contacted me regarding the "reversed  polarity" of the output capacitor on the discrete component audio amplifier that appeared in Part 4. The schematic error would have most like caused a smoking of the capacitor (or a very loud bang followed by the smoking). Thank you for bringing it to my attention. The corrected schematic is shown below,

Pete N6QW

 

 Soldering Surface mount can get a bit intense so what is needed is some loud music in the background to sort of calm the environment. For your listening pleasure some "Solderin Music"

 

 



Simpleceiver ~ Part 6

Dual Gate MOSFET Direct Conversion Receiver

 

Based on inputs I have received either in direct comments on the blog or from email messages, there seems to be a desire to better know the "why" of various choices and actions. In this particular post we will look at the Dual Gate MOSFET being used in a Direct Conversion Receiver (DCR). We will also use an LT Spice simulation to demonstrate the "why".

 

In the Part 5 we described the Direct Conversion signal frequencies and the resultant outputs. Essentially to receive an 800 Hz CW signal on the 7.030 MHz QRP frequency we would need to supply a local oscillator signal at either 7.0292 MHz or 7.0308. Again the Direct Conversion Receiver is simple to build and is quite sensitive; but does not give single signal reception. You will receive the same signal at TWO places on the dial!

 

Below is a schematic representation of a Direct Conversion "detector" using JFET's configured as a Dual Gate MOSFET. We have chosen two JFET's for this evaluation and includes the very popular 2N3819 and the 2N4393. The same circuit was used to evaluate both devices and the only difference is the device used in the test bed circuit. The incoming signal has been set at 0.3 Microvolts and the LO is 1.414 volts. The output scan is from 10 Hz to 50 kHz. [Note these photos are GIFs as I was severely criticized by one blog reader for using JPEG's the reasoning for which is still not clear to me but to stop receiving emails --they are GIF's.]

 

 

 

You only need to connect the audio amplifier to this circuit, connect an antenna to "Gate 1" and your favorite Local Oscillator to "Gate 2" and you are in business. Keep in mind the LO signal frequency must be in the same range as the incoming signal.

 

As homebrewer's the usual process is to dig into the "junque box" and find a couple of devices and heat up the iron AND then wonder why the receiver seems dead. Well this is where my term "noodling" comes into play. Turning on the soldering iron should be the very last step. Evaluating what you are doing and how you are doing it IS the first step!

 

If you start with the circuit above utilizing the LT Spice simulation you would see below the following expected response. In the first case we use the ever popular 2N3819 and in the second case is the 2N4393. The output curves are very similar BUT the 2N4393 has about a 6dB greater gain than the 2N3819. Will they both work --yes but the 2N4393 is more sensitive to weak signals.

 

 

 

 

Keep in mind that you need a real antenna to hear signals. Throwing a 10 foot piece of wire on the ground is a compromise (a poor compromise) in comparison to a 40 Meter Dipole at 30 feet. Hooking your Direct Conversion Receiver to a rain gutter may provide some signals but is not as desirable as a real antenna. Put you time and resources into an antenna and then you can remove that as a variable in the reason "why the receiver seems deaf".

 

Having a signal from a Local Oscillator is one thing but having a signal of one volt or better (1.414 Volts Peak to Peak is 7 dBm) is needed to make this play. Some of the LO devices (AD9850, Si5351) are output frequency sensitive. Thus at lower frequencies there is plenty of output; but at higher frequencies the voltage output drops off and thus may not be sufficient for the mixing process. Thus an outboard amplifier may be needed between the LO and the detector. But unless you measure the output over the frequency ranges you may not realize that insufficient LO drive is causing marginal performance.

 

In the next post I will have an actual  test hardware amplifier that is based on Parts 5 & 6.Stay tuned!

 

 

Pete N6QW







Simpleceiver ~ Part 5

The Product Detector ~ Dual Gate MOSFETS

Plots added for the 2N3819 (10/19/2015)

Data Plots for Additional JFETs Added 10/20/2015

Having covered the audio amplifier stage for the Simpleceiver (again the choice is yours) we will now move on to the Product Detector stage. As the name product detector implies, the output of this stage is a product of the mixing action of two signals.

