In the PSK-30, Dave uses an intermediate frequency of 4.000MHz and a local oscillator employing a 6.144MHz crystal. The oscillator is pulled into place to match the PSK31 center of the 30m band.
In order to get the LO down to our QRSS/WSPR range, one may consider just pulling the oscillator further. However, this possibly compromises stability.
My suggestion here is to pen down a 6.144MHz standard crystal to 6.1387MHz, which is very easily done.
Information about penning down a crystal, you will find here on this blog.
Please not, one needs to make sure that the BFO is set for USB!
Tuesday, November 30, 2010
SmallWonder Labs PSK-20 QRSS/WSPR mod
Some time ago I built a PSK-20. Even though PSK31 can be fun occasionally,I was thinking of added value to the radio.
The radio uses an intermediate frequency of 9MHz, which is mixed with a 5.0688MHz "computer" crystal oscillator.
I see two possibilities:
Actually, I may start with option #1, to keep the original functionality.
The radio uses an intermediate frequency of 9MHz, which is mixed with a 5.0688MHz "computer" crystal oscillator.
I see two possibilities:
- Make the 5.0688MHz crystal replaceable with a 5.000MHz crystal. This mod will get you to the 20m QRSS band at 14.000800MHz and the radio will still be usable for PSK31.
- There is no WSPR in this mod? Yes, there is, it would be all about penning down a 5.120MHz crystal to 5.0956MHz, which is quite a stretch but doable.
- Some additional frequencies in the upper digi-mode band (14.101-14.112MHz) are reachable in a similar way.
- Finally, there is a 5.200MHz crystal, which would make up to a perfect single channel SSB DXpedition transceiver. I guess one needs to look at the IF-filter response in this one.
- Change the intermediate frequency to 10MHz and the local oscillator to 4.000MHz.
- PSK31 operation will be gone, since there is no (cheap) crystal for 4.070MHz. OK, the last statement is not entirely true, one could pen down a 4.096MHz crystal to 4.069MHz, although, 27kHz is a lot.
- But, WSPR is on the easy side by using a 4.096MHz xtal in the LO.
- Additionally, one SSB channel is available with the LO running at 4.194MHz; I guess one needs to look at the IF-filter response in this one. 14.194MHz would be ideal for SSB DXpeditions.
Actually, I may start with option #1, to keep the original functionality.
Monday, November 29, 2010
Clarifier Calibration Idea
Inexpensive receivers as the HF3 need occasional calibration of the clarifier since such receiver to exhibit some temperature drift. One option is zero-beat a known carrier, another option is adjusting a known carrier to create a beat close to the audio frequency we want to use/listen to, e.g. 2Khz, and display it on a spectrum display.
And here would be my planned approach to the second option. A micro-controller (PIC, PICAXE, ATMEL, etc.) programmed as frequency counter of particular kind. Lets count as precisely as possible around 2kHz.
Here are some ideas how to display the deviation from 2kHz:
The following idea is for the more advanced builder. It should also be seen as a modification to the receiver. The clarifier-potentiometer could be replaced by some circuitry creating/controlling the clarifier varactor. PWM could be an idea here. The concept would be to "visit" a known carrier, activate the counting and adjust the varactor voltage such that the counter counts a 2kHz beat. Now deactivate counting and keep the varactor voltage constant. Actually, in a grabber setup, one may consider to have such "calibration visits" periodically (maybe every 3h) executed by the micro-controller, e.g. by switching between memory channels.
And here would be my planned approach to the second option. A micro-controller (PIC, PICAXE, ATMEL, etc.) programmed as frequency counter of particular kind. Lets count as precisely as possible around 2kHz.
Here are some ideas how to display the deviation from 2kHz:
- 5 LEDs: red (+/-10 to -+/-5Hz), amber (+/-4 to +/-2Hz), green (from -1Hz to +1Hz)
- 7 segment display: deviation in Hz, decimal dot a negative sign indicator
The following idea is for the more advanced builder. It should also be seen as a modification to the receiver. The clarifier-potentiometer could be replaced by some circuitry creating/controlling the clarifier varactor. PWM could be an idea here. The concept would be to "visit" a known carrier, activate the counting and adjust the varactor voltage such that the counter counts a 2kHz beat. Now deactivate counting and keep the varactor voltage constant. Actually, in a grabber setup, one may consider to have such "calibration visits" periodically (maybe every 3h) executed by the micro-controller, e.g. by switching between memory channels.
