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Recent tinkerings (19 May 2012 edition)

May 19th, 2012

I try not to do these “meta-posts” too often, but time has been of the essence lately and it’s been hard to find enough time to sit down and write something coherent when most of my “ham time” has been devoted to DXing or antenna work.  This post covers tinkering and operating from K8GU since January (!!).

I am not at Dayton this year.

Worked 7O6T on three bands (20/17/15) on CW and also on 20-meter SSB.  The only one I spent more than five minutes for was 20CW, which was during the first few days of the operation.  Normally, I would have waited, but since this was in the land of pirates and AQAP, I decided to play it safe in case there was an international incident that curtailed the operation.  My friend Steve, K0SR, gave me a hard time when I bragged about working them with 100 watts and a dipole.  You can do that on the East Coast.  He’s right.  DXing and DX contesting from the Upper Midwest (aka The Black Hole) is hard.

Did not work 6O0CW (Somalia) or 9M0L (Spratly).  XX9E (Macao) is doubtful since it’s a short DXpedition and I’ve only heard them once so far.

My 2011 Sweepstakes “Clean Sweep” mug arrived.  Sarah banished it from the kitchen because it’s canary yellow.  I think it’s hand-wash anyway, so it will continue to hold baby-proofing outlet covers and look good on the top shelf in my shack next to the liquid-crystal painted Jicamarca mug.  Speaking of baby-proofing, Evan is on the move…

I built a gate that fits in the aperture of my shack desk.  An unintentional feature of this is that I can still reach the keyboards through a gap at the top.  It’s a little hard to send CW through there.  But, it keeps curious Evan away from the jungle of wires that make up this “wireless” station.

In January, I took down my VHF antennas from the main house chimney.  I had estimated the wind surface area of the chimney and determined that the wind load of the antennas increased it by 15-20%.  Since I know that the guys (it was built in 1946ish, so yes, guys) who built the house didn’t do any calculations I figured that the safety factor was at least a factor of two.  But, I was growing increasingly uneasy about the torque exerted by the antennas on the chimney, so I took them down.

In March, I had the opportunity to pick up (from K3AJ, who beat me by three QSOs in ARRL SS CW last year…need to be disciplined since I left 4 hours on the table) a M2 2M9SSB Yagi for two meters on great terms (per usual).  This antenna is lighter and stronger than the homebrew K1FO that I had been using.  I cut up the elements from the 2-meter K1FO to make Yagis (also K1FO designs) for 222 and 432 on 10-foot booms.  Need to finish those and put them up.

We have another, shorter chimney on the addition that houses my hamshack.  This chimney has served as the anchor for my 10-meter rotable (by the Armstrong method) dipole for a while now.  Branches from a nearby tree have impinged on the rotation somewhat, but since it’s bidirectional it hasn’t been a big deal.  But, I decided that this might be a good location for the new 2M9SSB, the A50-3S (3-el 6-meter Yagi), and the 10-meter dipole.  I himmed and I hawed.  Then, I climbed the tree and sawed.  It’s a miracle I didn’t end up with poison ivy.

I upgraded the 10-meter dipole using hardware from DX Engineering so it could be mounted to a mast (old method was not mechanically sound, especially for something that would be rotated with a T2X).

A few weeks ago, I assembled and installed the whole mess…see photo at the top of the post.  I’m now using a Hy-Gain T2X (purchased at Dayton in 2005—I showed up at my in-laws’ grinning ear-to-ear with the motor in one hand in the control box in the other—they still love to tell this story) instead of a CDE TR-2 rotator.  The T2X can probably turn the house.

