I bought one Chinese antenna tuner and soon found out that I could not install the variable capacitors and their knobs. But in my collection of ancient radio parts I found suitable ersatz.? So I built the circuit and found that losses were quite high. Using a toroid from Amidon improved things. Then I decided to change the circuit from T to L with a series inductance because I do not like that small parallel inductance of the T-network. So the only things that remained from the original tuner were the pretty case and the SWR meter which I supplemented with a moving coil meter to make it more sensitive and usable in bright sunlight.

The 500pF variable capacitor C1 in series with the coil compensates an adjustable part of the coil inductance. So the inductance is not limited to 12 discrete values. When tuning for lowest SWR one begins with C1=500pF.

Greetings all,

?

I've no wish to stir up the debate about which supply voltage QDXs should be built for, but in reading the manual, I saw where it says that the power slider in WSJT-X has no effect on the QDX and that any RF output reduction should be accomplished by lowering the supply voltage. So...

?

1) For those who have done the 12V build and adjust the supply voltage to change the RF output, what problems (if any) have you had?

?

2) Is the QDX tolerant of supply voltage change while powered up or do I need to turn it off before I make a change?

?

An example of why I would want to reduce the RF output is that I normally run ~1W when operating as a WSPR beacon, yet I usually operate FT8 at 2.5-3W, sometimes going up to 5W.

?

I appreciate the information!

?

Charles Johnson

KF4AYT

I am not sure I understand what you are reporting.? When you say the VSWR meter doesn't budge, do you mean when in setting the forward power mode??

It also helps to know the firmware installed on the QDX.? You can get this using the terminal program on the startup page or reading the file names when the QDX is in update mode.

It would help if you could tell us what the input to the QDX current readings are on receive and transmit.?

I suggest you have a dummy load connected to your QDX when doing any testing, as it is easy to damage the BS170 MOSFET finals.

Since PSKReporter has spotted you, you are putting out some power.

73
Evan
AC9TU

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That's not USB over Ethernet, it's USB over TIA-568 (CAT-{5,6,7}) _cable_

I have the QDX from last December (rev 2 I think?).? Somehow I managed to show up on PSK reporter for the nearest monitoring stations on my first try, but nobody was responding to my CQ or acknowledging my replies.? Hooked it up to a VSWR meter and the needle doesn't budge when I hit the 'tune' button in wsjtx, tested in both 20m and 40m.? Receive seems to work fine, I'm decoding ft8 just fine, but all I can do is listen.? Any recommendations for where to start with troubleshooting??

Tim,

Your doing great.

When I built my 50w amp I needed help with the troubleshooting before initial startup. Mistakes are expensive both in terms of time and replacement parts.

I found a great Youtube video for troubleshooting the 50w amp. What I found were simple mistakes that I repeatedly overlooked. Sometimes it takes a second set of eyes. Not having more than two, I switched gears and approached from another perspective. I found a very nice youtube video by NA5Y for troubleshooting or as in my case just making the final check before first power-up, which is what I did. It was a good thing I did to. I found several simple mistakes I made as a result of watching the video and following the tutorial. I don't know if the mistakes would have been catastrophic or not. What I did learn is to approach the challenge from a different perspective than what I was already doing. The video goes through a methodical approach with excellent explanations along the way so that I learned something in the process.?

I believe you will appreciate this video:?

--
KE4LJH
Steve,?
Florida

I believe the early version of QDX used a different chip. When it became unavailable
because of world wide shortages, Hans had to change to a higher current substitute.
The QDX today draws about 140ma on RX, plus or minus 10ma.

Don

Looks like there are USB-over-ethernet devices that do this:??
You could add Wifi on both sides but that starts to get a bit messy.

73, Mike KK7ER

?

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Hi Chris,

How about this one:

?

Just a simple search got this result.? Did the .fake site generate enough for this plus shipping?

Nah, not really.

I thought, it be the kind of gimmick we techno-nerds like, but anyhow, I had some fun fiddling with the undocumented API.

... but of course you are still free to contribute, we need to keep Hans spirits high to continue to get good kits & upgrades from him ... ?? - Here you go again, if you like:

Vy 73

Stefan.

-- 
Stefan U. Hegner    <db4st@...>
              * * *
DB4ST --- German Ham Radio Station
D-32584 L?hne ----- Locator JO42IE 
              * * *
GPG-Key | C3CC 23A4 FBA8 622B 48AE
F-Print | 4F19 D0EE E39E ABDC 2BCE

The QDX requires a specific "driver(s)".? There just isn't any direct Bluetooth interface (that I know of) with this kind of driver option
In order to avoid a driver, you would need to directly stream the USB data over Bluetooth.?
?? A USB-B streaming to Bluetooth device (didn't find any) 'could' provide exact USB stream at the other end of the Bluetooth connection,
????? and the driver could be on that second computer.
?? I just haven't seen any device like that.? All Bluetooth dongles are USB-A and have a specific driver themselves.
NOTE: there are audio to Bluetooth device, and serial (CAT) to Bluetooth devices, but with the QDX, both of these are on one USB stream
??????????? and the driver MUST separate them into 2 devices that the computer understands.

