in this case gate capacitance is not the issue as 2xBS170 parallel and one FDT86256 has almost equal capacitance.?
I'm not sure you're comparing like with like. The capacitances of the FDT86256 are quoted at vDS = 75 V, whereas those in the BS170 datasheet are quoted at vDS = 10 V. Everything in these devices is a curve and when it comes to capacitances, they are higher at lower voltages.? ? The problem is gate driving voltage is low.
Anyway - yes, I think this is probably the main issue, yes... typical threshold voltage for a BS170 is 2.1 V but for a FDT86256 it is 3.5 V. Which means 5V isn't enough to allow sufficient drain current to get full power output. The capacitances make this all worse at higher frequencies.
A great misunderstanding about these inexpensive MOSFETs like BS170 or IRF510 is that they are switches. And that somehow by some magic, an expensive "real RF amplifier MOSFET" like a Mitsubishi?RD16HHF1 is somehow a more linear type of amplifier. Mostly marketing spin. Look at the transfer characteristics for each, and you'll see what I mean.?
The MOSFET is only like a "switch" if it is driven by a sufficiently large and square drive signal. The "threshold" voltage is not the voltage at which a MOSFET switches on. The drive signal gets less and less square as the frequency goes up due to the gate capacitance so everything gets worse, this is why high frequency bands tend to produce lower output. A higher level squarewave drive helps to counteract this, hence the improvement with 6V supply to the driver.
73 Hans G0UPL
?
?
--
?
73, Barb
|
Last Minute Change CW Practice / Rag Chew 15:00 EDT 19:00Z
SORRY,
Life got in the way. I had to change the time. It is now 15:00 EDT
/ 19:00 UTC
Ed
AB8DF
On 4/9/2025 11:39 AM, AB8DF Ed Kwik via
groups.io wrote:
On 4/08/25 I had a CW practice / rag chew
session on 30 meters. I worked three stations:
| Date
/ Time |
Call |
Bnd |
Frequency |
Mode |
Power |
Rec |
Snt |
Name |
SPC# |
Comments |
Off |
| 4/8/2025
14:14 |
W9TO |
30 |
10.111 |
CW |
50 |
559 |
559 |
Tom |
OH |
K3
at 50 watts 100 ft sloper doublet |
14:28 |
| 4/8/2025
13:44 |
KC9HEK |
30 |
10.112 |
CW |
60 |
599 |
569 |
Brian |
NY |
K3
at 60 watts 100 ft sloper doublet |
14:04 |
| 4/8/2025
12:54 |
NM1I |
30 |
10.109 |
CW |
50 |
579 |
559 |
Butch |
MA |
K3
at 50 watts 100 ft sloper doublet |
13:37 |
Conditions
were OK. 30 meters seemed to be better than what I
have been experiencing on 20 . SSN = 167, SFI = 162, A
= 13, K = 2.
My next CW practice session will be April
11 at 09:00 EDT / 13:00 UTC on 30 meters.?Anyone
and everyone is welcome. This practice is intended
for operators who are new to CW or they need some
practice. IT DOES NOT MATTER HOW POOR YOUR CW IS.
Mistakes are OK. Poor fists are OK. Slow speed is
OK. Really slow speed is OK. This practice is
meant for you to improve your CW. I will do my
best to adjust to your skill level. Operate at any
power level. If several stations show up, I will
operate as a round-table control station. I will
do it as a round-table so everyone gets a chance
to transmit. Please listen to my directions.
Details:
Date - April 11 2025
Time - 09:00 EDT ?13:00 UTC
Band - 30 Meters
How to find me - I will find a clear frequency and
call CQ. Go to the Reverse Beacon Network and
search for my call sign AB8DF.
That
will tell you what frequency I am on. Tune your
station to that frequency and if you hear me give
me a call. If there is a QSO in progress, please
wait for a break in the action. Then send your
callsign. If I hear you, I will invite you to join
the QSO and start a round-table QSO.
Reply to this email if you have questions.
IT DOES NOT MATTER HOW POOR CW IS
Ed
AB8DF
|
Brent,
?
in this case gate capacitance is not the issue as 2xBS170 parallel and one FDT86256 has almost equal capacitance.?
The problem is gate driving voltage is low.
?
--
?
73, Barb
|
Barb,
?
Read the 7806 datasheet, you definitely need a cap at the output to ground.
You may already have the required cap for the input pin close enough, but also check that.
?
Jerry
?
On Sat, Apr 12, 2025 at 07:55 AM, Barb WB2CBA wrote:
I got couple of emails how to power 7408 with 6V in QMX+.?
This is how I modified mine, lift pin 14 of 7408 from pcb carefully. Add a 7806 voltage regulator to 12V input and connect lifted up pin14 to that 6V regulator. That’s all. This will improve your high bands dramatically.
|
Gate capacitance usually limits performance at HF.
--
Brent DeWitt, AB1LF
Milford, MA
|
Thanks Barb !
--
73 ChuckR
|
Re: Winlink and VARA HF setup for QMX
Please search the prior messages in this group for "Winlink" or "VARA".
The QMX details for setting up these modes has been recently described.
But they won't help you understand how to use Winlink/VARA - for that, you need to go to a winlink-related site and ask, or google some youtube videos.
|
Re: Help with partially fried QMX
On Fri, Apr 11, 2025 at 06:28 PM, Austin K4HYD wrote:
the device still powers on immediately upon being connected to power,
You need to fix this first, before worrying about anything else.
And yes, please continue to use the low voltage until you get it booted up successfully.? You only need higher voltage/higher current to transmit; all normal cpu and receive functions will work at 7V and 250mA.