A spring wind storm dislodged the branch that supported my 80-meter wire vertical and one end of the 20-meter dipole.  So, I cleaned that up last weekend.  By “cleaned,” I mean I took both of those antennas down.  I also took down the 160-meter TEE because one of the TEE wires was very close to the new VHF array.  At this point, I was only QRV on the “Technician bands”…minus 80…40/15/10/6/2.  I almost got the 160-meter wire all the way out of the tree except the rope that supported the center (TEE junction) bound up with the junction about 10 feet off the ground.  So, I improvised a hot knife on a stick to cut the poly rope:

It worked great.  As she should have, Sarah gave me a hard time.  There are two types of people: those who watch Red Green and there are those who inspire Red Green.

Taking a wonderful brilliant hint from N4YDU, I replaced my 30-meter coax-fed dipole with a 30-meter open-wire-fed dipole.  While I prefer resonant single-band antennas for contesting (clean patterns and nothing to touch when changing bands), every other kind of operation can tolerate tune-up.  The open-wire-fed 30-meter dipole not only tunes well on 17 and 12 meters, it just has a slightly narrower pattern!  An aside:  After the 2010 ARRL 10-meter contest, I posted to the PVRC reflector that I had been running 100 watts to a dipole at 30 feet.  This prompted my neighbor (who lives about 2 miles away, a neighbor for bands below 76 GHz) K3KU to pay me a visit because I had beat him in every pileup that weekend.  He thought surely I was running a KW to 5 elements at 60 feet!  He runs an open-wire fed 135-foot long dipole on all bands through a tuner.  The pattern of that antenna looks like a sea anemone on 10 meters!

Worked D3AA on the third call on 30-meter CW last night.  So, I guess that antenna is working.  Also worked VP9GE on 6 meters. There’s a certain amount of satisfaction working DX with a transverter you designed (mostly) and built yourself.

I have a wicked RFI problem on 6 meters when I run the amp (150-watt Mirage brick).  It’s probably RF on the power lines, although it doesn’t set off the CO detector like 40 meters does.  So, it could be RF pick up on the audio wiring in my shack.  In any case, need to get that worked out before the ARRL June Es contest.

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QST Digital Edition beta

April 22nd, 2012

The other day I received, like some unknown number of others, an invitation to try the QST Digital Edition beta for the May 2012 issue.  I am not a hard-core mobile/digital media user.  But, Sarah is a librarian who has specialized in management and procurement of electronic journals and books.  So, she gave me the low-down on what to look for.  And, over the years, I’ve given her what-for about eBooks because, as I like to say, “I am willing to risk a single print copy of something by taking it places I wouldn’t risk taking an electronic reader.”  That sums up the perspective I took when reviewing e-QST.

You can read about the Digital Edition on ARRL’s FAQ here.  The desktop version requires Flash to use in-browser or Adobe Air and an enormous download to go stand-alone, neither of which really warmed my heart.  But, it does work in the web browser of a mobile device.  I have a 2nd generation iPod Touch running iOS 4 and it worked great in Safari.  I now have a bit of insight as to why people might love their iPads (which I have always viewed as a more-expensive, less-convenient version of the iPod Touch or iPhone).  There appear to be only two levels of zoom: fit page width and zoomed-in.  No matter how good your eyesight, you need to be zoomed in to read because the characters don’t render legibly otherwise.  I think iPad’s larger screen might make reading it easier.

Browsing page thumbnails was OK, but it’s difficult to actually know what you’re looking at before you select the page.  It also would be nice if the pages were numbered in thumbnail view.

One of the big advantages of the Digital Edition is that you can do things you can’t do with the print version, like including audio of JT65.  Granted, I think almost anyone who’s active on HF CW or digital knows what JT65 sounds like, but it’s a basic demonstration of the kinds of things that will be possible in the new format.

Given that I’m usually done with one month’s issue by the time the next one comes out, the Digital Edition is alright for basic browsing and reading.  It’s much faster to skim the print issue, at least with my barebones 768 kbps DSL connection and the higher visual bandwidth of print (read Tufte’s essay The Cognitive Style of PowerPoint for more on this and other interesting reasons to hate slide decks).  The mobile version also requires you to be connected to the Internet to browse.  It turns out that an entire issue is on the order of 350 MB to download stand-alone on a computer.  This makes it difficult to take places where I often want to read QST (on airplanes, for instance)…  It is possible to print from the desktop version (I tried it using 32-bit Windows XP and Firefox), although it seems to be slower than the mobile version (not entirely unexpected).

