Re: One question only...

Arv Evans

Giles  F1BFU

I am not close to my hamshack to check for accuracy. 
The attached drawing shows the general idea from what I can remember.
Looking at this reminded me that with very little change it could be made
into a CW or swept frequency signal generator (Si5351a out through mixer
and attenuator, with audio into mixer to modulate carrier).  Every time I look
at this it seem to suggest yet another modification. 


On Sun, Aug 5, 2018 at 12:13 PM Gilles Delpech <gilles.f1bfu@...> wrote:
Hi Arv

your experimentation interests me. I'm finishing building QRPLabs VFO / SigGen with Relay Card to switch LPFs. I also have a K5BCQ attenuator. I would like to understand your use of the QRP Labs Signal Generator.
Please can you give me a little diagram of your editing ?

Many thnaks Arv

Le dim. 5 août 2018 à 20:05, Arv Evans <arvid.evans@...> a écrit :

The design won't stay still long enough to write an article.    8-)

It is actually pretty simple.  I used a 50 ohm resistor as the input to the balanced mixer.
That lets me use the step-attenuator (also home-brewed) for input calibration.  Plug-in
filters can be added to the front-end but normally I just use a tunable series LC to suck
out unwanted frequencies (2nd or 3rd or other harmonics of the LO).  Output of the mixer
goes through a termination (stolen from the BITX BFO mixer design), followed by an
emitter follower 2N3904 to feed audio to a voltmeter, or oscilloscope, or fldigi on Linux.

A PCB would be nice if I could ever settle on not making any more modifications.  To do
that I would have to draw a schematic, which has not happened yet.  It is just one of those
things that sets on a shelf above the workbench and gets used whenever needed.


On Sun, Aug 5, 2018 at 11:51 AM Jack Purdum via Groups.Io <> wrote:
That would make a great article!

Jack, W8TEE

On Sunday, August 5, 2018, 1:46:23 PM EDT, Arv Evans <arvid.evans@...> wrote:


Several years ago Hans G0UPL started marketing his SI5351a based VFO kit.  With that as
a very stable LO and a balanced mixer to LPF to Audio voltmeter it is possible to make a simple
receiver for chasing spurs, harmonics, and gremlins.  Of course it was impossible to resist
adding oscilloscope display and rewriting the software to scan specific frequency ranges.  Now
I have a direct-conversion spectrum scanner that can be calibrated and used to track ghosts
and goblins emanating from my home-brew builds.  Calibration is done by use of a fixed-value
step attenuator for 1, 2, 4, 5, 10, 20, 40, and 50 db. 
This has been a work-in-progress for several years and just keeps getting better as I find ways
to modify and to use it. 


On Sun, Aug 5, 2018 at 10:07 AM Gordon Gibby <ggibby@...> wrote:
How could we make measurements of signal level accurately? Compared to fundamental?   Note  I would probably be using a 2nd uBitx as the receiver.


On Aug 5, 2018, at 11:53, ajparent1/KB1GMX <kb1gmx@...> wrote:

On Sun, Aug 5, 2018 at 07:55 AM, Doug W wrote:
A KW is the minimum power according to some. ;)

Snark:  For me 100W is serious QRO for HF.  At VHF I'm just warming up the driver.


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