Tag Archives: Homebrew

My Spectrum Analyzer Addiction (and Education)

I recently returned to amateur radio after a 50+ year absence, and have been assembling a collection of vintage radio gear, and vintage and more modern test instruments to maintain this gear. While I have a long, strong background in electronics and am familiar with and have used a wide range of test instruments over the years, prior to a few months ago I had never seen a spectrum analyzer and was only vaguely aware of their purpose and functioning. While cruising the classifieds at eHam, QRZ, and QTH a few months ago, I happened to notice an Agilent 8560E spectrum analyzer in working condition for sale at a very low price. After doing a little research online, I emailed the seller with an offer at an even lower price, and he accepted my offer. A few days later, this beast arrived, all 40+ pounds of it. It did not come with a user manual, but I was able to purchase one on eBay and did enough reading to figure out how to fire the SA up and do a preliminary checkout. Sure enough, it worked just like the manual said it should, and was in very good cosmetic condition, with just a few minor battle scars on the case. This instrument listed for about $50,000 in the mid-eighties when it was in production. So, with this acquisition, I thought I was set for life as far as SAs go. Wrong!

A few months later, I was cruising the classifieds again, looking for some Collins S-line gear and happened across a listing for a Tektronix 495P spectrum analyzer which was described as “works and looks like new,” and, again, at a tiny fraction of the $30,000+ original selling price around 1990. I was skeptical of the “looks new” description, but “new” is good, so I asked the seller to confirm this. He emailed some details of the history of the instrument and more photos, all of which convinced me that he was accurately representing this instrument. The “want” side of my brain quickly overcame the “need” side and I emailed an offer which he accepted. As before, a few days later, this beast arrived in the original Tektronix shipping carton, weighing 70 lbs; this weight included the SA, hard copy user and service manuals, and a few accessories. And it did, indeed, look like new. Turns out some branch of the U.S. government had purchased a bunch of these, sealed them in new, unopened cartons in humidity resistant packaging, and stashed them in a warehouse for years, finally offering them for sale as surplus much later, when the seller I purchased from bought one. And after reviewing the manual and stepping through the initial checkout chapter, I found it did work to spec. Now I was really set for spectrum analyzers! Wrong!

A few weeks later, the guy I bought this one from emailed and told me he had another Tek 495P that “almost works,” and which he had acquired for parts, as the 495P has not been supported by Tek for many years. Then he made me an offer I couldn’t refuse: he would give it to me if I would pay the shipping cost from CA, about $70. How could I possibly say “no”?  Here we go again! It took him three months to get around to shipping it, but eventually a 50 lb package arrived. Having seen quite a few “parts” 495s for sale on eBay, I wasn’t expecting much. But, I was pleasantly surprised. While it could not be accurately described as “looks new,” it was quite decent for an instrument manufactured in 1991 (according to the Tek inspection tags inside), and, it worked! Well, … sort of. In stepping through the initial checkout section of the user manual, it displays traces that resemble the illustrations in the manual, however, according to the messages displayed at boot up (this is a microcomputer controlled instrument), it thinks it is a 492AP model SA rather than a 495P. The 49x series of SAs share a common base of microcomputer code, with the specific model type selected by DIP switches on a memory board. There is enough functionality that I decided to try to fix it rather than use it for parts, and I am now launched on that path.

This is an amazingly complex instrument. The two-volume service manual runs some 700+ pages. Fortunately, the problem I am seeing is in the microcomputer controller subsystem, where I am somewhat competent, and not in the analog/RF subsystems, where I am not. This repair effort has travelled an interesting path, along which I have met (online) some helpful and accomplished people and found a number of resources I was not previously aware of. One of these is the [email protected] forum which is mainly focused on keeping vintage Tektronix gear running. This has been a great learning experience and I am confident the fix is close at hand. We’ll see! Still much to learn, however.

My cup runneth over with spectrum analyzers. I’m not sure if there is a 12 step program for SA addiction, but I may need one. I find myself still eagerly looking at for sale listings. I am thinking that I should at least have one of the modern Rigol SAs to balance out my vintage collection. Sure seems rational to me!

Rick, K8EZB

Daiwa CNW-419 Tuner Repair

Although I am brand new to the hobby of ham radio, I have been playing around with electronics and digital circuits for as long as I can remember. I am a software engineer by trade and have always loved the problem-solving challenges that software and hardware engineering offers.

Given my unfamiliarity with the ham radio world, however, I thought it might be fun to find a project in that space. Enter the Daiwa CNW-419 manual tuner.

Our Next Victim

My father found this poor soul on eBay, and it was in a bit of a bad way. It had some missing feet, the tuner button “didn’t work”, and there seemed to be a couple of loose pieces in the pictures, but generally the interior of the tuner looked very clean.

After looking up some reviews of the tuner and finding nothing but praise, I thought what the heck, paid the $75 and took the plunge.

It arrived carefully packaged, and after unwrapping it, I found that the tuner switch was indeed broken. In addition, the switch to change the antenna (it supports two antennas), didn’t seem to be working properly either. Both of the switches were push buttons, and neither of them would latch.