Tuesday, November 23, 2010
CompuLab Fit-PC2 1.1GHz
It arrived, and I had some time to play with it. Here are some first thoughts.
This PC is damn small! Really!! As everyone else who did a review on this tiny piece of art work, I have to state, the things is smaller that I thought it would be! To stay in QRP standards, the PC is just a fraction bigger than two Altoids tins.
So, here's what my impressions are.
My PC came w/ ubuntu 9.10 ... and that is what it should run, I think. The problem with ubuntu is, it motivates you to update it.... don't do it! Some drivers seem not to be compatible with more recent versions.
Playing with some other operation systems, the following remarks, WinXP works ok with the drivers found on CompuLabs wepage. Win7 worked, however, I got a crash or two, I could however not find out why.
Finally, ubuntu 9.10 came out best and hence will be the OS on my Fit-PC2 (WLAN works too).
A final test concerning the OS will be running Jolicloud on it... I will report about this by updating this posting.
Some words on the hardware. The device does not employ a fan. Even though the case looks like cheap plastics, it actually is made from Al and serves as a heat sink. The device can develop some temperature...
The manufacturer however design the PC for 24/7 up-time, I therefore believe that the temperature is not issue here.
As indicated in the title, I bought the 1.1GHz version. This may have been a mistake, not a big one however. This version is the only one of the Fit-PC2 which wont be able to read miniSDHC-cards. So, 2GB is the limit on SDHC-cards. With a built-in 160GB HDD this is no real issue to me.
QRM: The USB-keyboard/mouse created some rf-noise. I also could hear the attached LCD-screen in the receiver. The switching 12V PSU that came along with the PC created some QRM too. I have not yet figured out how noisy the PC itself is.
Since this is a relatively weak CPU, my impression is that the operation system should be made a light as possible, meaning, all services not required should be disengaged. The usual linux-distro carries a lot of stuff which would not be required on a daily basis, all this could/should be disabled for enhanced system performance.
Should I ever buy one of those PCs again, I would choose a more powerful model, in particular for the added miniSDHC capability, I do however not regret having bought the one I got.
This PC is damn small! Really!! As everyone else who did a review on this tiny piece of art work, I have to state, the things is smaller that I thought it would be! To stay in QRP standards, the PC is just a fraction bigger than two Altoids tins.
So, here's what my impressions are.
My PC came w/ ubuntu 9.10 ... and that is what it should run, I think. The problem with ubuntu is, it motivates you to update it.... don't do it! Some drivers seem not to be compatible with more recent versions.
Playing with some other operation systems, the following remarks, WinXP works ok with the drivers found on CompuLabs wepage. Win7 worked, however, I got a crash or two, I could however not find out why.
Finally, ubuntu 9.10 came out best and hence will be the OS on my Fit-PC2 (WLAN works too).
A final test concerning the OS will be running Jolicloud on it... I will report about this by updating this posting.
Some words on the hardware. The device does not employ a fan. Even though the case looks like cheap plastics, it actually is made from Al and serves as a heat sink. The device can develop some temperature...
The manufacturer however design the PC for 24/7 up-time, I therefore believe that the temperature is not issue here.
As indicated in the title, I bought the 1.1GHz version. This may have been a mistake, not a big one however. This version is the only one of the Fit-PC2 which wont be able to read miniSDHC-cards. So, 2GB is the limit on SDHC-cards. With a built-in 160GB HDD this is no real issue to me.
QRM: The USB-keyboard/mouse created some rf-noise. I also could hear the attached LCD-screen in the receiver. The switching 12V PSU that came along with the PC created some QRM too. I have not yet figured out how noisy the PC itself is.
Since this is a relatively weak CPU, my impression is that the operation system should be made a light as possible, meaning, all services not required should be disengaged. The usual linux-distro carries a lot of stuff which would not be required on a daily basis, all this could/should be disabled for enhanced system performance.
Should I ever buy one of those PCs again, I would choose a more powerful model, in particular for the added miniSDHC capability, I do however not regret having bought the one I got.
Sunday, November 21, 2010
The Inside of an Indicator Buoy
Sort of off-topic...a signaling buoy on my boat required maintenance... in other words, it was not up to its task anymore, and will be replaced. Those things are supposed to be mounted to a lifesafer, so that it can be found by the MOB (Man Over Bord), and further, that the MOB can be found by the crew of sailors.
Now, let's have a peak what is inside....
