Wednesday, December 14, 2005

Updated aa6e.net site

The ham and family web site at www.aa6e.net is now updated and reformatted with CSS styles. Unfortunately, upgrading the content will take a while longer...

Tuesday, November 15, 2005

Optimal Callsign Lookup Page

If you want a quick and minimal callsign lookup, you could do worse than www.aa6e.net/lookup.html.

Monday, November 14, 2005

Orion, recalibrated

Previously, I blogged about the Orion's Frequency Calibration. I was able to tweak the Orion's TCXO to within a couple of Hz at 15 or 20 MHz, after warmup. The ambient room temperature was 80 F.

So now, after about 3 months, I recheck and find the oscillator has drifted about 14 Hz low (dial readings 14 Hz high) at 15 MHz. The room ambient is 73 F. This is still within +/- 1 ppm, and the oscillator is spec'd at +/- 3 ppm over 0 - 50 C.

The upshot: just because you can adjust the oscillator to +/- 0.1 ppm with care doesn't mean it will hold up for too long, as the oscillator ages and ambient conditions change.

Note: I'm getting ready for the ARRL Frequency Measurement Test tomorrow. The Orion's slow drift doesn't really matter. I will have to measure the the apparent WWV frequency anyway and apply the correction to the measurement. It doesn't matter how closely I can set the TCXO, I still have to do the correction.

Thursday, October 27, 2005

Linux & Blackfin for ham radio?

I have discovered the Analog Devices "Blackfin" DSP/controller lately. Using uClinux, you can run "real" software in this chip, with many options for I/O, including Ethernet and audio codecs. Cheap development boards and free software are pretty attractive. I am looking for anyone who is using this technology (or anything similar) in an amateur radio application.

The chip is powerful enough for a full SDR implementation, but I'm thinking more about building an intelligent controller & digital audio interface for conventional rigs.

Tuesday, September 27, 2005

DSL Wars, 2005

It's not ham radio, but it's communications.

I recently upgraded my QSB-laden 384 kbs DSL line to a shiny new fiber-fed 1.5 Mbs version, but it was not very easy, unless you like to chat with India.

The story is at my static website .

Wednesday, August 03, 2005

Orion Frequency Calibration

The Ten-Tec Orion Transceiver is specified for frequency accuracy of + or - 3 ppm over the temperature range 0 - 50 C. That amounts to +/- 30 Hz at 10 MHz, or nearly +/- 90 Hz in the 10 meter band. In an SSB QSO, an error of 50 Hz is pretty noticeable. In a PSK31 QSO, a whole QSO fits into a 30 Hz band, so such an error could be quite serious. Fortunately, we rarely need to set our VFOs with such accuracy. We need precision, but we can just tune for best reception. It does matter near a band edge, but it would be unusual to have to work within 50 Hz of an edge.

The most likely case where good accuracy can help in the HF bands is when we operate in roundtable mode on SSB. Frequently, a group sets up on a specific frequency, like 3813.000 kHz. If we don't have good accuracy, and if we don't all tune up carefully on one station, we may have to use the RIT every time a different person is speaking. The better our absolute setting accuracy, the less trouble we will have in net operations.

So, how well can we do with a little effort on the Orion? I developed a technique for measuring my frequency error against WWV. (See note below.) My zero beat setting before adjustment was typically about 9.999987 MHz after warmup, 13 Hz low, corresponding to the master oscillator running high by about 1.3 ppm, well within Ten-Tec's spec.

The master oscillator in the Orion is a temperature-compensated crystal oscillator (TCXO) running at 44.55 MHz. It is a Siward series TXO32, apparently, with a mechanical fine adjustment. The following is my record of how I adjusted my oscillator.

