20m FSK-QRSS MEPT
Initial design
First revision
Showing posts with label mept. Show all posts
Showing posts with label mept. Show all posts
Saturday, January 4, 2014
20m MEPT
Thursday, February 17, 2011
Just an Idea
From VHF and UHF operations we know to use preamps at the antenna feedpoint as to improve SNR. SHF and EHF amateur radio operation is usually done by having the transverter at the antenna's feedpoint, since losses in the transmission line would eat up the signals completely...
So, what's the idea? Well, in QRSS, we also hunt for the best possible SNR. So, why not moving half or more of a QRSS station's circuitry to the antenna?
Half? Yes, I would prefer/advice to have frequency determining blocks, i.e. oscillators, in a controlled environment, e.g. the shack.
DC-Feed
The basic trick on all of the following would be feeding DC from the shack to the device at the antenna, whatever the device will be. Feeding is done in the well known way for active aerial or mast-head preamps.
TX
Easy things first, lets have a look at transmitters. The only bit that needs to be at the antenna feedpoint would be the final amplifier. The only thing to watch out for would be the Ohmic loss of the transmission line, since the final stage will require some current. If one cares about the voltage which the final is driven from, one should take this transmission line DC resistance into consideration.
RX
Reception is somewhat more challenging. Why do it in the first place? A preamp could do that. Yes, it could. However, some designs (e.g. w/ the NE612) do not really need pre-amplification...
Here's a look at the different cases:
Direct Conversion
In this case, the LO would be in the shack, and the whole rest of the receiver remote at the antenna location. It should not pose any problem to combine/split LO-RF, RX-AF and DC. However, the supply DC can carry mains hum residuals. A decent high-pass will be necessary before the AF can be fed into any sound-card.
Supersonic-Heterodyne (Superhet)
In such a scenario, front-end, mixer and IF filter (xtal-ladder) would be distal. LO, BFO, product detector and AF-amp would proximal. It is conceivable/advisable to add a second xtal-ladder to split IF and BFO frequencies. The downside would be the more complex frequency splitting at the distal part. A crystal filter would come handy here, and therefore, a "cheap crystal combination" would be recommendable for such a design, however tempting a DDS design would be.
RX&TX
Now to the tricky stuff... RX/TX-toggle could possibly done by polarity reversal, e.g. by diodes and relays.
I would like to leave it to your imagination what would be possible...
Conclusions
This may not be necessary to think about at all...
However, in case of reception, having all the low-noise stuff at the distal location, one may consider using cheap twin lead cable to connect the remote head with the shack.
For transmission, the obvious advantage would be that the final could be matched to TX-aerial, whatever it may be in balance and/or impedance.
So, what's the idea? Well, in QRSS, we also hunt for the best possible SNR. So, why not moving half or more of a QRSS station's circuitry to the antenna?
Half? Yes, I would prefer/advice to have frequency determining blocks, i.e. oscillators, in a controlled environment, e.g. the shack.
DC-Feed
The basic trick on all of the following would be feeding DC from the shack to the device at the antenna, whatever the device will be. Feeding is done in the well known way for active aerial or mast-head preamps.
TX
Easy things first, lets have a look at transmitters. The only bit that needs to be at the antenna feedpoint would be the final amplifier. The only thing to watch out for would be the Ohmic loss of the transmission line, since the final stage will require some current. If one cares about the voltage which the final is driven from, one should take this transmission line DC resistance into consideration.
RX
Reception is somewhat more challenging. Why do it in the first place? A preamp could do that. Yes, it could. However, some designs (e.g. w/ the NE612) do not really need pre-amplification...
Here's a look at the different cases:
Direct Conversion
In this case, the LO would be in the shack, and the whole rest of the receiver remote at the antenna location. It should not pose any problem to combine/split LO-RF, RX-AF and DC. However, the supply DC can carry mains hum residuals. A decent high-pass will be necessary before the AF can be fed into any sound-card.
Supersonic-Heterodyne (Superhet)
In such a scenario, front-end, mixer and IF filter (xtal-ladder) would be distal. LO, BFO, product detector and AF-amp would proximal. It is conceivable/advisable to add a second xtal-ladder to split IF and BFO frequencies. The downside would be the more complex frequency splitting at the distal part. A crystal filter would come handy here, and therefore, a "cheap crystal combination" would be recommendable for such a design, however tempting a DDS design would be.
RX&TX
Now to the tricky stuff... RX/TX-toggle could possibly done by polarity reversal, e.g. by diodes and relays.
I would like to leave it to your imagination what would be possible...
Conclusions
This may not be necessary to think about at all...
