Concise introduction
Installation of the software
How to measure-examples
Final remarks

Concise introduction


Many thanks to Dieter, DL2BQD, for translation

The most technical measurements in the fields of high frequency are based on a stable tuneable radio frequency oscillator and an RF voltage meter. Together with some external small additional components one can do a lot of measurements and alignments. My aim was to construct a simple gadget which offers some more possibilities for own creative extensions. The sample device – which nearly needs no copper boards – has a bit more than 50 parts only, can be easily aligned, needs few energy, and is a bargain compared to a commercial grid dip oscillator. One only needs some parts customary in trade, a computer and you’ll get a complete measuring station to wobble with.

Wobbelmessplatz miniHFM34 ---> Bandfilter ---> click to enlargen



The main part of the circuit includes the USB controller and the DDS generator.

Schaltung miniHFM34 ---> click to enlargen

The upper part of the parted metal housing contains the complete circuitry / assembly.

Schaltung miniHFM34

The 200 Ohm source resistance of the generator is adapted by a transformer to the 50 Ohm low pass filter.
Alternatively a video broad band amplifier could also be used when the output level is raised at the same time-

non-symmetric tansformer 4:1 ; symm. 8:1

An RF probe provides a direct voltage which is proportional to the logarithm of the RF input voltage.

Messkopf ---> click to enlargen

The RF voltage probe.
It’s output is connected to AN0 (pin2) of the IC1. This connection is not critical due to its direct voltage only.


The DDS generator produces only a low output level which does not correspond with the dynamic range of the RF probe. So I used an additional video amplifier LT1252. It’s load resistance will be adapted by the voltage divider (R202 & R203) to 200 Ohm and now corresponds with the source resistance hence the transformer coupling is not needed. The low pass filter is calculated for this characteristic impedance. At the output end of the LT1252 the 50 Ohms resistor R204 is the source resistance of that device to match with the following low pass filter. Since this amplifier did not show a distortion poor output level at 5 v supply voltage, it is fed by a DC/DC converter (SW2-0512S or other) with 5v input and 12 v output voltage. Now the amplifier produces a clean RF level of about 10dBm.

Breitbandverstärker ---> click to enlargen

Nearly the whole dynamic range can be used now with this level. The picture shows one run of the wobbler. An attenuation combination was switched in steps of 20 dB from -80 dB to 0 dB. The -80 dB lines indicates the lower characteristic curve kink of the AD8307 and there are 2 dB to 3 dB differgency. From -70 dB the linearity is excellent. (The picture shows the results of the new software “hfm11lin”)

Installation of the software


There is an older Windows Version for miniHFM34. In the meantime I changed to LINUX and offer a version HFM11, Dec. 2007, which runs on both systems. They are similarly programmed and can be started as hfm11win.exe or hfm11lin.

Program HFM11 and PIC Firmware from here – HFM9/HFM11 web page

The wobble system is operated by the program qrpHFM9x.exe or hfm11win.exe or hfm11lin.

The PC program doesn’t need any installation. You copy it into a folder and it can be started from here or from a desktop icon. The data default.lng (configuration file) and the help file qrpHFM9x.hlp or hfmhelp.htm (help files) should be in the same folder.



I recommend this procedure for the first start

-plug hardware to USB port
-now Windows will start the hardware manager - please point to file
A virtual COM port is created.
- disconnect the hardware from USB now.
-start program
qrpHFM9x.exe or hfm11win.exe w i t h o u t hardware and confirm the error message.
-click/open register „Settings“ (German “Einstellungen”) and click “search for port“ (German „Portsuche“). You will see a list of all ports.
-connect hardware
miniHFM34 again and wait a moment. The driver is loaded
(perhaps you will see a short flickering of the PC disc led only, no further messages)
-click “search for ports” once more. The list of ports has increased now by one. This is the port number which is used for this very gadget (see top left)
-entry COM port and DDS internal clock frequency (50000000 resp. 75000000) in Hertz into the top left mask
--press button “Accept” (German “Uebernehmen”) to confirm the new values. If all is OK so far the number of the up to date version of the hardware –mH34 should be displayed when you press the button “version” (German “Version).
-save all config data via the menu “File/Save” (German “Datei/Speichern”) or Key F2 in the file “default.lng “
They will be re-loaded for each new start then.


Here I only mention openSuse but I think that for the other Linux distributions there will be similar handlings.

-copy all data into an own folder
-connect hardware to USB port. It will be automatically registered as CDC RS 232 emulation. You can see it in the info centre there.
-open a terminal and register as root “su root” (enter) password for root
-check by command “ls /dev/ttyACM*” whether there is a driver/port.
 These are the ports for the serial emulation. Is there only one gadget connected then there will also only be one ttyACM0
-it might be to change rights to get access to the port for other users, command:
 “chmod –v a+rw /dec/ttyACM0 “
--check whether all ports correspond with the correct access data of the user for config and save data files of the hfm11 programs
-change user, leave root
-start program hfm11lin and confirm error message
-click register “Settings” (German “Einstellungen”) put in as COM port /dev/ttyACM0  and DDS beat frequency ( 50000000  resp  75000000) in Hertz mask top left
-confirm by clicking button “Accept” (German “Übernehmen”), now the number of the new hardware version - mH34 – should be displayed when pressing button “Version”
-save all under “default.lng” to be reloaded with each new start

Of course you must do all this actions only once per computer.
In case all was done properly it will run easily: connect hardware – start program – measure

Since I use the program together with different hardware I start it with a copy of the DEFAULT.LNG (you can use another name if you like e.g. mini.cfg) which then contains all the specific data ( …/…/ hfm1 1Win.exe mini.cfg).

In this very copy one will find all the saved specific elements data interface, data speed, DDS beat etc…

Hint: organise the link – search for the program – add copy of the +.lng – organise working root to be the same path – name the link

How to measure


You see an adaptor for calibration and pre –alignment of bandfilter (modules) . In the right part there is an attenuator combination which can be adjusted by wire jumpers 0dB to 40dB. For measurements use the left BNC socket of the probe and the filter is plugged in.

Schaltung miniHFM34

One can use a lot of additional little circuits for other more even extended RF measurements. The little pieces of extra circuitry are very simple and restricted to their basic functions though.

Descriptions of extra circuits and their usage

Final remarks


It was intended to develop a useful measuring equipment for the radio ham with a minimum of hardware. There will not be top performance compared with other NetWorkAnalyzers, but it was not the basic intention to reach this goal. The miniHFM34 shall be a simple, versatile, cheap instrument which can really help to do some jobs in the RF electronic workshop Hardware and software were developed in my modest amateur radio shack and I don’t claim to have constructed a piece with the features of a High End instrument with all bells and whistles. I myself wanted to learn more about the USB interface, and it is clearly dedicated to ham radio. You can get the complete software and I even offer to program your PIC in case you are not able to do it. No costs for you – please only pack a PIC carefully and add proper postal fee with a self addressed envelop. If you want to use this service please drop a line to dk3wx (at) Subject HFM34, your call It is not allowed to use all these documentary – neither partly or as a whole - , software and info for commercial use without my personal permission.