Alan, one more thing.
The bandwidth of the Tayloe circuit can be adjusted up or down by the
selection of the integrating capacitance at I and Q. It can be made
very narrow by using larger capacitors, or made wide by using smaller
capacitors. The charging resistance of the mux switches and related
circuitry also enter into the equation. Getting a wideband IQ channel
to support a spectrum waterfall is no problem at all.
JZ KJ4A
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On Sun, Oct 22, 2023 at 3:58?AM John Zbrozek <jdzbrozek@...> wrote:
"The large spike seen is the LO feedthru of the mixer interfering with your vna.
Gary
W9TD"
Simulation doesn't back that assertion up. The double balanced Tayloe
circuit does a great job of suppressing LO feedthrough.
The NanoVNA receiver should be able to confirm that.
BTW, Dan Tayloe himself described exactly the response that Ton's
bench test (and simulation) is showing.
JZ KJ4A
On Sun, Oct 22, 2023 at 3:15?AM Alan G4ZFQ <alan4alan@...> wrote:
On 21/10/2023 22:52, Gary W9TD wrote:
The large spike seen is the LO feedthru of the mixer interfering with
your vna. Gary
Yes.
I can not imagine how anything else could produce such a peak.
In "wideband" Tayloe SDRs you can get 192KHz flat with just that spike
in the middle (if not suppressed in software).
73 Alan G4ZFQ
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"The large spike seen is the LO feedthru of the mixer interfering with your vna.
Gary
W9TD"
Simulation doesn't back that assertion up. The double balanced Tayloe
circuit does a great job of suppressing LO feedthrough.
The NanoVNA receiver should be able to confirm that.
BTW, Dan Tayloe himself described exactly the response that Ton's
bench test (and simulation) is showing.
JZ KJ4A
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On Sun, Oct 22, 2023 at 3:15?AM Alan G4ZFQ <alan4alan@...> wrote:
On 21/10/2023 22:52, Gary W9TD wrote:
The large spike seen is the LO feedthru of the mixer interfering with
your vna. Gary
Yes.
I can not imagine how anything else could produce such a peak.
In "wideband" Tayloe SDRs you can get 192KHz flat with just that spike
in the middle (if not suppressed in software).
73 Alan G4ZFQ
|
On 21/10/2023 22:52, Gary W9TD wrote: The large spike seen is the LO feedthru of the mixer interfering with your vna. Gary Yes. I can not imagine how anything else could produce such a peak. In "wideband" Tayloe SDRs you can get 192KHz flat with just that spike in the middle (if not suppressed in software). 73 Alan G4ZFQ
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Re: Low power output (~0.5W) on QDX. How do I troubleshoot?
13.8v will definitely roast BS170s. And quite possibly IC5. I know from personal experience.
I now limit all of my QRPLabs gear to 12v with a linear regulator and have made well over 1000 FT8 contacts without a failure since.
--
Randy, N4OPI
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The large spike seen is the LO feedthru of the mixer interfering with your vna.
Gary
W9TD
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Great job Joe!
Randy, K5HJ
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I use a NanoVNA V2 Plus4, which has much less noise compared to older models (and does not require a new calibration every time I change the frequency scale or steps), but I think we got the idea of how the mixer input impedance looks like from your traces. Thanks for all your effort.
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I used my old nanovna for this so I was curious about frequency accuracy. I bought a "spare" nanovna that I have only had for a few days. It reads the same frequency for the peak on 10 meters, 28052. So, I imagine the readings are pretty close to correct.
Tony
AD0VC
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All right, so the mixer input impedance for the practical QMX BPF/matching network design purposes, we can agree that the mixer input is 75 to 120 ohm (maybe even higher on lower bands), a bit reactive. It's good to confirm my working assumption was reasonable.
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Solder suckers are "less than optimal" for desoldering.? Wicking with a braid soaked with flux, works very well, if you have the patience to do it.? It is also the most safe way, provided the iron temperature is set right...? Wicking is especially good, if the "lands and vias" are tiny and very fragile...
Regards
wb7ond
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Re: DRA818V as a CW Beacon ?
On Sat, Oct 21, 2023 at 11:26 AM, Da Amazin' man G0FTD wrote:
On Sat, Oct 21, 2023 at 07:21 PM, Hugh Duff wrote:
DRA818V VHF
Try another group.
This is for QRP LABS products.