?
Since you see this with the display/control panel removed, it is a fault on in your SMPS or on the main board, not the switches.
The things that can cause this are:
1) The PWR_ON signal is shorted low.? Either on the main board, or on the 5V SMPS connector, or in the interconnect.? Note that PWR_ON and PWM_5V are adjacent pins in the connector, so if PWR_ON is shorted to PWM_5V, this would happen.?
2) The PWR_HOLD signal is held high, shorted to some signal that goes high when power is plugged in.? One place this can happen is in the interconnect, the PWR_HOLD signal is adjacent to the VIN voltage in the connector.
3) VIN shorted to +12V.
4) Less likely, but multiple input component failures on the input part of the 5V SMPS.
?
You can debug a lot of this with a multimeter.
Perhaps the easiest place to start is to remove and test the two SMPS boards independently, as described in the wiki here:
And while removed, measure (on the main board) the resistance between all of the pins of the power connectors.? They should all show at least a few k-ohms to ground, and to each other.? If they don't, there is a fault on the main board that needs fixed.
?
Good luck, Stan KC7XE
|
Re: Help with partially fried QMX
Hello Austin,
?
you may test the two SMPS boards off line (see QMX QMX_Plus Power supply test Process ). Immediately switch on could be caused by a failure between "V_IN" and "+12V" on Plug-in PCB #1 (see schematics page 1). ?
If the two SMPS boards are removed please check resistance to GND for all the lines to the SMPS. A failure here could also switch on the QMX without pressing the encoder
?
Reading QMX QMX_plus Startup you will find a description of the start process, which signal should show which level at which step of switch on. There is also a link to a sketch to identify the signals at the mainboard. ?
Please let us know your results.
?
73 Ludwig
|
Will QRP Labs be seller the QMX+ kit at FDIM and Hamvention? Looking to acquire the following:
?
- QMX+ 160-6m, 5W multi-mode transceiver ??
Assembled or Kit: Kit
Optional Enclosure: Including enclosure
Add kits: QLG3 GPS/GNSS Receiver
Add kits: 2.1mm power plug
?
Joe N7QPP
?
?
|
Re: Here's hoping for QMX+ v2
But, if the CAT had a command to simulate the pressing of the four UI buttons and the turning of the two UI encoders, then the serial interface could drive the radio anywhere the front panel could go,?except perhaps for powering on.? ?But it wouldn't know where it was without the contents of the LCD panel, so CAT would also need to be able to pull those updates.? Note that this would open up a lot of automated testing possibilities that you don't currently have.? Like reading the bar graph?off the LCD and seeing if it agrees with the signal or mismatch presented to the RF input jack.
Ok got it, thanks Jack. All noted
73 Hans G0UPL
|
Re: Here's hoping for QMX+ v2
It says 5V @ 2A, which is much higher, but a lot more performance, too.
Jack, W8TEE
On Saturday, April 12, 2025 at 11:04:54 AM EDT, Peter LaRue via groups.io <peter.f.larue@...> wrote:
Jack,
Unlike the original Pi Zero, the Pi Zero 2W has a quad-core 64-bit ARM Cortex-A53 processor clocked at 1GHz, still for only 15 USD.? According to the marketing material, this makes it up to 5 times as fast as the original Pi Zero.
I have not done any measurements of electrical power consumption to compare the two models.
Peter LaRue
AI7YN
|
How to turn QMX-Hi into QMX-LOW band?
#qmx
Hi dear All,
I have a _not assembled_ QMX-HI kit (20, 17, 15, 12, 11 and 10m) version .
I changed my mind, I decided to build a QMX-LOW (80, 60, 40, 30 and 20m) version.?
For this purpose, will it be enough for me to buy aditionally the set of band-specific parts for the QMX low-band option (80-20m, product Code: QMXLOW)? It includes all capacitors, all powdered iron toroids, wire, and ferrites (binocular cores and toroids).
Are the QMX board and board-mounted SMD components the same for all versions?
?
Thanks in advance for your advice and recommendations,
Wlado?
73
|
Re: Here's hoping for QMX+ v2
Jack,
Unlike the original Pi Zero, the Pi Zero 2W has a quad-core 64-bit ARM Cortex-A53 processor clocked at 1GHz, still for only 15 USD. According to the marketing material, this makes it up to 5 times as fast as the original Pi Zero.
I have not done any measurements of electrical power consumption to compare the two models.
Peter LaRue
AI7YN
|
I got couple of emails how to power 7408 with 6V in QMX+.?
This is how I modified mine, lift pin 14 of 7408 from pcb carefully. Add a 7806 voltage regulator to 12V input and connect lifted up pin14 to that 6V regulator. That’s all. This will improve your high bands dramatically.
?
--
?
73, Barb
|
Re: Help with partially fried QMX
Hi Bruce,
I've verified that there is an air gap between the dc jack and encoder. I will put some electrical tape on the back of the DC jack to be safe.
I also did some additional testing and observed that the device still powers on immediately with draw when the LCD board and controls board are removed. Checked again for any solder bridges or solder flakes and was unable to see anything overtly wrong.
|
Re: Help with partially fried QMX
Could the body of the left encoder be shorting the DC jack?? You could put tape or thin plastic between them.
|
Chuck,
?
This ham is selling on Tindie:
?
?
?
--
?
73, Barb
|
That should have stated POWER MOD BOARD!
--
73 ChuckR
|
Hi all, is the circuit board availble to purchase and where to order? This would possibly solve a problem with my starion setup.
--
73 ChuckR
|
Barb WB2CBA
Brent DeWitt
jjpurdum