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Hello again folks:
Just finished the build of my new QM (Rev3 - latest -017 firmware).
Measured the following RF Output Watts during basic, short, transmit-tune checks ( and some real, live on-air testing on 20M that closely matched).
20M? ? ?3.76
17M? ? ?5.46??
15M? ? ?2.39
12M? ? ?3.69
10M? ? ?4.23
I think I've seen and read about folks adjusting LPF inductor winding spacings to tweak the final output RF.
Thought I'd ask for pointers in the right direction(s) . . .? ?:)
I think I'd like to get all 5 bands at about 4 Watts out.?
I think that would be a good target for working FT8, J8Call, and WSPR without frying the QMX finals and I can easily work even smaller level QRP with a capable, adjustable attenuator of modest cost since it would only need to tolerate 4 Watts or so (Hello Elecraft ?)? Perhaps I need only figure out how to tweak 17M down a bit and 15M up a bit?
Thanks in advance,
Greg? KI4NVX?
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Hi Greg,
Here is what I would do:
1) check all the caps in the lpf section - make sure you installed the correct values in the right places.
2) double check the turns on each toroid
3) if all above is good, I adjust each band¡¯s set of toroids. ?I use a small plastic tipped tuning tool. ?(A pointy end of a bamboo skewer works also). ?I don¡¯t use metal.
here is what I do for each band:
identify the two toroids that are configured in the lpf band configuration (in the terminal program). ?Before making an adjustment, note the power out. ?Start by reducing the spacing of one toroid, check power, it if increases, keep squeezing turns until it doesn¡¯t help more. ?If all turns are tightly squeezed together, you may want to rewind that one with one more turn and try again. If squeezing turns decrease power, then try to increase separating the distance between each turn and keep separating turns until no improvement. ?Do one toroid at a time
then do the same thing for the second toroid for that band.
its easy to identify which toroids go with each band. ?The default band config for a hi band unit is 0, 1, 1, 2, 2, 2. ?There are only three low pass filters for 6 bands. ?So there is sharing. ?0 is the lowest frequency lpf. Those toroids have the most turns. ?1 is the middle lpf. ?2 is the highest frequency lpf. ?It has the least turns.
good luck,
Jeff
W1NC
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Thank you Jeff.
I appreciate the info. Tomorrow I plan to get familiar with the Terminal programs and will double check the powers out against an Elecraft dummy load for consistency against the QRP-Guys meter.
If similar enough I'll then start on windings adjustments as you suggest.
Greg
On Mon, Mar 11, 2024 at 6:59 PM, Jeffrey W Moore via groups.io <jeffreymoore@...> wrote: Hi Greg,
Here is what I would do:
1) check all the caps in the lpf section - make sure you installed the correct values in the right places.
2) double check the turns on each toroid
3) if all above is good, I adjust each band¡¯s set of toroids. ?I use a small plastic tipped tuning tool. ?(A pointy end of a bamboo skewer works also). ?I don¡¯t use metal.
here is what I do for each band:
identify the two toroids that are configured in the lpf band configuration (in the terminal program). ?Before making an adjustment, note the power out. ?Start by reducing the spacing of one toroid, check power, it if increases, keep squeezing turns until it doesn¡¯t help more. ?If all turns are tightly squeezed together, you may want to rewind that one with one more turn and try again. If squeezing turns decrease power, then try to increase separating the distance between each turn and keep separating turns until no improvement. ?Do one toroid at a time
then do the same thing for the second toroid for that band.
its easy to identify which toroids go with each band. ?The default band config for a hi band unit is 0, 1, 1, 2, 2, 2. ?There are only three low pass filters for 6 bands. ?So there is sharing. ?0 is the lowest frequency lpf. Those toroids have the most turns. ?1 is the middle lpf. ?2 is the highest frequency lpf. ?It has the least turns.
good luck,
Jeff
W1NC
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The main LPF function is to cut 1st and subsequential harmonics while maintaining as low as possible losses on band in question.
So adjusting only for max power (lowest losses on the band) you can transmit harmonics above permitted level.
I am building QMX now but I would have a ques that connecting nanoVNA to LPF should give you better results and ensure that both power and harmonics are at optimal level. Saying than I am not sure if input impedance of LPF is close to 50ohm. Maybe someone can comment on that.
