Tuesday, August 4, 2015

Contacting MARS: A Saturday on the Radio

                The ship was off the coast of Bermuda on May 9th and 10th and it was time once again for the annual Amateur/ Military Affiliated Radio Service (MARS) cross band operations test.  I had been sent information about the event via PACTOR email from Brad, KA3YAN out of Charleston, SC, so I was ready to work the bands contacting stations via single side band and also copy the secretary of defense’s message via various digital teletype modes.

                The way that the operation works is that the radio operators at the military station would transmit a call on a military frequency and announce the listen frequency in the nearby amateur band.  The amateur, in turn, would use the split capabilities of the HF rig to listen to the military frequency and transmit on the announced amateur frequency.  The teletype was sent on a published frequency at a certain time and with a certain mode to be copied and printed by the receiving station.  This text can be mailed to the appropriate MARS liaison for a certificate.

                The military stations that were participating spanned the globe and were either MARS stations on military facilities, or in a few cases, museum ships that have retained MARS capabilities.  Four branches of the government were represented by various stations: US Army, US Navy/Marine Corps, US Air Force, and even the US Coast Guard got involved.  The flagship station was station WAR located in the Pentagon.

                My little pistol station consisted of a 100W HF radio feeding a remotely tuned sloper antenna with about 30 feet of wire.  The antenna was 100 feet off of the sea and grounded to the ship’s structure.  It may not have power or much wire in the air, but with a nearly perfect ground plane and no nearby RF interference sources, it is a fine station indeed.  The military stations were using a variety of antennas including Log Periodic beams to wire arrays.  Many of them were also using amplifiers to put out a better signal.

                During the course of the day, I worked stations as far to the West as Indiana and Texas,  as far north as Upstate New York, as well as a number of East Coast stations.  I did manage to work WAR on 20 meters, and the USCG Atlantic control station NMN.  My favorite was working NWKJ, the Ex-USS Yorktown (CV-10) in Charleston, SC Harbor.  I have a special affinity working ship to ship stations.  I was able to work stations on the 40M, 20M and 15M bands to round things out.

                Copying the Secretary’s message proved to be a bit of a challenge, as most of the digital modes being used were fairly unusual in today’s amateur world.  I was able to copy two stations and used four different modes to get the copy.  The first was from station AAC on 13 MHz which is an Army station that was transmitting on Military Standard 188-110 FSK.  This is a wide band RTTY station that operates at 75 baud and is 850 Hz wide.  The standard amateur RTTY is 45 baud and 170 Hz wide.  Fortunately for me, the FLDigi program I use has a setting for just this mode and I had fairly clean copy for the message.  The second station was Navy Station NBL in Groton, CT.  They transmitted on 14MHz, just above the amateur 20M band in Amateur RTTY, AMTOR Mode B, and MT63.  FLDigi was able to copy them all, but I had to cheat with the AMTOR by using the SITOR setting in the program.  Since AMTOR is the HAM variation of SITOR, I was able to get clean copy.  MT63 also proved to be a challenge as there are a number of variations to the mode.  I could tell from my waterfall that it was 1 KHz wide, but whether it was long interlace or short wasn’t readily apparent.  I simply switched between the two and saw which one it decoded (it was 1 KHz Long). As NBL gave several RYRY strings prior to sending the message, it was easy to get tuned in and on the right mode.

               I was able to get my copy of the SECDEF's message off into the US Military postal system in Djibouti and a few weeks later a QSL card from USAF MARS was in the mailbox.  As of this writing, I am still waiting for the Army and Navy QSL cards, but good things come to those who wait.

                It was an enjoyable exercise, and made me think outside my normal comfort zone with radio and mode configurations, and perhaps in some civil emergency, such skills will be put to use for real.  For me, experimentation and being prepared to lend our radio skills to those in need is what amateur radio is all about.

Monday, April 7, 2014

Powering TNC's While Operating Portable

I have been a Icom user for years and most of the SCS TNC's have the ability to draw power from the Rig via the communication cord.  This means that I have not had to run many power cables for the SCS modems while using Icom rigs. 

Now that I have a Yaesu FT-897D radio for portable operation, I have had to rethink powering TNC's in a portable environment. Unfortunately the Yaesu doesn't offer the option of using the internal batteries for powering external TNC's except through the CAT port which is being used to power the dedicated tuner. 