The orange body of the buoy is closed by a transparent cap, sealed by a black rubber gasket. The inner life of the buoy consists of a PCV tube which holds (from left to right) some Fe-ballast, an opening for loading 4 D-type batteries, a spring for those batteries, a PCB w/ a flasher circuit, an Hg-switch and a mount for the bulb.
I leave it to your imagination what to do w/ this info... The only thing I can say is, if you find any flaw in your safety gear, discard w/o hesitation, lives will depend on the stuff! You don't want to have an indicator buoy not flashing properly if yours friends live in on the line.
Look after your safety gear, respect expiry dates and replace on time!
Allzeit eine handbreit Wasser unter'm Kiel!
Now, let's have a peak what is inside....
The orange body of the buoy is closed by a transparent cap, sealed by a black rubber gasket. The inner life of the buoy consists of a PCV tube which holds (from left to right) some Fe-ballast, an opening for loading 4 D-type batteries, a spring for those batteries, a PCB w/ a flasher circuit, an Hg-switch and a mount for the bulb.
I leave it to your imagination what to do w/ this info... The only thing I can say is, if you find any flaw in your safety gear, discard w/o hesitation, lives will depend on the stuff! You don't want to have an indicator buoy not flashing properly if yours friends live in on the line.
Look after your safety gear, respect expiry dates and replace on time!
Allzeit eine handbreit Wasser unter'm Kiel!
Wednesday, November 17, 2010
HYmini - a QRPp Wind Generator
Steve G0XAR brought up a "Wind Generator", which could be useful for powering an MEPT. Guess what, I could not resist and bought one.
This is what I got for just £9.95:
What you see is, the wind generator, a USB-cable and a set of adapters to connect a device to be charged. Interestingly there is a 5V PSU supplied, which, at first sight seems not to make any sense.
However, the device is called "portable power bank" and actually carries an internal 1200mAh accumulator. Meaning it is supposed to be carried about for charging up other gadgets with 5V supply voltage. As preparation for outdoor activity, the internal accumulator could therefore be charged from mains supply.
Surprisingly, the optional bike mounting bracket was included in the package! Many thanks to "ecohamster"!
Very unfortunately, the device is not weather proof. The manual reads that the wind generator must not be used under wet conditions. That is, I believe, a huger downer!
This is what I got for just £9.95:
What you see is, the wind generator, a USB-cable and a set of adapters to connect a device to be charged. Interestingly there is a 5V PSU supplied, which, at first sight seems not to make any sense.
However, the device is called "portable power bank" and actually carries an internal 1200mAh accumulator. Meaning it is supposed to be carried about for charging up other gadgets with 5V supply voltage. As preparation for outdoor activity, the internal accumulator could therefore be charged from mains supply.
Surprisingly, the optional bike mounting bracket was included in the package! Many thanks to "ecohamster"!
Very unfortunately, the device is not weather proof. The manual reads that the wind generator must not be used under wet conditions. That is, I believe, a huger downer!
Wednesday, November 10, 2010
The HC-8 CW QRP Transceiver
I got something on my mind, which is probably not too hard to design, and could be a nice trx to take along on journeys: a modern days clone of the HW-8.
The design will entirely be based on 74HC digital electronics, hence the name HC-8.
It will employ a 8.867MHz super-VXO. Reason for this being the HW-8 itself (find out more about this in an earlier post).
The CW portions of 160, 80, 40, 20 and 17 can easily be covered by such a super-VXO in combination with some cheap crystals. 30 required some more efforts. For good measures, I will include the already shown list:
As mentioned above, the plan is to use digital gates as much a possible.
This would be possible solutions:
Practical Considerations
With the 74HC240 running from 8V (upper limit for this particular chip) one could imagine to drive a class-E switch-mode PA (IRF510) that easily would produce 5W RF.
The HC-8 wont be providing any IF filtering. I intend to go for pure direct conversion, (super) VXO on 8.867Mc and r.i.t. on the respective other oscillators. I have not yet figured out how to do this the best
way.
Switching low pass filters in a multi-band transceiver can pose a problem, therefore I am envisaging to go for 2 bands only (switches are available, small and not too expensive), but build two rigs:
Added Value
You're missing 30m? OK, here is 30m, it's a tricky one however, in particular for filtering! Frequency division would be available using 74HC74 Flip-Flops. Signal source: a 5.0MHz xtal or a not so common 38.0MHz oscillator.