However, in case of reception, having all the low-noise stuff at the distal location, one may consider using cheap twin lead cable to connect the remote head with the shack.
For transmission, the obvious advantage would be that the final could be matched to TX-aerial, whatever it may be in balance and/or impedance.
Monday, May 31, 2010
MEPT Idea
One my search for detailed information about the Sangean ATS-909 (aka Radio-Shack DX-398, Siemens RK777 and Roberts R861), I was able to locate schematic diagrams.
The reader may ask what that's got to do with a MEPT... well, nothing up to now... BUT:
When checking the receiver's control PCB schematics, I found something, the main micro-processor generates the PLL reference signal. Maybe it is always done like that, I don't know, but it looks remarkably simple to me.
In the upper right corner, that would be the micro-processor. The chips leads X1 and X2 are connected to a 4.332MHz crystal. This oscillator is the classical Pierce configuration, as we know it from so many digital applications.
The crystal's cold end is provided with a trimmer (TC301) for frequency tuning.
The crystal's hot end is connected to an RC low-pass filter (R389,C363) which further feeds the signal into the PLL chip.
BTW: Can someone explain the function of C359 to me? It seems to couple GND to GND.... hmmmmm(!)
So, here's the MEPT idea (actually, this was done before, sort of, by Clayton from Down Under): clock the keyer (e.g. 12F629) by its high speed built-in oscillator, using a crystal for a QRSS frequency and couple the signal out in the way the professionals do :-))
There is just one down-side to this, the controller's clock is now at a somewhat odd frequency, odd for controllers that is, so timing could be off. I will check if compilers (I am programming in C, not in assembler) are able to compensate for that...
Now that we got the signal, what shall we do with it? Well... amplify?!
For another project, I happen to study switch-mode amplifier, aka class E or F. F seems a little bit too much work, but E seems fine for a MEPT, as Hans proved with his Caribbean beacon. Hence, a class E amplifier seems appropriate; I guess, the crystal's hot end will have enough voltage to switch a FET.
The chip could serve for than just the oscillator and the keying device.
During my time at various physics experiments I experienced the difference between fast control and slow control. In our experiment slow control was taking care of temperatures...
So, with seeing the keying as "fast" control (well, sort of fast), controlling the crystals temperature could be integrated as slow control. Those PICs got ADCs, which could easily be used for measuring temperature.
My present vision for mini-MEPTs is presently:
The whole story could have some other advantage.... I realized that, depending on the TX frequency, some PICs stall when RF leaks in. If the controller is clocked with the same frequency and phase, this should not occur.
Next step: design something! Stay tuned, I will let you now as soon as I got more. For now you may click on one of the "sponsors" to find your way out of this blabla...
The reader may ask what that's got to do with a MEPT... well, nothing up to now... BUT:
In the upper right corner, that would be the micro-processor. The chips leads X1 and X2 are connected to a 4.332MHz crystal. This oscillator is the classical Pierce configuration, as we know it from so many digital applications.
The crystal's cold end is provided with a trimmer (TC301) for frequency tuning.
The crystal's hot end is connected to an RC low-pass filter (R389,C363) which further feeds the signal into the PLL chip.
BTW: Can someone explain the function of C359 to me? It seems to couple GND to GND.... hmmmmm(!)
So, here's the MEPT idea (actually, this was done before, sort of, by Clayton from Down Under): clock the keyer (e.g. 12F629) by its high speed built-in oscillator, using a crystal for a QRSS frequency and couple the signal out in the way the professionals do :-))
There is just one down-side to this, the controller's clock is now at a somewhat odd frequency, odd for controllers that is, so timing could be off. I will check if compilers (I am programming in C, not in assembler) are able to compensate for that...
Now that we got the signal, what shall we do with it? Well... amplify?!
For another project, I happen to study switch-mode amplifier, aka class E or F. F seems a little bit too much work, but E seems fine for a MEPT, as Hans proved with his Caribbean beacon. Hence, a class E amplifier seems appropriate; I guess, the crystal's hot end will have enough voltage to switch a FET.
The chip could serve for than just the oscillator and the keying device.
During my time at various physics experiments I experienced the difference between fast control and slow control. In our experiment slow control was taking care of temperatures...
So, with seeing the keying as "fast" control (well, sort of fast), controlling the crystals temperature could be integrated as slow control. Those PICs got ADCs, which could easily be used for measuring temperature.
My present vision for mini-MEPTs is presently:
- one PIC clocked by a QRSS-xtal
- one FET as PA
- oven control by the PIC
- telemetry?
