Friday, November 24, 2017

Three options for putting a signal on 630 meters

What follows is a summary of a few equipment combinations that will enable transmission on the new (US) 630-meter band.

Most of the info below is scattered here and there among various postings on my blog but I thought it might be helpful to have it summarized in one place. I have built and am using all of them, depending on what I want to do on the band on any particular evening.

For a cheap and effective receive-only option, click here.


Ultimate 3S (80m version) + GPS receiver + 22-watt amp from WA3ETD

Total cost - $130

Ultimate 3S on 80m driving 22W WA3ETD amp on 630m WSPR
All three of these items are kits. As kits go, I rate them as "Easy to build". The Ultimate 3S can be ordered with a variety of options. The only option necessary here - and it's not an absolute necessity, but makes operation much easier - is the companion GPS receiver for the U3S.

The 22 watt amp requires an 80m input in order to produce a 630m output. At 22 watts out, the amp's small heatsink get very warm, but not hot, and cools down almost immediately after transmissions end. I've noticed no degradation of power over the 2-minute WSPR cycle.

This combination has allowed my WSPR transmissions to be decoded in 34 states (including Hawaii on a regular basis). I had low expectations of what might be possible with only 22 watts (that's 1 watt ERP for me) on 630m but the results have been surprisingly favorable.

An option unmentioned online but described in the assembly manual for the 22-watt amp is the ability to add 6 small parts to the amp's circuit board that enable the amp to pass received signals back to the exciter. This is only beneficial if you're using a transceiver as the exciter since the U3S is transmit-only. This $5 option allows the same antenna to be used for both receive and transmit, albeit with some receive attenuation due to the fact that it is an unamplified path where some loss will occur. I hope to be adding these components and testing the functionality of transceiving this weekend (25-26 Nov).

(The WA3ETD amp alone, without the U3S/GPS, will allow any 80m rig to put a signal on the air on 630m for only $75 - just keep in mind that input power to the amp must be less than 1 watt. My U3S drives it to 24 watts (14.5V) with 500 milliwatts).

Advantages: low price, no computer or big rig needed (GPS controls timing, grid square input for WSPR and frequency calibration for U3S), small footprint, available

Disadvantages: Only WSPR, QRSS CW, CW beaconing are possible if using the U3S (since the U3S is transmit only, a transceiver with crossband capability is needed for QSO modes (TX on 80m, RX on 630m)

Summary: I recommend the U3S because of the lack of need for a computer and its ability to serve as exciter for the next option (below). This is also a great way to dip one's toes into this new band - the cost is low for an effective WSPR set-up. This will allow a station to make gradual improvements to the antenna while (hopefully!) seeing improvements in number of WSPR receiving stations and the dB levels at which they typically receive you. Propagation characteristics over time can also be assessed with this set-up.

Ultimate 3S + GPS receiver + G0MRF 300-watt amp

Total cost  - $150

Unhoused Ultimate 3S on 950 kHz & 300W G0MRF amp
This combination also makes use of the U3S but in a slightly different configuration. The GPS receiver is still desirable for the same reasons already mentioned but the U3S is configured to produce an output of 944 to 958 kHz. This input will be halved as part of the 300-watter's amplification process. This relegates the amp to non-linear modes - CW, JT9/65, FT8, WSPR - but that's 98% of what's on the band anyway.

Furthermore, the U3S does not need a low pass filter on its output (although each U3S kit comes with your choice of one band filter) since it is the clock output from the U3S that is required by the amp. These square waves are applied to the amp's finals (FET's) and gate them on and off at an RF rate - the sine wave typical of an "RF drive signal" is not required. In fact, according to both G0UPL (U3S) and G0MRF (300-watt amp designer), the square wave before any filtering is more desirable than a filtered sine wave.

The amp's output is varied by controlling the supply voltage to its FET - increasing it from 12 to 32 volts raises the RF output from 35 to 300 watts, so 30V, 10A variable power supply is needed.

Again, if a U3S is used as the driver, only transmitting will be possible - no reception. If transceive capability is desired, the main transceiver will need to meet two requirements:

  • It will need a transverter output capable of producing a ~950 kHz signal of sufficient amplitude to switch the amp's FETs on and off. I can confirm that the output of the Flex 6XXX series is capable of this when set to 10 mW.
  • Crossband operation is required. You'll be transmitting on 950 kHz and receiving on 475 kHz. Again, the Flex 6XXX rigs are good to go here since they set the LP filters as needed for receive on 630 meters.