?
--
- 73 de Andy -
Which uses DRA818V!
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All right, so the mixer input impedance for the practical QMX BPF/matching network design purposes, we can agree that the mixer input is 75 to 120 ohm (maybe even higher on lower bands), a bit reactive. It's good to confirm my working assumption was reasonable.
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Good for you! While testing my QCX-mini, I managed to short the board and blew out a couple of traces. This was my first build and I went to Hans, thinking I needed a new board. His suggestion was to simply solder wire to replace the traces. I got some 30ga Kynar wire and successfully made the repair. Excellent advice to a novice builder I¡¯m glad to hear your story. You don¡¯t learn as much from your successes as you do from overcoming problems and obstacles! -- Thanks and 73,
Tim
VE1XR
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28.074MHz with 250Hz resolution.
Tony
AD0VC
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Thanks for your effort.
So, 10-12kHz away from the LO frequency the input impedance drops in half on 20m. So, in order not to complicate the IF/baseband signal processing to optimize for the best image rejection, I think it is best to keep the mixer input signal line to a reasonably
low level. We still get some of the preselector performance boost but not as much as possible with a direct conversion detector case.
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Thanks for your effort.
So, 10-12kHz away from the LO frequency the input impedance drops in half on 20m. So, in order not to complicate the IF/baseband signal processing to optimize for the best image rejection, I think it is best to keep the mixer input signal line to a reasonably low level. We still get some of the preselector performance boost but not as much as possible with a direct conversion detector case.
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PITA. I have to recalibrate every time I change a frequency sweep setting. With 5 averages it looks better but takes forever to do.
I increased font size.?
14074 Zoomed, 250Hz resolution, 5 averages
Tony
AD0VC
Oh, ok. We were writing on the same thing simultaneously.
Can the trace be made smoother by increasing the number of averaging?
The impedance peak looks like two-tier structure and I am curious about those each peak. Hope that the broader peak is wide enough for ideal superhet and image rejection...
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PITA. I have to recalibrate every time I change a frequency sweep setting. With 5 averages it looks better but takes forever to do.
I increased font size.?
14074 Zoomed, 250Hz resolution, 5 averages
Tony
AD0VC
toggle quoted message
Show quoted text
Oh, ok. We were writing on the same thing simultaneously.
Can the trace be made smoother by increasing the number of averaging?
The impedance peak looks like two-tier structure and I am curious about those each peak. Hope that the broader peak is wide enough for ideal superhet and image rejection...
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Re: DRA818V as a CW Beacon ?
Hugh,
QRPLabs products include LightAPRS which uses this module.
If you enter 'DRA818V' in the search engine in the topic, you can see the comments related to the topic.
If you want to read about LightTracker, .
--
Gyula HA3HZ
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Re: DRA818V as a CW Beacon ?
That sounds like an ideal transceiver for packet radio... though 25kHz channel separation.
If keying is sought without QSK capability, you could try dong that with a PIN diode attenuator so that the transmitted power is absorbed by designated resistor(s). The easiest is to use two diodes in a series-shunt config with a quarter-wavelength coax as the impedance inverter. Another way, which requires a few more components but wide band, is a T-network attenuator configuration. Either way, the attenuator is bypassed during receive.
I'd look into GMP4201-GM1, GMP4215-GM1, MPP4203, etc. for the diodes.
If you are going to build an amp for a bit more power, keying can be done in the drive and the final, as well.
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Re: DRA818V as a CW Beacon ?
On Sat, Oct 21, 2023 at 07:21 PM, Hugh Duff wrote:
DRA818V VHF
Try another group. This is for QRP LABS products. ? -- - 73 de Andy -
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Hello group.
I've read a bit of chatter on the DRA818V VHF transceiver module around here but I'm wondering if any of you have successfully used one of these as a 2m CW beacon ???The well known TX-RX turnaround delay seems to render the prospect of keying the PTT like a CW transmitter useless. Can this thing handle 100% duty cycle (I would use it in low power mode and heatsink it as necessary) and has anyone delved into the pcb to find a suitable place to key the TX chain without creating any chirp or other undesirable effects ??
BTW, does anyone have a link to a schematic for this module ?
Thanks, Hugh VA3TO
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Gary W9TD
Randy Ott
Ryuji Suzuki AB1WX
Barb WB2CBA
Tim Delaney
HA3HZ