Orion bottom
First, remove the bottom cover of the Orion. There are 4 screws on the sides and many little Torx head screws around the rear lip. The top cover can stay in place. After the cover comes off, you are treated to the spacious glory of the Orion underchassis. The TCXO (circled) is on the A10 synthesizer board at the top.


tcxo
This is the temperature compensated crystal oscillator (TCXO)


adjustment
Here we do the actual adjustment. Note the pickup loop for the Icom R-8500 receiver to monitor 44.55 MHz. Fortunately, the TCXO does not require a non-metallic adjustment tool. An ordinary jeweler's screwdriver works fine. The adjustment feels a little coarse if you are trying for exact zerobeat with WWV -- i.e., sub-1 Hz beat. Keep in mind that 1 Hz at 15 MHz is .07 ppm, much finer than the specified oscillator accuracy. Because the oscillator temperature will be substantially less than normal with the case open, you do not want to zerobeat WWV. (See text below.)

R8500
The Icom R-8500 communications receiver was useful to monitor changes to the TCXO. It has its own internal TCXO reference. Such a receiver is not required for the Orion adjustment, but it is a help if available.

sticker
At the end, we put it all back together and give ourselves a professional-looking (?) calibration sticker.


Procedure
Before attempting the adjustment, it is useful to study the warmup characteristic of the Orion TCXO by zero-beating WWV over several hours, as the operating temperature stabilizes. Room ambient temperature was about 78-80 F. Naturally, you need to do this with the transceiver in its operating position with the covers on. Here is a typical warmup run monitoring WWV on 15 MHz.

Time
(min)
FrequencyError
(ppm)
014.999 9801.3
1115.000 0000.0
3814.999 9950.3
7314.999 9890.7
8514.999 9860.9
10114.999 9841.0
13714.999 9831.1
17714.999 9801.3

It would have been interesting to measure temperature along with time, but I did not have a temperature probe. (The A10 board runs pretty hot to the touch, and it is in a poorly ventilated area under the chassis. I would estimate the operating temperature is around 50 C.)

After running the warm-up curve, we note that the TCXO ends up 1.3 ppm high. The dial reading is 1.3 ppm or 20 Hz low. Therefore, we want to trim the TCXO so the dial reading increases by 20 Hz. That should bring the TCXO very close after warmup.

Another issue is which WWV frequency to use: 2.5, 5, 10, 15, or 20 MHz. Other things being equal, the highest frequency gives the best setting precision. One Hz at 20 MHz is .05 ppm. Propagation is a concern, however. We need a strong and steady signal. If the signal has much QSB (fading), it is likely to have a lot of frequency dispersion. You won't be able to find a steady zerobeat. You may want to avoid periods of significant solar or geomagnetic activity for the same reason. (Check http://www.n3kl.org/sun/noaa.html for current data.) For the most part, for my path the 15 MHz transmission worked best. I compared my results at 15 MHz with 10 MHz as a check. They were in good agreement.

Conclusions
The Orion's TCXO can be adjusted to within a few times 0.1 ppm, and it will stay put if the transceiver's operating temperature is stable. Crystal aging is a factor, however, so the calibration may have to be repeated periodically.

---------------

How to Zero Beat the Orion with WWV.

I have tried two methods of finding a precise zerobeat between the Orion's effective local oscillator frequency and a reference frequency transmission.
  1. Zerobeat using CW Spot tone. (easiest for me) Set up for normal CW reception with say 300 Hz bandwidth. Hold down the Spot button and tune until you hear the beat note when the signal frequency equals the spot tone. Again, you should find the zerobeat within +/- 1 Hz.
  2. Zerobeat on noise. If the IF passband offset (PBT) is set for say -100 Hz and the bandwidth is 200-300 Hz, set the AGC to "fast" and the mode to USB or LSB. The Rx audio deemphasis should be zero or positive. The tuning step needs to be 1 Hz. Find the beat note and adjust slowly for lower and lower audio tones. After the tone becomes sub audible (about 60 Hz depending on your speaker), carefully tune to zero. When you are within one or two Hz of zero beat, you should hear the receiver noise fluctuate up and down with the beat. (This is the effect of AGC.) It should be possible to locate the zerobeat to +/- 1 Hz. This method requires a fairly strong reference level.
--------
Note added (1/8/2006): An alternative procedure is given by K6SE at http://www.n5na.net/download/Orion_Freq_Calibration.pdf .