That forces you to connect the QDX directly to a computer (Single Board Computer like a Pi works).
At that point, it is probably better to use WiFi rather than Bluetooth.? Most SBC (including Pi Zero W) can be easily setup as a "WiFi HotSpot".
Using a SBC using WiFi options:
1.? With VNC on the SBC, the application run on the SBC, "right at the QDX".
???? No need to transfer the audio and CAT information back and forth to your location - with any issues that could cause.
2.? I am sure there are tools for audio and CAT over TCP/IP - if preferred
--
Rob KB8RCO

Thanks Hans,
not when VNCing to a headless Raspi. :(. Tried it via a direct connection to a laptop and it does as you say. Guess I will have to find how to do ‘sticky keys’ via VNC link :).
73 Ken g4apb?

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Don't confuse the DC input with the power dissipated in the finals. ?Power goes elsewhere, and (hopefully) a large fraction of that power goes out to the antenna (and does not come back).

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Strangely enough, just ran across this picture of my Decwriter II (300 baud! ?30 characters per second!) that was hooked up to my S-100 machine running CP/M. ?Had one in high school that was a _serious_ upgrade from the KSR-33 teletypes (thought the teletypes had paper tape read/write mechanisms, so you could punch 5x7 alpha letters on tape with the appropriate program), and when I had the chance to buy one for my home computer, I jumped at it. ?8*) ?Just to be topical, you could hit <CR> on that or the VT-220 or VT-240 and it would be the console.

Hi all,

The outcome of my tests with the QDX connected to the 50W class C PA (for FT-8) is as follows:
- QDX with T1 3:2, operated at +10V DC
- 50W PA operated at +18V DC
- direct BNC 50 Ohm connection from QDX output to the PA input
- direct 3.5mm PTT cable connection between them

I get approximately 20W output power into a 50 Ohm D.L. on 20m without overheating of either equipment.
I had to improve the QDX PTT +5V output line for that to work well:
- 100R 0604 parallel to R10 470R,
- 1k from Q12 drain to GND.
This was necessary to come closer to the QCX PTT like output.

With +18V DC the PA I.L. at RX (PTT = 0V) is at 0.4 dB on 20m, which is easily overcome by a QDX great sensibility.
I am quite happy with what I got.

73 Bojan S53DZ

On Fri, Aug 12, 2022 at 02:23 AM, Donald S Brant Jr wrote:

Andy: I am with you 100% on Anritsu menus!
73, Don N2VGU?

HP stuff was always my favourite.
They seemed to have a habit of collecting around my workbench.
At least the boss always knew where to come if he needed one ;-)
?
--
- 73 de Andy -

Hello all,

I'm curious about the general consensus for setting receive audio levels on the QDX. I've been using WSJT-X mainly in FT8 and FT4 with an occasional check in WSPR. I like the fact that QDX doesn't have AGC so that really strong signals won't squash weaker ones.?

IIRC, receive levels in WSJT-X should be set so the level indicator is ~30 dB or so. But, under what band conditions does this apply?
When the band is busy the level indicator can start hovering around 60 dB or so.

An aspect of this is the wide graph's "Zero" levels for waterfall. I'm used to seeing a light blue in the waterfall (using the default color scheme) as the zero point but on some bands it's black and no amount of slider adjustment will bring it up. It seems like if you find a happy medium in FT8 and then switch over to WSPR, which almost always is going to have less activity, you have to switch over to terminal mode to bring audio levels up.

Thanks!

--Al
WD4AH

One key point to remember is that the manufacturers spec sheet doesn't
quite tell the truth in reality because to save their butts they deliberately
underspec the ratings.

I can prove that by saying that I have been running a bunch of QRP Labs
beacon transmitters for some 10 years now, all using BS170's.

The longest unbroken period of 100% duty cycle operation is probably about
5 years.

Now then, in that time I have fed something like 2.4 watts DC input, obviously
more than the? 0.85 watts specification.

Remember once again that is continuous operation for at least 5 years non stop,
and PROVES that spec sheet is very conservative.

But I do ensure that the antenna is pre-matched before transmitting.

That is vital, because as I have found out, if I run them into something like an
SWR of 2.5 for example then they start failing.

So the answer to the question falls upon the end user to do what any sensible
person would do, use a properly matched antenna, and as engineers have known
for almost 100 years now, you don't take take liberties with components.

It's not like we haven't had the? time to discover this stuff ;-)

- 73 de Andy -

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