Analog Signal Processing

In the November issue of CQ magazine, there was a great article on an interesting kit. The kit is a regenerative audio filter. The filter, according to the designer, Phil Anderson W0XI, removes or scrubs galactic and man made noise from the audio, leaving only the CW note. At first I thought, interesting, but really??

First, some background. Band noise on some receivers can really get bad, not only bad but teeth grinding, chalkboard scraping annoying. I got rid of a transceiver which was nearly unusable on 40 meters. The noise blanker did nothing to touch the noise. Currently, I am now using a Yaesu FT-817ND which a month or so ago, I was in the backyard with a wire in a tree checking into the NAQCC Rocky Mountain QRS net. It was a rugged contact. The noise level that day was really bad. It started me thinking about different options to deal with the noise level. My two choices were the NEQRP SCAF filter (Temporarily out of stock) or the W4RT installed BHI DSP filter. The SCAF is about $30-35, and the BHI is $169 installed. I was pondering the two when I bought the November CQ magazine to read a review on the Elecraft KX3 and found the article on the CW regenerative filter by Midnight Science.

Meanwhile....

I walked into my wife's sewing room who looked at me and said: “You look bored”. I replied, “I am”. She then said, “You need a kit” First rule of marriage, do not argue with a woman, especially when she is right. Between the CQ article and the need to melt solder, I ordered the regen kit. I went the full meal deal and got the case along with it. It is a basic through hole component kit with 5 chips, resistors, capacitors, all the hardware and a voltage regulator. It is a high quality kit with everything included and integrates nicely in the case.

Now the performance, I was blown away by the ability of this filter to remove noise from a signal. After completing the kit, a random wire was connected to my FT-817 and the filter switched in. You have the option of bypassing the filter, if you wish, by pressing a button. I was amazed at how much static and junk was removed from the band noise. Indoors at the time, when I switched on a fluorescent light, I got a load of extra noise. When the filter was switched in, the lamp noise, along with most of the static, was just......GONE. It was flat amazing. I went to 20 meters and found some CW signals to tune. When you cross the designed frequency (You have the choice of building for 500, 600 or 700 Hz) the signal noticeably peaks. The noise is gone and stronger signals are a pleasure to listen to. I then tuned to a weak signal which was going in and out of the noise. I brought up the regeneration setting until the filter broke into oscillation and then backed it off a skosh. The signal had a slightly hollow, slight echo quality to it at the sweet spot of regeneration. I switched the filter out and listened until the CW started into a deep fade, I then immediately switched in the filter and the signal popped into my headphones. From completely in the noise to easily copyable, the filter is flat amazing. Even if you are not listening to a weak signal, back off the regeneration and use the filter just to clean out the noise, you can listen for longer periods without fatigue. This is one of the best purchases I have made.

72,

Bob

USBlink Digital Interface

One of my favorite modes is PSK31. I had seen the USBlink project on the fine website of Julian, G4ILO, and the project looked downright useful.

http://www.g4ilo.com/usblink.html

Julian used a cheap USB sound card dongle. Mine cost under 5 dollars US including shipping. The rest of the USBlink is the Skip Teller digital interface circuit for PTT to the transceiver. There are several things I like about this interface project. First is the USB cable. I built the original Skip Teller KH6TY interface from the June 2009 issue of QST. I like the function of the interface, but not the two audio cables hanging out. The USB cable is a nice alternative, no fumbling with which cable is mic and which is phones, just plug in the USB. I built the interface with a six pin din connector. The main reason for the six pin din was my FT817 and Icom IC703 have that connector for digital connections. Interestingly enough, both radios have the same pinout. I can make one cable with straight through connections and not worry which end is plugged into the radio or the interface.

I made only two departures from the USBlink original. First was the the USB connection, I wanted the B type USB connector so I could use a standard B to A cable which you can steal off your USB printer in a pinch. I picked up a female B and a female A connector and wired them together. The dongle plugs into the A connector and the external USB cable plugs into the B connector. The second difference was the green LED. Just like Julian did, I clipped off the green LED from the dongle and soldered wires to a larger LED mounted on the case. I noticed however, the green LED was much brighter than the red Transmit LED. I wanted both LEDs to be about the same intensity so I put a 1K resistor in series with it and now they are visually comparable.