All of the TNC's that I own have power requirements in the 200-300 mA range at 10-20V except during firmware updates where power requirements can get up to 500 mA, but that is the exception rather than the rule.

I am trying to minimize the size and weight of batteries for my portable station, so the idea of lugging around a 40 AH wet cell doesn't sit well with me, and that much energy is a bit over the top for the project. 

I have formed two solutions to this problem, each to be used depending on how much bulk I am willing to carry with me. 

For maximum portability, I have wired two AA cells along with a 9V battery in series.  This gives a nominal 12V and runs my SCS tracker easily due to the low current draw.  While the 9V battery can't be expected to supply much current for long, it seems to provide enough power for low power use, and is a very light package.  I did try this with the DR-7800 modem, but the Dragon's thirst was a bit much for this power supply since this modem needs 300-400 mA to operate and the loaded voltage out of the battery pack was 6 V, too low to run the modem. 

To handle the increased load of the Pactor modems, I went to step two, a 7 AH wet cell housed in my Celestron Power Tank.  This device is a portable light and power supply that has a small flashlight, a 800,000 candle power spot light, two 10V/10A cigarette lighter plugs, 3, 6 or 9V/1A coax plugs, and posts that come directly out of the battery for high loads.  I ran 12G wire with rig lugs from the posts to supply a RigRunner 4005 which supplies up to 5 outlets using Anderson PowerPoles for connectors.  This supply will have enough power to run the TNC's and my portable antenna coils for a prolonged time.  This configuration also allows me to have some lighting, run my HT’s through the mobile cigarette power supplies.

Power to the HF rig is still supplied by the internal batteries, but the 7 AH battery has enough energy to supply the designed load for as long as the rig batteries will last in a package that is still reasonable to carry.

Operating Clover

Clover is one of my favorite high frequency (HF) modes.  It was developed in the early 90's and was brought out as a proprietary digital mode in the early 1990's by Hal Communications.  There are currently 3 variations of the mode in current use, Clover II, Clover 2000, and Clover 2500.  A good history and technical discussion can still be found at Hal's website http://www.halcomm.com  I won't try to rehash all of the ins and outs of the mode, but will instead give a fairly brief overview of the mode.

Clover II was the first commercially available iteration.  It consisted of 4-tones sent sequentially in a 500 Hz pass band.  Each tone shifted phase in order to pass binary characters. The number of phases increased with better band conditions until it reached 16 phase shifts.  In addition, in the highest modulation schemes, amplitude modulation was added to pass more data.  All of this was done at the low symbol rate of 31 Hz.  Clover II was targeted at both the amateur and commercial interests.  Unfortunately the cost of the mode was too much for the amateur community and only caught on with some, primarily US based, commercial interests.  Data rates for Clover II range from 125 bps to 750 bps and was available new until recently in several modems.  The last Hal unit to carry Clover II was the DSP4100

In 1999 Clover 2000 was introduced.  The basic modulation was the same, but the number of tones was increased to 8 and the bandwidth spread to 2 KHz.  Additionally the symbol rate was doubled for more throughput.  Hal decided that this mode was a bit of overkill for the amateur community and marketed it almost exclusively to commercial interests.  The modems remain expensive, but the increase in throughput was impressive at 500 to 3,000 bps.

In 2011, Clover 2500 was introduced in the late model DSP4100/2K and DSP4200 modems.  The symbol rate was increased even more to 71.125 baud which lead to an increase of bandwidth to 2.5 KHz.  This shows the practical limit of Clover in standard SSB transceivers and seems to be marketed in response to a rival's introduction of a new mode at approximately the same time.  The data rate for Clover 2500 is 625 to 3750 bps.

While there are published reports about the technical specification of Clover on the internet, there are few, if any on-air reports available except those found in relatively old equipment reviews of clover II.

I have fairly extensive experience with Clover II over the last 10 years or so, primarily with my DXP-38 modem.  This was the last modem marketed to amateurs with Clover in it.  It featured a tuning indicator which was omitted on commercial modems which primarily operate on fixed frequency channels and should not require manual tuning.

Clover II operation requires precise tuning, to within 20 Hz for link establishment.  The modem does not have the ability to compensate for frequency drift, but with statistics passed between the modems on a regular basis, the radio can be slowly (no more than 10 Hz at a time) zeroed in to each other.  Amateurs using the mode tend to have a set frequency to meet on (14.065.5 LSB dial is the most common) and fine tuning for rig errors can be done once the link is established. 

