Recently in Amateur Radio Category

Callsigns in IPv6

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http://mesa-arc.org/operating/IPv6 reports that:

Embedded Callsigns in IPv6 Addresses

Club Members Jacques N1ZZH and Vinnie N1LQJ have developed a method of embedding a 2x5 (7 Character) callsign plus up to 185 nodes, plus 1 universal bit and three reserved bits in the 2nd octet, and a 16 bit amateur radio identifer at bit 24 of an IPv6 /64 Subnet address. 

Sample programs and information on this proposed standard can be found at http://sourceforge.net/projects/hamv6



NICE!

GMSK Tutorial and Implementation

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From Spread Spectrum Scene, http://sss-mag.com/index.html (go read everything they have!), there's an app-note from MX about GMSK entitled: Practical GMSK Data Transmission.

Here's the link from the 'scene: http://sss-mag.com/pdf/gmsk_tut.pdf and a local link.

This PDF explains and shows the phase-discontinuous nature of PSK and other modulations:  http://www.emc.york.ac.uk/reports/linkpcp/appD.pdf
 
What people don't immediately realize is that GMSK is MSK, with rounded edges. Why is that important? Because square waves are by definition made up of the fundamental frequency and all of the odd harmonics of that frequency. However, when you cram a square wave into a multiplication process, like modulation, it creates mixing products -- lots of them. We call these products "sidebands" and typically try to reduce them through filters in some way.

Filtering can be done before or after modulation. It is more effective, and a better use of power to filter before the modulation process than after. In the case of GMSK, a specially designed Gaussian filter is used, which has two effects on the signal. One effect the Gaussian filter has is that it is intentionally set lower than the frequency passing through it. This causes it to have a rather pronounced effect on the signal passing through; specifically on the Gaussian filter, this gives rise to "InterSymbol Interference" or ISI. This interference happens because the filter causes the bits to lag a little in the time domain, causing the receiving modem to occasionally decide a bit is a one when it should be a zero or a zero when it should be a one. The second effect of the Gaussian filter is that it turns the sharp, square edges of the data into a rounded spike-like pulse. This rounded pulse has advantages.

The rounded Gaussian pulse has many advantages. Recall that in FM radio, a modulating signal is applied to a modulator. As the signal sweeps in one direction, say from zero to V+, the resulting frequency of the transmitter rises to a set maximum. Likewise, as the signal sweeps from zero to V-, the transmitter lowers in frequency to another set minimum. The advantage to the rounded spike is that, much like a plotter connected to an oscilloscope, the path is easily followed with smooth transitions. This is extremely important, as sudden jumps in amplitude and frequency cause phase discontinuities which make the signal hard to process. In Frequency Modulation, the signal must always remain phase-continuous without rapid reversals. The reason for this is manyfold, but I'll settle on two: 1) If it wasn't, then it isn't by definition FM, and 2) because the most common amplifier used to amplify FM signals, the often 80% efficient Class C, requires that the signal "ring" or spend half the time per cycle coming out of a RC "tank". So the Gaussian pulse allows the modulator to follow along, smoothly, generating a signal with minimal harmonics as a result of the modulation process. Again, because of this smoothness of action, rather than jumping around like QPSK or QAM, the GMSK signal is FM-complaint, allowing common, off the shelf gear to be used to generate, receive and amplify the GMSK signal. In short, GMSK appears to be a preferred way to transmit FSK signals, mostly due to removing unwanted sidebands which would otherwise be wasted as heat in the filters following the modulator. Bt=0.3 seems best, apparently the commercial data guys are aiming for 0.25 and 0.27.

Remember, of course, that MSK is defined as the shift at half the frequency of the data, and the modulation index is 0.5. GMSK doesn't get all the way down there, but it's still spectrally more efficient than FSK. Often, the same gear can receive GMSK as FSK, particularly the MX589 used by Kantronics in the KPC9612.

From the commercial perspective, I want to point out a few things:

1) Motorola has for years, since the Syntor X series, provided a split low-frequency and high frequency modulation path. This allows the CTCSS tones to be modulated at the lower frequencies that the VCO's PLL would otherwise automatically remove as detected frequency error.

2) Motorola has also used multi-level FSK to transmit and receive trunking control information.

FSK has the advantage of simple transmission -- attach the data stream to the modulator -- and simple detection: one need only use a data slicer to recover the data if the center frequency or one of the frequencies is known. 