 

Think of the product detector as a "black box" where two signals are input to the box and the single output contains two products. One product is the sum of the two input signals and the other contains the difference. Filtering at the output port can remove one of the products.

 

In its simplest form the "black box" can be the basis of a direct conversion receiver where a variable frequency oscillator (known as a Local Oscillator, LO) is connected to one of the ports and signal from the Antenna (after passing through a stage of RF amplification) is connected to the second port. The sum frequency would contain the LO + Antenna signals but the difference would be in the audio range. Now one of the down sides of the Direct Conversion Receiver is that you get the same  audio signal for two values of the LO, where the LO is above AND below the incoming signal. Thus it is not single signal reception. But that does not detract from its capability as a simplistic receiver.

 

Here is the math part of what is being said. The antenna is tuned to 7.030 MHz and one supplies a LO at 7.0292 and the difference is 800 Hz (nice CW sound). Now if the same 7.030 MHz Antenna signal is mixed with 7.0308 LO signal then the difference is 800 Hz (again a nice CW Sound). In one case the LO signal is above the incoming and in the second case it is below the incoming. BUT it is the same audio signal so you will receive the same signal at two places above the dial. [This also is important in visualizing USB and LSB.] With direct conversion you will receive the same signal at two places on the dial but for a simple receiver this is only a slight inconvenience!

 

Another example of a product detector response is when a signal is input at 12.0945 MHz ( a BFO signal) and the RF signal at 12.096 MHz( coming from a crystal filter) the two outputs would be: 1) 24.1905 MHz (sum) and 2) 1500 Hz (difference). For the product detector, the  one we want is the 1500 Hz as this is then the audio output.

Typically we add a low pass filter after the product detector so only the difference (audio signal)  is passed. This filter is a Pi type comprised of a 10 NF at either end with a 1 mHy choke in the middle which now will only pass the difference frequencies. Note in this case because the input signal is coming from a Crystal Filter you will have single signal reception which is now governed by the placement of the BFO signal. To receive the opposite sideband you would need a BFO frequency of 12.0975 MHz

 

Our "black box" can take many forms including 1N4148 diode ring, packaged Double Balanced Mixer's like the SBL-1, Gilbert cells such as the SA602 or SA612, vacuum tubes like the 12AU7, or a Dual Gate MOSFET. Of course the most famous Dual Gate MOSFET is the 40673 which today are on the unobtainable list. Some of these devices have no gain, in fact have a loss while others provide a substantial amount of gain. 

 

Since the Simpleceiver is a minimalist approach we have chosen to use the Dual Gate MOSFET, which is one of the devices that has gain in the conversion process. There are a whole new crop of RF Dual Gate MOSFETs and one in particular is from NXP and is the model BF991. Most of these unfortunately are Surface Mount Devices that for many newbie homebrewer's is an anathema. The Simpleceiver shown in an early post video now has a BF991 installed --so if a homebrewer is not shy about SMD --just drop one of those into the circuit.

 

Why use the Dual Gate MOSFET?

I would like to take just a few lines to explore the why of our choice to employ the Dual Gate MOSFET in the Simpleceiver given that there are so many new technology "black boxes" at our disposal. Many would say use the SA602 or SA612 which are also gain devices which even have a "twofer" capability wherein you can have the detector and carrier oscillator in a single 8 pin device. Simply plug in a crystal and a few caps between pins 6 and 7 where you have an instant BFO.

 

The Dual Gate MOSFET is not a black box like the Sa602 or SA612. As my friend Bill, N2CQR would say about a DGM, "you can better visualize the signals being applied to the device and have greater in depth understanding of the signal conversion process." This also satisfies his term of "more homebrewedness" with discrete components.

But the SA602 or SA612 can be used equally as well with the choice is left to the builder. BUT we do have as a goal for the completer Trans-receiver project to use the Dual Gate MOSFET in many of the circuits and given we bought them for 20 cents a piece (delivered) that is far less expensive than the Gilbert Cell SA602's/SA612's which cost about $3 USD --each!