Even long-wave would would be available (although such a rig would maybe not that practical for such low frequencies):
Note: For some bands the VXO is required to oscillate above 8.867MHz. Some thought should be invested when designing the VXO. Maybe for the reason of frequency coverage, the VXO should involve discrete transistors in place of digital gates.
As antenna to go along with the rig I see the RockLoop as best fitting. Very narrow-band antennae have the advantage of good harmonics suppression. Alternatively a high-Q transmatch should be used for the same reason.
The design will entirely be based on 74HC digital electronics, hence the name HC-8.
It will employ a 8.867MHz super-VXO. Reason for this being the HW-8 itself (find out more about this in an earlier post).
The CW portions of 160, 80, 40, 20 and 17 can easily be covered by such a super-VXO in combination with some cheap crystals. 30 required some more efforts. For good measures, I will include the already shown list:
- 160m: 8.867 - 7.000 = 1.867
- 80m: 8.867 - 12.406 = (-) 3.539
- 40m: 8.867 - 1.843 = 7.024
- 20m: 8.867 + 5.185 = 14.052
- 17m: 8.867 + 9.216 = 18.083
As mentioned above, the plan is to use digital gates as much a possible.
This would be possible solutions:
- 74HC00 - oscillators, drivers, AF-amp
- 74HC04 - oscillators, drivers, AF-amp
- 74HC86 - oscillators, drivers, mixers
- 74HC4066 - oscillators, mixers, signal routing, class E "driver"
- 74HC240 - driver, PA, AF-amp
Practical Considerations
With the 74HC240 running from 8V (upper limit for this particular chip) one could imagine to drive a class-E switch-mode PA (IRF510) that easily would produce 5W RF.
The HC-8 wont be providing any IF filtering. I intend to go for pure direct conversion, (super) VXO on 8.867Mc and r.i.t. on the respective other oscillators. I have not yet figured out how to do this the best
way.
Switching low pass filters in a multi-band transceiver can pose a problem, therefore I am envisaging to go for 2 bands only (switches are available, small and not too expensive), but build two rigs:
- 80/40 for NVIS
- 20/17 for DX
Added Value
You're missing 30m? OK, here is 30m, it's a tricky one however, in particular for filtering! Frequency division would be available using 74HC74 Flip-Flops. Signal source: a 5.0MHz xtal or a not so common 38.0MHz oscillator.
- 8.867 + (5.000/4) = 8.867 + 1.25 = 10.117
- 8.867 - (38.000/2) = 8.867 - 19.000 = (-) 10.133
Even long-wave would would be available (although such a rig would maybe not that practical for such low frequencies):
- 8.867 - 9.000 = (-) 0.133
Note: For some bands the VXO is required to oscillate above 8.867MHz. Some thought should be invested when designing the VXO. Maybe for the reason of frequency coverage, the VXO should involve discrete transistors in place of digital gates.
As antenna to go along with the rig I see the RockLoop as best fitting. Very narrow-band antennae have the advantage of good harmonics suppression. Alternatively a high-Q transmatch should be used for the same reason.
Monday, November 8, 2010
HB-1A now Ten-Tec R4030 & R4020
Interesting... the HB-1A QRP-transceiver, made by BD4RG, which disappeared from ebay where it was sold for a while reappeared at Ten-Tec's product range as R4030 and R4020. The manual, download-able from Ten-Tec, even shows "HB-1A 3 Band CW QRP Transceiver".
Funny, the original 3 band TRX is now available as 2 different 2 band TRXs. I wonder why this limitation, which most likely is just a bit of code in the main controller, was added. In particular since the DDS still is mentioned to deliver a receive range from 5-16MHz, as in the original HB-1A. Looking at the schematics, the only reason that I can see is the switchable low-pass filter. Probably some FCC requirements about spurious transmissions. I have doubts about commercial reasons; who would by two transceivers being more or less the same. When going on a trip, the three bands 40, 30 and 20 seem ideal. Now the OM has to select, either the band that is open around the clock, or the band that delivers the best dx results in average.
For myself, if I would consider trying to get my hand on a radio like this, I would go for the original HB-1A. Harmonics suppression in my travel kit is done by the aerial, which usually is a very narrow-band "rockloop".
When it all comes to buying, I would very likely go for the real original, the Elecraft KX1, which nowadays covers all band from 80 to 20.
UPDATE: Today, 10.11.2010, I decided to order a Hendricks PFR-3 kit. The design is thought through and straight forward. The controller however allows only for 40, 30 or 20m HAM-band action, no BC-RX though. In my view, this is a tiny downer...