Seeing as how the Motorola Spectra, Saber, and X9000 lines are based heavily off of the 68HC11, and the Kantronics KPC-9612, -9612+, -3, and -3+ all use the HC11 as well, I would not be surprised if Motorola was bit-banging data in from the trunking control channel without a modem much like how Kantronics recovers data in the 1200 BPS port of the above mentioned TNCs.

Update: I've just become aware that GMSK is being referred to by some as "GFSK with a modulation index of 0.5." GFSK is "Gaussian Frequency Shift Keying", per Analog Devices ADF7023-J product information: http://www.analog.com/static/imported-files/data_sheets/ADF7023-J.pdf

Motorola Mitrek and TinyTrak3

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I can't believe this hasn't come up, but a little searching seems to indicate that not very many folks interface a Motorola Mitrek to a TinyTrak3.

I ran into an issue with a Motorola Mitrek radio and a TinyTrak3. I was trying to determine what the radio was expecting as far as a modulating signal was concerned. Motorola, in the lowband Mitrek manual, indicates that a 1KHz tone should be generated at 1V peak-to-peak and feed into the microphone input through a .33uF capacitor. The DEV adjustment should be turned until deviation reaches 4.8KHz, and PL deviation should be between 0.5 and 1.0 KHz.

Short story since I'm light on time. Remove/don't install R8 into the TinyTrak3. This is used to couple PTT to TX Audio or vice versa. It simulates how HT external microphones used to be wired (2.2Kohms to ground to transmit). Short R5. I tried halving the resistance with another 220Kohm resistor for 105Kohm... Just nix that altogether and short R5. This can be done with a solder bridge, leaving you the option of going back to 220Kohm later if you need to.

I repeat: don't install R8 or remove R8 and short R5.

Short version again: Short R5 on the TinyTrak3 if you need more drive. See page 15 of the TinyTrak3Plus manual: "No audio is heard on a receiver." See page 14 of the TinyTrak3 manual under the same heading. It's the same paragraph verbatim.

Then set the  R6 to maximum. Tell the TinyTrak3 to generate both tones and adjust the IDC pot on the channel element for -/+5.0KHz deviation. Then adjust R6 for 4.0KHz deviation.

(The reason for doing this is that when the IDC (limiter) kicks in, it introduces clipping, distortion, and harmonics to the signal. By setting the channel element for 5KHz, the limiter is high enough to prevent introducing distortion through normal peak clipping. The stock Mitrek microphone circuits contain a brick-wall splatter filter to prevent excessive modulation/sidebands/harmonics.)

This message is my basis for that assumption of 4.0KHz deviation:
http://groups.yahoo.com/group/MicroTrak/message/844

Reproduced here:

From: WA8LMF

Michael Crowder wrote:
> Rudy, Thanks for the assistance.
>
> I've tried re-loading a new config, but I still have the problem that
> the 1200Hz tone is twice the amplitude of the 2200Hz tone. I'm using
> the TinyTrak3 configuration program to cause the MicroTrak8000 to send
> the separate tones, and then looking at the received signal on my PC
> using AGWPacket engine. Anyone have any ideas what may be causing the
> different levels in tones?
>
> --
> M


This is perfectly normal if you are taking the audio off the speaker
terminal of the receiver.

You are seeing the normal de-emphasis curve of a voice FM receiver. At
the transmit end, audio fed into the mic jack has the high frequencies
boosted relative to the low. Ideally, this boost or pre-emphasis should
be 6dB/octave over the range from 300 to 3000 Hz. The over-the-air
deviation or level of the tone is directly proportional to it's
frequency; i.e. a tone at 2400 Hz should have twice the deviation as one
at 1200 Hz. At the receiver, a corresponding de-emphasis network
(high-frequency cut) cancels out the boost applied at the sending end
for a net flat (equal levels for all audio frequencies) response at the
speaker.

However, if you apply the TX audio to the 6-pin mini-DIN "data" or
"packet jack" (on radios that have it) instead of the mic jack, no
transmit pre-emphasis is applied -- both tones go out at exactly the
same level. [Note that the MicroTrak integrated TT3 and transmitter has
no mic input with pre-emphasis - the TT is coupled directly to the TX
modulator with net flat response.] At the RX end, you continue to
apply the high-freq roll-off (de-emphasis) [assuming you are taking the
RX audio off the speaker or equivalent] with the result that the
attenuated 2200 Hz high tone is now about HALF the amplitude of the 1200
Hz low tone.