Another thing that’s a bit different is that if you download the offline content to your desktop, you still need to authenticate to open it.  It’s not clear whether this continues if you drop your ARRL membership.  It is a bit different than owning boxes of back issues…even if you drop your membership, you still have the magazines.  I don’t think this is a huge concern for most hams, who probably wouldn’t be interested in old QSTs if they dropped the membership.

In summary, I like the concept of the Digital Edition, but I wish I could carry off-line issues around on my mobile device.  ARRL hints at this in the FAQ, so I am hopeful.

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OAx/K8GU

April 3rd, 2012

Loyal readers know that from time to time, I am fortunate to travel to interesting and exotic locales for work—they usually come in pairs, so Greenland and Peru are it for a while.  Although the motivation is usually field work, occasionally a conference pops up.  The International Symposium on Equatorial Aeronomy occurs every three to four years and can be counted on for an exotic locale.  Sarah had such a good time when we attended the 12th ISEA in Crete in 2008 that she insisted on attending the 13th in Peru with me this year.  Of course, Evan complicated that a bit, and so we evaluated the pros and cons of leaving him with grandparents or bringing grandparents along, eventually finding a willing pair of grandparents to come along.  If you’re interested in a general travelogue (and following posts) and some photographs, you might check out my father’s blogs.  This short post is mostly focused on radio aspects of the adventure.

In retrospect, it may not have been such a good idea to bring ham gear to this meeting.  Between being the most seasoned traveler in my family and the only one with a functional command of the Spanish language, plus Evan, plus hours of meetings and collaborations each day, there was little time/energy to actually operate.  Getting to Peru was uneventful—we took an American Airlines codeshare flight on LAN Airlines via Miama to Lima and got there early in the morning.  Unlike their neighbors to the south, Peruvian Customs is by far the most curious I’ve encountered while carrying radio gear—just a minor headache but Sarah was a bit concerned when they took me away for additional questioning.  I carry modest gear—a Yaesu FT-840, Astron SS-30 (this should be replaced with something smaller, but it’s what I have), WKUSB, Palm Mini-Paddle, the K8GU portable antenna system, and various cables to connect it all up.  After clearing Customs, we boarded a bus to Paracas, where the meeting would be held…

Paracas, which is about four hours’ drive south of Lima, was the site of a major earthquake several years prior and is still in recovery.  The hotel that hosted the conference and a few nearby hotels had all been rebuilt from the ground up since the earthquake.  The city is on a small bay that is protected from the Pacific.  It’s very beautiful—desert sands that go right down to the bay.  After a few days at the meeting, I managed to get the antenna set up.

One of the things that surprised me was an excellent JA opening on 20 meters just after sunrise before I went to breakfast and then the meeting.  I am pretty sure it was a direct-path opening because the signals did not sound like long path and the long path crosses the southern auroral oval, whereas the direct path does not.  (Auroral absorption, by the way, is one reason that the long path can be more effective than the short path.)  Any time I called CQ as OA5/K8GU, I was greeted with a roaring pileup.  Not bad for an antenna propped up on my veranda.  Verticals on the beach rule, and this one wasn’t even really on the beach.

At the request of a friend, I made a special effort to operate on 12-meter CW in the afternoon.  The portable antenna would not tune up on 12 meters with the wire radials I had laid out.  In a moment of desperation, I assembled some extra pieces of my portable antenna to produce a tuned radial that I clip-leaded to the ground lug as depicted in the photo above.  It worked right away and I was quite popular there as well.

