SynthHD Microwave Signal Generator with an External Reference


At Windfreak Technologies, my main goal is to have very satisfied customers.  One of my biggest jobs is customer service, both before the sale and after the sale.  Below is a good example of how I like to help my customers, plus it has some good info for those that plan to use our devices with an external reference.  Thankfully this dialogue ended in success, but if not we quickly repair or replace failed units, no matter what caused them to fail.  You can also see I try to timely respond.  If you have ever contacted me without a response please try again!  Maybe try my email address on the Contact Us page, or try the web form, or call the phone number.  Sometimes SPAM filters are hard to overcome.  If possible please add to your whitelist.

(The dialogue below is an email thread copied and pasted with the name of my customer changed for privacy.  Read from the bottom up to get chronological order.)

Happy US Independence Day!

David Goins

July 1st, 2016

Quantum-Sensing Lab, Department of Physics, Univeristy of Basel

Hi Jake,
Thank you for checking that out. It sounds like the output amplifiers are not burned out and I think we can fix the rest over email…
There is a schematic with your CD that shows the circuit for the reference. In short, when you have either reference on, it is fed back out the REF I/O port. When set to external, both are muted and powered down so you can feed in your external reference. When you set the external reference the reference frequency box is “ungreyed” so you can input what frequency you are going to feed it. So if 10 MHz you need to type in 10MHz. Ideally you will feed it an amplitude of 2 – 3.3Vpp. Every time you power down the SynthHD it will forget your settings unless you click the button “Save to ROM” in the Extras Tab. So if this is the way you plan to run it all the time then maybe its best to use that feature so you don’t forget. Just use Save to ROM carefully because it saves every setting in the GUI to the device. You want to save it how you want it to power up every time so it saves you work resetting everything back up.
A rev or two of firmware ago, the device was still forgetting the reference frequency, but I believe you have bought recently enough that your firmware should work like described above.
Please let me know if you get it straightened out.
Best Regards,

From: Jake
Sent: Friday, July 1, 2016 9:10 AM
To: David <>
Subject: Re: question regarding synthHD

Dear David,

you were right. As we use several signals coming from different sources, we use a 10MHz reference signal from our main MW source (a RF signal generator from Stanford Research, i.e. the SRS84) to synchronize all other devices. This is why I set the reference of the synthHD to external.

Now, for testing the synthHD at my office computer, I switched it back to internal reference and the outputs are working again (both outputs are fine for both, 10MHz and 27MHz internal reference). So this is good news I guess.
However, with the synthHD working in external reference mode, i.e. when it is connected to our setup, the outputs don’t work. Any idea why? Does the device output a reference signal when it is in internal reference mode?

As you were asking: we use the amplifier ZHL-42W+ to amplify our MW signals.

Am 30.06.2016 um 16:37 schrieb David:
Hi Jake,
This setting worries me:
x) Reference (external=0, int 27MHz=1, int 10MHz=2) 0
Do you have an external reference hooked to the device? If not please go into the GUI Extras Tab and select internal reference of 27MHz and try setting some frequencies to see if they come up.
Can you give me the model number of the amplifier you have been driving?
Best Regards,

From: Jake
Sent: Thursday, June 30, 2016 9:54 AM
To: David <>
Subject: Re: question regarding synthHD

Dear David,

I am very sorry for the inconvenience. Regarding your questions:

1) How was it used when it started to fail?
I am not sure when exactly it failed and therefore I don’t know what happend that made the generator fail. In general we are using the synthHD to output a MW signal to an amplifier. The frequency of that signal is either kept constant or continously swept between two values. The sweep is triggered externally with a TTL pulse coming from a National Instruments card.

2) Where you using both channels?
Not at the same time, but we tested both outputs. In the beginning both worked, now none of the two works.

3) What RF loads were you using?
Everything is terminated with 50 Ohms and I made sure that, when an output was not used, it was also terminated correctly.

4) Have you used custom Matlab code or only my GUI?
Mainly our own Matlab code, but in the beginning mainly your GUI. Again, in the beginning both worked, now none of the two ways of communicating with the device does.

