Monthly Archives: October 2010

The impact of SWR on QRP

Although I’ve had my NorCal 40A on the air for several weeks now, I’ve only rarely made contacts and began to realize that I probably had to investigate the antenna side of the equation.

I spoke with Ron, N7CE, about it and he offered to let me use his tuner/SWR/watt meter. I had built a watt meter but had yet to use it. Ron stopped by at work and was good enough to loan me his MFJ-904 unit. Yesterday evening I hooked the 904 up to my NorCal 40A and immediately realized that the reason for my meager list of QSOs was extremely high SWR, on the order of 3+:1. I’m lucky I didn’t damage the 40A considering how high the SWR has been.

With the antenna and transmitter now well tuned my SWR dropped to about 1.2:1 and I could see that my power out was now just above 3w. Nice. That’s what it should be.

At about 0100Z I heard a CQ from NW6R (outside Sacramento, CA) and responded. Web and I had a 20-minute QSO! Great Circle distance from his QTH to mine is about 625 miles, that’s about twice my previous record with the 40A during a brief QSO into Pocatello, ID a few weeks ago.

I like the display on the MFJ-904 because it’s possible to know both power out and SWR. And the unit is well built. Other comparably built units feature only indicator lights so you know when you’re tuned, but there is no indication of power out or true SWR.

First NAQCC Sprint

Now that I’ve got my NorCal 40A on the air, I decided to try my first contest: the NAQCC Sprint which ran 0030Z – 0230Z this evening. There was one change to the frequencies due to a PJ DXpedition expected to cause QRM near QRP freqs. Unfortunately the shift to 0710 and up, left me out in the cold since my 40A only covers 7023-7066. Undaunted, I left work early to get home in time to join the fun.

40M was in good shape until about 0100Z at which point QRN went through the roof. It appered to be some kind of environmental noise as it started with a distinct “click.” Regardless, I pressed on. Mostly listening through the QRN and occasionally sending my CQ NA. 90 minutes later I called it quits – QRN was just too much.

Came out to talk with the XYL and told her I didn’t make any contacts because QRN was too intense on 40M. Mentioned it was odd how QRN seemed to switch on very suddenly. She suggested that maybe it was the lights. (We had installed these IKEA track lights ourselves some weeks ago.) I decided to see if perhaps my QRN source might be the lights. Fired the 40A up again, heard the QRN as usual. Had the XYL shut off the track lights … presto! QRN disappeared!!

So, even though I had no success on the NAQCC Sprint, I did learn that I need to make sure the track lights are off when I’m on the air. I guess it was all worth it.

40A is on the air!

Although I completed my NorCal 40A several weeks ago, I discovered that while the receive section worked great, I had no output on the transmit side. Took it to work for N7CE to look at on an o-scope and discovered that I appeared to have a cold solder joint on a JFET. Removed and reinstalled the JFET, but still no output.

Then, through pure serendipity I discovered the K9YA Telegraph newsletter. The sample issue I read from 2008 had a brief review from K9PL who had just built the 40A. Interestingly, upon completing his kit he had the same issue I did: great receive but out output. He rewound T1 and, voila! All was well. On the strength of that suggestion I uninstalled, rewound and reinstalled T1 in my 40A and…voila! I scored a QSO on my first call with W0WN in Pocatello, ID. A few minutes later I had a nice chat with KE7LKW in White Salmon, WA.

So, finally I’m off and running. I plan to participate in my first QRP contest on Tuesday: the NAQCC Sprint. Can’t wait!