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Re: QCX+ RF Power #qcx

Al Sines
 

Hi Reg

Yeah I know that’s why it’s called obsessive compulsive DISORDER!🤣

73,  Alan W3AL. 


On Sep 13, 2020, at 14:24, R. Tyson via groups.io <tysons2@...> wrote:

Hi,

You are getting 4.5 watts output.... good.
You want to fiddle about to get another 0.5 watts so you have 5 watts.....  hmmmm.

Why ?  You would have to increase your 4.5 watts to 4 times that level i.e. to 18 watts in order to gain 1 S point on the other guys reception of you. Why be OCD about 0.5 watts ?

Reg           G4NFR


Re: QCX-mini update

R. Tyson
 

Now then... I think I know what is going on here.

Hans teaches junior ops. to hold a soldering iron as soon as possible. There is a problem with them always wanting to put things in their mouth to start with. They will quickly desist though.

Junior ops. grow and suddenly the QCX is being produced in a larger form. Little fingers are not so little any more.

Along comes a new junior op. Allow a few weeks for the training around the soldering iron and all of a sudden.....    A new, miniature version of the QCX is announced.

Coincidence........      ?

Reg      G4NFR


Re: QCX+ RF Power #qcx

R. Tyson
 

Hi,

You are getting 4.5 watts output.... good.
You want to fiddle about to get another 0.5 watts so you have 5 watts.....  hmmmm.

Why ?  You would have to increase your 4.5 watts to 4 times that level i.e. to 18 watts in order to gain 1 S point on the other guys reception of you. Why be OCD about 0.5 watts ?

Reg           G4NFR


Re: #40m #40m

KN6HGG
 

TX on tip of cable's plug is standard, and is correct for the QCX+ (tx goes to rx, and rx goes to tx). A 5v serial cable is ideal, but 3.3v should work. The "standard" part number for this cable is TTL-232R-5V-AJ, but there are a lot of copies and counterfeits that could cause issues.  I have already returned one from Amazon because it was obviously fake (way too short, handmade, possibly counterfeit chip, and losing data). I just ordered this one
Hopefully I got a real one this time...


50w PA failure, Where to start?

 

Hello, Recently, I was utilising my 50w PA with my QCX+, when spontaneously, a fault occured. The PA kept turning on and off repeatedly, First i checked to see if it was my power supply, and, it was not. I unplugged the PA from power,rf,etc as to not cause any more damage, and have only gotten around to investigating now.

Do note, The behaviour of it turning off an on repeatedly WAS a powersupply thing (Laptop PSU's do this, apparently), And on other, dumber powersupplies, it would flash on, then turn off indefinitely.

After investigation, I noticed that the leads off of q2 were breaking off, however, after soldering them again, the problem did not go away. I noticed specifically, that q2 got very, very hot fairly quickly, but q1 did not.

Where should I begin to find the fault? Should I preemptively replace both q1 and 2?


Re: Low pass filter advice #40m #80m #vfo

Steven Dick
 

I assume it was properly terminated at both the load and the source.  Otherwise you will not get the proper filter response curve. You shouldn't feed the output of the filter into a high impedance scope input. It should include a 50 ohm termination at the filter output before it goes into the scope. You can improve the source termination by using a 50 ohm 3dB or 6dB attenuator at the input, rated for the power used.   Depending on the LPF design, it is possible to get a peak.  A Butterworth design  should give a smooth fall-off with no peak. Other designs may have a slight peak near cutoff or a rising response in the bandpass.

-Steve K1RF

------ Original Message ------
From: "Peter GM0EUL" <gm0eul@...>
Sent: 9/13/2020 9:28:14 AM
Subject: Re: [QRPLabs] Low pass filter advice #40m #80m #vfo

Thanks Alan- that puzzled me, I wasn't expecting a peak and don't know what to make of it or what sort of artefact may have caused it.  I want to try and understand it before I do anything to change it.

73
Peter GM0EUL

Virus-free. www.avast.com


Re: QCX-mini update

Tech Guy
 

Sounds wonderful Hans. Thank you for your efforts again
John N4HNO 


Re: Low pass filter advice #40m #80m #vfo

@CurtisM
 

Peter

Find your way to the website of AA8V, use your search engine to find Digital VFO for Vintage Transmitters.

https://www.frostburg.edu/personal/latta/ee/vfo/vfo.html

Of course the drive impedances are different for thermions. You might enjoy your visit to professor Latta's website.

73 Curt


SMT Zerobeat kit

Ben
 

Today I built the wb9kz SMT Zerobeat kit. Nice looking zerobeat LED display! Would be a nice visual addition to the QCX+




Video on imgur: https://imgur.com/gallery/QE9aXU9https://imgur.com/gallery/QE9aXU9https://imgur.com/gallery/QE9aXU9


Re: Low pass filter advice #40m #80m #vfo

Peter GM0EUL
 

Thanks Evan
That seems to have done it.  With 47 Ohm across the scope it behaves exactly as I would expect i.e the 40m filter is flat to about 8.2 MHz then drops off quickly.  Testing the 80m filter now but I'm expecting that to behave itself too.

Noted about the need for a transformer when coupling the vfo to the transmitter.  It isn't expecting 50 Ohm I don't think, but not sure what it is expecting.  I'll see if I can figure it out.