Historically, 1200 baud packet has been a "jam it in the mic jack of any
radio" (with the corresponding pre-emphasis applied) convention, while
9600 baud packet has been coupled directly into the transmit modulator
(with the resulting flat response). At the receive end, 1200 baud has
customarily been taken off the (de-emphasized) speaker output while 9600
receive has to be taken directly off the receiver discriminator (flat
response) before any high-freq de-emphasis is applied.

Traditionally, 1200 baud packet devices have been set to yield about
3.5-4.0 KHz deviation on the high tone which yields about 2.0-2.5 KHz
deviation on the low tone. Devices such as the Kenwood APRS radios and
the Microtraks that transmit "flat" response at 1200 baud are in
conflict with decades of packet convention that says 1200 baud
transmissions should be pre-emphasized.

[
Many hardware-based TNCs are very intolerant of unequal tone levels,
especially when the high tone is LOWER in level than the low tone. The
AGW Packet Engine and MixW software modems, on the other hand, are quite
tolerant of mis-matched tone levels. The result is that you may be able
to successfully decode your own transmissions with skewed tone levels in
your soft TNC setup, while a digipeater equippped with a TNC2 or KPC3
hardware TNC connected to the (de-emphasiszed) speaker out of it's radio
will not.

The solution is to apply pre-emphasis to the transmitted signal. Place
a small capacitor (probably somewhere between .01 and .005 uf -- you
will have to experiment) in series between the TinyTrak TX audio out and
transmitter audio-in. If the cap is small enough, it will attenuate the
low frequency relative to the high frequency enough to create a net
pre-emphasis effect. In your RX setup with de-emphasis, you should then
observe that the two tone levels are now nearly the same.


--

Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com --OR-- http://wa8lmf.net

The service monitor verifies these levels, total deviation around 4.0KHz (below the IDC limit) for both tones or the high tone, and around 2.5KHz deviation for the low tone alone.

Another suggestion from Bruce Lane via The Batboard is to set the 40W radio to 15W. This appears to limit current draw to about 6A at 13.8V. Seeing as how Motorola said not less than 55W on the 100W Syntors, I'm guessing it's not a good idea to go any lower on the Mitrek lest the PA become unstable and transmit spurs:

http://batboard.batlabs.com/viewtopic.php?f=1&t=13319&start=0

Youbetcha. I've had excellent results from a modified Mitrek. The mods involved were changing two capacitors in the transmitter section (so the multipliers would tune up -- I had the 150.8-174 split radio), and having International Crystal re-do the channel elements for 144.3900.

The only other change I made was to turn down the output power to about 15 watts (40-watt radio). Not only will this make the PA last just about forever, it also cuts down the amount of current needed on transmit.

If you go with a Mitrek, let me know. I can help with a step-by-step.

73 de KC7GR

Repeater-Builder website is a great central resource:
http://www.repeater-builder.com/mitrek/mitrek-index.html

SEITS has some info as well:
http://www.seits.org/repeater/mitrek/mitrek.htm

SRGClub has a great write up with some images you might need if you're like me and don't have the service manual in front of you.

http://www.srgclub.org/images/Mi_YesCR903-Schem.jpg
http://www.srgclub.org/images/Mi_YesCR903-Layout.jpg
http://www.srgclub.org/images/Mi_noCR903-Schem.jpg
http://www.srgclub.org/images/Mi_noCR903-Layout.jpg

R909 is TX Power, R927 is TX Limit.

Get a good pair of power cables, start turning the power up until you get to about 2W above rated. Then turn down the operating level. On mine, Limit is the blue pot, Operating Level is the red one.

I shouldn't have done it, but I cranked them both wide open. I got 58.3W out of a 40W rated radio. I didn't leave it that way -- I set it to 15W, then noted that I'm losing about a watt and some change in a RG-174 jumper. The service monitor only reported 13.3W.

The power supply was providing 13.73VDC, and because I was doing a power calibration, I hooked the radio up with a #2 welding cable and some half-inch ground braid I'd recovered and had handy. Losses inside the radio made the voltage at the back of the interface connector at 13.55VDC at 15W, and 13.45VDC at 45W.