The PFR-3 transceiver carries a built-in manual transmatch and a preselector, which sounds "old skool"... and it is! And that is why I ordered the kit.
Funny, the original 3 band TRX is now available as 2 different 2 band TRXs. I wonder why this limitation, which most likely is just a bit of code in the main controller, was added. In particular since the DDS still is mentioned to deliver a receive range from 5-16MHz, as in the original HB-1A. Looking at the schematics, the only reason that I can see is the switchable low-pass filter. Probably some FCC requirements about spurious transmissions. I have doubts about commercial reasons; who would by two transceivers being more or less the same. When going on a trip, the three bands 40, 30 and 20 seem ideal. Now the OM has to select, either the band that is open around the clock, or the band that delivers the best dx results in average.
For myself, if I would consider trying to get my hand on a radio like this, I would go for the original HB-1A. Harmonics suppression in my travel kit is done by the aerial, which usually is a very narrow-band "rockloop".
When it all comes to buying, I would very likely go for the real original, the Elecraft KX1, which nowadays covers all band from 80 to 20.
UPDATE: Today, 10.11.2010, I decided to order a Hendricks PFR-3 kit. The design is thought through and straight forward. The controller however allows only for 40, 30 or 20m HAM-band action, no BC-RX though. In my view, this is a tiny downer...
The PFR-3 transceiver carries a built-in manual transmatch and a preselector, which sounds "old skool"... and it is! And that is why I ordered the kit.
Saturday, November 6, 2010
SW+ Transceivers for QRSS
I was shopping for QRSS kits once again. And, once again at K1SWL.
The RockMites work great for QRSS, however, this time it was the SW+ Series Transceivers.
The SW+ design employs a three pole crystal ladder filter and a VFO tuned by a varicap.
Lets look at the different models and what would get us to a QRSS range.
SW+ 80
This model uses a 8.000MHz intermediate frequency. Subtractive mixing with a 4.500MHz crystal (standard but maybe harder to find) gets us to 3.500MHz.
The color-burst range is reached by subtractive mixing with a 4.433618MHz crystal. The result will be 3.566382MHz, somewhat low, however, the 4.433618MHz xtal can easily penned down to 4.420MHz. Mixing would then result in 3.580MHz.
SW+ 40
This model uses a 4.000MHz intermediate frequency.
Additive mixing with a 3.000MHz crystal gets us to 7.000MHz.
Subtractive mixing with a 11.000MHz crystal gets us to 7.000MHz.
Subtractive mixing with a 11.059MHz crystal gets us to the novice range 7.0599MHz.
With the help of crystal-penning, the novice range is reachable by additive mixing with a 3.072MHz standard xtal results in 7.072MHz, with some penning 7.0599MHz should not be any problem.
SW+ 30
This model uses a 7.68MHz intermediate frequency. I can't think of any cheap crystal to match up with that frequency. However, there is help!
The 7.68MHz i.f. could be changed to 6.144MHz. From here on, with penning again, additive mixing with a 4.000MHz xtal-oscillator will result in 10.140MHz.
SW+ 20
This model uses a 9.000MHz intermediate frequency. Additive mixing with a 5.000MHz crystal gets us to 14.000MHz
Non-qrss bonus mod: 5.0688MHz super-VXO for regular QRP work.
Further option: use a 10.000MHz intermediate frequency. With a 4.000MHz oscillator we arrive at 14.000MHz. An (additional) alternative 4.096MHz XTAL will result in the vicinity of 20m WSPR.
A 80m QRP-XTAL will result in 22m hifer gear at 13.560MHz.
Possible Mods
The first option keeps the original function, that's nice! Secondly, since the 4.500MHz crystal may be hard to get, one may consider using a 9.000MHz oscillator, based on a 27MHz standard crystal, and divide the frequency by two before, as to obtain 4.500MHz.
The second option renders all VFO parts essentially obsolete. However, the VFO is realized by means of a varicap, which could be used to pull the crystal for coarse frequency adjustment.
FSK modulation can easily be generated with the help if some sort of diode pulling the TX converter's XTAL in the usual fashion.
Audio for the sound-card could be tabbed off just at the AF final's input, just behind the muting transistor.
Due to the 100% duty cycle of FSK-QRSS, the TX output should be reduced.
Conclusions
The RockMites work great for QRSS, however, this time it was the SW+ Series Transceivers.
The SW+ design employs a three pole crystal ladder filter and a VFO tuned by a varicap.
Lets look at the different models and what would get us to a QRSS range.