The whole story could have some other advantage.... I realized that, depending on the TX frequency, some PICs stall when RF leaks in. If the controller is clocked with the same frequency and phase, this should not occur.
Next step: design something! Stay tuned, I will let you now as soon as I got more. For now you may click on one of the "sponsors" to find your way out of this blabla...
Saturday, May 1, 2010
30m - 10m Diplexer for QRSS use
Just an idea....
Diplexers are very popular for running VHF and UHF transceivers into the same (simple) antenna. This works since 435 is three times 145. A 1/4-wave radiator for the 2m-band is a 3/4-wave radiator for the 70cm-band.
Could this trick work on shortwave too? The 10m band is about a third of the 30m band ... well... sort of. I figure, I suitable diplexer would separate frequencies below and above about 20MHz, maybe 19MHz for good measures.
The hope is that a vertical of about 7m length would form a 1/4-wave radiator for the 30m-band and a 3/4-wave radiator for the 10m-band.
The numbers tell the following story:
wavelength for 30m: 300/10.14=29.6
wavelength for 10m: 300/28.32=10.6
30m radiator length (assuming a velocity factor of 0.95): 29.6*0.95/4=7.03
10m radiator length (assuming a velocity factor of 0.90): 10.6*0.90*0.75=7.15
A compromise could therefore be a radiator length of 7.1m to suit the 30m grabber and the 10m MEPT at the same time.
Next step, think of a 19MHz diplexer design.
Diplexers are very popular for running VHF and UHF transceivers into the same (simple) antenna. This works since 435 is three times 145. A 1/4-wave radiator for the 2m-band is a 3/4-wave radiator for the 70cm-band.
Could this trick work on shortwave too? The 10m band is about a third of the 30m band ... well... sort of. I figure, I suitable diplexer would separate frequencies below and above about 20MHz, maybe 19MHz for good measures.
The hope is that a vertical of about 7m length would form a 1/4-wave radiator for the 30m-band and a 3/4-wave radiator for the 10m-band.
The numbers tell the following story:
wavelength for 30m: 300/10.14=29.6
wavelength for 10m: 300/28.32=10.6
30m radiator length (assuming a velocity factor of 0.95): 29.6*0.95/4=7.03
10m radiator length (assuming a velocity factor of 0.90): 10.6*0.90*0.75=7.15
A compromise could therefore be a radiator length of 7.1m to suit the 30m grabber and the 10m MEPT at the same time.
Next step, think of a 19MHz diplexer design.
Tuesday, February 2, 2010
RM80-MEPT, power measured
Terminated the MEPT with a 50Ohms 10Base2 terminator (boom boom!) and wired the whole thing up to my lab-TV.
The signal actually looked nice a clean, and was reading almost exactly 3Vpp. Some elementary maths would reveal the power being 22.5mW.
The signal actually looked nice a clean, and was reading almost exactly 3Vpp. Some elementary maths would reveal the power being 22.5mW.
Monday, January 18, 2010
Ramsey QRP80C mept conversion update
Keying as originally designed, was a no no, since with both inductors installed, no stable oscillation was obtained at all.
The removal of one of the inductor resulted in stable oscillation but sluggish keying. Tuning range at this stage was about 5kHz.
The only radio-activity I showed today was to remove the second and last inductor of the oscillator. The tuning range is now down to 1kHz, keying is instantaneous.
Up to now I only made use of parts supplied.
The removal of one of the inductor resulted in stable oscillation but sluggish keying. Tuning range at this stage was about 5kHz.
The only radio-activity I showed today was to remove the second and last inductor of the oscillator. The tuning range is now down to 1kHz, keying is instantaneous.
Up to now I only made use of parts supplied.
Sunday, January 17, 2010
3 Band QRSS Fireball
This idea is rather old, came back however when playing the 3579.545kHz lately. I feel, it is now the right time to publish it...
You may know about this discontinued kit:
http://www.njqrp.org/fireball40/
Well, in this design, one starts with a 28.322MHz crystal and divides it by two several time by means of flip-flops they could have used a 74LS93 instead and spare one IC). The FB40 reaches the frequencies 28.322 (obviously), 14.161, 7.0805 and 3.54025. All frequencies are in rather busy regions, good for QRP, not so good for QRSS.
Why not doing the same trick with the color burst harmonics? Starting with a 14.31818MHz oscillator, resulting frequencies are 7.15909 and 3.579454. One could also consider to double the frequency, which will get us to 28.63636.
But, because of all this dividing and doubling, FSK is somewhat out of the game. But, in contrast to the original FB40, the available frequencies could be amplified simultaneously, making some three band QRSS operation thinkable: three PAs, three low-passes. From a propagation standpoint, that would be a nice daytime night-time experiment, displaying the opening and closing of the respective bands.
