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Homebrew 630-meter QRP portable: 2-way QRPPP CW QSO’s in books!

– Posted in: 630 Meter General Topics, 630 Meters
Portable Station

I’m a little late with this report but on October 3, 2014, Steve Parks, KF5RYI, and myself were able to get the GW3UEP 630-meter QRP QTX setup in his front yard for the first on-air test and hopefully a 2-way QSO!

Admittedly, the setup was a bit chaotic compared to the bench tests, but we finally got everything hooked up and working well again.  I should point out that we had tried the same setup a week earlier and had a bizarre failure of the driver/VFO.  All indications are that this was a dumb luck failure that ultimately resulted in the replacement of the 4024 binary counter.  Once this was done, the system was working as planned.

The antenna for this setup was very simple.  Steve had recently built an twin-lead fed doublet with legs that were 22-feet long for use on HF while on a backpacking trip.  Using a fiber glass fishing pole and tying the leads together at the feed point, this seems like a reasonable Marconi-T.   Using the homebrew reflectometer and a cheap Harbor Freight VOM, we were able to find a reasonable match for the 1W PA by selecting the appropriate tap on the ferrite rod loading coil.  Adding a single, short radial, the SWR was around 2:1 after adding a parallel capacitor of about 30pF.  Ideally a variable capacitor would have been used but all of the caps I had on hand were designed to handle kilowatts and would have been a heavy overkill for 1W to the coax and hundredths of a milliwatt ERP.

I rushed home for a QSO, about 2 miles away. Sure enough, Steve was relatively easy copy and he had no problems hearing me (NOTE:  I had left the system setup from the previous night’s session so I was running about 250 watts to the coax for an ERP near 7 watts.  I should hope he would hear me well!)  I was so excited, in fact, that I failed to start Audacity to make a recording of the event.  After we completed the QSO, I headed back to his house for redux and take down.

We learned quite a bit with this test.  First, we learned that there is too much clutter.  Using multiple small Altoids tins connected with large BNC jumpers was a bit much.  A better solution would have been to build all of this into a single large box with connections only for power, a key and antenna output.  In fact, this may be a reality at some point.  One has to remember that this project was a “junk-box special” and no parts were purchased to make this system work (aside from the jumpers, which will have dual purpose).  Secondly, straight keys can be a beating in the field, particularly when the contacts are not in good shape.  This problem is easy enough to resolve and an iambic keyer could easily be built into another enclosure allowing the use of a micro-paddle.  Third, the T/R switching is a bit cumbersome.  This action is literally accomplished using a toggle switch.  If the operator forgets to flip the switch, the PA is transmitting into an open circuit.  Not a big deal with these small signal transistors but the station won’t be heard so that needs to be addressed.  Finally, with an antenna this small and so little power using so few radials (one radial during this test and it was only 20 feet long!), this experiment is more of a novelty and proof of concept.  Plus it was a fun field experience and piqued Steve’s curiosity and interest in homebrewing, portable operating and most importantly, 630-meters!

Our story doesn’t stop here!  The following weekend was going to be an even bigger test of both the equipment and Steve:  A solo outing at Hill City Park, about 5 miles away.

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Like a champ, Steve hauled the kit to the park, which I was unaware even existed, and did a fantastic job setting up and matching.  Initial tests yielded a problem, however:  there was no signal received at my station.  I knew I should hear him and had Argo running on the station machine looking for even the slightest trace.  There should be something there.  I’ve detected significantly weaker signals!  Two problems were noted:  First, the radial (radials?) was accidentally excluded.  Fortunately Steve had a spool of wire with him so he was able to add a single radial.  That’s a start.  The second problem was a design problem on my part.  The ferrite rod loading coil was mounted on a piece of phenolic board.  The taps terminate at brass bolts also mounted on the phenolic board which represent clip-lead points for the antenna connection.  The back side of the board is not insulated and was sitting on the grass.  Was RF really flowing directly to ground?  Who knows but it sure should would have been a big problem while running QRO so would likely be at least a small problem at QRP so placing the board on leather case used to hold the cables has become the standard operating procedure.

Once the adjustments were made, the signal was actually quite loud, really surprising given the amount of power and the antenna system.  Unfortunately an approaching storm system resulted in very unusual daytime noise levels and static crashes.  That’s OK.  This test showed that the results using the system were repeatable in spite of how cumbersome the setup was.  Steve did a great job organizing the components and placing only the necessary items on the camping table operating position.   The test also represents what is probably the only QRP portable work being done on 630-meters.  Hopefully going forward this can expand.  I’ve always thought that the QRP community was a good fit for MF and 630-meter specifically.

So what happens next?  As previously stated, this exercise is more novelty than anything.  In the interest of practicality, more power, simpler setup and better antenna will be necessary and it all has to be compact for portable use while camping, hiking, or just spending the day at the park.  The solution seems to be the use of the Elecraft KX3 with an MF Solutions transmit downconverter plus a larger coil wound on a 6-inch PVC tube that can be used to hold the KX3, downconverter, battery, phase meter, and associated cables during transport.  This arrangement will allow 20-22 watts of power to the coax which should result in a more practical portable operation and the larger coil will be more efficient than the ferrite rod.  The downside will be the necessity of equipment for accurate impedance matching and a phase meter utilizing the sense components typical to the scope match solution should be able to be sufficiently miniaturized for portable use.  High voltage safety will be a necessity as well.  While a larger portable antenna is in the works, depending on the radial system used and the quality of the local ground, system voltages could range from 700 volts to well over 1600 volts.  Proper antenna placement will be a necessity and considerable time will be spent with this component to ensure operator safety.  We don’t need to be starting any forest fires either!

We will continue this project through the winter in hopes of  having a workable system by the time spring rolls around in 2015.