OH2GAQ Microwave Transverter Controller V2

Version 2 of the Microwave Transverter Controller has similar but not identical functions to the Version 1 MTC. The functions for the original MTC and their implementation are described in reference 13 below. Version 2 is smaller, has additional modulation modes (as well as SSB USB and LSB it also supports AM and FM modulation) and is fully integrated into one box plus PC.

SDR

(modified Peaberry V2)

28 to 30 MHz

USB HUB(modified TRENDNET

TU2-400E)

Control Module

Keypad

Display

Shaft. Enc.

Mic. Input

Mic. Pre-amp

144 / 28 Transverter

28MHz In/Out x2 /TX

28MHz. In / Out

144MHz In / Out

144MHzIn / Out

Power

Supply

+26 +12 +5 +6.5 USB20V In.

12V In.

10 MHz

Rubidium

Reference

10MHz. Ref. Out

Control 1&2

In/Out

Trans. 3&4

Rub.

Lock /Tx

PTT2 & PTT4 & PTT3Trans. 1 & 2 Control

Trans. 3 & 4 Control

J5

J4

J3

J1

J9

J10

116 Mhz Xtal PLO + Isolation Amps.

/144 / 28

J2

USB Audio I/F(Behringer UCA222)

J7

USB IF to PC

Line In

Line Out Amp

. + Spkr

Commercial. Components

J8

USB

Phones /Spkr

J6

Figure 1. Functional Block Diagram of the MTC version 2.

The major implementation difference is the use of SDR technology to provide the basic Rx. and Tx. functionality. In this case a modified Peaberry SDR V2 board is used. The present major modification is to add a 28 MHz pre-amplifier to the Rx. side of the device, to make up for the somewhat poor sensitivity as a receiver. Additional modifications to reduce the noise spurs have been made in the power supply (Tantalum caps). The performance of the modified SDR is quite good when you move away from the Zero Frequency noise area. A major objective of this project was to understand if a simple and low-cost SDR could be used rather than a conventional transceiver.

144 MHz (Transverter plus Peaberry plus pre-amp as above)

Carrier set to 144.4 MHz.S9 set to 50 uV (-73 dbm)RBW 2.9 Hz, no averaging.

Noise Floor -137 dbm20 db S/(S+N) -117 dbm10 db S/(S+N) -126 dbm

Figure 2. Measured performance of receive chain using Peaberry plus OH2GAQ 144 MHz transverter.

Rx Input vs Signal measurement

-120

-100

-80

-60

-40

-20

0

20

-140 -120 -100 -80 -60 -40 -20 0 20

Input (dbm)

Indi

catio

n (d

bm)

Figure 3. Overall linearity of Peaberry Rx. part plus 144 MHz transverter. SW used was HDSDR version 2.7 beta 4.

The MTC V2 is physically implemented into a surplus HP measuring equipment enclosure.

Figure 4. Opened-out view of the MTC. On the left side (lower part) you can see the USB hub, underneath it the control PCB and in front the Rb. Oscillator and 116 PLL and 10 MHz distribution amplifier. On the top tray is the Power Supply, AF amp and MIC-preamp board, the 144 MHz transverter, the Peaberry V2 SDR and the Behringer UCA222 USB to AF interface card.

Figure 5. Front view of the MTC V2. The original HP pushbuttons and their PCB have been re-used. The legends on the panel indicate the current functions, and don’t necessarily match the printed function on the buttons. A high-quality Optical encoder is used with the tuning knob. The dial shows the tuned frequency, the tuning resolution selected, the status of the frequency control system, a bar indicating the TX. Power level as monitored in the attached transverter (empty area under the Frequency readout) and the control state and operational mode.

The operational mode (modulation type: USB, LSB, AM, FM), frequency and RX/TX can be controlled either by the function buttons / knob on the MTC or from the HDSDR SW. A Mic PTT switch is also implemented.

As the MTC uses an SDR, an attached PC is required. This can be any Windows (at least XP, W7 and W8.1) PC with a reasonable processor. One reasonable performance USB-2 interface is required in the PC.

The author has collaborated with the HDSDR author in order to specify some additional functionality for HDSDR. This functionality is now available in the 2.7 release of the HDSDR SW.

In order for the MTC to be conveniently used in the field, it was felt that Tuning, Modulation Mode setting and PTT operation must be available without using the PC screen, so basic operations could be made without using mice, etc (at least after starting up the PC). The 2.7 release of HDSDR allows control of Tuning, Modulation Mode and PTT locally or remotely. The control is done via the Omnirig interface module, which itself has primitives to support PTT operation.