There are cheap crystals and oscillators for 3.579545 and 14.31818, none for 40m however. The 80m and 20m frequencies have been shown suitable in earlier tests.
There is a point in the FB40 which I don't like, the oscillator is keyed. This make the design less suitable for QRSS. Also would I go for one low-pass filter for each band.
In the case I am going to build the 3 band qrss mept, that's what I am going to through together:
You may know about this discontinued kit:
http://www.njqrp.org/fireball40/
Well, in this design, one starts with a 28.322MHz crystal and divides it by two several time by means of flip-flops they could have used a 74LS93 instead and spare one IC). The FB40 reaches the frequencies 28.322 (obviously), 14.161, 7.0805 and 3.54025. All frequencies are in rather busy regions, good for QRP, not so good for QRSS.
Why not doing the same trick with the color burst harmonics? Starting with a 14.31818MHz oscillator, resulting frequencies are 7.15909 and 3.579454. One could also consider to double the frequency, which will get us to 28.63636.
But, because of all this dividing and doubling, FSK is somewhat out of the game. But, in contrast to the original FB40, the available frequencies could be amplified simultaneously, making some three band QRSS operation thinkable: three PAs, three low-passes. From a propagation standpoint, that would be a nice daytime night-time experiment, displaying the opening and closing of the respective bands.
There are cheap crystals and oscillators for 3.579545 and 14.31818, none for 40m however. The 80m and 20m frequencies have been shown suitable in earlier tests.
There is a point in the FB40 which I don't like, the oscillator is keyed. This make the design less suitable for QRSS. Also would I go for one low-pass filter for each band.
In the case I am going to build the 3 band qrss mept, that's what I am going to through together:
- 20m: oscillator 14.31818MHz, spectral filter by means of a crystal, buffer (keyed) and amplifier (74HC240), low-pass
- 40m: divide the oscillator frequency by two (7474 or 7493), spectral filtering by Ls and Cs, (keyed) buffer and amplifier (74HC240), low-pass
- 80m: divide the 40m frequency by two (7474) or use the appropriate division of a counter (7493), spectral filter with a crystal, (keyed) buffer and amplifier (74HC240), low pass
Sunday, January 10, 2010
500kHz - here's the plan
Brainstorming together helps sometimes. Here comes the plan:
When using this in transverter mode, I would go for a 3.000MHz canned oscillator, since no pull is required.
- build a MEPT for 3500800Hz using a crystal (e.g. from Nick)
- build a down-converter using a 3.000MHz standard crystal
When using this in transverter mode, I would go for a 3.000MHz canned oscillator, since no pull is required.
Saturday, January 9, 2010
Ramsey QRP80C considerations
My first awareness of that kit was in 1995, when there was a German supplier for this sort of stuff. I looked at it, and since is was a long way from being spectacular, I forgot about it again. Until recently the search for QRSSable kits started. The manual, which contains all vital information, besides the schematics diagram, can be downloaded from Ramsey electrics' webpage. With all parts listed, block and layout diagrams, it is no problem at all to reverse engineer the schematics; which I did. For reasons of copyrights I will not publish the result however.
As I said, the kit is not really spectacular, that what my understanding of the circuit is:
As I said, the kit is not really spectacular, that what my understanding of the circuit is:
- Colpitts xtal oscillator (2N3904)
- common emitter buffer (2N3053)
- class C power amplifier (2N3053)
- crystal pulled by two varactor diodes
- comes with color burst crystal (3.579545MHz)
In the manual it reads that the oscillator can be pulled 7kHz about the nominal frequency. For 80m I feel that is somewhat ambitious, but can't tell until I have built the kit (just ordered).
There is a switch that toggles between two crystal positions.
Now let's see what can/should be changed:
- There is a jumper JMP1 which supplies the tuning potentiometer R1 with 12V. I my view this jumper must be replaced by a voltage stabilizer, such as a 78L08. OK, will provide a little less pull, but should be much more stable.
- The oscillator is keyed, OK-ish for QRP, not acceptable for QRSS. Here there are a couple of options, supply the oscillator from the voltage stabilizer and key the PA instead (heavier keying transistor required!), key the buffer only or used FSK only.
Running the oscillator from the stabilizer:
Cut the PCB between R5 and R7, run a wire from R1 (tuning pot.) hot end to R7.
For keying the buffer, nothing will change, since the base of the buffer is pulled up by the keying voltage via R8. If the load change on the oscillator is not too great, this should not be creating too much chirp (to be tested!). - Add some resistor/transistor/what not stuff to supply a tiny bit of FSK voltage to the point where R1, R2 and C1 are joint.
