Hi, happy new year; let me add few points here. As you said, it is T configuration high pass filter; it doesn't mean that this will pass all the ham band frequencies above the resonant one. The shorting bar, as the name implies, is to short out the excess windings when you want to work on the higher end of the HF spectrum. Coming to the SWR/Power meter circuits, the coupler is the regular Bruene bridge on the rear pcb. The metering pcb is found on the front. That is the usual practice. MFJ has not done any shielding to both pcbs. That really is not the correct practice. It is always better to shield even for qrp power levels. The circuit has to be redrawn as you have done already. In the standard literature like the ARRL handbook, it is a regular practice to draw both circuitry separately with mention about the screening (with good grounding) The 50 ohm dummy load can be connected to the radio to check the built-in power meter on the radio. The SWR/Power meter can be arranged to be terminated into the dummy load (before hooking it to the antenna) for calibration assessment. Yes, antennas like long wire and twin lead fed systems can be tuned (to within reasonable impedances). Remember that it uses a 1:4 Ruthrof voltage BalUn for the twin lead feeder systems; it is not to match the characteristic impedance of the twin lead feeder but only for the purpose of extending the limits of impedances (higher than) that can be handled without a 1:4 voltage step up transformer. Essentially it is a compromise and is not a "genuine" tuner meant to be fed to a twin lead feed antennas. Of course, the twin needle or cross needle analog (D' Arsenval moving coil meter is a useful, attractive feature where one can asses the forward power and reflected power simultaneously. The SWR is read against the marking on the dial where both needles intersect during operation. The PEP function requires power from the 9V battery for the comparator circuit that would charge an appropriate value capacitor for the power range and hold the needle on the dial before getting discharged. The dial incandescent lamp on the dial requires the external 12V power; it can be replaced by a white/blue tinged LED for better illumination and cool lighting. Many have trouble finding the correct impedance match and tend to get arcing in the capacitor plates; some have even managed to burn the shorting bar on the roller coaster inductor..hi..hi.. Because on more than one setting of the inductor, and the tuning and the loading capacitors, you may find "dips" on the meter; but only one position will be the correct one when most of the power is getting coupled to the antenna via the feeder with minimum loss in the inductor. The arrangement dictates minimum inductance to the ground and maximum capacitance in series with the antenna. The accompanying manual will instruct how to proceed initially and to find out how to optimize the settings for various bands. One can simply start by setting up with a high level of static noise on reception before even putting any power from the radio. One can find a simple explanation of the working of the T tuner on the project by VK5AJL. De VU2RZA
I did exactly this some time ago as well. I terminated the output with different impedances and looked at the effect of all the controls on the S11 measurement. It was really cool to see the L and C component moving the impedance on their respective circles of the Smith chart.
This was a very good aid informational video. Thank you. I just bought an older unit of the same type. The face of mine is grey. I haven't used it yet but will soon. I like the idea of a roller inductor.
I have an MFj-969 in regular use with an Icom IC-7100 (100 W). I like the bypass function as my antenna is fully resonant on some bands. The meter lamp burned out and there was no replacement available from our MFJ dealer, so I replaced it with a white LED + resistor. The shorting tab on the coil has evaporated, however the tuner works OK. HNY DE SV1XV
With all of the lab grade test gear you have it'll be interesting to see how accurate these simple power and SWR meters are. I'm looking forward to your whole video series with this tuner.
How accurate do they have to be? Ur just using capacitance and inductance to match the transceiver to an antenna... usually looking for nulls an peaks.
I'm looking forward to the deeper dive! Your videos are far superior to any of the electronics classes I had in high school or college, and dead simple to understand.
I have an older MFJ tuner from the early 1980s that is rated for a kW. Similar design but older with larger components and uses a rubber band to drive the turns counter. Only problem with is was that the band gave out and finding a new band was kind of challenging. Have used it with a variety of antennas and it works well with my old TS-830s.