The procedure you suggested does unfortunately not work. The software says that the device is outputting 20dBm, but I can only measure -12dBm at the synthHD. I have copied the settings of the device below:

) Control Channel (A(0) or B(1)) 0
f) RF Frequency Now (MHz) 1000.0, 1000.0
W) RF Power (dBm) 20.000, 0.000
V) RF Calibration success? 0, 1
a) VGA DAC Setting (0=mim, 45000=max) 33429, 18612
~) RF Phase Step (0=mimimum, 360.0=maximum) 0.0000, 0.0000
h) RF High(1) or Low(0) Power 1, 1
r) PA On(1) or Off(0) 1, 0
E) PLL Chip En On(1) or Off(0) 1, 0
I) PLL output power 2, 2
U) PLL charge pump current 6, 6
d) PLL mute till LD 1, 1
m) Muxout function 6, 6
T) Autocal On(1) or Off(0) 1, 1
b) Feedback select Fundamental(1) or Divided(0) 0, 0
i) Channel spacing (Hz) 1000
v) Show version (0=firmware, 1=hardware)
e) Write all settings to eeprom
x) Reference (external=0, int 27MHz=1, int 10MHz=2) 0
l) Sweep lower frequency (MHz) 2840.9000000, 1000.0
u) Sweep upper frequency (MHz) 2900.0, 3000.0
s) Sweep step size (MHz) 0.6000000, 200.0
t) Sweep step time (mS) 16.000 ms, 50.000 ms
[) Sweep amplitude low (dBm) 0.00, 0.00
]) Sweep amplitude high (dBm) 0.00, 10.00
^) Sweep direction (up=1 / down=0) 1, 1
k) Sweep differential frequency seperation (MHz) 1.0
n) Sweep differential: (0=off, 1=ChA-DiffFreq, 2=ChA+DiffFreq) 0
X) Sweep type (linear=0 / tabular=1) 0, 0
g) Sweep run (on=1 / off=0) 0
c) Sweep set continuous mode 0
w) Enable trigger: (0=software, 1=sweep, 2=step, 3=hold all) 0
F) AM step time in microseconds 8
q) AM # of cycle repetitions 65
A) AM Run Continuous (on=1 / off=0) 0
P) Pulse On time is 1, 1 us
O) Pulse Off time is 10, 10 us
R) Pulse # of repetitions is 10, 10
🙂 Pulse Invert signal (on=1 / off=0) 0, 0
G) Pulse Run one burst
j) Pulse continuous mode 0
D) Pulse dual channel mode 0
<) FM Frequency is 500, 500 Hz
>) FM Deviation is 10000, 10000 Hz
,) FM # of repetitions is 100, 100
😉 FM Type (sinusoid=1 / chirp=0) 0, 0
/) FM continuous mode 0
p) Phase lock status (lock=1 / unlock=0) 0, 0
z) Temperature in degrees C
*) PLL reference frequency MHz 27.0
+) Model Type
-) Serial Number
?) help

Do you recognize something suspicious?

Am 29.06.2016 um 19:36 schrieb David:
Hi Jake,
Im sorry to hear you are having issues with output power.. Any ideas how it was being used when it started to fail? Where you using both channels? What RF loads were you using? Have you used custom Matlab code, or only my GUI?
Can you do a procedure for me?
1) Make sure all continuous modulation Sweep FM AM and Pulse are off on both channels.
2) Go to the Extras Tab and click “Save to ROM”.
3) On the Extras Tab and click “Re-init settings to default”.
At this point you should have full power running at 1GHz on Channel A.
If not, something bad has happened and I need you to send it back for failure analysis and replacement. Im very sorry about this inconvenience. These devices so far have been reliable in the field..
Best Regards,
PS. One other quick test.. After the above procedure with still no output, please copy and paste the results of the “Read” Tab to me. Should look something like below:
C) Control Channel (A(0) or B(1)) 0
f) RF Frequency Now (MHz) 1000.0, 1000.0
…..(other settings)
+) Model Type
-) Serial Number
?) help

From: Jake
Sent: Wednesday, June 29, 2016 6:04 AM
To: David Goins <>
Subject: question regarding synthHD

Hi David,
thanks for sending us the synthHD that quickly! I have been playing around with it a little bit and it seems to fit our needs very well.
However, since a couple of days, I am not able to output any signal on none of the two outputs. I can communicate with the device using the software or Matlab, e.g. I can set parameters, read them out. I can also softwarewise switch on the outputs, but no signal is generated and the green LEDs that indicate an active output, also do light up. I also connected the synthHD to a spectrum analyzer but could not see any spectral weight at the frequency I set the output to.
Another test I did was to connect the synthHD to the power monitor of the synthNV. When switching on the synthHD, some power is measured (so I guess the synthHD is outputting something), but 0dBm output power of the synthHD are measured as -55dBm (-57dBm is base level for synthHD output off) by the synthNV (see attached screenshot).
I am not sure why the device is not working properly so I was wondering whether you have any idea?
Thank you very much for your help!