Taking It All Apart

A first look under the covers

Time to take the cover off and see what was going on. With just the top cover off, we can see the two problematic switches in the back. If we’re going to get to those switches, a lot more stuff is going to need to come off.

After removing the bottom, and disconnecting the back panel, we get a better view of the switches. Some black charring there, perhaps some RF arcing took place? Looking at the rest of the box and how neat and organized the soldering and wiring is, this looks out of place. I am beginning to suspect something is amiss here.

After pulling the switches completely out, there definitely appeared to be some sort of overload. Or perhaps just bad soldering? More investigation is clearly required.

Our problematic switches

The Game is Afoot

Examining the part number for the switches I pulled out, I was able to find the equivalent switch on DigiKey. The schematic for this switch indicated that it was simple non-latching push button ON-ON DPDT switch. Clearly not the original part, as the tuner front panel artwork indicates that these are latching push button switches.

At this point, I headed back to google to see if I could find what the original switch was, but could find nothing. Finally, I stumbled across an interior shot of the tuner from a guy in Thailand. After some zooming, it looked like an ordinary latching switch.

But First Some Math…

The tuner is rated for a maximum of two hundred watts, so we should figure out what our switches need to be able to handle. We don’t want to trust the previous components ratings since they were not original.

One hundred watts at fifty Ohms yields an RMS voltage of about seventy volts which is what my receiver puts out. Since the tuner is rated to two hundred watts our max RMS voltage should be one hundred volts. 125VAC switches are plentiful, and to be safe we should also probably shoot for a switch that can handle around five amps. Eight dollars and fifty-two cents later, we have a pair of switches rated at 125VAC and seven amps. Perfect.

Putting It All Together

I took lots of photos and notes while removing the switches but knowing that they could have possibly been installed incorrectly, I took a little extra care in laying out the connections for the new switches.

The switch for the antennas was straight forward enough. This was simply a DPDT doubled up and wired as a SPST with the center poles connecting to the center pole output of the tuning circuit switch.

The new switches installed

The switch for the tuning circuit was a little peculiar. When the tuning circuit is disengaged, the switch should connect the output from the amp making sure it passes through the metering circuit and bypasses the tuning circuit. Originally, the switch connected the first pole to the second pole of the switch using only the thin wire of a small capacitor hanging down. This was clearly insufficient, and somewhat dangerous as that thin wire would be passing the full power RF output of the amp. I suspect this probably happened at one point as the capacitor wire was extremely brittle, and broke after I removed it.

A Puzzle for Our Readers

The dangling capacitor was likely a power filter circuit (that’s my guess). You can find these on regular power circuits where a high voltage cap connects the power to ground. I assume they are also used on RF power circuits. Is this correct? Ham radio experts feel free to chime in. I tested the untuned circuit path both with and without the cap filter but could discern no difference. I suspect it might have been affecting my output signal, but I had no way to test that. In the end, I left it connected, figuring I would not do much transmitting with the tuning circuit disabled.

Tuning it Up

Time to test it out. Here it is with some new rubber feet from the hardware store ($2.47) sitting on top of my FT-450D.

The new, and the slightly less new

I purposely detuned my vertical, disabled the ATU on my receiver and checked the SWR. Infinite SWR readings for both the tuner and my receiver. Great. The auto tuner on my receiver can’t touch that. I then enabled the tuning circuit on the Daiwa, found the best band setting, and tuned it up. In no time I had the SWR down to one, and the forward power at maximum.

I love this thing.

Antennas: Where There is a Will…

The 2017-2018 contest season featuring the “big four” events (CQ WW SSB, CQ WW CW, ARRL DX CW and ARRL DX SSB) recently came to a close with a resounding thud. The Solar Flux Index seems to have flat-lined below 70 as we bottom out in the current sunspot cycle. This translates to little DX above 20 meters. For 40 meters and down to Top Band, however, no sunspots are good. I remember the fun I had during the last cycle bottom when I roamed Top Band as an avid bottom-feeder pulling in choice DX from the Pacific and Asiatic Russia. I had a pair of K9AY loops oriented in a cross configuration to enable me to select the four cardinal directions. The loops worked wonders at reducing the high noise levels on 160 meters. They also worked well on 80 meters during noisy conditions.

Alas, being in the land of CC&R and clandestine antennas (read: low, short wires and verticals), Top Band operation is non-existent. Yes, there are some diehards here who have a convoluted run of wire that is heavily loaded and fed with a tuner struggling to make a match. Working FL, GA, AL, Cuba and the Bahamas becomes the high point in a Top Band contest. If 160 meters is not practical, perhaps there is something to be done for 80 meters.