73
Peter GM0EUL


Re: Low pass filter advice #40m #80m #vfo

Evan Hand
 

Peter,
If I am reading the filter specification right, you might want to start with a 50ohm termination on the output of the filter before the input to your scope for your test.  Rerun the test to see what you get. 

You may also want to verify the impedance of the transmitter to be sure that it is expecting a 50ohm source.  If it is different, then either a resistor pad or a transformer may be needed.

Just a couple of suggestions.
73
Evan
AC9TU


Re: Low pass filter advice #40m #80m #vfo

Peter GM0EUL
 

Thanks Alan- that puzzled me, I wasn't expecting a peak and don't know what to make of it or what sort of artefact may have caused it.  I want to try and understand it before I do anything to change it.

73
Peter GM0EUL


Re: Low pass filter advice #40m #80m #vfo

Alan G4ZFQ
 

The amplitude doesn't vary much from about 4 to about 9 MHz then it shoots up and peaks at 9.2 MHz then rapidly falls off and is almost fully suppressed by about 10 to 11 MHz.
Peter

Your description makes me wonder about the technique you used.
A LPF is flat until it begins to reject HF. There is no peak.

73 Alan G4ZXF


Low pass filter advice #40m #80m #vfo

Peter GM0EUL
 

Hi All
Can I request a bit of a reality check before I take my next steps.  I've made the vfo kit to add to my one-valve transmitter (this is the one that's the same as Hans's first transmitter, so arguably an ancestor of the QCX!).  The vfo has the 40m and 80m low pass filters and I had a look at their characteristics because I wasn't getting as much output as I expected.  

I've measured the peak to peak voltage output from the 40m filter on a scan from about 4 MHz to 11 MHz (have a look at the 1 min video here https://youtu.be/Lozyyh2OO9w  )  Ignore the actual numbers but look at the amplitude of the wave against the frequency (bottom left readout) The amplitude doesn't vary much from about 4 to about 9 MHz then it shoots up and peaks at 9.2 MHz then rapidly falls off and is almost fully suppressed by about 10 to 11 MHz. 

The 80m filter has similar characteristics and the peak output is at 5.3 MHz and its suppressed by just over 6 MHz 

I think I need to tweak the filters so that the peak output is at the bottom of the bands of interest (i.e pull it down by about 2 MHz by fiddling with the coils) is that right or am I interpreting the data wrong or misunderstanding what its telling me?

Any thoughts or definitive wisdom appreciated.

73
Peter GM0EUL


Re: QCX-mini update

Bill Cromwell
 

Hi,

Would that require a fine tip Sharpie Marker or can we get by using the standard size Sharpie?

73,

Bill KU8H

bark less - wag more

On 9/13/20 4:53 AM, Lex PH2LB wrote:
---snip------

from a employer point of few, the cutting of the SMD part strips from the reels and writing the values on them (not all 0603 components have values) would be a punishment for Hans's co-workers.


Re: #40m #40m

Don Blachura
 

Hello Bob,
Thanks for the reply. I have checked amazon and found the usb to ttl  interface. 
also found a usb to ttl cable with a mini plug on it, but the tip is tx not rx. Can you explain 
how it should be hooked up to the rig?I am not very good at all this new  tech. See the interface,
now I am lost.

TU 
Don...w2xb


Re: BPF 80m

Alan G4ZFQ
 

it is the negative sign that I was referring to.
Geoff

Did you look up what Korinthenkacker means?

Razvan knows he used a double negative but what does it matter?
Everyone knew what he meant.

73 Alan G4ZFQ


Re: BPF 80m

geoff M0ORE
 

Hi Razvan,

I am not saying that insertion loss is negative, it is the negative sign that I was referring to.

Geoff

On 13/09/2020 00:14, DL2ARL wrote:
 geoff M0ORE

I humbly excuse my english as not being breed at Oxford.
As for the insertion loss being negative, I know a word that fits  marvelously: in german they say to it Korinthenkacker.
Your fine remark has helped a lot to  clear the problem described above, thank you.
Enjoy your digestion.

Yours Razvan DL2ARL


Re: Compressing or expanding turns on a toroid.

geoff M0ORE
 

The late W4ZCB described a simple L & C oscillator to which you added the un-known component and then measure the frequency and by using a simple bit of maths or a spreadsheet calculate the un-known parameter. You needed a good reference capacitor to do the initial calibration, I was lucky to be able to borrow a 0.1% tolerance to make my own standard. Not perhaps  as good as a lab standard but I am aware of the limitations.

On 12/09/2020 23:53, wb8yyy via groups.io wrote:
Yes nice explanation that physical arrangement of the coil adjusts inductance.

One can measure inductance by resonating with a capacitor, measuring frequency,  and calculating inductance from that. Here in US the njqrp once offered a little kit that measured inductance and capacitance, in era before cheap lcd. Read them out in morse. I don't know what's out there now, but an LC meter would be a nifty offering,  yeah take advantage of a market here too focused on their coils.

73 curt


Re: QCX+ Resistor hot

K3YV <eeb3568@...>
 

Hi Curt. Thank you. The cover plaque was fun and really appreciated. I am changing the resistor value to adjust the brightness and solve the dissipation problem. Lots of room for two resistors. 73

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