This is a great idea for a video series,... and that from a dude who is never satisfied! Looking forward to seeing how well this thing works. cheers dan
When I got mine, that flippy-doo looked like it had arced against the inductor and made a rough spot in it. I removed the flippy-doo and cleaned up the rough spot on the inductor, and it seems to work fine that way. Iunno. :O
I love your videos. They are an inspiration and education for a hobbyist such as me. But please oil you chair with oil or silicone spray before the new year. Best wishes to you and your family for next year. Oh, I have a MFJ 948 combined with a artificial tuner. Love them both.
The roller inductors... as new parts (if you can get them) are really expensive. Hams did ... at one time make them. The coil is supposed to be silver wire, or tubing... but, not for a long time... and since the Hunt brothers drove up the price of silver.... more like silver plated copper wire, or tubing. Anyway, silver is the best conductor... and it would be interesting to know the minimum plating thickness, for the max freq. used, given the max resistance required?
My MFJ 941 also has a dummy load both sides....tuner and by pass. Nobody has been able to tell me why it has the dummy load also on the tuner side.....any ideas anybody.
They are using a transformer to couple the signal to the peak detector (diode, resistor, capacitor) and then the high input impedance, and low output impedance of a 2N3904 in a common collector configuration... to drive the meter... so that the meter doesn't load the capacitor of the peak detector circuit. (a kind of voltage to current converter) The 9V is for powering the transistor.
Hello, Congratulations ! I am a beginner in mobile CB. I have just finalized my mobile CB registration with a DX27 helical antenna (1m80) + MC KINLEY+ KL-203P. So I have a beginner's question for you.👇 You must start by configuring (tuning) your antenna in "Tune" mode ('Tune' button activated) to lower the TOS/SWR, do we agree? Then, when the antenna is tuned with the MC KINLEY Tx linear amplifier, I can return to "ByPass" mode (BPS) and use (modulate to AM/FM/SSB) my CB radio? Sincerely
I have the exact same device. My main use for it so far has been to adapt the impedance between a 27MHz oscillator+power amp to a RF plasma enclosure. It worked well for that purpose. Nice plasma generated with various gases. :)
would you be willing to do an experiment for me and others to seen what a out of the box icom 7300 looks like on a spectrum analyzer then mars mod it and see if any alignment is necessary after the mars mod is done me others on fb have a discussion going because they think it wont but i think it will
This will be an interesting series. My Elecraft T-1 tuner just died so I will have to go back to one of my MFJ cross-needle ones (one for HF, one for Six). I own a lot of MFJ gear and never had trouble with any of it. Snobby hams give it a bad rap, but it works for years just like my Elecraft gear. Less sophisticated for sure but great value (not that Elecraft isn't too).
MFJ = "Mighty Fine Junk" - all of these I've seen and many of their other products have either bad solder joints or rivets used as electrical connections that are not electrically connected 😅
I have a transceiver, two analyzers, two tuners, two beams and many accessories and NEVER had ANY issues with any of it, 'Junk' is a myth. I HAVE had trouble with Elecraft. @@ejholden8851
Hi, happy new year; let me add few points here.
As you said, it is T configuration high pass filter; it doesn't mean that this will pass all the ham band frequencies above the resonant one.
The shorting bar, as the name implies, is to short out the excess windings when you want to work on the higher end of the HF spectrum.
Coming to the SWR/Power meter circuits, the coupler is the regular Bruene bridge on the rear pcb. The metering pcb is found on the front. That is the usual practice. MFJ has not done any shielding to both pcbs. That really is not the correct practice. It is always better to shield even for qrp power levels.
The circuit has to be redrawn as you have done already. In the standard literature like the ARRL handbook, it is a regular practice to draw both circuitry separately with mention about the screening (with good grounding)
The 50 ohm dummy load can be connected to the radio to check the built-in power meter on the radio.
The SWR/Power meter can be arranged to be terminated into the dummy load (before hooking it to the antenna) for calibration assessment.