For cases where additional processing is required (for example use of Olivia or JT65) this SW can already interface to HDSDR, so employing the MTC for moonbounce or low signal scatter modes is possible.

Details of the SW implementation are given in a later section of this document.

Figure 6. HDSDR application receiving the 10 GHz Pasila beacon. The Multipsk application is decoding the morse code. In this trial the 10 GHz transverter was operating with an 80 cm dish antenna close to ground level, and the signal was scattered from the Espoo TV Tower mast. The near field is partly occluded with trees, but without leaves. In summer time there is no signal noticeable from the same path, due to the foliage.

Figure 7. HDSDR application plus MTC at 144.439 MHz. The noise is about -130 dbm. The signal is the Inkoo OH2VHF beacon.

Figure 8. Detailed view of the zero-frequency noise at a centre frequency of 144.1897 MHz. The deep null at the centre frequency created by the automatic nulling in HDSDR is clearly seen, and the remaining noise spurs can be clearly seen. Outside a band about + and – 200 Hz from the zero (HDSDR LO) frequency, there is no observable noise above about -135 dbm. Interestingly, it does not appear that the noise spurs are in any way related to the normal mains related spurs at 50 Hz or multiples of 50 Hz.

One of the major challenges in this project has been the reduction in the various noise spurs that appear in the integrated solution. The Peaberry SDR, when in the original format and when connected to only an antenna, is pretty clean. However when put into a system, that is not necessarily the case. Noise spurs appear near the LO frequency at relatively high amplitude (-100 dbm) at 1 KHz intervals for a few KHz each side of the LO frequency. A tantalum bypass on the input to the 5V regulators plus cleaning up the USB cabling seemed to fix that issue. Another one is a set of spurs that appear when the LO is tuned to exactly 29.000000 MHz and for frequencies up to about + - 10 KHz each side of this frequency. These seem to be caused by slight leakage of the highly stable 116 MHz LO used in the 144 MHz converter into the Si570 or other associated parts of the Rx. side of the SDR. At 29 MHz the LO in the SDR is running at 116.000000 MHz also. A few changes in cable placement and the addition of some common-mode decoupling toroids seem to be able to much reduce this effect. Probably a better solution would be to put the Peaberry SDR into a separately shielded enclosure.

SW Architecture

Figure 9. Hardware and SW architecture of key parts of the MTC V2. The yellow shaded boxes represent some key HW blocks in the MTC V2. The green shaded blocks represent major SW components running in the PC. Solid lines show the audio signal paths, dotted lines show the control signal paths. Key characteristics of the signals are shown also.

The SW is divided amongst several entities, and the description that follows and the picture above is a somewhat simplified view of the total situation.

The SW in the MTC V2 is a simplified and modified version of the MTC V1 SW, it consists of a core set of functionality for each major function (screen, keyboard, A/D measurements etc), plus a simple main program which carries out the integration of the functionality. It is written in 8051 assembly language. All the maths functions use fixed-point libraries. The serial I/O and timer, tuning knob increments, button pushes, etc are interrupt-driven. A small client for communication with the PC Omnirig SW which implements the Tuning, Mode and RX/TX functions is implemented in this SW, this provides the link to HDSDR via Omnirig. Depending on the desired operating mode of HDSDR and the MTC, the MTC can act merely as a repeater display for HDSDR, or as both a display and control source for HDSDR, where the tuned frequency, operational mode (USB, LSB, AM or FM) and RX/TX mode in HDSDR are fully controlled by the MTC.

The PC SW is based on readily available “free” or low-cost SW, apart from the OS. The author has used both Windows XP Professional and Windows 7 Professional as OS environments. It would be expected that Windows 8.1 would work as well, but it has not been tried as yet.

With respect to the HDSDR SW controlling the Peaberry V2 SDR, there are several additional components that are included in the box labeled HDSDR above. Please refer to the Peaberry SDR Instruction Manual for details of the needed SW installation. The additional parts are mainly concerned with the frequency control of the SiS 570 LO source in the Peaberry, or providing control functionality (see HDSDR on-screen notes) between HDSDR and external HW or SW such as HRD, WSJT etc. A null-modem SW functionality such as com0com can be used between WSJT, HRD DM780 etc and HDSDR programs to control RX/TX switching, essential for JT65x working. This control function is represented by the diagonal dotted arrow between the optional HRD etc box and the HDSDR SW in Figure 9 above. A rig description

file for the MTC for use with Omnirig is available from the author. Please refer to the HDSDR website plus linked material for more information about this SW.