- A second crystal could be 3.500MHz or, as soon as there is one, 3.600MHz.
- For QRP, the place for the second crystal could be populated with a 3.58MHz ceramic oscillator which will have a much wider pulling range. With a chance of 99.9% I will do this! So there will be one QRSS and one QRP mode for this transmitter.
- Also for QRP, two identical crystals could be installed in parallel, this would be a so called "superVXO". The PCB offers sufficient space so that two crystals could easily be installed where only one was once planned.
- When no receiver is going to be attached to J2, or RX/TX-toggle is done externally, J2 could serve as an input for the FSK keying. In this case the diode D1 can be replaced by a jumper. The parts L5, R11, L4, D2, R12, R13 and C19 must/can be omitted when D1 is replaced by a jumper.
I consider that a keying circuit can be build in place of the RX/TX-switching stuff:
The place of C19 could be used for a 10k resistor connected to the base of a NPN transistor (somewhere close to the tuning pot.). Said transistor could influence in one way or the other the tuning voltage.... - The resistor R9, which feeds the buffer, should be increased in order to not overheat the PA transistor in a 100% duty cycle. A trimmer could be added in series to R9 to allow for variable output power.
Alternatively, a resistor could be wired in series with the choke L3 which feeds the PA transistor.
Those are the mods that came to my mind. There may be more....
Another more general idea: When looking at the parts layout diagram, two pulling inductors are foreseen for the 80m version. For less pull, one could certainly omit one by shorting it (temporarily?), which will allow smoother tuning for QRSS.
Looking forward to receiving the kit!
Saturday, January 2, 2010
QRSS TRXs for 40m and 20m
Cheap single channel QRSS gear
With my 30m d.c.-receiver now running successfully for months, it would be time, I though, to "design" dedicated receivers (transmitters) for some more bands. The basic idea will follow the 30m-Polyakov design, just not using a canned oscillator this time. (for the schematics, please have a look at my web-page http://www.qsl.net/dl1gsj/).
40m version 1 (7059,9kHz)
Jan's comment on my 40m RX ideas brought me to the conclusion, that it would be desirable to use 3.530MHz crystals for a Polyakov receiver, additionally, with a slightly different pull, the same oscillator could be used in a transmitter design with a frequency doubler. When going for an active doubler, it could be switched off, so no carrier will be present during RX.
The downside, no side-band filter, which, in this portion of the band, seems crucial to me.
There is hope however, Rich offers a 7.058MHz crystal, which could be used as a notch filter in such a receiver.
20m version 1 (14096kHz)
Rich also sells a crystal 7.050MHz, this could be used in a similar fashion as mentioned above for the alternative 20m frequency. Even having the same side-band problem as the above idea bit no obvious solution to it. One could consider to receive in LSB such that the USB will be on the IBP-beacons, which could be an interesting addition...
Probably a superhet-RX with 10Mhz and 4.096MHz crystals would be the safer bet here; alternatively: 18.096MHz and 4.000MHz. In such a RX-TX combination, all oscillators could run the whole time.
40m version 2 (7000,8kHz)
Nick offers crystals for 3.500MHz, which make wonderful subharmonic local oscillators for 7000.8kHz. Additionally, there would be a 7.000MHz crystal available at box73.de, which could be used as a sideband filter, even though, I think, that 6999.2kHz would not be that crowded. Again, the L.O. could be used with an active doubler for TX....
20m version 2 (14000.8kHz)
As stated before, there is a 7.000MHz crystal available. Now, same concept as for the second version 40m. With a 14.000MHz crystal available (conrad), one could image a side-band filter... but, what will be on 13999.2kHz?
Conclusions
Seems that some crystals will have to be ordered in Florida, since 7059900Hz has priority with me and all crystals are available from one source.
Since no canned oscillators are available for, the idea would be a classic approach using transistors, hence no L.O.-xtal-filter, as in my 30m design, will be required.
Prospects
I have not tried it yet, but it sits on my workbench (30m version) quite some while now, using the subharmonic mixer in reverse for generating a DSB signal. With either passband or notch filters, a single side-band signal could be generated, just like in Gene Marcus' design of a 30m WSPR TRX. Could be used with an XORgan ;-)
With my 30m d.c.-receiver now running successfully for months, it would be time, I though, to "design" dedicated receivers (transmitters) for some more bands. The basic idea will follow the 30m-Polyakov design, just not using a canned oscillator this time. (for the schematics, please have a look at my web-page http://www.qsl.net/dl1gsj/).