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73 de Marek SP9TKW
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Good point. I do have a VNA, but still learning how to use its many functions. I've only used mine so far for SWR antenna checks.
Am I correct that there is some, likely very small, maximum input RF a VNA can accept??
On Tue, Mar 12, 2024 at 5:40 AM, Marek SP9TKW <sp9tkw@...> wrote: The main LPF function is to cut 1st and subsequential harmonics while maintaining as low as possible losses on band in question.
So adjusting only for max power (lowest losses on the band) you can transmit harmonics above permitted level.
I am building QMX now but I would have a ques that connecting nanoVNA to LPF should give you better results and ensure that both power and harmonics are at optimal level. Saying than I am not sure if input impedance of LPF is close to 50ohm. Maybe someone can comment on that.
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73 de Marek SP9TKW
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On Tue, Mar 12, 2024 at 05:40 AM, Marek SP9TKW wrote:
The main LPF function is to cut 1st and subsequential harmonics
.....SECOND and subsequent harmonics... The "first" harmonic is the desired fundamental frequency. 73, Don N2VGU
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On Tue, Mar 12, 2024 at 09:51 AM, Greg McCain wrote:
Am I correct that there is some, likely very small, maximum input RF a VNA can accept??
There are power limits for VNA ports, which will vary by device.? This should be specified by the manufacturer/designer.?? I would suggest 0dBm as a reasonably safe upper limit.?? When measuring amplifiers I put an attenuator, of approximately the expected amplifier gain, ahead of the device to keep its output power approximately the same as the power from the analyzer, that is, a net gain of about 1 or 0dB. 73, Don N2VGU
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Many thanks. Makes good sense.?
I have a 20db broadband attenuator I purchased for another project. I'll check the measured decrease against the rated VNA specs before proceeding.??
On Tue, Mar 12, 2024 at 10:03 AM, Donald S Brant Jr <dsbrantjr@...> wrote: On Tue, Mar 12, 2024 at 09:51 AM, Greg McCain wrote:
Am I correct that there is some, likely very small, maximum input RF a VNA can accept??
There are power limits for VNA ports, which will vary by device.? This should be specified by the manufacturer/designer.?? I would suggest 0dBm as a reasonably safe upper limit.?? When measuring amplifiers I put an attenuator, of approximately the expected amplifier gain, ahead of the device to keep its output power approximately the same as the power from the analyzer, that is, a net gain of about 1 or 0dB. 73, Don N2VGU
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@ Donald yes you are right, I used wrong description.
As for nanoVNA, you do not put power through it. S11 (source) goes into Input side of nanaVNA and S21 into output (ANT?) end. You should see classic curve for LPF filter. QMX is not connected to the power at that stage.
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73 de Marek SP9TKW
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Marek,
When QMX is unpowered, the PIN diodes are all in a high resistance state. No particular LPF is selected. What would the VNA measure?
When QMX is powered on, an LPF can be selected, but the VNA is at risk of damage from an inadvertent transmission.
Am I?missing something here?
JZ KJ4A?
On Tue, Mar 12, 2024, 11:50?AM Marek SP9TKW < sp9tkw@...> wrote: @ Donald yes you are right, I used wrong description.
As for nanoVNA, you do not put power through it. S11 (source) goes into Input side of nanaVNA and S21 into output (ANT?) end. You should see classic curve for LPF filter. QMX is not connected to the power at that stage.
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73 de Marek SP9TKW
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Perhaps you intend to solder connections to the unpowered LPF you desire to test?
JZ
Marek,
When QMX is unpowered, the PIN diodes are all in a high resistance state. No particular LPF is selected. What would the VNA measure?
When QMX is powered on, an LPF can be selected, but the VNA is at risk of damage from an inadvertent transmission.
Am I?missing something here?
JZ KJ4A?
On Tue, Mar 12, 2024, 11:50?AM Marek SP9TKW < sp9tkw@...> wrote: @ Donald yes you are right, I used wrong description.
As for nanoVNA, you do not put power through it. S11 (source) goes into Input side of nanaVNA and S21 into output (ANT?) end. You should see classic curve for LPF filter. QMX is not connected to the power at that stage.