Saturday, July 23, 2005

Morse Code, we hardly knew ye.

The handwriting has been on the wall for some time. First, the International Telecommunications Union (ITU) lifted the Morse Code requirement for ham licenses capable of international communications (mainly in the HF "shortwave" bands). Then many national communications agencies began removing the Morse component of radio amateur license requirements. Now, after some delay, the U.S. Federal Communications Commission (FCC) is proposing the same for the U.S.

Morse still has an avid following among ham operators. (I just joined the FISTS organization myself.) The Morse requirement is entwined with the long history of amateur radio. Recent changes to "water down" the license qualifications have been controversial. Often the arguments are of the type "When I was a boy..., men were men...".

Meanwhile the world has moved on. Demographically, the young experimenters who once sustained the hobby have moved on to video gaming and the Internet. The number of licensees seems to have peaked around 600,000 and has started a slow decline. (Removing the Morse barrier may give the numbers a boost.)

Technically, the operating modes available to hams have exploded. Beside traditional Morse and voice, there are now many computer-assisted options: keyboard-to-keyboard (many flavors), file transfers, digital voice and video, special modes for weak and bursty channels (moonbounce, meteor scatter), and more. Fortunately, we do not have to prove competence in each of these to qualify for a license.

Morse code is an anachronism, but we like our anachronisms. Listen to the low end of most HF amateur bands and you will find hams "pounding brass". Join in!

Tuesday, June 28, 2005

Grounds & Lightning, more

The ground system (described earlier) is now "complete". The shack's Single Point Ground (SPG) panel is now connected to the copper waterpipe entrance via ~30 ft of 1.5-inch copper strap. The attachment is adjacent to the AC service entrance ground clamp. It would be better to go immediately out the window by the SPG to "ground" -- only a few feet away, except that that ground is dry (under a stone walkway) and there is only 4 or 5 inches of soil on top of granite ledge.

The next improvement in this system, in my opinion, would be to lay a perimeter ground loop around the house, attached to a large grid that extends over the ledge under the soil. A lot of work for a not super-high-risk area.

This morning at 5 AM, we had the first test of the system as a lightning rich storm front passed through. There were apparently some hits in the neighborhood, but all equipment survived here.

We are left with an S9-plus source of HF noise, however. It sounds like power line arcing, and it's bad over at least 40-12 meters. The good news (?) is that it's not in our house. The beam indicates a strong maximum at about 10 degrees azimuth, which is the direction that power comes in in the neighborhood.

Your comments are appreciated!

73, Martin

June 29 note: The intense RFI disappeared by evening. I had predicted to the XYL that it might just "burn itself out". I did a little neighborhood sniffing and found the noise was coming from a nearby house. By its sound (very spikey 60 Hz related), it could have been a burned-out diode in a battery charger, caused by a lightning surge. (One neighbor reported their phones went out of service.) I saw a smaller version of this when the 12-volt switcher "brick" for my computer's LCD display went bad. Lots of RFI, and the brick got quite hot to the touch.

So the RFI disappeared, I did not have to complain to anyone, and the neighbor's house did not burn down.

By the way, this was the first time I got to test the Orion's noise blanker function. (At this QTH, there is rarely much impulse noise.) The hardware NB was quite good, up to 5 S-units suppression on 20 meters. The DSP NB helped some, but not nearly so much.

Tuesday, May 31, 2005

W1YU - Signs of Life at Yale

As an historic college radio club looking for a new way, the Yale Amateur Radio Club - W1YU - is reinventing itself. We are using email and the web to bring together a community of faculty, staff, students, alumni, and retirees.

A first step is to institute a "roaming club station", similar to the FISTS rotating callsign KN0WCW. If you are related to Yale and a ham, you can have the W1YU callsign for a time.

See the new club website: www.yale.edu/w1yu .

Friday, May 13, 2005

Free Software and Ham Radio: The Hamlib Project

A great feature of Amateur Radio is the range of activities you can join in. Everyone can find a home with some operating style or technology work. Some of us combine on the air work with computer programming.