An important note on operating digital modes with a divide-by-two amp:

Since the amp divides the input frequency by 2 in order to achieve a 630m output, it is also dividing the spacing between tones that make up WSPR, JT9 and other digital modes. This needs to be compensated for in some way. If you are using the U3S as a driver, there is a menu option labeled "X2". This parameter needs to be toggled to an active state, ie "1" instead of the default "0".

If you are using a regular ham transceiver as the driver, WSJT-X contains the option: Settings>Advanced>X2 Tone Spacing that performs the same function for WSPR only in the current regular version of WSJT-X. The rc-03 version of WSJT-X allows this function for FT8 and JT9 in addition to WSPR and the next standard release of WSJT-X will as well (tnx G0MRF, K1JT).

The amp has two T/R relays, a KEY-in and a PTT input. In addition to the variable 12-30V input for the final FET's, it also needs a fixed 12V input for the other circuitry. The amp also contains protection circuitry to guard against high SWR and over current. These circuits require a simple alignment to set where the limits occur. LED's are included so that a front panel indication will be available if any of these conditions occur.

This amp is not for the beginning kit builder. Although the parts themselves are large and easy to work with, you are not stepped through the process of building it Elecraft- or Heath-style. There are a few parts of the process that, to me, were vague or unexplained. Some parts are indicated on the schematic but have different values mentioned on the parts list, one part is on the list but nowhere to be found on the schematic. I emailed David G0MRF before proceeding with any step I wasn't sure of. He got back to me quickly with clarification and my build was successful but, IMO, these issues need to be addressed with updated and corrected documentation.

As is it, the build method is "add parts to the board based on the schematic and parts list". This created a problem for me in that a required jumper is not listed as a "component". I built the kit by installing a part and then checking that part off the parts list. When I'd finished, I thought I'd completed the kit. But the jumper was not installed. This resulted in a 6 watt output where 30 watts was expected. David asked me to send him some photos of my completed circuit board...he immediately emailed me back, I installed the jumper and all was well. England to Texas - ain't the internet great!

It is up to the builder to find an appropriate heat sink and housing. Attached to the heat sink are both FETs and two resistors. I now have a 4x6-inch heatsink that seems more than adequate at the 175-watt level (the heat sink in the photo was for testing a low power only). Without a fan blowing on it, it gets warm at that power level during a WSPR cycle, then quickly cools. This was into a dummy load for 2 hours. I have not yet transmitted at a higher power level since I will only require about 120W out for the 5W ERP legal limit.

The finished product performs well and I tend to use it with the Flex transverter output more than with the U3S but it's nice to have a 2nd option available and to know that a sub-watt signal will drive this amp to full output.

Advantages: Relatively low cost for a legal-limit, no big rig or computer needed 630m (CW/WSPR) beacon. Built-in T/R switching (via relays), joy of construction - and something beyond and much different than the many QRP kits that are available
Disadvantages: Documentation assumes you have experience building projects that are not documented to the degree of Elecraft, Heathkit, etc.
Summary: For those who can produce a 950 kHz output and operate crossband, this converting amplifier offers the ability to add a new band to your station - and to do so with an output that will almost certainly allow maximum legal ERP.

Monitor Sensors 630m Transverter

Total cost - $660 ($705 delivered to US in 3 days from VK)

Seamless integration of MS 630m and main rig
This is not a kit but rather a plug-n-play 160m to 630m transceiving and amplifying converter from Roger VK4YB. This is the Cadillac. No crossband necessary (your big rig is tuned to 160m during both TX and RX), no funky frequencies for division, no transverter output is necessay and plenty of status readouts to keep you informed of various parameters during both rx and tx.

This very well-built transverter operates in a linear fashion so all modes are fair game, even SSB since the rules don't forbid it. 4.3 watts in produces 50 watts out with 14VDC and no time limit, a quiet fan (whose speed changes based on internal heat sink temperature). Built-in circuits protect against over drive, high temperature, out of freq operation. The rx path is amplified so no losses occur there.

With this converter and any 160m-capable rig, you can be operating on any mode on 630m in a matter of minutes (provided you have an antenna of course). On my first evening I easily made my first 2-way QSO's on both JT9 and CW, then transmitted and received WSPR for a while, all at 50 watts out (2 watts ERP).

Advantages: Plug-n-play. Easy, clean installation, accurate SWR and in/out power displayed, 6 dB receive gain, small for what it does
Disadvantages: Limited to 50 watts - this provides less than half my legal ERP, no "I built it myself satisfaction"
Summary: The ability to transceive on every 630m-legal mode with any 160m-capable rig outweighs the power penalty (for now!).

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