[And then I found out the RG-174 jumper was bad and replaced it. Read more below...]

Those pictures are from this excellent write up:

http://www.srgclub.org/Mitrek_Rp_conversion.html

Here's another:

http://kf8kk.com/wi0ok/mitrek-conv1.htm

Connector pinouts:
http://www.n1uec.org/n1uec/mitrekrepeater.html

How I mocked up a control head:
http://www.repeater-builder.com/mitrek/mitrek-interfacing.html#Carrier_Squelch

Again, I suggest a service manual, but if you don't have one and you've seen one in the past, you might be able to wing it. 73 and good luck...

TinyTrak3 Manuals:
http://blog.catonic.us/kirby/tinytrak/TinyTrak3.pdf
http://blog.catonic.us/kirby/tinytrak/TinyTrak3Plus.pdf

TX Delay Settings:
http://info.aprs.net/index.php?title=NorCal_APRS_Regional_Info

My actual info on TXD comes from listening to the audio unsquelched and squelched while transmitting packets. The Mitrek is up and on the air in about 60ms. Since it's a crystal-based radio, it's on-channel as well -- no warm up needed. So a TXD of 8 or 80ms is long enough for the radio to send about 20 ms of preambling.

At 9600 BPS, these radios can be backed off to TXD 6 or 7 and used at speed.

The venerable Alinco DR-1200 needed a TXD of 33, mostly due to the broad and sweeping behavior of the VCO. That thing transmits Chirp FM spread-spectrum before it gets on frequency! It's at power before the VCO stabilizes. I'm surprised the FCC let them get away with it.

Most radios should be able to do a TXD of 33. If you listen and notice that the first part of the signal sounds like two alternating notes -- it is. That's the preamble. In practice, you want that to be as short as possible, while still decoding packets correctly. Much of that depends on the other radio returning from transmit to receive quickly. This is why the DIGIs now transmit immediately after hearing a packet. Because if you sent it, you're still waiting to swap back from transmit to receive, and the digi is taking advantage of the pause to blurt the message out.

I set the TinyTrak to a TXD of 18, as shown in the link above. The issue, again, is not the Mitrek, it's every other radio out there. Even with the reed relays, the Mitrek is a fast piece of 1970s technology.

SSID settings:
http://aprs.org/aprs11/SSIDs.txt
http://zlhams.wikidot.com/aprs-ssidguide
http://info.aprs.net/index.php?title=SymbolsAndSSIDs
http://vk3.aprs.net.au/aprs_ssid_usage.htm

In my case, I went with KE4AHR-12, ("one-way trackers"). Since it vehicle-borne, it will change to -9 sooner or later, and my bicycle will be -12 or some other SSID.

TinyTrak generic:
http://www.nwaprs.info/ttconfiguration.htm

03/28/12 Edit:

Per N8DEU, I backed the deviation off to 3.5KHz. I found the RG-174 jumper in the case was bad, and replacing it with another pre-made one caused the power out to jump from 13W to 18W with no change in current. After retuning the Mitrek to 25W (out of the box) the current draw was about 6.25A at 13.6V. The cigarette lighter is fused at 10A, so this gives me a few amps for operating another radio and charging a few mobile devices.

As deviation goes down, power efficiency goes up, however gains are on the order of 3dB, if that. You need at least 6dB to notice the difference.

I use a 1/4-wave antenna for my tracker. Its relatively small for the band used, and gives good performance out to certain angles. My perspective at this time is more coverage-testing of the existing nodes, and the dipole allows me to communicate using knife-edge diffraction. Now if only we'd implemented the system using 9600 BPS instead of 1200 BPS....

On the receive side, I mocked up a control head using a 10K ohm resistor between "Detected Audio" and "Squelch Wiper". A 3.3K ohm resistor connects "Squelch wiper" to audio ground. This gives a fixed squelch response. Then I connected the + side of the upper audio capacitor on the interconnect board to the backside of JU-3C, which connects to L18 -- the third large pin in the Mitrek control cable interface connector. From there, I routed the signal into the Signal Present line on the TinyTrak and set the voltage at about 3V. Reprogram the TinyTrak to invert DCD, and then set the bias so that it operates in a reasonable fashion. Net result is that the reciever works correctly when there is noise at -124dBm, or when there is a signal at -119dBm. The receiver actually starts hearing around -130dBm.