---------------------------------
73 de Marek SP9TKW
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John I think you are correct. I believe I would need a spectrum analyzer to correctly and safely measure the final output harmonics. Might invest in a TinySA.?
Greg
On Tue, Mar 12, 2024 at 12:02 PM, John Z <jdzbrozek@...> wrote: Marek,
When QMX is unpowered, the PIN diodes are all in a high resistance state. No particular LPF is selected. What would the VNA measure?
When QMX is powered on, an LPF can be selected, but the VNA is at risk of damage from an inadvertent transmission.
Am I?missing something here?
JZ KJ4A? On Tue, Mar 12, 2024, 11:50?AM Marek SP9TKW < sp9tkw@...> wrote: @ Donald yes you are right, I used wrong description.
As for nanoVNA, you do not put power through it. S11 (source) goes into Input side of nanaVNA and S21 into output (ANT?) end. You should see classic curve for LPF filter. QMX is not connected to the power at that stage.
---------------------------------
73 de Marek SP9TKW
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On Tue, Mar 12, 2024 at 12:37 PM, Greg McCain wrote:
Might invest in a TinySA.
I have a TinySA and it sits mostly unused since I got the TinySA Ultra.? Well worth the price increment in my opinion for the greatly increased performance and features.?? Also be aware that you will need to keep the total power input to the SA to a fairly low level, in the order of -20dBm or lower into the mixer, in order to avoid generating internal harmonics or intermodulation products.?? Check this by adding attenuation and noting whether the harmonic/intermod changes (improves).? if it improves it is internally-generated, add more attenuation until it doesn't. A step attenuator or good selection of fixed attenuators is almost essential.? I have surplus commercial stuff but the ones on AMZN or EBay seem to be pretty good.? The "6GHz" attenuators are outstanding at HF.? Watch your power levels, both instrument and attenuator. 73, Don N2VGU
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Hello again Jeff and the group.
Got Terminal mode 'smart' earlier today and ran LPF sweeps.? Saved the graphs.
Then tweaked the windings, one toroid at a time for the LPF 1 pair, which are for 17 and 15 Meter Bands.
Opening up the spacing on L508 (the upper one of the pair) to more closely match the provided picture in the instructions did not make a difference in the power output.? The tweaks here were very, very small.
Opening up the spacing on L 512,? DID the trick. My spacing is a bit more spread out than the provided picture, BUT now I have the following:
20? ? 3.94 17? ? 3.41 15? ? 3.43 12? ? 3.69 10? ? 3.85.
LPF sweeps of 17 and 15 meter bands show virtually identical graphs, with the footer intercepting the -30dB line a bit sooner for one and a bit later for the other. There is a bit of 'an 'up pip' (maybe 1dB) on 17 around? 40Mhz that wasn't there before but it is still way below -30dB.??
It will do just fine for how I expect to use my QMX.?
73, Greg? KI4NVX
Greg McCain gamccain50@...
On Monday, March 11, 2024 at 06:59:17 PM EDT, Jeffrey W Moore via groups.io <jeffreymoore@...> wrote:
Hi Greg,
Here is what I would do:
1) check all the caps in the lpf section - make sure you installed the correct values in the right places.
2) double check the turns on each toroid
3) if all above is good, I adjust each band¡¯s set of toroids. ?I use a small plastic tipped tuning tool. ?(A pointy end of a bamboo skewer works also). ?I don¡¯t use metal.
here is what I do for each band:
identify the two toroids that are configured in the lpf band configuration (in the terminal program). ?Before making an adjustment, note the power out. ?Start by reducing the spacing of one toroid, check power, it if increases, keep squeezing turns until it doesn¡¯t help more. ?If all turns are tightly squeezed together, you may want to rewind that one with one more turn and try again. If squeezing turns decrease power, then try to increase separating the distance between each turn and keep separating turns until no improvement. ?Do one toroid at a time
then do the same thing for the second toroid for that band.
its easy to identify which toroids go with each band. ?The default band config for a hi band unit is 0, 1, 1, 2, 2, 2. ?There are only three low pass filters for 6 bands. ?So there is sharing. ?0 is the lowest frequency lpf. Those toroids have the most turns. ?1 is the middle lpf. ?2 is the highest frequency lpf. ?It has the least turns.
good luck,
Jeff
W1NC
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Marek SP9TKW
Donald S Brant Jr