I’ve found a particular corner of ham radio called the Hamlib project, initiated in 2000 by Frank Singleton (VK3FCS/KM5WS) and Stéphane Fillod (F8CFE) and supported by dozens of hams around the world. The Ham Radio Control Libraries are intended “to provide a consistent interface for programmers wanting to incorporate radio control in their programs.” This project is an example of “free and open source software”, developed by a large group of people who volunteer their time. You’ve heard of Linux and the Mozilla and FireFox browsers? They were created the same way.

You may know about “software defined radio” (SDR). That’s not what Hamlib does. Hamlib manages the control functions of radios, including DSP and SDR rigs, but it does not do signal processing itself. Hamlib is largely developed in the C language under Linux, but it is adaptible to other operating systems (MacOS, Windows) and languages (C++, Python, Perl and others).

If you’re a programmer using Hamlib, you can write applications to work with many current and older radio devices that permit computer control. This is a big benefit, because you can spread your time investment over the greatest number of potential users. Most radio control packages today are written for specific devices (“rigs”), but the potential “market” for software for one radio model is always limited. Even hams who write “free” software think about market share!

The Hamlib project is ambitious, aiming to support over 200 rigs and variations, ranging from scanners and shortwave receivers to exotic computer-based DSP transceivers and some antenna rotators. The strategy (Figure 1) is to provide a library that adapts many different radios to a higher-level application program. If you are a typical ham who is not a programmer, you can download a software application package that is built “on top” of Hamlib. A number of Linux applications are already available for digital mode support, logging, etc. Check the Hamlib web site at http://hamlib.sourceforge.net .



Figure 1: Hamlib is the “glue” that connects applications programs to ham rigs.

Hamlib is tackling a big problem. How do you provide for scanners with a thousand memory channels, priority sampling, and so on in the same program with multi-band VHF transceivers and computer-based DSP HF radios?

The problem is not as bad as it might be, since rigs tend to fall into categories (receivers, VHF transceivers, HF transceivers, scanners, etc.) and into product families that share similar interface protocols (Icom, Ten-Tec, Yaesu, Kenwood, etc.) It is also possible to define a useful subset of each rig's functions -- at minimum. frequency, mode, and transmit/receive. For many rigs and applications, such as QSO logging, that is sufficient.

If you want to write a ham application program to talk to a radio, you have an interesting choice: Should you aim for the best possible interface for a particular rig on a particular operating system? Support a particular rig on multiple operating systems? Support many rigs, as Hamlib does, on a variety of operating systems? It's a trade-off of man-hours, features, and desired market share.

[A shortened version of this article is scheduled for publication as a "Stray" in QST.]

Friday, May 06, 2005

Why I'd like a digital IF output on my Orion

What could you do with a digital IF output from the Orion transceiver connected to your PC? I have a few ideas. Maybe you can add more.
  • Custom IF DSP filters in your PC - like an optimized RTTY filter. (The Sharc DSPs are efficient for DSP, but modern PCs should be plenty fast enough to process a 20 kHz band.)
  • Support interesting modulation modes (ISB, synchronous AM, DRM, PSK31, and all the other strange modes). Avoid the compromises of audio soundcard interfaces.
  • Detect multiple data streams simultaneously
  • Record your IF for later playback and analysis
  • Real time spectral display.
If you had a digital IF input for Tx, you could generate interesting modulations in your PC, multiple audio/data streams (ISB or multiple SSB, digital audio) - FCC permitting.

The programmers among us would be able to enhance Orion's "software defined radio". Eventually there will be killer signal software for general use on everyone's PC.

Wednesday, April 27, 2005

What is CW?

There are some interesting threads on the tentec@contesting.com list about CW. The question came up "What is CW?", both as to technology (how is it generated) and regulation (how is it defined.) Here are my 2 cents on the subject.

(If you're new to ham radio, CW stands for "continuous wave". In traditional Morse radiotelegraphy, your transmitter sends a steady wave when your key is down and no signal when your key is up.)