A comment about computers—my standard work-issued computer is a MacBook Pro, which although perfect for my work, is essentially useless for amateur radio.  I know this will generate a torrent of discussion, but if you are accustomed to real contest/DXpedition logging software available for DOS and Windows, you know that the stuff for the Mac doesn’t cut the mustard.  I have logged DX operations on paper (CE/K8GU), or in the case of the OX/K8GU operation, brought along a second computer.  However, in a long-delayed flash of insight, I bought and installed VMware Fusion on the Mac in February.  It runs Windows XP and TR4W with the WKUSB just brilliantly and with no special configuration.  Aside from having to press Fn+F1 to CQ, this was an epic win.  KB9UWU tells me that there’s an option in VMware to eliminate this nuisance as well.

After the meeting in Paracas, we returned to Lima, where we celebrated the 50th anniversary of the Jicamarca Radio Observatory.  The cornerstone of the Jicamarca facility is a 49.92-MHz radar that feeds an 18,720-element phased array, pictured above.  Jicamarca is one of the most powerful radio transmitters in the world, capable of 4.5 MW output, and is used for a variety of atmospheric, ionospheric, and space science experiments.  Like Arecibo, it was originally designed to perform incoherent scatter measurements of the ionospheric electron density profile.

Lots of fire in that wire!  Have you ever seen a coaxial cable that’s rated for over a megawatt at 50 MHz?  This is the feedpoint of the phased array.  There are a few tuned stubs in there, too.

Here’s one of the four 1.5-MW transmitter cavities.  A maximum of three are used together.  When configured for three transmitters, the driver stage puts out 7 kW!  Needless to say, everything is custom made on site.  The transmitting tetrodes (8973s, if I recall correctly) are refurbished by the manufacturer as needed.

After Jicamarca, we went to Cusco, which is south and east of Paracas, and much more lush than the deserts around Lima and Paracas.

We spent a lot of time being tourists in Cusco and vicinity and I had some difficulty with my computer so I only made a handful of OA7/K8GU QSOs from Cusco on 17 meters.  It is quite remarkable how much better the bands were from the coast.  As someone who has operated from W3, W8, W9 and W0, I can attest to that difference as well.  I missed my morning JA run…

A final thought—we drove through a lot of towns and communities in OA4, OA5, and OA7, on this trip.  Nearly every town, no matter how small, had at least one building with an HF fan dipole on the roof.  HF is alive and well in a mountainous country like Peru!

QSL information:  If you worked OA5/K8GU or OA7/K8GU, the best way to get a confirmation is through ARRL’s Logbook of the World.  I have been responding to direct cards (to my FCC address) with a one-day turn-around lately.

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A Portable Vertical Antenna

March 23rd, 2012

With the loss of my preferred frequent flyer status, airlines tightening their checked luggage allowances, and the addition of another traveler to the family, I’ve been contemplating a new portable antenna that is easier to pack than my usual DK9SQ mast and dipoles.  I don’t do high-priced reduced-size antennas if at all possible since portable installations usually have other efficiency-reducing problems.  Multi-element antennas take up additional space and have feeding and installation complications that are unnecessary for the casual DX operator.  So, that leaves us to choose between a vertical and a dipole.

A few words about efficiency:  Dipoles have a distinct efficiency advantage over verticals in almost every practical installation for 40 meters and up, except when the vertical is physically placed in or over salt water.  Radiation efficiency tends to be dominated by near-field conditions, pattern is dominated by stuff that’s farther away.  This is why vertical dipoles work so well for long-haul DX when placed within a few wavelengths of salt water.  They don’t need the near-field efficiency enhancement as much as base-fed verticals, but they still leverage salt water for developing their far-field radiation pattern, especially at low angles required for long-haul communication.

I’m a casual DX operator, not a DXpeditioner, so I never operate on 160 or 80 meters.   That is, considering the discussion above, why I have been using dipoles with the DK9SQ.  But, verticals have a distinct advantage over dipoles in the sense that they are self-supporting.  I decided to build a vertical because: 1) my next DX trip would include time near a beach and 2) I wanted to be able to bring my own support as I had with the DK9SQ.

