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630m Band Exploration

Latest Updates:
April 11, 2019: A serious amplifier for 630 Meters.
July 2018: New. QST (Pg. 36) An Antenna for 630 to 10 Meters
March 2017. My 630 M Transverter.
June 17, 2016: 630 Transverter.

Author: Hansen, Markus, VE7CA

Encouraged by my friend Steve, VE7SL in June 2016 I built a tranmitter for the new amateur radio band, 630 Meters (475 KHz). Check Steve's blog for further inforatiom about local BC activity on 630 meters: ve7sl.blogspot.ca/

For my first 630 Meter transmitter I used GW3EUP's design . Here is his URL,


The vfo and amplifier was composed of two parallel IRF510's run in class D followed by a low pass filter. At +12 Volts it put out 14 watts.

March 2017. A 630M TRANSVERTER:

. In order to be able to use the digital modes like WSPR, JT8 etc, I decided to build a transverter to convert the 10 MHz band of my TEN-TEC Omni VI+ to the LF band. The Omni VI does not have a low power output connection so that was the first thing I had to do. Since I use a separate antenna for receive, the output from the transceiver converter is connected directly to the Omni VI auxillary antenna input jack. Using a small signal relay I interrupted the transmit signal just before the Omni VI power amplifier to bring the transmit output to a PL259 connector which drives the transmitter portion of the 630 M transverter.

Here is a hand drawn diagram of the circuit that I used.

The following picture shows the front panel and the following picture the inside of the transvert showing just the transmitter portion. The 630M receive converter is located inside the copper shielded encloser.



To increase power ouput to the legal limit of 5 Watts ERP a higher power amplifier was needed. I decided to replicate WB4JWM's design. He used two IRFP250 MOSFET's in parallel in Class D to produce 100 watts ouput with a 24 volt supply. By increasing the supply voltage to 36 volts the IRFP250's will safely produce 225 watts. What I like about this circuit is it includes a SWR Shut-Down circuit if the antenna SWR exceeds a preset amount. You can find WB4JWM's description and circuit at NJDTechnologies Web site:


Here is a photo of the amplifier housed in a repurposed old AM transmitter enclosure I found in my attic.

The next photo is looking inside the amplifier and reveals the PC board that I built the SWR shut down circuit and the MOSFET amplifier on. With a 24 Volt supply to the MOSFETs and terminated in a 50 ohm dummy load I measured the output power at 132 watts which equates to 87.2% efficiency. All harmonices are -58dB or more below the carrier level.

As previously noted one feature of Tom's circuit is a SWR Shut Down feature. This circuit will shut the MOSFETs off if the antenna SWR exceeds a preset number, say 1.5:1 or 2:1. MOSFET'S do not handle avalanche breakdown caused by reactive loads. In other words as an RF amplifier they like to work into a low SWR antenna, in this case 50 ohmns. If you turn the transmitter on and you mistakenly do not have the transmitter connected to the antenna, or your antenna comes disconnected or falls down you will blow the MOSFET's. Believe me, I have! So, this Shut Down circuit is a big benefit.

I did not have a BF244A for Q1. A J310 did not work as I could not lower the source standby voltage to 0.62 volts without drawing excess current. A MPF102 worked with the source resistor at 830 ohms. Tom, the author of the circuit indicated that the 27 ohm resistors in series with the diodes that are attached to the gates of the MOSFET's can be reduced in value or elliminated if the MOSFET's do not not completely shut down when you engage the Test button. Instead of the BAT46's series diodes I used IN5819's as they can safely handle more current if needed. The SWR unit is mounted in the bottom of the repurposed chassic as seen in the following photo. I used phono connectors for the input and output connections so that I could reverse the SWR coupler to null the reflected power to zero with C1 when connected to a 50 ohmn load.


73 VE7CA