OCTOBER 2015: THIS PAGE IS NOW AN ARCHIVED PAGE AND NO LONGER SUPPORTED IN ANY WAY
The miniVNA is a very compact antenna analyzer, covering 100
kHz – 180 MHz. It is PC-controlled via a USB serial communications link. The
miniVNA can commanded to output a very stable single frequency, rather than
sweep a frequency range. So the miniVNA can be used as an RF sine wave
generator. It has a 0 dBm output.
Most of the available miniVNA control software includes a simple signal generator GUI. One application for such a signal generator is a VFO. However, in most applications, the VFO frequency is not the same as the dial frequency (carrier frequency): it is a function of that dial frequency, and the IF-offset of the transmitter/receiver:
VFO frequency = (Dial frequency x A) + (IF-offset frequency x B)
In some transceivers, such as the Drake TR4C, the IF-offset depends on the selected frequency band, and for some bands, factor A or B is negative. For such radios, it is rather awkward to use a simple signal generator as a VFO, as it requires mental calculations of the actual frequency to be commanded. This is why I decided to make a small application that provides all the functionality that is needed:
Implementation of the above VFO-frequency formula, with:
Eight user-definable frequency band selections.
For each band: user-definable IF-offset, factor A, and factor B [-1 or +1].
For each band, a user-definable preset dial-frequency.
User-modifiable miniVNA frequency correction.
User-modifiable miniVNA frequency-to-DDS multiplication factor.
User-selectable COM-port. Yes, it is possible to design software that automatically scans all available COM-ports to find the one to which the miniVNA is connected. However, implementing the required functionality is complicated and time-consuming. It is not included in the current version of my software.
Ability to revert to a simple signal generator.
A nice, easy to use GUI (OK, this is subjective).
I have made a small program that does just that! I created it with a LabView development suite.
the above control panel, there are two user-input boxes for frequency: “Sig
Gen frequency” and “Dial frequency input”. The frequency in each box
can be changed 1) by typing-in a value and hitting ENTER on the PC keyboard, and
2) by using the up/down buttons on the left side of each box. By holding down
the SHIFT key and then using the up/down button, the frequency value will
increment/decrement faster. The increment/decrement step size is 1 kHz, but you
can type fractional kHz in the input-boxes.
When clicking on a "VFO - Band Selection" radio-button, the button will turn green, and the associated preset frequency appears in the “Dial frequency input” window. For the curious user, the calculated VFO frequency is also displayed. If “VFO” is selected with the toggle-switch, then the frequency input-box of the “Sig Gen” function is greyed-out, and vice-versa.
When starting the program, it normally opens with the “Config” tab shown:
All user-defined parameters, other than the COM-port number, are read from an
initialization file. The default initialization file looks like this:
The first 8 rows contain the 8 sets of frequency-band parameters:
Column 1: the label for radio-button of each of the (up to) 8 frequency bands.
Column 2: the decimal factor A for each frequency band (A may be negative).
Column 3: the decimal IF-offset in kHz for each frequency band (may be negative).
Column 4: the preset dial frequency (in decimal kHz) for each frequency band.
The 9th row has 4 parameters. From left to right:
The calibration frequency-offset correction (in decimal kHz) for the specific miniVNA device (as determined in the calibration mode of other miniVNA software).
Not used / don’t care.
The DDS conversion factor from desired frequency (in kHz), to the frequency command string that must be sent to the miniVNA. The standard factor is 10737.41824, but it may be adapted to the specific (calibrated) miniVNA.
Not used / don’t care.
My program does not automatically search for the COM-port to which the miniVNA is attached. That functionality is rather complicated (for me), but may be included in a future update of the program. If the actual port number is not the same as the default port number (COM5) the program won’t start. The port-number must be selected manually, in the pull-down menu.
The software has been beta-tested by my dear friend Rolf, DF7XH, in 2012 with his Drake TR4C transceiver.
I have developed the application with LabView (LV) Pro 8.0 - because I have access to it. For private use, it is prohibitively expensive. LV Pro can make an .exe that runs without LV development suite. However, it requires a very large Run Time Engine (RTE) be installed, as well as a particular version of the NI-VISA RTE (to make the serial communication work). Both RTEs are available for free from the National Instruments LabView website. The RTEs are available for Windows, Linux, Mac OS.
Update of July 2018: the Labview .vi design file, two .lvm initialization files, and a a brief description of the communication protocol can be downloaded here. The .vi and .lvm files appear to work fine with Labview V11 and even with the miniVNA Pro.
I can make the design files and the .exe avaible. It comes without guarantee, warranty, or liability Please note that I do not have the time to provide support for its installation or operation. Sorry! .
©2012 Frank Dörenberg N4SPP