My remaining requirements were now simple:

  1. A vertical antenna that requires no additional supports.  Guying is OK.
  2. The antenna must be full-size (quarter wavelength) on 40 meters and above.
  3. Experience has shown that multi-band operation is desirable, but instant band switching is not necessary.
  4. The longest piece must fit inside my suitcase (20 in / 50.8 cm maximum length).
  5. Field assembly and repair with only a Leatherman tool.
  6. Minimum cost, minimum weight, minimum volume, minimum installation time.

And this is what I came up with:

There are 21 aluminum sections, most with a “swaged” (actually, a poor-man’s swage to be described in a moment) end and a slit end.  They are shown here bundled perfectly inside a section of cardboard shipping tube.  An 18 x 2.5 x 0.125-inch aluminum plate serves as the base.  I used DX Engineering resin support blocks to insulate vertical from the base.  A point could be fashioned on the bottom of the base and a foot plate attached to push into soft soil, but that has not been done.

Most sections fit together using overlapping joiner pieces that I previously referred to as “poor-man’s swaging.”  I’m not sure that it’s actually a savings over paying a local shop to swage the ends for you when time is considered in addition to material, but I cut telescoping pieces six inches long and fastened them three inches deep in one end of a 17-inch section of tubing with two offset and orthogonally-placed aluminum pop rivets for a total length of 20 inches.  This geometry not only fits in my suitcase, but results in a very small amount of wasted material as well.

The other end of each piece is slit about 2 inches and they mate with an all-stainless steel hose clamp.  The first 10 feet of the antenna are 0.75-inch 6063-T832 tubing followed by telescoping sizes down to 0.375-inch at the very top.  The transition pieces are a full 20 inches long and are slit on both ends.  The full-size antenna will stand in a light breeze, but guying is a good idea.  Guy rings are fashioned out of flat washers drilled in three places.

Tune-up is easy…the more radials you use, the less critical their length.  After about 8 or 10, you’re in the clear here.  I never attached enough to prevent them from affecting the tuning.  If you only plan to have a couple of radials, go ahead and cut them to 1/4 wavelength (even though ground proximity will detune them).  Then, set the length of the antenna using the required number of 17-inch sections (the 234/f formula is surprisingly close) with the last section being a variable length for fine tuning.

I’ve intentionally left out most of the details of the antenna itself because I don’t expect anyone duplicate it exactly.  But, here are a few notes for anyone considering building one themselves:

  1. There are lots of parts vendors out there.  McMaster-Carr and DX Engineering will get you there in one order from each.  There is a surprising amount of overlap in their inventories.  Get the hose clamps from McMaster…even if you get stainless-stainless (stainless band, stainless screw), they are about 1/3 of the DXE price.  On the other hand, the resin support blocks are cheaper from DXE.
  2. I carry a compact antenna analyzer (Autek Research VA-1) with me.  Field tune-up is a snap and it runs on a single transistor battery.  It’s about 1/4 the size and weight of an MFJ-259 and good enough for amateur work.  Oh, and I bought mine used for a fraction of the MFJ.
  3. A tubing cutter is fine if you only have a half-dozen or so cuts.  But, if you have a chop saw or need an excuse to buy a chop saw, it will make cutting the tubing far easier.  My hands were raw for a few days after cutting the tubing by hand.  I’m sure the antenna performs better on account of it, though.
  4. Find a friend with a metal-cutting bandsaw to slit the ends of your tubes.  I went through a half pack (McMaster mega-size pack) of cut-off wheels for my rotary tool doing my slits.
  5. McMaster only sells the aluminum plate in 36-inch pieces.  If you don’t have the aforementioned chop saw, an angle grinder with a cut-off disk does a surprisingly good job.
  6. I pack a combination-screwdriver that has hex drivers that fit the hose clamps and #6 nuts.  Even though the antenna can be erected with only a Leatherman tool doesn’t mean it has to be.
  7. The small parts box shown in the top picture holds all of the parts for the antenna—it was 2 USD at Home Depot.
  8. The final and most critical component is a clip-lead that can be used to attach various nearby metal structures to your ground plane.  I have used it to make a temporary radial out of excess tubing sections on 12 meters as well.