Yes, antennas like long wire and twin lead fed systems can be tuned (to within reasonable impedances). Remember that it uses a 1:4 Ruthrof voltage BalUn for the twin lead feeder systems; it is not to match the characteristic impedance of the twin lead feeder but only for the purpose of extending the limits of impedances (higher than) that can be handled without a 1:4 voltage step up transformer. Essentially it is a compromise and is not a "genuine" tuner meant to be fed to a twin lead feed antennas.
Of course, the twin needle or cross needle analog (D' Arsenval moving coil meter is a useful, attractive feature where one can asses the forward power and reflected power simultaneously. The SWR is read against the marking on the dial where both needles intersect during operation.
The PEP function requires power from the 9V battery for the comparator circuit that would charge an appropriate value capacitor for the power range and hold the needle on the dial before getting discharged.
The dial incandescent lamp on the dial requires the external 12V power; it can be replaced by a white/blue tinged LED for better illumination and cool lighting.
Many have trouble finding the correct impedance match and tend to get arcing in the capacitor plates; some have even managed to burn the shorting bar on the roller coaster inductor..hi..hi..
Because on more than one setting of the inductor, and the tuning and the loading capacitors, you may find "dips" on the meter; but only one position will be the correct one when most of the power is getting coupled to the antenna via the feeder with minimum loss in the inductor.
The arrangement dictates minimum inductance to the ground and maximum capacitance in series with the antenna.
The accompanying manual will instruct how to proceed initially and to find out how to optimize the settings for various bands.
One can simply start by setting up with a high level of static noise on reception before even putting any power from the radio.
One can find a simple explanation of the working of the T tuner on the project by VK5AJL.
De VU2RZA
I did exactly this some time ago as well.
I terminated the output with different impedances and looked at the effect of all the controls on the S11 measurement.
It was really cool to see the L and C component moving the impedance on their respective circles of the Smith chart.
This was a very good aid informational video. Thank you. I just bought an older unit of the same type. The face of mine is grey. I haven't used it yet but will soon. I like the idea of a roller inductor.
That is a very good tuner. MFJ does make great equipment.
I have an MFj-969 in regular use with an Icom IC-7100 (100 W). I like the bypass function as my antenna is fully resonant on some bands. The meter lamp burned out and there was no replacement available from our MFJ dealer, so I replaced it with a white LED + resistor. The shorting tab on the coil has evaporated, however the tuner works OK. HNY DE SV1XV
With all of the lab grade test gear you have it'll be interesting to see how accurate these simple power and SWR meters are. I'm looking forward to your whole video series with this tuner.
How accurate do they have to be? Ur just using capacitance and inductance to match the transceiver to an antenna... usually looking for nulls an peaks.
I'm looking forward to the deeper dive! Your videos are far superior to any of the electronics classes I had in high school or college, and dead simple to understand.
Happy New Year, always interesting content! Looking forward to more!!
I have an older MFJ tuner from the early 1980s that is rated for a kW. Similar design but older with larger components and uses a rubber band to drive the turns counter. Only problem with is was that the band gave out and finding a new band was kind of challenging. Have used it with a variety of antennas and it works well with my old TS-830s.
Ya, I've got a similar tuner driving a ladder line ...and a 830s ... I prefer that setup over the more modern radios I have.
Best wishes for the New Year!
I have one. You got a great deal! Great tuner, but (as usual with MFJ), you should check all internal solder connections.
I've a Palstar AT2KD & it had a missing solder connection on the main SO239.
This is a great idea for a video series,... and that from a dude who is never satisfied!
Looking forward to seeing how well this thing works.
cheers dan
When I got mine, that flippy-doo looked like it had arced against the inductor and made a rough spot in it. I removed the flippy-doo and cleaned up the rough spot on the inductor, and it seems to work fine that way. Iunno. :O
i had one of them guy that gave it to be must have tried to run 1KW it was roached..
Two and a half hours before midnight at my place, so, happy new year, sir.