Having nothing better to do, I went to the FCC website to read up on Part 97 regulations and what they say about CW. The relevant sections are 97.3 which refer back to 2.201 and 2.202. Some excerpts are at the end. Classical amateur CW might be 100HA1A, specifying 100 Hz bandwidth, or simply A1A. The ARRL FCC Rule Book has some useful material, too.

It seems that the FCC is interested in the signal that shows up on the air and not how it is generated. Fair enough. Normal amateur CW is A1A, I believe. Some generation methods (like audio tones into a not-so-good SSB rig) are worse than others. FCC requires signal purity to observe good engineering practices, or words to that effect, and that may rule out the KWM-1 technique nowadays. The DSP method (e.g., Ten-Tec Orion) can be as perfect as you're willing to pay for.

As the Rule Book (8th ed.) explains, it would be possible to narrow the "100 Hz" DSB spectrum of an A1A signal by eliminating one sideband (50 Hz) and suppressing the carrier. (However you make it, CW does have a carrier and sidebands just like a voice signal.*) I wonder if anyone has ever done it, and whether a half-width carrier-less CW (or psk31?) signal would be decodeable after HF propagation. You'd need really tight frequency and passband control.
--------
*A carrier? What about between characters? Yes, mathematically the carrier is still there -- even after you turn your rig off. Of course, there are also very low freq sidebands that conveniently cancel out the voltage... So your rig had better be very very linear or it won't be safe to shut off the power! Don't lose sleep over it.

Thursday, April 14, 2005

A Little More Python for the Orion

I've posted a nifty little tester for the Ten-Tec Orion at my main website. It lets you send & receive arbitrary ASCII strings to the serial port. It's in Python, and Python is supported on many OS platforms. I have recently verified that the software will run under Windows, using Python for Windows, win32all, and pyserial for Windows. (The only module missing in Windows/Python is a "curses" package for my original octl program.)

Work continues on the Hamlib driver for the Orion. Latest: TT designed the antenna switching matrix "inside out". You select the transmitter/receiver(s) that want to be attached to a particular antenna, instead of the other way round. Oh well, we can fix it in software. We recently declared the driver to be "beta quality". Anyone care to prove me wrong?

Tuesday, March 29, 2005

Ten-Tec Orion S-meter & Hamlib

We have been making some progress with the Ten-Tec Orion backend software in the "Hamlib" package, an open-source project to provide a device-independent programming interface for amateur radio equipment in the Linux/POSIX world.

Here's a tid-bit you won't find everywhere: the Orion S-meter calibration curve.
#define TT565_STR_CAL { 15,  {
{ 10, -45 }, /* S 1.5 min meter indication */
{ 13, -42 },
{ 18, -36 },
{ 22, -30 },
{ 27, -24 },
{ 30, -18 },
{ 34, -12 },
{ 38, -6 },
{ 43, 0 }, /* S9 */
{ 48, 10 },
{ 55, 20 },
{ 62, 30 },
{ 70, 40 },
{ 78, 48 }, /* severe dsp quantization error */
{ 101, 65 }, /* at high end of scale */
} }
The first column is the Orion's response to the "?S" command in computer units. The second column is indicated decibels (dB) as read on the actual S-meter.

(Literary event: I just defined "S meter" in the Wikipedia! See my article.)

The Orion has a couple of peculiarities when measuring power. The minimum reading (on my unit) is about S 1.5 on all bands when looking at a dummy load. What does that mean? If S9 = 50 µV, then S1.5 is 6 dB x 7.5 S-units or 46 dB down in power = 2.5 x 10-5. The voltage ratio is the square root of power, or about 5 x 10-3. So the equivalent RF voltage level is 50 x 5 x 10-3 = 0.25 µV. The Orion's sensitivity spec (main receiver) is "< 0.18 µV" says that the receiver's internal noise will be about this level, which is consistent with the meter reading. In other words, Ten-tec seems to have this right.

(On the other hand, the tried and true RST system says that S1 means "Faint signals barely perceptible". That's an argument for using 5 dB per S-unit, as some have defined it, at least with our current generation of receivers.)