I think I may have found a way. About a month ago while the family and I were on a cruise, I noticed a three-masted sailing vessel at one of our ports of call. I was intrigued by the mess of ropes and sails on the ship and wondered how the sails were hoisted. Each sail is attached to a series of collars that ring the mast. As a sail is hoisted, the collars ride up the mast, much like a shower curtain that is pulled close. As my few brain cells coalesced on the concept, it occurred to me that I could do something similar with my PVC flagpole. In lieu of a sail, I thought of an extendable fiberglass mast like those usually found at hamfests. The base for the mast would be two or three feet away from the flagpole to hide it from direct view of the street. My thought is to erect a 40-foot mast using the sailing vessel approach to guy the mast against my flagpole. This approach would provide a support near the 22-foot top of my flagpole with a couple of guy ropes off the top of the mast. The mast to flagpole connection would be fixed at the 22-foot point with the mast.

So what kind of antenna will go on the mast? I did some modeling with EZNEC to see what an inverted V for 80 meters would look like. Each leg would be about 56 feet long if the anchor points are out 40 feet from the mast. First look at the antenna should reasonable performance – above 3900 kHz; not an area of the band I care to operate in. I added some inductive loading at the feedpoint to electrically lengthen the antenna. I was able to get good SWR performance for the lower 100 kHz which encompasses the CW and digital parts of the band.

(Note: The casual observer may notice that a 40-foot structure in a CC&R territory is begging for a visit from the local vigilantes. This problem is adequately mitigated by the fact that 80-meter propagation favors darkness so I would not raise the antenna until after sundown. I would have it down before most folks get through their first cup of coffee.)

Now that I have a sporting chance with something other than the fat coil plus 3-foot wire that I currently have with my 6BTV vertical for 80 meters, I needed to come up with a better receive antenna. While power-washing the moss and mildew off the side of my house I experienced another epiphany as well as a tired back. My house has vinyl siding, good for growing moss and mildew but it also non-conductive. I had been thinking of a K9AY loop but the loop needs a vertical support and has to be away from large objects such as a house. I looked at other receiving antennas such as the flag and pennant antennas, so called because of their physical resemblance to said shapes. These antennas have a length similar to the K9AY loop and function the same way, i.e. the intended receive direction is the feedpoint and the opposite leg is terminated in a non-inductive impedance. The antennas are mounted about 20 feet at the top point so that the lower leg allows clearance for people and critters.

While I am not able to raise a receiving antenna up 20 feet, why not slap in on the side of my house? I have an expanse of siding about 32 feet long by 8 feet high without windows where I could install a pennant antenna. The antenna vertical section would be about 8 feet at the top and about 0.5 feet above the ground at the bottom. The sloping parts of the pennant would run to the front corner of the house where the termination/junction point would be conveniently hidden by shrubs. The feedpoint, located halfway up the vertical section, would be hidden along the edge of one of my bedroom shutters. I can use yellow wire for the pennant to match my house color to add more stealth. If nothing else, I can always pass the pennant off as artwork on the side of my house. Many homes in The Villages has decorative metal artwork on the walls so I would fit right in.

So how would a “slap-on” pennant work? Back to EZNEC for some more modeling. I checked the antenna patterns for a frequency of 3.550 MHz and a termination resistance of 900 ohms. At an elevation angle of 35 degrees, I have a gain of -31.4 dB and a front-to-back (F/B) of 21.0 dB. I compared the performance of my pennant with a design by K6SE that has a 14-foot vertical section and is 6 to 20 feet above the ground. Total wire length is within a foot for both antennas. At 3.550 MHz, the K6SE pennant shows a gain of -26.6 dB and an F/B of 21.6 dB. Not bad.

To compare my pennant design to the K9AY loop, I ran patterns for 1.8 MHz since I had data for the K9AY loop for 160 meters. The K9AY loop sports a gain of -23 dB while my pennant manages a gain of -41.9 dB. It is likely that such a difference will also be the same for 80 meters. It is a good thing there are preamps available.

Now that I have the will, I just need to find the way to make it happen in time for the next contest season.

Ed, K2TE

Breadboarding Software

Here is some best free virtual breadboard software to design electronic circuits. You can design a sequential or logical circuit on a breadboard and then simulate that too. Just drag and drop the circuit components on the board.

Breadboard Software

FRITZING offers a long list of electronic and electrical devices that you can add to the breadboard. Export the design as PDF, JPG, PNG and other formats. Free but donation suggested. FRITZING

Breadboard Software

BREADBOARD SIMULATOR is free and quite powerful. It not only lets you design a circuit on breadboard but you can even simulate it. The software is portable so it can be used from a USB drive easily. Design, hit the PLAY button and if it is correct, save the project but you can only save the project in the software itself. Breadboard Simulator

Breadboard Software

IC on Bread is free and open source. It is a simple software for newbie students to design a basic IC circuit and simulate that. It can be exported as an image. You can make wire connections and add different LEDs at different positions. After design switch on the power supply and see the flow of the current and analyze it. IC on Bread

SOURCE ARTICLE: http://www.ilovefreesoftware.com/01/featured/free-virtual-breadboard-software-design-electronic-circuit.html

I have not personally checked out these programs but I hope this article can benefit our Members and Website visitors … Layne AE1N