I love your videos. They are an inspiration and education for a hobbyist such as me. But please oil you chair with oil or silicone spray before the new year. Best wishes to you and your family for next year. Oh, I have a MFJ 948 combined with a artificial tuner. Love them both.
I've tried twice before, I'll try and locate the qweek again.
The roller inductors... as new parts (if you can get them) are really expensive. Hams did ... at one time make them. The coil is supposed to be silver wire, or tubing... but, not for a long time... and since the Hunt brothers drove up the price of silver.... more like silver plated copper wire, or tubing. Anyway, silver is the best conductor... and it would be interesting to know the minimum plating thickness, for the max freq. used, given the max resistance required?
Great topic, should make an interesting series
Happy New Year
Would have liked to see this unit in action.
What I see is that there is no isolation. Need a plate to isolate electronics and RF. The varicaps are way too exposed to the low signal measuring.
Thanks 👍
I have the ability to get one of these from my local electronics surplus store! I might get it!
Brand new they are about 350 or so
Why don't we normally use antenna tuners with frequencies higher than HF, such as 2 meters, 70cm, etc.? I've always wondered about that.
because the small size allows us to make correct length antennas and they are usually only one or two bands.
I have a Six-meter band tuner from MFJ. It's a pretty wide band. And getting it right is important up there!
My MFJ 941 also has a dummy load both sides....tuner and by pass.
Nobody has been able to tell me why it has the dummy load also on the tuner side.....any ideas anybody.
Thanks for the new information, but unfortunately I won't try this because I don't have any of the components 🙂
All the best in the new year 🙂 Tom
So, what is the battery doing ? Is it for the peak reading function ?
It's for the meter circuitry. The match circuitry is purely passive, in those units.
They are using a transformer to couple the signal to the peak detector (diode, resistor, capacitor) and then the high input impedance, and low output impedance of a 2N3904 in a common collector configuration... to drive the meter... so that the meter doesn't load the capacitor of the peak detector circuit. (a kind of voltage to current converter) The 9V is for powering the transistor.
Hello, Congratulations !
I am a beginner in mobile CB. I have just finalized my mobile CB registration with a DX27 helical antenna (1m80) + MC KINLEY+ KL-203P.
So I have a beginner's question for you.👇
You must start by configuring (tuning) your antenna in "Tune" mode ('Tune' button activated) to lower the TOS/SWR, do we agree?
Then, when the antenna is tuned with the MC KINLEY Tx linear amplifier, I can return to "ByPass" mode (BPS) and use (modulate to AM/FM/SSB) my CB radio?
Sincerely
Is that IMSAI 8080 a replica or an original?
ua-cam.com/video/DLFIBQ1WlmU/v-deo.htmlsi=dFbyZob3gm2siB2s
I have the exact same device. My main use for it so far has been to adapt the impedance between a 27MHz oscillator+power amp to a RF plasma enclosure. It worked well for that purpose. Nice plasma generated with various gases. :)
would you be willing to do an experiment for me and others to seen what a out of the box icom 7300 looks like on a spectrum analyzer then mars mod it and see if any alignment is necessary after the mars mod is done me others on fb have a discussion going because they think it wont but i think it will
sorry, no. Unless someone gives me another 7300 to hack.
This will be an interesting series. My Elecraft T-1 tuner just died so I will have to go back to one of my MFJ cross-needle ones (one for HF, one for Six). I own a lot of MFJ gear and never had trouble with any of it. Snobby hams give it a bad rap, but it works for years just like my Elecraft gear. Less sophisticated for sure but great value (not that Elecraft isn't too).
MFJ = messed up, almost always.
MFJ = "Mighty Fine Junk" - all of these I've seen and many of their other products have either bad solder joints or rivets used as electrical connections that are not electrically connected 😅
I have a transceiver, two analyzers, two tuners, two beams and many accessories and NEVER had ANY issues with any of it, 'Junk' is a myth. I HAVE had trouble with Elecraft. @@ejholden8851