The other feature of note on the S-meter is the behavior at very high signal levels. As you can see from the calibration table above, the raw S-meter units are spread out roughly 8 units per 10 dB. However, the meter reading is highly quantized. You only see values of S9+48 and S9+65, nothing in between. This indicates that the software computation of received power has a quantization problem. Of course, it's hard to complain too much, because such power levels are almost never seen in real life. (If they are, better switch in some attenuation!)

Monday, March 21, 2005

Toward a Provisional Philosophy of Grounding

About grounding. There's so much information and advice out there that is sometimes contradictory. Partly this is what it means to be a radio amateur. Some folks have some credentials, but it's hard to know how to interpret what you read.

My background is in Physics, Radioastronomy, EE, and IT. So I have some textbook knowledge of electricity & magnetism and some practical experience with radio telescope systems. I would not claim to know much about lightning protection, but I know enough to be skeptical.

The basic problem is that few if any hams are able to test their grounding systems. Some people survive some dramatic "events", and their equipment sometimes does and does not. But in most cases there's no statistical significance. The commercial tower people probably know a lot, but they don't try to integrate RF systems into their residences. A few hams in high-risk locations survive multiple strikes every year. They're the ones to listen to.

There are some general principals that can guide us. Mainly, you want to provide a low impedance path to ground from "up high" that will not pass through you, your house, or your equipment. In a residential environment, there are always compromises. The ideal ham shack would be a windowless metal building on its own pad with a carefully laid out grounding grid and protection on every wire coming in and out. (Like a cell phone hut.) Failing that, it is probably a good idea to have as many ground rods out there covering as much territory as possible. If you don't "bond" your ham ground to your AC ground (and other lightning protection grounds, if any), you run the risk that there will be high potential differences between them during an event. What would happen if your AC plugs (all 3 wires) suddenly were at 20 kV relative to your equipment?

My local SPG system is an attempt to establish a locally bonded system that will forestall large potentials from occuring between anything near my ham gear. I will try to connect it to the AC entrance ground and a new ground rod system, difficult as that is on a granite ledge.

I don't have confidence (in a statistical sense) that this will work against the likely threats. It was fun to build. At least, it will improve the RF and AC safety grounding by a bit.

Read below to see the project at my QTH.

Ham blogging

After working with web sites for quite a while, I am just easing into the blogging world. WA1LOU had an ARRL Web Article (June, 2004), but it took a while to bubble up to my keyboard.

I did a search recently and turned up a number of interesting sites. See my links at the right. There's a lot of room for growth here!

From an email to Dan, KB6NU:
... Interesting what you come up with on http://www.globeofblogs.com/ when you look at their "amateur radio" category. I did register there, and now you can find me among the SWLs, podcasters, and what-not...

This is really cutting edge stuff, I have to say -- ham blogging. Ham
radio, for me, has morphed into 10% on-air and 60% Internet, with maybe 30% non-Internet reading and building. (I've been retired for a couple of years.)

Ham radio as a literary form! Unfortunately, [a lot] of hams can't relate to that. I recently looked at QST's guide for authors. Their advice about avoiding high falutin' language is quite charming. Or maybe I could find another adjective.

Saturday, March 19, 2005

In-shack Ground System

The grounding project is coming along. We now have all the radio gear, computers, and internet devices protected against a Single Point Ground, which is a bus plate on the wall of the shack. For now, the SPG is referenced only to a waterpipe (hydronic, at that) ground that is good at 60 Hz, but not for fast surges. The SPG also ties back to the house AC ground through a green wire connection to a power wall-plate, but this is not much protection.

Here is some construction information. Maybe it will help others who are contemplating a similar project.

The SPG plate will attach to the shack wall, right over the existing panelboard. A backing of 3/4 inch plywood will sit behind the copper panel.


Wall attachmentBack panel

The SPG panel itself, after lots of work.

SPG panel

Here are a few details. The custom cut copper sheet is 15" x 20" x .0647" Copper 110 = 16 ga. or 48 oz, supplied by OnlineMetals.com. They provide great service. You can see a number of 1/4-20 wingnut connections for miscellaneous ground strap connections. There is also a clamp for 1.5" copper strap, for eventual connection to a new external earth connection. The Polyphaser PLDO and ICE 348 devices are described in earlier posts below. The Hyperlink DSL protection is also visible, along with a number of PolyPhaser coax surge devices. Various antenna switches surround the panel, but are not part of the grounding system.

