Re: QDX burned on start-up
I would put getting the RF out of your power supply high on the priority list.? First rule of troubleshooting is to fix what you know is wrong.
I would not be comfortable with my power supply voltage (or DMM) swinging around like that.??
I have a nice old Simpson analog meter which seems to be immune to RF; it is good for a check.
73, Don N2VGU
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OK, so I pulled the BS170¡¯s and made a simple circuit to test them. ?The LED lights up on all four. ?Is there a better test?
--
Marc
N8LO
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
This will be an informative article for you.
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I think Colin meant?
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Re: QDX v3 Lost transmit on 20/30/40
From:?Colin Kaminski
Date: Sun, 14 Aug 2022 17:30:06 CDT
Normal receive current at the power supply is 140-150ma. NOT MW
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Re: QDX: Receiving great but needs more audio output gain in order to xmit for more than 250 milliseconds.
Willie,
This first step is to do a very close and?thorough inspection of the board for shorts or bridges between traces.?
What happens when you use the Terminal Transmitter Test program?? Does it still drop out?
I think you might have a short occurring when you go into transmit mode.? That could be across the 5volt regulator output as it supplies all of the QDX logic ICs.? Can you monitor the output of IC2 when you go into transmit to see if there is a sudden drop, and then it comes back?? This could be an IC5 failure.? Does the LED continue with the 3 pattern flash?
If you have a hot air SMD rework station, I would remove IC5 to see if the transmitter drops out after the 1/4 second.? If not,? then replace IC5 and remove the BS170s.? Try again,? If you can, test the BS170s with a transistor tester.? Replace all 4 if one is bad.
The above are just suggestions.? I could be misinterpreting the symptoms you are describing.? Please proceed at your own risk.
73
Evan
AC9TU
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Re: QDX: Anyone else having a problem with image rejection?
#qdx
Thank you Hans,
It took me a few days to check everything. I am only using the built in tools. They have changed since the manual and I didn't notice the scale changes till today.
I am using a Rev 3 board. I ran through T2 with a fine tooth comb. It had one extra winding at the beginning so I removed it. The solders have continuity. I am attaching 10 screenshots of the built in diagnostic tools. I played with the 40M RF filter for some time. The peak is still too high at 20 turns on both inductors. I am wanting to fine tune everything as much as possible before I close up the case. This is an exercise in understanding as much as anything. I am interested in what you see?
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Colin Kaminski - K6JTH
https://www.qsl.net/k6jth/
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OK, so it's only one way, but it adds evidence that this little QDX - no bigger than a pack of cigarettes - has a good transmitter indeed !
Over the past 24 hours, I've made probably 50 or so 2-way contacts on the 80, 40, 30 and 20 meter bands.
But, 20 is providing a bit of Delta Xray !
My antenna, fed by an Icom AH-4 remote autotuner, is an end-fed wire, approximately 80 meters in length, averaging 5 meters AGL - not so good, especially on the lower bands.
Anyway, I'm having a blast.
Thank you, Hans, all the gang at QRP Labs and, of course, the gentleman who sold the QDX to me and all list members/owners who lent tremendously helpful hands in getting the QDX going !
73,
Bill, N4QA
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
Just some final thoughts after rethinking and calculating the levels.
When using a BS170 buffer you come up with something like 150mW output RF power on 50 Ohm.? This is the RMS voltage around 2V.? To get to the required 1V RMS you need to add a simple 6 dB resistor attenuator.? With the attenuator you gain three things:
- protection of a SiLabs CLK0 output
- proper level signal for a TS
- good return loss to a TS 50 Ohm input (RL = 12 dB)
73 Bojan S53DZ
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
Please have in mind also that the Si5351A CLK0 output is a square wave 5V signal with a 2.5V DC component.? TS VFO input must be a sinus AC signal.? So don't forget C1 to decouple.
73 Bojan S53DZ
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Thanks Evan, I will pull the mosfets and test them. ?Hope that fixes my issues. ?I will let you know how it goes.
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Marc
N8LO
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
But, no matter what that test might show to you I would suggest you do the buffer amplifier with BS170 to protect the Si5351A output.