That’s it.  The antenna goes up in a few minutes, especially if not used at full length.  I used it successfully last week as OA5/K8GU, which will be detailed in a future post.

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W1GHZ 903-MHz TX Gain Compression

March 5th, 2012

I managed to sneak into the lab again at lunch today for a few minutes and hooked up the now-packaged W1GHZ 903-MHz transverter to do a transmit gain compression test.  This test is a quick and dirty way to find the linear operating region of the transverter in addition to the expected conversion gain on transmit.  These two parameters determine the IF transmit level and what kind of power amplifier or driver stage will follow.  It’s an easy test to run if you have the equipment.  I locked the transverter in transmit by applying 8 volts to the TX MMICs and used a Rodhe and Schwarz SMR40 signal generator as the IF transmitter at 147.100 MHz.  On the transverter TX output, I simply connected the HP 8565E spectrum analyzer that I’ve used in the past.  Spectrum analyzers are not great power meters, but they give you a good enough idea of what’s going on.  The 1-dB gain compression point (that is, the point where the actual device gain sags 1 dB from the linear gain) is at an input of -3 dBm or an output of just under 10 dBm.  This compares favorably with the datasheet for the mixer and discussion with N3UM.

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903-MHz cavity filter tune-up

February 28th, 2012

For reasons that will become clear in a future post or series of posts, we’ve been busy lately—don’t worry, it’s a good thing.  I did manage to sneak away from my regular (usually desk-bound analysis) work into the lab and tune-up an eBay-special cavity filter for 903 MHz with our new network analyzer.  It’s really amazing how you can dial these things in if you have the right tools.  This one is a 3-cavity filter about 10x8x3 cm.

Passband insertion loss is about 1.2 dB.  Harmonic rejection at 1.8 GHz is 70 dB down.  I’ll take it.

I also have some eBay-special helical filters that were advertised to be for 432 MHz.  So, I need to cobble up some carrier boards to try them out.  Another day, another project.

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A Winter Trip to Greenland

February 3rd, 2012

Last year, I managed to scrape together some equipment funds at work to buy a small spectrograph system for studying atmospheric light emissions (airglow and aurora).  A co-worker secured the funds and contacts for us to install it at an observatory in Greenland.  Because we need to make the measurements at night, and because the instrument was delivered in early December, we made immediate plans to go to Greenland as soon as possible.  (Sarah is certainly laughing at this point because the plans were actually far from immediate and we bought our passage just over one week before departure.)

Greenland is only a short (4- to 6-hour) flight from the NE U.S., however the only route that operates in winter (and indeed the only commercial route) is on Air Greenland via Copenhagen, which operates four round-trip flights per week in winter.  This turned getting there into a two-day affair of perverse travel arrangements totaling over 12,000 air miles to go about 4200 miles round-trip on the great circle.  I met my co-worker, a United Airlines devotee (myself an American Airlines devotee), in Copenhagen and we flew to Kangerlussuaq (Sondrestrom) on Air Greenland.