Once the link is established, Clover is pretty much on auto pilot.  All the operator has to do is type or send files.  The mode works on automatic overs after certain amounts of data is passed.  The length of these blocks between overs is determined by the amount of data to be sent and can last several seconds.  Overhead and a small amount of keyboard data are sent via short blocks with a very robust waveform while data blocks are longer and will be sent at the highest speed possible as determined by conditions on the other end of the link.

I have also experimented with Clover 2000 several times.  This mode is much more difficult to operate than Clover II, especially with lower power systems such as amateurs often use, and me especially.  The same amount of power is now spread over 2 KHz and 8 tones instead of 4 tones in 500 Hz.  This means that there is a lower average power on the other end of the link requiring more ERP and better conditions.  Clover 2000 is also set up to run with fewer error retries and is very prone to link failure if struck by fading.  Still, when the conditions are right, Clover 2000 will move data very quickly, even at it's more robust waveforms.

Clover is unique in current modes in that statistics for both sides of the link are readily displayed.  Waveform , amount of online error correction used, S/N ratio, frequency offset, throughput, and phase dispersion are all shown to the operator.  The most important to judge the link condition are S/N and PHS (phase dispersion).  The former shows the relative strength of the signal and higher numbers are desirable.  The second shows how much phase distortion is being caused as the waveform is propagated.  lower numbers are better in this case.  Since Clover relies on being able to determine phase shift, higher amounts of dispersion require fewer shifts per tone, and that will mean less throughput.  SN around 30 and PHS in the teens indicate a good link and will allow speedy transfer of data.  PHS in the 40's and S/N in the teens will expect low throughput.  Any worse than those numbers, you can expect link failure or at least numerous error signals. 

For Keyboard chats, using Clover 2000 is both frustrating and wasteful of spectrum.  The enhanced signal conditions that are required coupled with the relatively slow rate typing and reading make the mode difficult to use.  Save this mode for passing traffic.

Clover II is a very nice keyboard mode due to it's speed and semi-duplex nature.  Also the link status panel is of interest to radio enthusiasts.  It can also serve as a relatively fast file transfer mode provided the file isn't very large.

There is a yahoo group dedicated to Clover operating with a small but dedicated following.  So if you see a Hal modem online that has the mode for cheap, have a go at it.  If you think that clover alone isn't worth even the modest used prices of these modems, you can still use them as great RTTY or Pactor I modems.

Saturday, December 21, 2013

ARRL Petition to eliminate the symbol rate restriction on HF

Like most rule changes, this petition has drawn fierce opinions both for and against it.  The problem is that most of the arguments against it are not technical in nature, but against the idea that wide modes will be allowed on the digital sub- bands and thus cause interference.

Ironically, this petition will impose a bandwidth restriction on the HF bands for the first time.  As the rules stand now, you could have a 6 KHz wide digital signal as long as the symbol rate didn't exceed 300 baud.  The new rules will allow any baud, but the signal can only be 2.8 KHz wide. 

The thing with both of these signal properties is that they are effectively self-limiting.  Higher baud rates are subject to fading and multi-path distortion so they are effectively limited on HF, especially the lower bands.  Bandwidth is limited by the standard SSB radio bandwidth of about 2.8 KHz, with most being closer to 2.4 KHz.  Granted some SRD radios could have wider front ends, but this is far more the exception than the rule.

What opponents miss by their disdain of Pactor 4 (the most prominent mode that is driving this petition) is that increasing the baud rate can actually lead to a variety of faster modes with less bandwidth.  Most multi-tone modes can use fewer tones at a faster symbol rate and move as much data than they could with more tones at a slower baud rate.  This would allow a reasonably fast data stream in a 1 KHz bandwidth that would deliver a higher power density and eliminate the need for a 2 KHz wide mode running at a lower baud rate.  This is effectively the difference between Pactor 3 and 4 in general. 