73 Bojan S53DZ
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Hans, In your design of the BPF (L12), did you assume, or measure, stray circuit capacitance? ?My calculations, using a nominal AL of 4.9nH per turn squared, suggest that the capacitance values need to be 10-15pF more than the manual values. ?This appears consistent with an input capacitance of 13pF on the A terminal of the FST3253. ?
Am I missing something?
toggle quoted message
Show quoted text
On Aug 10, 2022, at 3:05 AM, Hans Summers <hans.summers@...> wrote:
? Hello Milt
I think there are some problems if the sweep goes beyond the specified band limits. However I have corrected this in a beta version that I am working on.? On Tue, Aug 9, 2022 at 6:39 PM Milt < w8nue@...> wrote: Hans, Are the frequency limits ignored during the filter sweeps?? That is, can the start frequency be less than frequency min, or the maximum of the frequency sweep be greater than frequency max as set in the band configuration? On Aug 6, 2022, at 11:00 AM, W8NUE <w8nue@...> wrote:
?Hans, Thanks for keeping us posted on updates/changes.
I do have a question regarding the band configuration: since it shows a selectable Start Frequency and Step Frequency I conclude that I need to know the Default Number of Steps to be able to control the Sweep Width.? Is this correct?? Is that number about 50?
Have I missed something? On Aug 6, 2022, at 9:46 AM, Mont Pierce KM6WT <de.km6wt@...> wrote:
?On Sat, Aug 6, 2022 at 05:56 AM, Hans Summers wrote:
The vertical marker showing the band center went missing in version 1_04.
I noticed that for 20m the Band Sweep setting was different than 80/60/40 so I just changed 20m sweep step from 100000 to 50000 (like 40m), and the center frequency appeared. Nice to know you're on top of it though.? I'll update to 1_05 when it's released. Each firmware release always seems to have some goodies?? hi hi Thanks, Mont
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Re: QDX burned on start-up
Hi Al, Good news! Just want to mention, the diode will drop 0.7V across it in this application. This is the reason the FET is used since it has a lower voltage drop across it.
This is will contribute to the lower current draw in Transmit (0.69 A). It's lower than what's usually seen. Thanks for pointing that out. I'm aware of the voltage drop and this is a price I'm willing to pay at the moment, I compensate with a bit higher voltage if needed. :) Do you have a way to measure transmit power out in Watts into a 50 Ohm (dummy) load? I'm just wondering if maybe one of the PA FETs (BS170's) is open and giving you the lower current reading. I don't want to be an alarmist, but it's something to consider. I can estimated by measuring the peak voltage on the dummy, which is 13,89 V at input of 9 V (-0,7 V) and 7 A, so in the 3 W region I would guess. When connecting an antenna the input voltage and current are different than with the dummy load. I observed that my PSU changes voltage depending on the antenna, band and load ... maybe RF getting back in it. For example when I set 8 V on 30 m while receiving, while sending the PSU goes to 9 V and the QDX draws 1,1A. On 80 m it goes from 8 V to 11,1 V and draws 0,77 A... So now for every band I dial it in to have 9,7-10 V with load. This seams to work reasonable well, WSPR goes over the Atlantic on multiple bands and I had some QSOs on 40, 30 and 20 m around Europe. Maybe I need to decide on one band and build the 50 W amp. :D Hi Wayde, I use the following SWR bridge and tuning indicator with mine so that the max SWR 'shown' to the QDX will be 1:2... A fun and easy kit build and seems to work well as insurance for me! That looks really nice! I'm thinking about going the extra mile and building a full tuner like this ZM-4 ATU . 73 Alexander DM8TE
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Bertel,
The Elecraft W1 power/SWR meter is the most RELIABLE.
Charles Brown
N4SO
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
Yes it can be connected but in that case it would not be 1V any more.? If the rig needs 1V rms at 50 Ohm then you still have to do.?
Anyway you can connect the CLK0 over C1 direct to the LPF input and try out the output level.? It should come to about 0.7V!?? Guessing from the field with my mobile in the hand.?