One of the things that strikes you about Greenland as you approach Kangerlussuaq is how otherworldly and remote it is.  Kangerlussuaq is the site of the former U.S. Sondrestrom Air Force Base, and one of two runways (the other is at Thule) on the island large enough to accommodate aircraft capable of flying to Greenland from abroad (this is a mild, although amusing exaggeration).  Air Greenland has its hub there, shuttling passengers off to towns around Greenland on twin-engine turboprops like the Dash-8.  It is, as our host explained, “…not your typical Greenland town.  It is far inland at the end of the fjord and not on the coast.  The only reason it exists is because of the airport.”  Fuel and supplies are all brought in from outside.  Like most current and former U.S. military installations worldwide, it is reliant on diesel fuel for its on-going existence.  It’s sobering to be someplace that is totally unsustainable, although one might argue similarly of many U.S. cities, but I digress.

Kangerlussuaq is also near “the dog line,” north of which sled dogs are very common.  Here is one of the two road hazard signs we saw while driving around…dogsled crossing:

The instrument set up easily the first afternoon and we were able to collect some data with it that night.  As we were setting the instrument up, we heard reports of an Earth-directed CME from the Sun and hoped for aurora over the next few days. We were not disappointed…

The second night, I stood “aurora watch” in the cold while my warm-blooded co-worker processed the previous night’s data.  Soon, I saw some faint cloudy white sheets way down on the horizon and I ran back in to alert him and retrieve the camera tripod.  This photograph was taken facing toward the east southeast.

And, the 3.5-MW peak L-band incoherent scatter radar was running.  The dish is blurred because it is moving.

And, here is a shot of my fan dipole strung up on the DK9SQ mast.

Speaking of radio, I did manage to make a few QSOs as OX/K8GU on 17 meters, but not as many as I would have liked.  The combination of high absorption in the auroral oval (mostly to our south during our stay), little sunlight, a poor low-angle shot (required to avoid the auroral zone) to North America, short openings, and the fact that we were well-occupied with work for the four days we were there conspired to keep my contact count low.  QSOs will go into LoTW soon—the certificate was issued yesterday.  I have not yet designed a card, but there will be a special card.  Thanks to those who did contact me.

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7-bit Barker Code and Matched Filter

January 8th, 2012

Teaching Evan the basics of radar signal processing with this baby-block 7-bit Barker code and its matched filter.

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The Spam Report

January 8th, 2012

First of all, Happy New Year, loyal readers.  I have been exhorted by several enthusiasts of the blog to write more.  The months of November and December are busy around the Miller household with the CQ WWs, ARRL Sweepstakes, Thanksgiving, Christmas, and an annual professional conference on the West Coast between Thanksgiving and Christmas.  So, this is a drought time of year for writing.  A number of projects around the station have been started or completed and those will be written up as time allows.  Travel and potential DX operation is on the horizon, etc, etc.  However, today’s topic is WordPress comment spam.

I hadn’t checked the moderation queue on the blog comments for about six weeks until recently.  There were some 1500 comments pending.  Exactly two of them were from real commenters.  (Thanks, by the way!)  I could subscribe to a service (like Akismet) to stem the flow of spam, but I’m a cheapskate and skimming the spam is a bit like reading the police blotter in your local newspaper—a guilty pleasure.

The Internet democratizes the sale of nearly everything, legal or not, by providing a low-cost storefront for a business that can be based anywhere in the world, plus  (semi-)anonymous payment.  This is great for obtaining otherwise unobtanium surplus electronics and parts.  But, it’s also great for anyone selling anything else that is high-risk (for vendor or purchaser) or low-volume in a standard retail setting.  The difficulty for everyone is getting your business noticed.  Enter search-engine optimization (SEO):  techniques that game search engine algorithms to increase your visibility in a search.  Google’s PageRank, for example considers the number of links to a site as a measure of its popularity.  So, blasting every blog’s comment boxes with links to your site is a brute-force way to game that system (except the smart engineers at Google have weighted PageRank with the “quality” of the linking page and a whole host of other trade-secrets).  Some SEO schemes appear also to develop trees of “link farms” to improve “quality.”  But, this is just an arm-chair assessment.