Tabletop Ground Bus

Using another copper sheet, 6" x 48" x .0647", we constructed a tabletop "ground distribution system" to provide a well-defined reference for the radio desk.

wide shot of table

detail shot of table

One connection bonds the ground bus to the metal office desk. Another connection goes a couple of feet across to the SPG plate on the wall. One-inch tinned braid is convenient for these connections.

Sunday, March 13, 2005

ICE 348 Surge Protector

The model 348 from International Communications Engineers is an 8-terminal device intended to protect rotator control wires. I am using 3 of these: one for a Yaesu G-1000DX rotator and two for a SteppIR 3-element yagi controller. Here is what we see when we open the box:



The MOV devices fire at voltages over 50 V. Bypass capacitors help reduce any RF problems. Construction is "basic", to be charitable. The MOVs are rated at 1000s of A of surge current, but it's not clear if the wiring will handle the rated surge gracefully. The top and bottom plates, not shown, are secured by 4 bolts to the rectangular extrusion seen here. There is no "reliable" connection to the mounting tabs, which are on the bottom plate, except compression of the alumninum plates. For a more reliable surge ground, I am using the screw terminals visible at either side.

Compared with the Polyphaser devices in the coax lines, I worry that the rotor/SteppIR protection with the ICE unit is fairly weak. The upside is that the Rotor and SteppIR controllers are relatively robust, and in the worst case they can be considered "sacrificial". Still, a multi-stage spark gap/inductor/MOV system (similar to the Hyperlink DSL device) would offer more security, at higher expense.

Saturday, March 12, 2005

Ground Map at AA6E

The figure shows the house plan at AA6E and how I am looking at the grounding problem. (Click for full scale view.)


Map of Proposed Grounding

The proposed stages of the grounding project, in order of increasing difficulty:

  1. Cross-connect ham radio "Single Point Ground" bulkhead to AC Service Ground at water pipe entrance using 1.5" or 3.0" copper strap.

  2. Develop a new buried ground system outside radio room. This would involve ground rods or cable buried in a trench in our shallow soil over rock ledge.

  3. Run a perimeter ground cable connecting the two lightning grounds, the AC service ground, and the ham SPG.
There is also an option 0, much inferior, which is to connect to the copper pipe hot water heating system that runs immediately adjacent to the SPG. This has a good DC connection, but obviously much higher inductance than other options.

One fairly strong argument for option 3 is that the tower is bonded to the lightning ground system (the bottom one), which could lead to problems if the ham SPG is not cross-connected.

6/16/2006 Note: Finally installed the 1.5-inch strap -- about 30 feet -- from the SPG panel to the waterpipe entrance ground (1-inch copper pipe). Before connecting the strap to the SPG, I measured a 3 mV AC differential. That's somewhat reassuring. "Soundings" in my lawn show that there is only 4 to 10 inches of soil above our rock ledge. That limits my ability to make a good new exterior grounding system.

Hyperlink HGLN-DSL surge protection

My DSL service is with SBC (formerly SNET). I seem to live at an electrically "long" distance from the Branford, CT central office. At any rate, I had quite a bit of trouble getting my modem to sync when the service was originally installed. Even now, while the service has been very stable, I am "capped" at 384 kbs download and upload.

[Note, 7/2008: I got upgraded not long after this. I now have AT&T "Elite" DSL, which is 6 Mb/s down and 768 kb/s up.]

As part of my station grounding project, I wanted to include my computer network in the "safe" area protected by a single point ground (SPG) and appropriate lightning/surge protectors. Devices for DSL circuits shared with POTS telephone ringing currents are not very easy to find. I decided on a Model HGLN-DSL-1S from HyperLink Technologies, available at www.SharperConcepts.com.