73 Bojan S53DZ
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ON Semiconductor bought Fairchild. Same parts, different name. Individual builders generally have no reason to care whether the parts are loose or tape and reel, so buy whichever is cheaper or easier to get.
On Mon, Aug 15, 2022 at 12:07 PM Conard Murray < cmurray@...> wrote:
I just downloaded datasheets for the BS170 from NTE, ONSEMI and Fairchild.
Fairchild claims max continuous drain current of 500 mA and 830 mW max power dissipation.
NTE claims 500 mA as well, but cautions the power dissipation of the TO92 package may force a lower current. They list 350 mW as max power dissipation.
ONSEMI claims the same 500 mA continuous current and 830 mW Pd as Fairchild does. These datasheets are not very complete, especially NTE¡¯s.
ON and Fairchild report a 1200 mA limit for pulse operation. I¡¯m thinking the class E PA would be eligible for that rating ¡ if so then the case power dissipation is the magic number not to exceed in my opinion.
73,
Conard, WS4S
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Re: QRP Labs VFO/Signal generator and Kenwood TS-520 VFO
Bojan,
Have installed all capacitors
C1, C4, C5, C6 C8
Jumpered W1-W0 and W2-W3.
Jumpered PA to 5v+
Installed R6
?Installed Q1 BS170/// Assembly instructions says Q1 and R5 pot not required
for the VFO kit.
R5 pot
There is no T1 toroid supplied with the kit, so
not able to build T1. If this is required, need to order a toroid.
The Low Pass Filter reads continuity from Input to Output.
The Kenwood requires 1.0 volts rms to the VFO input. My understanding is
that it requires a filtered sine wave from the Low Pass Filter, not a square wave.
On the right side of the Si5351A synthesiser at CLK0 it reads
1.076v. The voltage at RF output below the Low Pass
Filter still reads 0 volts.? The voltage would work if it were filtered from the
Si5351A..
I am reading voltage with a Simple RF Probe based on an N5ESE design.
Do not have an VTVM RF meter.
Can that 1.076 volts from the output of the Si5351A be
connected directly to the input of the Low Pass Filter?
It's not connecting on the board.
Charles Brown
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Re: Si5351A output buffer
Hi there,
Yes, this was also my concern.? 74LVC2G17 propagation delay is around 3.6ns.? So it is on its limit already. But I was quite happy with the behavior.? The limit of my osciloscope is at 200 MHz, so I do not have a complete picture of a waveform above that.? Just what I have seen from the spectrum.? Normaly I am using it as square wave to some 100 MHz, and rare to its limit at 290 Mz, where the square wave is not needed.? For that I have other RF generators.? So, yes, to have a solid square wave up to 200 MHz you would probably need a buffer driver with fc of 1GHz or higher.
73 Bojan S53DZ.
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Re: Si5351A output buffer
Bojan, I have been thinking of doing something similar to that.? However, I have a comment about the spectrum.? It has rather high levels of even harmonics.? A square wave should have very low levels of even harmonics.? Perhaps the 74LVC2G17 is being pushed to its limits at 200MHz and finds it difficult to respond in time.? This could result in a waveform that is a series of pulses that are narrower than they would be in a square wave.? Have you investigated this at all?
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I just downloaded datasheets for the BS170 from NTE, ONSEMI and Fairchild.
Fairchild claims max continuous drain current of 500 mA and 830 mW max power dissipation.
NTE claims 500 mA as well, but cautions the power dissipation of the TO92 package may force a lower current. They list 350 mW as max power dissipation.
ONSEMI claims the same 500 mA continuous current and 830 mW Pd as Fairchild does. These datasheets are not very complete, especially NTE¡¯s.
ON and Fairchild report a 1200 mA limit for pulse operation. I¡¯m thinking the class E PA would be eligible for that rating ¡ if so then the case power dissipation is the magic number not to exceed in my opinion.
73,
Conard, WS4S
?
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Donald S Brant Jr
Mark K9TR
Colin Kaminski
Alexander
Shirley Dulcey KE1L