This project is nice, compact, and inexpensive. I got the box and components from my junk box. The purchases were the USB connectors, the sound card dongle and the cable and din connectors. The entire project cost $15 tops. I was in need of a nice 4 conductor cable for the project so I went to RE-PC in Seattle and in the used cable area, got a 15 foot USB cable for one dollar. I clipped the ends off and have enough cable to make five, three foot cables. I don't have that many radio's but I'm sure the cable will come in handy for other projects.

72,

Bob, AD7BP

Low Noise End Fed Half Wave Antenna

This afternoon I grabbed my ATS-4 to hop on 20 meters and do some operating. My ATS-4 had 5-6 bars lit on the S meter display, which translates to NOISY, but not sure what the corresponding S reading is. I wish I had my FT-817 so I could have looked at a regular S meter. I tuned around and heard some signals, some were copyable, but it was just too noisy to really operate. This is obviously not the first time the noise was just too high to operate. I was, by the way, in the backyard with one of my end fed wires in a tree. I pulled the wire out of the tree and strung it across the ground and the S indication dropped from 5-6 bars down to 1-2 bars!!! So, I decided to FINALLY change one of my tuners to allow switching between two different wires. 

Most of my tuners are very small and compact to throw it in a pack and go into the woods. I have one large tuner with a real capacitor and added a switch and a second terminal for the “low noise” wire which lays across the ground. I guess the only downside to this arrangement is having to flip the switch going between transmit and receive. But, if I can knock down the noise by two thirds, it is more than worth the hassle. Since I mostly operate on 20 meters, I only have to cut a single wire.

72,

Bob, AD7BP

Summer Tomatoes

It is about time I made another food post, seems that ham radio is taking more of the bandwidth than food.

I love summer, my favorite part is the crop of produce which is available. My two favorites are fresh figs, which are past and gone. They were delicious though! And tomatoes. I was at the local Costco and there was a 25 pound case of California Roma tomatoes calling my name.

We like a simple pasta sauce of olive oil, garlic, basil and tomatoes. Being a fan of putanesca, I toss in capers and Greek olives with my serving. With sauce in mind, it took me nearly 3 ½ hours to cut up the tomatoes. The cut tomatoes were put into a 2 cup measure and poured into a food storage bag for freezing.

25 pounds of tomatoes yielded about 25 bags of tomatoes for the freezer. At $11.65 for the case, the tomatoes for each meal is roughly 47 cents. Considering one pasta meal a week, this one purchase gives 6 months of nice tomatoes for pasta night. I did have a thought. We normally grow basil to make pesto to freeze. Since we are stocked in the pesto department, no basil was planted. Major mistake! Though I like the flavor of dried basil, 4 or 5 leaves roughly torn and tossed into the tomato sauce right before serving gives the sauce a bright, fresh flavor. That mistake will not happen next summer.

Life is way too short not to make a meal which puts a smile on your face. Cooking need not be complex to be satisfying. Make something good this week!

Bob

Radio in the great outdoors

I finally got the week off I have wanted all summer. OK, truth be told, I got sucked into work Wednesday and a couple hours Thursday in the morning. But..... My friend Eldon, WA0UWH and I had a radio trip planned for Thursday. I hit home long enough to change into some proper outdoor clothes, lit off the espresso machine and back on the road. My radio gear was already packed and waiting. We went to Mt. Pilchuck, which is northeast of the Seattle area and drove up a forest service road to a nice vista looking west to Puget Sound.

One of my favorite terms is: “This is not my first rodeo” When it comes to outdoor ops, this is certainly not Eldon's first rodeo. As you can see below, we had a nice table, mast for the end fed antenna and shelter to keep the sun off of us.

Being in the Seattle area, I take trees for granted. There is always a tree that is much too high to throw an antenna wire into by hand. On Mt. Pilchuck, the tallest tree was 12-15 feet. Needless to say, my antenna paled in comparison to Eldon's 36' mast which elevated his wire, but shockingly enough mine worked well.

Propagation was not happening like we would have wanted, but we did get a few QSO's in the log, including a 40-45 minute PSK31 chat with a California ham at 5 watts using the internal battery (W4RT) in my FT817. Shortly after we signed, I looked at the voltage display on my radio, smiled at Eldon, went key down on CW, which shut off the rig. About 6 hours of operation, including the 5 Watt PSK contact, on one charge. Not too shabby.