 

At this point I will leave it to the reader to further explore the pros and cons of the Dual Gate MOSFET (DGM). Some will argue noise figure issues, while others will argue tendency to overload and lest I forget phase noise issues. There are always better mousetraps; but on the continuum of choices, for a simple project, the DGM passes muster as a viable candidate.

 

But realizing that those new to homebrewing do not have 50 years experience soldering their fingers together on a routine basis,  we offer the alternative of making a Dual Gate MOSFET from two individual leaded type J310 JFET's. These devices are plentiful and recently a 50 piece quantity J310's was purchased with shipping for around $10 USD.

In one of the earlier posts we mentioned the use of LT Spice to simulate the circuit that will be used in the Simpleceiver and so it is with our "homebrewed" DGM. Initially I missed the selection for JFETS and used MOSFETS. You certainly can get some interesting results using two IRF510's in Cascode (Source of one device connected to the Drain of the second device -- Read up on Cascode circuits using a Google search). Actually I think it will work -- but a better choice is the U309 which is close to the J310. The 2N3819 resulted in less gain for the same set of circuit values. So below is my simulated DGM using two JFET's in a Cascode Circuit. In the audio range -- the simulation shows about a 19 to 20 dB of gain.

This is the circuit that was simulated for our homebrew DGM (U309's in Cascode) and below is the output plot. This works!! In our next post (or an addendum) we will build the circuit and mate it up with the audio amplifier stage. Stay tuned.

73's
Pete N6QW

 In this post we mentioned that for the same circuit the use of the 2N3819 had less gain for the same set of circuit values. It is about 6 dB less and the plot for that is shown below. Do we now rise up like those who bash the Si5351 phase noise claiming that it is 6 dB worse than the Si570. NO is the answer! The 2N3819 is a viable device --it just has less gain. This is the value of LT Spice --no soldering is involved in the evaluation and we now can expect less gain with the 2N3819. Our frequencies of choice between 300 Hz and 3 kHz for the 2N3819 vary by only about 1.5 dB.

 
10/20/2015
 
The added value of the LT Spice simulation aside from assuring that a device will work in the circuit is the cost factor. The U309 is about $6 USD ( remember we are using the J310 which is 20 cents) and another good candidate is the 2N4393 which is about 1/3 the cost. So how would these stack up in an apples to apples comparison. I re-ran the plots for these two devices and the results are shown below. The striking difference is about 1/2 of a dB (your ears will never know) improvement at 3X the cost.  Gain variation as well as maximum gain must also be considered and the 2N4393 has slightly better overall gain than the U309 in this circuit. So this makes it an easy choice to go with the 2N4393 for this application.

The 2N3819 would be "Good Enough" but has about 6 dB less gain. The J310 is less expensive and when used in this circuit works better. I am trying to locate the data factors for the J310 so I can run this same plot. What I have now is practical data of how the J310 works versus the 2N3819 -- but for some who read this blog -- that is not good enough. [Usually I get an email that someone read on the EMRFD or BITX reflector that the J310 was not a good device yet they have no practical experience with the specific device!]

Pete N6QW

 

Belthorn (Bell Thorn) III Moved to 20 Meters

Belthorn III Moved to 20 Meters and Making QRP Contacts!

Several months ago I resurrected a project that was built some 12 years ago and updated the rig with a Si5351 + Arduino Controller, a color display and a new box. This radio had some innovations like using a Motorola Gain Block amplifier (CA2818C) which happens to be a 24 VDC device and led to embedding a DC to DC Convertor (MeanWell) into the project. It is a single conversion at 9.0 MHz and uses a GQRP Crystal Filter. The Arduino sketch includes a built in tone oscillator to provide a 988 Hz tone for tune up purposes.

 

The RF AMP is an IRF510 but I wished I had used a real RF Transistor like a 2SC3133 as the output on 20 Meter is slightly less than on 40 Meters. I am seeing about 7 watts on 20 Meters where I got close to 10 Watts on 40 Meters.

 

Now that I have a new beam antenna I decided to move the Belthorn III to 20 Meters and one of the first QRP contacts was with N0TUX/KH6. Thanks to Ron Taylor G4GXO for the original Belthorn design. Thanks Ron -- the Belthorn still perking along after 12 years!

