500 kHz Transmitter     Last update 2012-02-14
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Click to enlarge JUMA TX500 front view


JUMA TX500 is a digitally controlled CW transmitter for the 500 kHz amateur radio band (600 m). The transmitter is available as a component kit which inludes all the electrical and mechanical componets.

JUMA TX500 is using ultra high efficiency CMCD amplifier (Current Mode Class D) topology in the final RF amplifier. The final transistors produce negligible heat. This means that you get 60 watts output with only 5 amp current from a 14 VCD power supply. TX500 is infinite key down proof transmitter. See power and efficiency measurement graph. The frequency stability and the signal purity of JUMA TX500 are excellent.

JUMA TX500 is a versatile building block for 500 kHz, it includes antenna switching for RX and it can be connected to any 500 kHz receiver. TX500 will enhance your RX performance with the built-in narrow band front-end filter and with the selectable 10dB/20dB preamplifier. If a 500 kHz receiver is not available, you can switch ON the built-in high dynamic RX up-converter and listen 500 kHz band with a 3.5 MHz receiver.

Additionally JUMA TX500 can be configured for
a stand-alone beacon. You can enter a desired CW message and start a continuous beacon transmission.

You can download JUMA TX136/TX500 Windows control software. It is very useful especially in slow QRSS CW and supports speed down to 0.1 wpm. See a sample screenshot here.

The kit includes a ready programmed CPU. New forthcoming firmware versions can be easily downloaded from JUMA site and uploaded with a PC.

Click to enlarge
JUMA TX500 user interface (Click the picture)

Antenna application note for 500 kHz
WRC-12 allocated 472 kHz-479 kHz to amateur radio
Status of 500 kHz allocation by IARU
See also 136 kHz transmitter JUMA TX136
Click to enlarge JUMA TX500 rear view

General features
- RF output power 60 W key down proof
- Four power levels (MIN 4W, LOW 15W, HI 35 W, MAX 60W)
- Supply voltage nominal 14 VDC (range 12 VDC...15 VDC)
- Typical max current 5 A (with over current protection)
- Frequency range 450 kHz...550 kHz (step 10 Hz)

- Frequency step 1 Hz with Windows control software
- Top quality keyer with speed range of 1 wpm... 50 wpm
- Speed range 0.1 wpm...50 wpm with serial control

- Good clickless CW keying shape
- T/R switch with CW speed adaptive release delay

- RX preamplifier
- RX up-converter from 500 kHz to 3.5 MHz
- Beacon mode
- Windows software for PC control
- Small size, Width 180 mm, Height 60 mm, Depth 124mm

Multifunction LCD
- Output power
- SWR display
- Supply voltage indicator
- Drain current indicator
- CW speed indicator (WPM)
- State indicator (STBY, OPER, TX)
- Frequency display (5 digits e.g. 501.00 kHz)

Configurable features
- RX preamplifier (OFF, 10 dB, 20 dB)
- RX converter ON/OFF
- Sidetone frequency/ON/OFF
- Adjustable SWR protection, individual level for each power
- Keyer type (Dot priority, Iambic, Straight and Beacon mode)
- LCD brightness and contrast adjustment
- Serial communication settings

- Power supply nominal 14 VDC / 5A (Standard DC socket)
- Antenna 50 ohms (BNC
- RX
500 kHz or 3.5 MHz, 50 ohms (BNC connector)
- Paddle/Straight key (3.5 mm jack)
- RS232 for firmware/beacon programming (
3.5 mm jack)
- External PTT in/out (3.5 mm jack)

Modular construction
Building of JUMA TX136 is easy. There are two component kit modules to build
, the main module which includes the RF circuits and the control module which includes the control processor and the user interface. The modules are interconnected with flat cables, construction picture. Only two simple toroidal coils need to wound. The mechanical parts are ready for assembly and there are no adjustable parts on the boards.

JUMA TX500 kits are
available. You can order JUMA TX500 kit by online shop and get ready for the 500 kHz band.

Copyright OH2NLT and OH7SV. Specification subject to change without prior notice.

JUMA® is a registered trademark of Juha Niinikoski and Matti Hohtola.