Finally: Mountains, radio and man's best friend. (Eldon's dog Tess.) Who could want more?

72,

Bob, AD7BP

Pounding Brass

I really like CW keys, and I own a few of them, but a couple of things bother me. First is the cost, I have shelled out a few bucks for some keys and only one had the best ratio of cost to performance and that is my Czech Army key, it is the best key I own.

 Last week, I was using an old key that I got a when I got back into ham radio 9 years ago which is the brass key made by Ameco. I picked that one up because it was what I had as a Novice back in High School. I was using it the other day and it was horrible. At the contact point I could hear in my headphones the start of a dit or dah and it dropped out then in when I mashed the key contacts together. It sounded like a 600 Hz static right before the dit or dah. Enter my homebrew key. It is small, built in a 1.4 x 1.4 x 0.6 inch Hammond case. The heart of the key is a small microswitch. The microswitch makes a good, solid, clean, make and break giving me nice clean sounding sidetones in my ear, and hopefully nice clean CW out of my rig.

I built it intentionally small to go with my ATS-4 and MTR, Steve Weber KD1JV radios. Did I mention price? The switch and case are just over five dollars total for both. The rest of the hardware is in my junkbox. The rubber feet are from my favorite antenna store, Home Depot. All in all, it makes a great key for portable use. I have parts to make a couple more and am tempted to put a real CW key knob on the key, which will make it look even sillier than it looks now, but what the heck, it works well. Isn't that what matters?

72,

Bob

End Fed Half Wave Antenna

OK, call me an antenna snob, but in my opinion the End Fed Half Wave antenna is about as good as it gets for an easy to put up, great performing antenna. I am a coffee snob too, but that is another story. I came across EFHW antennas a while back when I was just starting to figure out antennas. My best and favorite source for end fed information is Steve Yates, AA5TB's great site http://aa5tb.com/efha.html The tuner is “Stupid simple” to assemble, but an antenna analyzer is really helpful in tuning the antenna wires. The only downside to EFHW antennas is the need to cut a different wire for each band. The upside to EFHW antennas is no long counterpoise. The antenna tuner needs a 0.05 wavelength counterpoise to work properly. Three turn primary from the radio and 24 turn secondary with a capacitor across it. That is it.

Lets take 20 meters, 468/Frequency = Half wavelength: 468 / 14.0 = 33.42 feet for the half wave wire.

Move the decimal point over one to get the 0.05 wavelength counterpoise of 3.34 feet.

I thought it odd at the time that a 3.34 foot counterpoise was necessary to make the antenna work, but when I disconnected it, the antenna would not tune very well. When I connected it back up, I could tune to 1.0:1. Below is the small version I built for my MTR radio. I typically use T50-2 toroids for most of my QRP tuners, but I did not have any of the T50-2's handy, so I substituted a T30-2 from the junkbox. Since the bandpass filters on the MTR use T30-2's, I figured the antenna tuner would be fine with that small a toroid. It did work! I used the tuner on 20 meters for the first time, for the first QSO, and made a nice contact with Gary, K5ON in NM at just over 1,200 miles. Nice!

Tuning the wire is an interesting process. AA5TB has you connect a 4.7K resistor across the tuner antenna connections and tune the analyzer to the band portion to which you want to center the antenna. Tune the capacitor on the tuner to get the lowest SWR. Leave the antenna tuner alone and start pruning the antenna wire until the SWR drops to the value with the resistor connected. One quick comment about that. Even though I tune for the CW portion of the band, the antenna SWR up in the phone portion is still very low.

I tune the the wire a tad different than AA5TB. (For 20 meters) The length of 468/14.0 drops you to around 13.8 MHz. What I do is fiddle with the analyzer and antenna tuner to get 1.0:1. Once I find the sweet spot on the tuner, I nibble a quarter inch at a time off the antenna wire and slowly walk the wire resonant frequency up to where I want it to be. You typically need to tweak the tuner a little bit (less capacitance) as you walk the analyzer up. Again, I tune the 20 meter wire for 14.050 MHz, but up in the SSB portion of the band, the tuner still tunes 1.2:1. Nice bandwidth too. One last thought, you can tune the EFHW by ear for max band noise. I know some of the QRP tuners have a resistive bridge LED SWR indicator gizmo attached, but you really do not need it.

Give an EFHW antenna a try. You will become a believer too!

72, Bob