 

There are two videos and the second is of the QRP contact. Check http://www.n6qw.com/ for more info on the Belthorn III.

 

73's

Pete N6QW

 

 

 



Simpleceiver ~ Part 4

Audio Amplifier Stage

Addendum 10/13: You Tube Video of  a Test Amp.

 

In our last posting we gave some advice about starting from the back end and working your way forward through the build. Not only does this chunk the project into manageable  pieces but also enables test as you go. Thus the completed assemblies in effect become part of the test system. You may argue with that approach; but it is a sound practice. Somehow soldering all of the project parts to a circuit board and hoping it works is only asking for trouble!

 

We received an input in our last post about the LM386 audio amp IC and the issue of distortion when run at 200X gain. At this point it is uncertain that this excellent input, by the way, is based upon an individuals experience or just information floating around reflectors. But we did want to further explore the input and to give our response and take on the subject.

 

By design the Simpleceiver is just that --a project with minimum part count and easy to replicate. The audio amp stage is what I call "Good Enough" to get you started and is a totally viable circuit. That brings up the other aspect of the Simpleceiver and that is the circuit block module approach. Once the radio is built the homebrewer is encouraged to test new circuits and devices.

Thus the Simpleceiver IS an experimenter's platform. So if a builder finds the LM386 an objectionable device then by all means substitute your favorite circuit or one that has been approved by some reflector like the BITX or EMRFD groups. The LM386 can easily be changed to an LM380 ( 8 pin or 14 pin version) which of course can put out as much as 2+ watts. You can also try the TDA7052 -- like I said I smoked six of those in the recommended circuit. Or you can use just the pre-amp stage (2N3904) and feed an external audiophile style amplifier. The important thing to note is experiment and adjudge for your self.

 

For those who would like to build a discrete version of an amplifier a circuit is presented below. It is the same pre-amp stage followed by a complementary amp stage (straight from the Internet). I do know that several hams have tried simulating the complementary circuit in LT Spice and were unsuccessful -- I am no help there --other than I have built and it works. While it has more Pout than the LM386 I would say it is on par with the LM386 insofar as perceived or real audio distortion. You will note --lots more parts and the need for an isolated output.

 

 

 

 

Discrete component audio amplifier stage

In the spirit of providing alternatives for the audio amplifier for those still skeptical about the use of the LM386 then we offer the following additional circuits. These have been built and used in several radios at N6QW. But I keep coming back to "simple and good enough".

 

The first uses an op-amp as the preamp and the device of choice is a low noise version of the NE5534 followed by the LM386 (Oh oh here we go again about distortion at high gain.). This audio amp circuit was used in my 2009 Tri-Band Solid State version of the Heathkit HW-100. You can see this as one of the links at http://www.n6qw.com/

 

The only reason this is being shown is to demonstrate how this circuit was later converted to use the LM380N. Important point again about experimentation and circuit improvement. In this case the real improvement with the LM380N -- 2+ watts Pout.

 

 

 



The next schematic is the same circuit as used in the KWM-4 transceiver project in 2012 and the changes involved replacing the LM386 with the LM380N. Known for its greater output power it also has less distortion than the LM386. In passing take a look at the specification sheet for the LM380N and the "innards circuit schematic" is not unlike the discrete component amplifier shown at the beginning of this post. Hmmm there is a story here.

 

Below is a photo of the LM380N amplifier as used in the KWM-4 transceiver project. There are island blocks in the center of the board and this is where the 10K audio gain pot connects. (I am just heading off any questions that there doesn't appear to be any connections to some of the blocks. Having a CNC mill sure makes it easy to crank out prototype boards like this. )

 

 

To recap the audio amp stage should be the first item built and get working! We have presented options and hopefully have addressed the input about distortion in the LM-386. My take it is good enough and if you find it objectionable then you have the option of even taking the 2N3904 pre-amp stage and fitting that to the LM380N. It is all about experimentation!

 

Please note that unless you solder the ground pins of the LM380 directly to the circuit board and have good contact with the body of the LM-380 to the copper board you will need to add a heat sink to the LM380. (Such as the case should you use a DIP socket.)

 

73's

Pete N6QW