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Photo Notifications #photo-notice

Group Notification
 

The following photos have been uploaded to the DRAKE TR-7 DIGITAL VFO photo album of the [email protected] group.

By: Dale Parfitt <PARINC1@...>

The following photos have been uploaded to the DRAKE TR-7 DIGITAL VFO photo album of the [email protected] group.

By: Dale Parfitt <PARINC1@...>

Group Notification
 

Paul Lukosius <plukosius@...> added the photo album Drake 2-NT Digital VFO : An EU station complained about my HA-5 drifting on 10M so I decided to put together a digital VFO. This is the QRP Labs VFO kit that uses the Si5351A synthesizer. Added a 5V reed relay to switch the output ON/OFF and use a 1N4007 blocking diode so it can be keyed by the 2-NT VFO Key line. Powered by a cell phone charger, it drives the 2-NT to full output on all bands.

The following photos have been uploaded to the Drake 2-NT Digital VFO photo album of the [email protected] group.

By: Paul Lukosius <plukosius@...>

 

Paul,

I'm curious as to the RF output voltage you're obtaining from your Si5351A VFO.? I suspect you're amplifying for use into the Drake 2NT??

I'm using the same Si board with a homebrew RF voltage amp (images below).? With a bifilar output transformer, it produces 30Vp-p from a +12V source.? That's enough to drive most boatanchor transmitters.

My only issue from these PLL and DDS VFOs is close-in spurs next to the carrier frequency.? They're not nearly as clean as a classic PTO circuit.? I typically see worst-case spurs at -35 dBc.? They're down quite a bit, but it's possible to detect the spurs from stations when propagation is good.?

Paul, W9AC



?
 

Paul,
That looks like a really nice VFO!
I am curious about amplitude too.? The Si5351 puts out 3.3vpp square wave.? Normally people say you need higher amplitude for a tube rig.

DDS means Direct Digital Synthesis.? The signal is generated by building a sine wave via a DAC (Digital to Analog Converter).? Small aberrations to the sine wave
create the close in spurs.? The better the chip, the less the spurs.? The low end AD9850/51 are pretty bad if used in a receiver (I tried) but are probably ok for a
transmitter.

The Si chips use a GHz PLL divided down.? They don't have close in spurs but do have phase noise but it not bad.
73,
Gary
WB6OGD
 

Paul L,
You can switch the Si5351 output off/on at >50WPM via software, no need for a relay.
73,
Gary
WB6OGD
 

Gary,

That would have been my first choice if the QRP Labs kit had software to support this function. I contacted QRP Labs after assembly and they confirmed that their kit does not support switching the output ON/OFF.

73
Paul, N9PL
 

Paul,
Too bad he won't give you the source code.
Rather than a kit, it is pretty easy to build an Si5351 VFO with an Arduino and available source code.
73,
Gary
WB6OGD
 

Paul L.,
We are still curious about the 2NT VFO drive level.? From the manual it appears the Si5351 by itself will not be enough above 40meters.
73,
Gary
WB6OGD

2nt.pdf
2nt.pdf

 

Gary,

I thought I had replied to W9AC's message. Not sure where it went, so here it is again.

The Si5351A output is adequate to drive the 2-NT to full output on all bands. As shown in the pdf you attached, when operating straight through, the 2-NT oscillator stage only requires 1V RMS to drive it. So on 20 and 15 meters I drive it with 14 or 21 MHz input and the 3.3V square wave is adequate. On 10M both the oscillator and driver operate as? doublers with a 7 MHz XTAL, but with 14 MHz input, the? oscillator operates straight through and 3.3V P-P is enough drive for full output.

Not nearly as slick as W9AC's vfo shown above, but it seems to be getting the job done.?

73
Paul, N9PL
 

Paul,

I'm sure I responded to your post, but don't see it here, so am responding again.

The Si5351A output is adequate to drive the 2-NT to full output on all bands. When operating straight through, the 2-NT oscillator stage only requires 1V RMS to drive it. So on 20 and 15 meters I drive it with 14 or 21 MHz input and the 3.3V square wave is adequate. On 10M both the oscillator and driver operate as? doublers with a 7 MHz XTAL, but with 14 MHz input, the? oscillator operates straight through and 3.3V P-P is enough drive for full output.

After seeing your VFO post here, I took a quick look at your QRZ page. Most impressive. I think most of us wished our home brew projects looked this good!

73
Paul, N9PL
 

Paul,
Thank you.? Very interesting.? I don't plan to ever get a 2NT but others will probably find that info really interesting.

Someone could go to ebay and by an Si5351 board for $5 and an Arduino for $4, display for $5, encoder for $2, and have a very stable nice VFO for cheap.
73,
Gary
WB6OGD
 

Paul,

?

Thanks for the feedback ¨C and to Dale, W4OP for posting his Si5351A spectrum result.?

?

I¡¯ll have another look at the PLL VFO¡¯s output.? My memory may be mixed up with the result of a companion DDS VFO I built that uses an AD9850 which is known for its close-in, low-level spurs.? ?That VFO is shown below.? It¡¯s a more complex design since it uses two microcontrollers, one of which is responsible only for T/R sequencing.? Because a PIC microcontroller manages several VFO functions, it¡¯s output results in 1-3 ms of random timing jitter.? A tiny Adafruit microcontroller solves the timing problem.? An on-board RF amp boosts output to +20 dBm with a separate adjustable Hi-Z output of 30Vp-p.? ? ?

?

Paul, W9AC?

??

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