Of course some argue that we amateurs don't need to move data that quickly on HF.  Pactor 2 and Clover II are plenty fast with their reasonable 500 Hz wide signal.  To this I have to point out that amateurs are trustees of a large swath of lucrative radio spectrum.  If we cannot justify our continued use of these frequency bands, then the government is liable to sell it to the highest bidder in the name of the common good.   Since radio amateurs seem to be falling way behind in the development of the radio arts due to a variety of factors, the ARRL has taken the tact with the government that we are a pool of trained communicators.  We can provide government and non-government agencies with communications capability at little cost in times of need.  Part of this scheme, and one of the most crucial, is supplying long-range email capability on HF.  This requires more than the 800 bps than P2 or Clover can provide.  Since a minor rule change will provide up to 5000 bps via Pactor IV and other similar modes, they are taking the steps necessary to make it happen.


Wednesday, May 15, 2013

Playing with APRS

APRS has seemed to be the most wide spread use of VHF packet mode for many years now.  I have been on the fringe of this system by having a mobile tracker in my car off and on for the last 10 years.  N1ZZZ-9 has had a nice run across the US several times, and in the areas close to my various home QTH over the years.   These days with a new car, and a XYL who isn't too keen on having it's finish marred by an external antenna, the Kenwood TH-7 has degraded from a mag-mount antenna to a rubber duckie.  Of course the rubber duckie antenna isn't very good at getting the signal out.

For the last two years or so, I have also had a portable station, N1ZZZ-7, on the air in the form of a Yaesu VX-8.  Again, when walking around with an H-t on your belt and a rubber duckie, your signal isn't going to get too far, but it sometimes manages to get my signal out to digipeaters.

I have been fortunate here in the Wilkes-Barre, PA area.  While standard packet is almost non-existent, the  APRS system is very strong, especially along the I-81 corridor.  There are several Digipeaters as well as a capable I-Gate to send the signals into the Internet for all to see.

What I have never done in all of these years, has been using APRS in it's most interesting incarnation, and that is with a fixed station, with a "real" TNC, and a mapping display to show where all of these beacons are.

This past week, I finally found a program that suited my needs and worked with the equipment I already had.  The program was APRSIS32.  The program was an easy download and installed quickly.  The program connected to the APRS servers via the WiFi port in my computer and immediately started to download maps and place beacons on the screen through the IGates.  The next step was getting my GPS to talk to the program.

  I have a Garmin GLO GNSS receiver that connects via a Bluetooth link.  This little receiver uses both the American military's GPS system and the Russian governments GLONASS constellation.  Getting this device to talk to the APRSIC32 program proved to be a very easy.  I turned on the GLO and enabled the GPS via Bluetooth in the program and it immediately found a fix.  Not only did the program display my position both in Lat/Long, but also gave me a grid locator.  The station's speed (0 at this time) is also prominently displayed on the screen.  Most interesting to me was that the program also displayed the number and status of satellites in both the GLONASS and GPS systems.  Even with my GLO on my desk near the window,  I am getting better than 20 satellites in the list.  These satellites' geographic position are also displayed on the screen as they float on by.

Getting my Kantronics 9612 TNC hooked up proved to me more difficult.  The TNC needs to be in KISS mode, but I also use it for normal packet, so I can't get the 9612 "stuck" in that mode.  I needed the program to start the 9612 in KISS mode, and then return it to Terminal mode when the program exited.  Kantronics TNC's are a bit fussy in my experience and this proved to be no different.   I knew that the computer was able to talk to the modem because I was able to use the AirMail dumb terminal was able to get me command prompts, but the APRSIC32 was not able to find it properly.  While the program claimed that the radio port was active, it would not key the TNC or get any packets from the radio. 

The problem is in the XML script located in the local folder where APRSIC32 is situated.  This is a far cry from the plug-and-play software that is the norm today.  To fix this problem, I had to do some internet research.  The program's wiki talks about the lines for a Kantronics KPC, but not the 9612 specifically.  In the interest of sharing the data, I will post the script from my XML file here so that anyone who needs it can cut and paste and get it working.

<RFPort Name="KAM">
<OpenCmd>XFLOW ON!!0</OpenCmd>
<OpenCmd>FULLDUP OFF</OpenCmd>
<OpenCmd>INT KISS!!0</OpenCmd>
<CloseCmd>TC 1!TS 1</CloseCmd>
<CloseCmd>TN 2,0!TN 2,0</CloseCmd>

A few notes:  1) the name of the port is up to you (KAM) in this case.  Your COMM port will also vary depending on your configuration.  Since I am using a Serial to USB dongle, I have a rather high COM4 number.  Most native Serial ports will be 1 or 2.    The big difference between the KPC and the 9612 are the commands to get into KISS mode.  For the 9612 the commands are "Int KISS" and then "reset"  The difference between the lines "reset" and "restart" escaped my notice the first time, so be careful.

