Very High Performance Transverter for 432 MHz

1. Introduction

As the JAVORNIK-144/14 happened to be quite a success we decided to design 70cm transverter with the same architecture. One of the design goals was to re-use as much circuitry and mechanics as possible.  So here is MENINA-432/21, a two RX converter transverter in the same housing as Javornik-144/14.

Much of the 2m xvrt technical description holds true for the 70cm xvrt with few exceptions: 

• it is hard to go from 432MHz to 14MHz and vice versa in single step without low-cost PCB mountable narrow filters (such filters are not readily available to hamradio homebrewers) -->  a 21MHz IF was choosen

• the minimum antenna temperature on 70cm is much lower than on 2m and coaxial cable losses are higher, so it is hard to build sensitive enough receiver without external, mast mounted, preamplifier -->  xvrt consists of 3 mechanical parts: one base xvrt and two LNAs

It has two (synchronous) receive converters that are composed of external LNA (ATF-54143) and high IIP3 stage in base xvrt with SGA-6389, BPF, 20dBm mixer and IF AMP. 

The local oscillator (137 MHz) uses the same design as the one in Javornik. The only difference is that 3 times higher LO frequency is needed, so the LO chain is a little bit more complex. 

The TX converter is basically the same as in 2m xvrt. The Mitsubishi FET power module RA45H4047M is used as the final amplifier delivering 45W of clean output signal.

Fig.1: MENINA-432/21 prototype on Franci's/s51rm desk.

2. RX Converter

The RX converter consists of an external LNA and base xvrt RX converter. The LNA uses ATF-54143 in a slightly modified YU1AW design. 

Fig.2: the base xvrt second RX converter block diagram. 

Fig.3: the base xvrt main RX converter block diagram (for table-top low power operation external LNA is not mandatory due to included LNA stage with HMC374). 

The overall NF of the RX system (LNA + cable + XVRT + IF RIG) is aimed to be below 1,0 dB (75 K) what is good enough for tropo work on 432 MHz. 

3. Local Oscillator

Fig.4: the LO block diagram. 

The local oscillator (137 MHz) is based on the Buttler design using low noise transistors BFR93a. It has single multiplication, amplification and filtering path that is used to power all 3 mixers  

4. TX Converter

Fig.5: the TX converter block diagram. 

The TX converter accepts 21 MHz IF signal with level from -20 dBm to +20 dBm. It has switchable IF amplifier for those HF RIG's that have low TRV drive level (-10 to -20 dBm). Output is a very clean 45W signal delivered by the FET power module RA45H4047M.

5. Configuring the RX path 

The RX path will vary a bit as different lengths and types of cables will be used. The following table gives predicted performance for different cable loss.

As can be seen the optimum compromise for tropo work is achieved at 5dB cable loss. The worst case RX S/N degradation would be 1dB (assuming minimum Ta of 180K).  

One can use his existing LNA and cables in front of the base xvrt. Net gain (LNA gain - cable loss) should be around 17dB for optimum performance (note that original LNA has 22dB of gain and 0,4dB of NF with IIP3 of +5dBm ).

The 12V power supply for the LNA is routed via central wire of the RX coaxial cable. The same supply can be used for high power antenna relais switching (those 12V are available at the LNA housing). Maximum current is 250mA per each RX connector. Although the LNA power supply includes current limiter it is recommended not to use base xvrt with DC short circuited RX lines. Also be carefull when using more than one antenna with its own LNA infront of the base xvrt and selecting them with an external relais - check the DC ratings of the relais contacts.

6. KIT kompleti

Na voljo so polni KIT kompleti. 

Informacije/naročila --> Sine/S53RM - s53rm pri hamradio pika si