40m version 1 (7059,9kHz)
Jan's comment on my 40m RX ideas brought me to the conclusion, that it would be desirable to use 3.530MHz crystals for a Polyakov receiver, additionally, with a slightly different pull, the same oscillator could be used in a transmitter design with a frequency doubler. When going for an active doubler, it could be switched off, so no carrier will be present during RX.
The downside, no side-band filter, which, in this portion of the band, seems crucial to me.
There is hope however, Rich offers a 7.058MHz crystal, which could be used as a notch filter in such a receiver.
20m version 1 (14096kHz)
Rich also sells a crystal 7.050MHz, this could be used in a similar fashion as mentioned above for the alternative 20m frequency. Even having the same side-band problem as the above idea bit no obvious solution to it. One could consider to receive in LSB such that the USB will be on the IBP-beacons, which could be an interesting addition...
Probably a superhet-RX with 10Mhz and 4.096MHz crystals would be the safer bet here; alternatively: 18.096MHz and 4.000MHz. In such a RX-TX combination, all oscillators could run the whole time.
40m version 2 (7000,8kHz)
Nick offers crystals for 3.500MHz, which make wonderful subharmonic local oscillators for 7000.8kHz. Additionally, there would be a 7.000MHz crystal available at box73.de, which could be used as a sideband filter, even though, I think, that 6999.2kHz would not be that crowded. Again, the L.O. could be used with an active doubler for TX....
20m version 2 (14000.8kHz)
As stated before, there is a 7.000MHz crystal available. Now, same concept as for the second version 40m. With a 14.000MHz crystal available (conrad), one could image a side-band filter... but, what will be on 13999.2kHz?
Conclusions
Seems that some crystals will have to be ordered in Florida, since 7059900Hz has priority with me and all crystals are available from one source.
Since no canned oscillators are available for, the idea would be a classic approach using transistors, hence no L.O.-xtal-filter, as in my 30m design, will be required.
Prospects
I have not tried it yet, but it sits on my workbench (30m version) quite some while now, using the subharmonic mixer in reverse for generating a DSB signal. With either passband or notch filters, a single side-band signal could be generated, just like in Gene Marcus' design of a 30m WSPR TRX. Could be used with an XORgan ;-)
Sunday, December 20, 2009
20m FSK/FM MEPT
Design idea here: use as much of the 74HCT240 as possible. Hence, one inverter as oscillator, three buffer (I know, this does not really make sense, but wait!) and the block of the other four gates as power amplifier, all four in parallel for use with a step-up transformer. The "PA" is equipped with an enable/disable switch.
So, here is comes, why use three buffers. Well, the first buffer is required since oscillator gate is operated in "linear mode". This first buffer inverts the signal, or in other words, phase-shifts it by 180 degrees. The second buffer inverts the signal again, providing a signal which is phase-shift by another 180 degrees, delivering an in phase signal to the oscillator. Who knows what this can be used for...
OK, now the third buffer seems really useless, but, it is not ;-) This buffer terminated the second one properly, so that always a nice signal can be drawn from either buffer 1 or buffer 2.
Thursday, November 12, 2009
40m Novice QRSS QRG
I have not looked into any possible scheme of privileges, this is what I found:
There are a couple of obvious candidates for which crystals are available:
There are a couple of other reasons why I would suggest a frequency between 7.093 and 7.097. First of all, it is very simple to build an oscillator for 14.200 with a single crystal, pull it down a bit and divide the signal using a FlipFlop. The second reason I would see in the possibility to create a very simple superhet-receiver (or transceiver) with the combination found under point 4. This combination could also be used as a simple MEPT, however, drift is more an issue in a design using the sum of two frequencies.
This leads to the obvious advantages of the two combinations using differences. Once again, a superhet is possible and in a difference of two frequencies, drift is less of an issue.
- U.S. 7.025-7.125
- The Netherlands 7.050-7.100
- Germany none
There are a couple of obvious candidates for which crystals are available:
- 7.100 => which can be generated by a 14.200 crystal (ESS) divided by two
- 7.059 => 11.0592 - 4.000
- 7.085 => 12.000 - 4.9152
- 7.096 => 3.000 + 4.096
There are a couple of other reasons why I would suggest a frequency between 7.093 and 7.097. First of all, it is very simple to build an oscillator for 14.200 with a single crystal, pull it down a bit and divide the signal using a FlipFlop. The second reason I would see in the possibility to create a very simple superhet-receiver (or transceiver) with the combination found under point 4. This combination could also be used as a simple MEPT, however, drift is more an issue in a design using the sum of two frequencies.