The unit appears well constructed, but when inserted in my DSL line, my modem immediately dropped sync and would not come back. There is a problem, at least with my rather weak DSL connection.

My modem, an Efficient Networks Model 5260, reports the following line parameters when the filter is not in the circuit:

Current SNR Margin 8.5 dB
Current Attenuation 66.0 dB
Current Output Power 12.0 dB

The modem also claims a maximum supportable transfer rate of 640 kbs with this SNR. This apparently is bad enough that SBC gives me a 384 kbs rate cap.

I tried a lot of things to get DSL back. The most significant was to replace my phone jack connection temporarily with 250 ft of Cat 5e cable -- using only one twisted pair of the four available. I didn't want to cut my 250 ft spool of cable, but the real run length from my telco entrance to the shack is more like 60 ft. Without the DSL filter, I now see the following modem report:

Current SNR Margin 10.5 dB
Current Attenuation 66.5 dB
Current Output Power 12.0 dB

Two dB better SNR is very good. That corresponds to a 711 kbs line limit, according to the modem. However, with the filter, the modem would still not lock up.

Time to take a look at the schematic: (Click for larger view.)



I was able to identify the components via Google. The Spark Gap SG is a type 3R-230 from Beijing Tehy. The spec says it has a trigger voltage of 230 V +/- 20% and an inter-electrode capacitance of <5 pF. The resistors are 3.3 ohms, 1 watt (?). The transient absorber is not actually as drawn. It is a composite of three devices, thus:



The transient suppressor seems to be similar to a Bourns CD214B "ER" type. The Bourns part has a breakdown voltage of 189 - 218 V and a junction capacitance of 2000 pF at 5 V standoff running down to 70 pF at 200 V. At typical phone line bias, 50 V, we should have 200 pF. The two cross-connected diodes seem to be similar to Diodes Inc. type FR1J, 600 PIV.

The short story is that the diode suppressors load my marginal DSL line too much. Unsoldering one end of the ER device allows the modem to sync up. I haven't run full tests to see if it is as reliable as without the filter, but there seems to be almost nothing left in the circuit that could plausibly degrade the signal.

Why does the surge suppressor cause so much trouble? The capacitance and resistance seem immaterial. Perhaps it is the non-linear characteristic with voltage that may add too much distortion.

So, will we have enough protection without the second stage of suppression? The modem faces a greater risk of being fried in an impulse event, but I expect that most of the "downstream" computer gear is protected well enough. One never really knows without full-scale and expensive tests.

Monday, March 07, 2005

The Polyphaser PLDO

The Polyphaser PLDO-120US15A Inline Impulse Suppressor is designed to protect equipment power circuits from large voltage surges. I am using it in my ham station in connection with a "single point ground" system to protect against lightning surges. The Polyphaser catalog does not give design details, but I wanted to know just how my equipment is going to be protected. Here is what I've found to date. (Click for more detail on photo.)



PLDO-120US15A Photo


The unit is solidly built. I traced the schematic: (Click for more detail.)



PLDO-120US15A Schematic


Most of the protection comes from MOV devices that begin to fire above 130 V. The inductors, by rough estimate, are about 1.2 µH. That converts to 15 ohms of series reactance at 1 MHz. If the second stage MOVs are in conduction, the inductor should provide a significant voltage drop. The series resonance of the two inductors and the capacitor is at about 400 kHz.

I am puzzling over the handling of the system grounds. The AC ground connection naturally goes to the PLDO case, which will bolt onto my local ground plane - where all the surge arresting gear is to be mounted. The AC ground is carried back about 30 feet to the AC service entrance. From that point to a solid earth connection (water pipe entrance) is another 40 feet or so. [I believe this is according to code. The situation is complicated by the location of the house on granite ledge, which rules out a driven ground rod.]

These ground paths go through the crawl space under much of the house. The ham shack antenna feed entrance and ground plane are on an exterior wall, with a possible earth ground only a few feet away. On the one hand, we shouldn't have the radio ground system with a separate ground from the AC, but on the other hand, that AC system "ground" is rather inductive and lengthy compared to a direct ground near the radio room.

ShareThis