Anyhow, the upshot is that there are a lot of keywords and links embedded in SEO spam.  The keywords generally reflect what’s offered for sale and they seem to reflect typical black and gray market goods—counterfeit designer clothing (Ugg boots are the informal favorite in my spam tin, with sports jerseys a distant second), pornography, and dubious medical products and home remedies (“tattoo removal creams” was a recent example).   Today, the bit bucket found a dozen or so messages such as these:

All point to the same site and contain keywords about amateur radio topics (except the SEO one at top).  So, I can infer that one of several things happened:  1. The site owner’s site got hacked and the SEO scumbags wove their material into it to make the SEO look somehow more “legitimate.”   2. The site owner acted (paid…*shudder*) on one of those spam e-mails every domain owner receives that offer to “increase traffic to your site.”  3.  The site owner is an SEO scumbag himself.

I’m leaning toward explanation #2, since the site itself makes him sound like the Homer Simpson line, “Oh, they have the Internet on computers now?!”  Whatever the case, this is inappropriate behavior and I refuse to mention the site owner by name, callsign, or link, lest the action be successful.  It’s the equivalent of splattering up and down the band on SSB when running high power to a good antenna.  You’re a lid.

Ok, I feel better now.

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SoftRock Ensemble RXTX IF modification

November 12th, 2011

This is a pretty simple modification that converts a SoftRock Ensemble RXTX SDR RF interface board from “common-IF” (RX and TX share the same antenna port) to “split-IF” (RX and TX have separate ports).  Split-IF is the standard for high-performance transverters on the 50-, (70-), 144-, 222-, and 432-MHz amateur bands.

So, I had a look at the RXTX schematics (here, here, and here) and considered the following options for where to break the RX and TX portions of radio:

The purple dots were the first option.  Unfortunately, these locations on the actual printed circuit board were not easily accessible to miniature coax and this process would involve significant surgery to perform and restore the modification.  The second alternative I considered was the red Xs…jumpering over the BS170 PA transistors.  By this time, I was looking for a way to avoid butchering the original circuit too much.  So, I elected for option three, which was to install a second T/R switch at the antenna jack (golden circle).  This had at least two advantages, the first of which was being minimally invasive.  The big advantage, though, is that the radio could be operated at its design output and run through a fixed or step attenuator on the TX side to the transverter.  This meant that I would be assured of having a reasonably clean signal to work with if I configured the radio correctly.  It also meant that I could operate the radio as designed if I simply disabled the the second T/R switch and connected the antenna to the default port.

So, here is the modification that I came up with using parts I had in my junk box.  KB9YIG ships the Ensemble RXTX with a couple of spare BS170 FETs that can be used in place of the 2N7000.  I just had a lot of 2N7000s and thought I’d save the BS170s in case I ever burnt one in the RXTX.

The interface to the transverter is through a DB9 connector.  PTT for this transverter is +12 volts (as done with the TS-930S) on pin 6.  Pin 1 is ground.  Pins 2 and 3 are shorted together in the transverter cable connector to enable the modification in the SoftRock.  The right portion of the schematic with the relay driver and Omron G6Y relay is based on the T/R switch from W1GHZ’s “Multiband Transverters for the Rover” that I decided not use on the microwaves when I found a cheap source of SMA coaxial relays.  An I2C decoder would be great to put band data on the other pins to select a transverter (or transverter cascade for the microwaves).

The whole mess works great from a switching standpoint.  When I key the PTT on Rocky or PowerSDR, it switches the TX line and keys the transverter.  I’m a little ambivalent about the quality of transmitted signal that’s actually coming out.  I think it’s good enough if you live in a sparsely-populated area, but I have a lot of VHF neighbors that I’d rather not upset.  So, I need to do some more testing on this—a lot of it is getting the RXTX and PowerSDR configured correctly.  It appears that the I/Q channels are flipped on my sound card (Audigy 2 ZS) between transmit and receive.  I don’t know if that’s a wiring error in my breakout box or whether it’s normal.  Spectra to come at some point…

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