This leads to the obvious advantages of the two combinations using differences. Once again, a superhet is possible and in a difference of two frequencies, drift is less of an issue.
I would go so far to state that there even is a kit for a transceiver, when 7.059 is considered. Well near enough at least. This rig would allow for transmission as well as reception.
The Ten-Tec 1340 is having an intermediate frequency of 11.000MHz. A VFO generates a signal around 3.97MHz.
And here comes the mod to the kit:
And here comes the mod to the kit:
- replacing all 11MHz crystals by 11.0592MHz xtals
- not building the VFO but an oscillator with a 4MHz xtal including a varactor for FSK
For QRSS I believe one would like to reduce the drive to the PA, since the final produces about 5W rf and would probably become hot in time. Maybe the final (2SC2166) could be left out all together. The driver is indicated to deliver 15dBm.
Further, the audio amplifier (LM386) could be left out in its entirety.
Saturday, October 10, 2009
40m / 20m two band MEPT
- MEPT for 14.000800MHz
- QRP crystal for 15m (21.060MHz)
- => 21.060 - 14.000800 = 7.05992
- inverts!
Tuesday, September 1, 2009
U.S. 40m QRSS XTAL combi
On the KnightsQRSS-list, recently a discussion about frequencies went on. Stu and Dave pointed out frequency restrictions of various license categories. QRSS transmissions have been done on 7.105MHz, as far as I recall.
Using an appliance, one can set the rig to any random frequency, agreed, operating an MEPT homebrew-style, here are two options:
There is a somewhat more difficult approach however which would involve penning down crystals:
73, Joachim
Using an appliance, one can set the rig to any random frequency, agreed, operating an MEPT homebrew-style, here are two options:
- 7.106 = 10.106 - 3.0
- 7.103 = 12.288 - 5.185
There is a somewhat more difficult approach however which would involve penning down crystals:
- 7.105 = 11.0592 - 3.9542 (1.)
- 7.105 = 11.000 - 3.895 (2.)
- 7.105 = 9.202 (3.) - 2.097152
- penned down 4MHz crystal
- penned down 3.9321MHz crystal
- penned down 9.216MHz crystal
73, Joachim
Friday, August 14, 2009
New QRSS xtal combinations
Following the idea having the QRSS region about 100Hz below the WSPR region on every band, new considerations had to be made in order to allow for MEPTs controlled by cheap crystals.
For the bands 40m and 30m the situation is very simple:
80m slightly more tricky, but no big deal at all!
For the bands 160m, 20m, 17m, 12m and 10m, a combination of two crystals will do the trick to generate a frequency in the QRSS range.
The following frequencies (in MHz) are reached by mixing of two fundamental crystal frequencies:
It seems appropriate to note that the 12m combination under point 6 uses a 10,180MHz crystal which can be found in older crystal-synthesized CB radios.
The 15m band can be reached by means of multplication and division:
Solution #2 looks more promising to me for the following reasons. 38,0 divided by two gets us to 19,0. Mixing products will be 21,097 and 16,903. We certainly would need a band trap for 16,9MHz, which should be doable. As divider I would propose the usual Flip-Flop. The best part is, there are canned oscillators available for 38MHz.
For the bands 40m and 30m the situation is very simple:
- 10,140MHz crystal available from N4ESS (no change anyway)
- 7,040MHz QRP crystal available
- 7,038MHz QRP crystal, which could serve as a basis for a d.c.-receiver
80m slightly more tricky, but no big deal at all!
- 3,595 = 7,190 / 2
For the bands 160m, 20m, 17m, 12m and 10m, a combination of two crystals will do the trick to generate a frequency in the QRSS range.
The following frequencies (in MHz) are reached by mixing of two fundamental crystal frequencies:
- 1,8372 = 8,8672 - 7,030
- 14,096 = 10,000 + 4,096
- 14,096 = 18,096 - 4,000
- 14,097 = 12,000 + 2,09715
- 18,106 = 8,000 + 10,106
- 24,926 = 14,7456 + 10,180
- 28,125 = 18,000 + 10,125
It seems appropriate to note that the 12m combination under point 6 uses a 10,180MHz crystal which can be found in older crystal-synthesized CB radios.
The 15m band can be reached by means of multplication and division:
- 21,096 = 4,096 + 2 * 8,500
- 21,097 = 2,09715 + 38,000 / 2
Solution #2 looks more promising to me for the following reasons. 38,0 divided by two gets us to 19,0. Mixing products will be 21,097 and 16,903. We certainly would need a band trap for 16,9MHz, which should be doable. As divider I would propose the usual Flip-Flop. The best part is, there are canned oscillators available for 38MHz.