PE-75 Generator Manual TM 11-900

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Original Post: 02-20-2012 @ 1:17:40

PE-75 Power Unit

2.5KW Generator, 120V, 22.5A, 1800 RPM
6.5HP Briggs & Stratton Model ZZ (with 'antique' updraft carburetor), 2400 RPM

330 lbs, mounted to steel frame.

Yes, I have a manual. Here's Part I, V1.0 of it:

[removed]

This is also known as TM 11-900.


This monster was a part of an SCR-197.

Here's some other manuals I found on the web. Mine, as you note, is slightly different:

http://blog.catonic.us/kirby/PE-75/

Edit: 6/25/2012

Now I have the whole manual. Both of these are about 10MB:

TM 11-900
TM 11-900 rotated for readability

My manual is copyright by me, Kris Kirby. All rights reserved. This manual may be used for non-commercial purposes only. This manual may not be included in derivative works, or compilations of works (i.e.: CDROM collections), or sold on eBay either in print form or on electronic media.

Please contact me if you have a desire to include the manual in distributed works; we may be able to come to an understanding.

I have much higher quality versions of this document already scanned at over 150 DPI, uncompressed. I'd be happy to work out a license for the higher quality works and/or commercial uses.

DRM hasn't been included in these works because I believe strongly in portability. My original manual was printed/produced in the 1940s. It has survived this long, but it will not survive forever. It is my desire to preserve this information, but not exploit it. It took me a long time to scan, process, and so on. And you'll note from the document that I didn't always get everything straight. I don't seek to recoup my time, energy, and hard drive space. But there is a significant personal investment of each of those.

If there's something you can't read on a page, let me know. I may be able to re-scan the page and change the documents. It was stored in the accessory box of the generator, so it is filthy and does tend to leave specks behind on the scanner.

I can be reached at kris ]a()t[ catonic d0t us.

Damn Cool Antennas

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http://www.athena-gatech.org/research/3DINTEGRATION-MATERIALS/index.html

Neat stuff.

Ramsey FTR-146

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I've just received an email from Ed over a Ramsey in the technical support area. I waited a few days and he patiently scanned the last manual they had for the FTR-146!

I'm sure they'll get a copy of it up on the website soon, but I'll mirror it here as well.
 
FTR-146.pdf

So the basic routine for programming is:

Take the Desired Frequency
Subtract 143.000 MHz from it
Multiply by 100.

For example:


146.940 MHz
-143.000 MHz
-------------------
    3.940
    x 100
---------------
       394


Then you set the PLL divider / diodes to 394 in binary.

394
-256
-----
138
-128
------
10
-8
-----
2

So you put diodes into 256, 128, 8, and 2. (and -600KHz if you're using the repeater).

That's it.

Packet Radio / TNCs

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Thoughts/observations:

Speed is important. Baud rates are limited by law, but Baud doesn't equal signal rate; baud is the baseband. Using QPSK, you can double throughput, and you can still throw bits away in FEC if you need to. Phil Karn is a huge proponent of this and for good reason; he had a critical role in developing Qualcomm's satellite-based terminal systems used by truckers everywhere.

6m might be good for this, but easily obtained radios (Motorola Syntor Xs, GE Deltas, etc.) are starting to disappear. Also, they are large, and without a small TNC/node hardware that fits inside the radio, there is little reason to deploy equipment because more parts can break. Of course, the radios themselves need about 30A on transmit, so that would also need to be dealt with in a manner that doesn't impact size and site power requirements.

There's very little reason why we can't push soundcard packet into smaller systems like the Alix line of micro-PCs. We can dedicate an Arduino to software packet detection, another to node/routing, and pass the data on to a host if need be. Or we can load the sound-card engine into memory as a TSR and boot the thing using DOS and a G8BPQ stack. With TNC-X, a KISS TNC, it's possible to do that and more. Ideally, speeds upwards of 19200 and full-duplex are desired. However, full-duplex generally requires real hardware on the "node" side of things, and duplexers are a generally fixed commodity.

Also, proxy ARP may be a better way to use TCP/IP over AX.25, stealing information directly from the NETROM maps or something. For instance, my state net is 44.100.x.x, but good luck trying to actually get any of that to route outside of Mirrorshades.ucsd.edu.