After my script was working, I was able to get the KAM to start putting stations on the map.  I checked this by disabling the Internet connection for a bit and clearing the station list.  Eventually the digipeaters starting giving me data that got the stations through my 2 meter rig and 9612 and to the software.

The next stage of this will be getting a SCS tracker online with Robust Packet on 30 meters to pull in the long-haul stations.  I just have to see if I can run two USB modems without things getting all sideways.


Monday, May 13, 2013

Pactor II verses Clover II

In the early 1990's DSP chips finally became financially feasible and two DSP based, phase-shifted modulation modes became available to hams.  Ham developers in the USA and Germany separately developed two HF digital modes that combined high data transfer speeds while remaining fairly robust and capable of maintaining point-to-point links over the HF radio spectrum.

The two modes were Clover and Pactor II.  Implementation of the phase shift modulation was slightly, different, but these two modes were generally the same speed and claimed nearly equal robustness in the face of low S/N ratios.

I have always been a big fan of both of these modes and have used both since about 2003.  These modes have be upgraded over the years, but the version two of these modes have always been very good for keyboard links. 

Recently I was on the air with Pactor II with VE1XL.  Conditions were poor with large fades in the path.  Even the robust Pactor II was having some trouble moving data.  It was still good enough for keyboard work, but the fades caused several error messages going back and forth as the data packets did not make it.  Given that these were adverse conditions, I suggested to VE1XL that it would be a nice opportunity to test Clover and Pactor head to head. 

We ended our Pactor link and switched to our DXP-38 Clover modems.  These are the latest of the Hal Clover II modems and gave the mode the best chance at keeping a link.

We were able to establish the link, but we had trouble with the data blocks.  Unlike Pactor, Clover uses what it calls Clover Control Blocks.  These are sent at a modulation scheme that is the most robust it can muster.  Unfortunately the CCB's modulation is not available for data packets.  This proved to be the deal breaker on this link.  Despite some error packets, the CCB's managed to get through, but as soon as the data packet tried to make it through, it was not able to get there.

Sadly eventually the link failed and we had to go back to Pactor.

So what shall we make of this?  While I still find Clover more fun to operate due primarily to the fact that it has a more effective semi-duplex paradigm, and the ability to exchange station data on both ends of the link, it still needs more power to keep the S/N ratios up to the point where data can make it through.  Pactor is a superior poor link mode, and this is a common consensus.


Monday, April 1, 2013

Experimenting at 461 THz

I went on YouTube ( http://youtu.be/pvj3KDp8Ae8 ) and found a simple circuit that allows modulation of a pocket laser pointer.  These red, 650 nm devices (461 THz) can be AM modulated with an audio transformer that varies the intesity of the light.  The modulated signal can then be demodulated by a solar cell directly wired to earphones (where voltage is directly related to light intensity.)

I went to my local electronics store and got my parts.  The solar cell was $5 and the audio transformer was about $3.  Depending on the laser pointer, most are 4.5V, you will need a 4-cell battery holder (I used AA-sized) and jump out one of the slots.  My laser pointers are 3V so I opted for a 2-cell holder.  The AA cells are larger capacity than the button cell or AAA cells normally used to power these pointers, so should offer enhanced life per cell during use.

The trouble I am running into with this experiment is that the audio transformer has significant impedence on one side.  Depending on how you wire it, you are attenuating either the laser power or the input audio.  The spec is 72 ohms on the input coil and 0.62 ohms on the other coil.  If you choose to attenuate the laser, your range is greatly diminished (my lasers are rated at < 0.5 mW).  If you attenuate the audio, you need much more audio drive into the circuit. 

While driving the input is easy enough if you are using a music device such as an MP3 player, it is more difficult if you are using a microphone.  The solution will have to be another circuit with an audio amplifier to add to the audio I wish to drive the circuit.  Unfortunately, my initial experiment had insufficient drive to generate the necessary signal. 

So tomorrow it is back to the drawing board (and the reference books) to make myself an audio amplifier that hopefully can be rated at 3 V so that I don't need another set of batteries.