The major issue faced has been easily-controllable audio interconnections. It is possible to get the system running without using the Virtual Audio Cable (VAC) SW, but it is not predictable and depends very much on the SW bundles included with the audio interfaces used in the PC. Some low-cost but reasonable USB audio interfaces don’t include the needed functions, and the Windows drivers are difficult or almost impossible to configure for these cards. Each version of Windows is different in this respect. HDSDR does not accept a stereo configured mic input stream (?), but seems to show an error if this is the case. By using VAC, it is easily possible to set the configuration to exactly that needed (for example mono and appropriate bit rate for the mic. input to HDSDR), and by using a batch file all the needed SW parts can be started with a single command. VAC also supports multiple “sinks” (for example audio can be directed to both the USB audio card line out via a VAC Audio Repeater and to the input of a digital processing program such as HRD’s DM780 or WSJT). The author suggests that anyone interested in this area should use a search engine (for example Google) to look for the many good descriptions on the web about these issues.

Conclusion

The conclusion of the author is that a simple, modern SDR rig like the Peaberry can provide acceptable performance in this kind of wideband tunable IF application. The cost, even including the cost of a PC needed for providing the SDR functionality, is more than reasonable, especially when there may be a need for a PC in any case to provide processing of the digital mode data. There is plenty of SW available for the PC world to allow configuration of a full-functionality system.

Acknowledgements and References

There are many hams and others who have, generally unknowingly, contributed to the design and implementation of this system. The many excellent websites maintained by hams who wish to share their ideas and/or kits with others are too numerous to mention. More details of the implementation of some parts of the controller, such as the PLL oscillator, are contained on the authors web site: (http://personal.inet.fi/private/oh2gaq/). For those who are interested in more exact constructional details of some parts of the system, for Eagle design files or SW source code, the author may be contacted thru the Finnish Amateur Radio society via their e-mail service. The address is shown on the website.

References:

1. John Stephensen, KD6OZH, “A Stable, Low-Noise Crystal Oscillator for Microwave and Millimeter-Wave Transverters”, QEX, Nov/Dec 1999.

2. John Hazel, G8ACE, “Constructional Notes for G8ACE MKII OCXO Sept2010 V2”, Available from G8ACE website: http://www.microwaves.dsl.pipex.com/

3. Analog Devices Data Sheet for ADF411x RF PLL Frequency Synthesizers.

4. Analog Devices ADIsimPLL version 3.30

5. W6PQL website: http://www.w6pql.com/Several excellent articles covering microwave transverters and useful sub-systems as well as actual kits for many items.

6. KO4BB website: http://www.ko4bb.com/Time and frequency control, measuring equipment and generally useful microwave related material.

7. KE5FX website: http://www.thegleam.com/ke5fx/Time and frequency control, measuring equipment and generally useful microwave related material.

8. Systronix RAD51 website: http://www.systronix.com/RAD51/RAD51.htmRapid Application Development Environment for 8051 family processors. Assembler language only.

9. AE9RB website: http://ae9rb.com. This contains links to the Peaberry SDR Version 2, including a well-supported Forum with plenty of comments on the SDR.

10. HDSDR website: http://www.hdsdr.de Here you can find the HDSDR SW, with help on what hardware is supported, etc.

11. VE3NEA website: http://dxatlas.com/OmniRig The website of Alex Shovkoplyas, Afreet SW, Inc. OmniRig client can be found here, as well as a lot of other amateur radio directed SW. Good documentation and examples of how to describe your own rig that you want to control with Omnirig.

12. Eugene Muzychenko’s website: http://software.muzychenko.net/eng/ Here you can download VAC (Virtual Audio Cable) which allows simple and effective connection of audio streams from various SW packages to other SW packages (e.g. from HDSDR to DM780 part of Ham Radio DeLuxe). VAC is not free, but it simplifies many often impossible Windows configuration issues and provides good performance and control over the audio format.

13. OHGAQ website: http://personal.inet.fi/private/oh2gaq Here you can find a re-print of the article published in QEX for July/August 2013 covering the Mk1 version of the Microwave Transverter Controller, and various microwave amplifier and transverter projects.