SW+ 80
This model uses a 8.000MHz intermediate frequency. Subtractive mixing with a 4.500MHz crystal (standard but maybe harder to find) gets us to 3.500MHz.
The color-burst range is reached by subtractive mixing with a 4.433618MHz crystal. The result will be 3.566382MHz, somewhat low, however, the 4.433618MHz xtal can easily penned down to 4.420MHz. Mixing would then result in 3.580MHz.
SW+ 40
This model uses a 4.000MHz intermediate frequency.
Additive mixing with a 3.000MHz crystal gets us to 7.000MHz.
Subtractive mixing with a 11.000MHz crystal gets us to 7.000MHz.
Subtractive mixing with a 11.059MHz crystal gets us to the novice range 7.0599MHz.
With the help of crystal-penning, the novice range is reachable by additive mixing with a 3.072MHz standard xtal results in 7.072MHz, with some penning 7.0599MHz should not be any problem.
SW+ 30
This model uses a 7.68MHz intermediate frequency. I can't think of any cheap crystal to match up with that frequency. However, there is help!
The 7.68MHz i.f. could be changed to 6.144MHz. From here on, with penning again, additive mixing with a 4.000MHz xtal-oscillator will result in 10.140MHz.
SW+ 20
This model uses a 9.000MHz intermediate frequency. Additive mixing with a 5.000MHz crystal gets us to 14.000MHz
Non-qrss bonus mod: 5.0688MHz super-VXO for regular QRP work.
Further option: use a 10.000MHz intermediate frequency. With a 4.000MHz oscillator we arrive at 14.000MHz. An (additional) alternative 4.096MHz XTAL will result in the vicinity of 20m WSPR.
A 80m QRP-XTAL will result in 22m hifer gear at 13.560MHz.
Possible Mods
- Preserve the original QRP-TRX: toggle between the LC-VFO and an external XO.
- QRSSify the TRX: replace the VFO's RC-network by the crystal.
The first option keeps the original function, that's nice! Secondly, since the 4.500MHz crystal may be hard to get, one may consider using a 9.000MHz oscillator, based on a 27MHz standard crystal, and divide the frequency by two before, as to obtain 4.500MHz.
The second option renders all VFO parts essentially obsolete. However, the VFO is realized by means of a varicap, which could be used to pull the crystal for coarse frequency adjustment.
FSK modulation can easily be generated with the help if some sort of diode pulling the TX converter's XTAL in the usual fashion.
Audio for the sound-card could be tabbed off just at the AF final's input, just behind the muting transistor.
Due to the 100% duty cycle of FSK-QRSS, the TX output should be reduced.
Conclusions
- SW+ 80: subtractive mixing cancels temperature drift partially
- SW+ 40: best choice: subtractive mixing 11.000 & 11.059MHz
- SW+ 30: there is a better kit for 30m: the PSK-30
- SW+ 20: the 10MHz i.f. mod will offer the most
Monday, November 1, 2010
136kHz Crystal Pair
Lately, I mentioned a local electronics shop, I guess they would also ship outside the Netherlands. As noted in the previous entry, they have some uncommon crystals in the assortment.
The specific one I would like to focus on today will enable 136kHz action, either by mixing with another crystal, or as superhet design with a couple of options.
Here we go, have a look at 4233.6kHz.... mix it with 4096kHz will get us to 8329.6kHz aaahhh... hmmm.... and:
137.6kHz
According to the band-plan, this is spot on for the lower edge of the QRSS section! Since at about 4MHz crystals can easily be pulled a couple of kHz, the whole band is easily covered.
You already guessed, we will have some options for superhet design too. I would recommend the filter being made from 4096kHz crystals, reason being the better availability. Additionally, the 4096kHz intermediate frequency allows for a 2048kHz subharmonic BFO.
The specific one I would like to focus on today will enable 136kHz action, either by mixing with another crystal, or as superhet design with a couple of options.
Here we go, have a look at 4233.6kHz.... mix it with 4096kHz will get us to 8329.6kHz aaahhh... hmmm.... and:
137.6kHz
According to the band-plan, this is spot on for the lower edge of the QRSS section! Since at about 4MHz crystals can easily be pulled a couple of kHz, the whole band is easily covered.
You already guessed, we will have some options for superhet design too. I would recommend the filter being made from 4096kHz crystals, reason being the better availability. Additionally, the 4096kHz intermediate frequency allows for a 2048kHz subharmonic BFO.
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