Wednesday, July 29, 2009
short update on the WSPR/QRSS trx
This project has been resting for a a while. Yesterday, some progress was made. The local oscillator now has got a buffer/amplifier producing much more power than the mixing stage would ever need. This stage uses a 2N2222A in an emitter follower like configuration.
Even though the signal is pretty clean, in order to sure, I added a crystal as filter. Output level is adjustable to the needs of the mixer by a trimmer.
Here's a photograph of what there is sofar.
Presently I assume that I would need something like 2V peak to peak to properly drive the Polyakov-mixer, thus the buffer will be run with stabilized 5V.
Oscilloscope shows 1V/div, no further surprise here...
Let's see how far I come today....
Saturday, July 25, 2009
FSK QRSS MEPT update
Well, I did the test, and actually started a revision of the design, check out the 2nd schematics on my webpage.
As I am running all my test with a regulated laboratory power supply, I not only can control the voltage, but also the current of the power source. Having done that, I realized that more power shows up at the output of the lowpass-filter at a particular reduced current. I measured the input current of the 74HCT00 and found out that it best performs at about 15-16mA (??, but OK). A little math in my head, and I added a 220Ohms resistor between the regulator and pin 14 of the quad-nand.
But now, running the NANDs in parallel, with optimum waveform and output, made the frequency shift much larger (???), something like 20Hz, in place of 5Hz before (!). Additionally, the frequency slightely dropped (well, ok, that I do understand).
No math helps here, pure experimentation. Remember, the shift is predominantly determined by the resistor connecting the HCT00 and the 12F629...
For sentimental reasons, I left in the 47kOhms resistor which started it all. It has now got a partner on its' side, they are even allowed to hold hands, a 470kOhms resistor in series. Seems that in the new arrangement, 0.5MOhm makes the trick, shift is now back to 5Hz. Ouuffff!!!
Seems there is a delicate balance between the few critical elements. And now limiting the current seems a factor too.... Am I using the HCT-gates in some sort of analogue mode?
And what about the results? Well, here we are. @ 50Ohms, I measured 0.8Vpp, resulting in about 1.6mW. Actually, the waveform looks even better now! Presently running a stability test (RX=FT817 w/TCXO).
FSK QRSS MEPT
under "20m MEPT".
More detailed explanations and keyer source code will follow soon.
Some first impressions of the MEPT in question.
Initially I wanted to squeeze the filter between the 12F629 (8 pin controller in a 16 pin socket) and the 74HCT00, however, I was running out of space... well, ok, in a very first version of this transmitter, the filter actually was there. With the appearance of the 47k resistor in that particular spot, the filter could not be fit in again :-(
Further one can identify the "high quality, high power" dummy load. Well, actually this dummy load really is high power for the setup shown... two quarter Watt 100Ohms resistors in parallel seem good for about half a Watt, right? And well, look at the display of my lab-TV blow...
First of all, it looks like a nice sine signal. The vertical division was set to 0.1V/div, making the signal a whopping 550mV @ 50Ohms or 740µW.
As one further test I will run the two "shaping NANDs" in parallel, just to see what this does.
Midnight Oil
Well, what a night! I severly was burning midnight oil, with results however.
Found a way to modulate a crystal oscillator, FSK that is, w/o any additional efforts. Not sure if it has been done in that way ever before. By now, I am too tired to create some schematics, I will offer something on the webpage (not here thus) soon.
To give an appetizer, I think, building a MEPT for QRSS on 20m is done in less than five minutes... with me having spent night on that, that is....
Friday, July 17, 2009
ahh!
Now we are getting somewhere. Frequency for the subharmonic L.O. reached. I actually got two parameters to play with for frequency adjustment, the capacitor in series with the crystal and the supply voltage of the ocillator. This is actually adjusted and measured at 5V. Oscillation stops at about 4V. The circuit itself however, is designed for stabilized 8V. Thus, here are some degrees of freedom for the final tuneup.
As a last resort, I blamed it on the crystal, as suspected before. The crystal I used in the first attempt was not good, as shown by the replacement which more of less on the spot produced the correct frequency. Ouf! I need to build myself a crystal tester, I guess. Could possibly spare me some sleepless nights ;-)
The signal itself is not that perfect yet. I will have to install some resonating filter, I guess, to smooth out those humps and bumps to something that comes closer to a sine-wave than that...
Finally, the Poliakov-type mixer works best with a well balanced sine-wave.
Oh, and if you are interested in what I actually used for transistor, it's a 2N2222A. The rest of the bits and pieces are somewhat obvious and not worth to be mentioned individually...
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