Really, something closer to the mesh-networking systems used for the next generation wireless networking systems would be better. To gracefully handle losing a node and multiple routes present in the network stack. You can't really do that on a Z80 with 16k of RAM at 10 MHz.

IPv6 needs to be implemented at some point, with a graceful handling of IPv6 addresses to allow for compacting unnecessary zeros.

Software TNCs/Minimal TNCs:

AVR:
http://www.byonics.com/tinytrak4/
http://vk7hse.hobby-site.org/wiki/index.php/Main_Page
http://www.garydion.com/projects/whereavr/

Arduino:
http://www.adafruit.com/blog/2010/06/11/aprs-radio-shield-for-arduino/
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1232745624
http://dangerousprototypes.com/2011/01/31/packet-radio-and-the-arduino-radio-shield/
http://wiki.argentdata.com/index.php?title=Main_Page
http://forums.adafruit.com/viewtopic.php?f=10&t=11763
https://sites.google.com/site/ki4mcw/Home/arduino-tnc
http://mhvlug.org/pipermail/mhvlug/2011-April/031359.html

PIC:
http://www.ringolake.com/pic_proj/pic_index.html

HF:
http://www.brazoriacountyares.org/winlink-collection/AGW/PE%20Pro/pehelp/6hf.htm
http://www.tapr.org/pr_intro.html
http://wa8lmf.net/ham/30m-magloop-ant.htm

Packet general:
http://www.kc2rlm.info/soundcardpacket/6modes.htm
http://www.enide.net/webcms/index.php?page=wb8wga-tnc
http://www.amsat.org/amsat/articles/kd2bd/9k6modem/
http://nonbovine-ruminations.blogspot.com/2008/05/ham-radio-internet-and-cell-phone.html
Buck's articles: http://www.buxcomm.com/catalog/ (look down on the left-hand side)
GMSK:
http://www.southgatearc.org/articles/highspeedpacket.htm

Ham general:
http://hamlib.sourceforge.net/

Nodes:
http://digined.pe1mew.nl/?Introduction
http://www.ir3ip.net/iw3fqg/uidigi-e.htm
 -TheNet:
http://vectorbd.com/bfd/thenet/index.html
http://nl3asd.tripod.com/thenet.html
http://g8kbb.roberts-family-home.co.uk/html/thenet_x-1j.html
http://servv89pn0aj.sn.sourcedns.com/~gbpprorg/Radio_Mods/MISC/PACKET/PACKX09.TXT
http://kf8kk.com/packet/jnos-linux/thenet-ops-1.htm
- IP use in TheNet nodes:
http://www.w7eca.net/forum/viewtopic.php?f=84&t=444
 - TheNet replaced by NOS:
http://62.49.17.234/thenet.htm
 - JNOS:
 INP something. I dunno...
edit: Ah, here it is. A European internode protocol:
http://dl6mpg.net/nordlink/ftp/pub/documentation/INP/inp3.pdf
 http://www.langelaar.net/projects/jnos2/documents/inp2011.txt
http://www.langelaar.net/projects/jnos2/news/
Intro to NOS: (packet sizes, numbers)
http://www.febo.com/hamdocs/intronos.html
http://kf8kk.com/packet/jnos-linux/whetting/whetting.htm
FlexNet:
http://www.afthd.tu-darmstadt.de/~flexnet/

DX cluster:
http://www.ab5k.net/Home.aspx
http://www.dxcluster.org/main/index.html

Antennas:
http://wa8lmf.net/ham/30m-magloop-ant.htm


Old Huntspac stuff:

http://www.qsl.net/n8deu/huntspac.htm

Most of the older stuff I saw fall out of use as people got older and fell into different modes / cliques / clubs



Amateur Linking and Backhaul

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I have given a lot of thought to this. One of the issues with linking repeaters in the amateur world is that we're trying to do things that have already been done, years and years ago. Fortunately, all of that wisdom and experience is available at our fingertips, or out of the mouths of those old enough to remember and willing to speak. All the way back to Ma Bell's Long Lines microwave relay system, there have been various concepts introduced.

Long Lines was a channelized system which relied on translation (the block conversion of a group of frequencies to another group of frequencies) of existing channels for repeating or relaying and added a capability called "add/drop." Add/drop is a term still used in the telco world on circuits and certain types of gear. Long Lines was largely based on frequency-division multiplexing (FDM) of 300-4000Hz single-sideband (SSB) amplitude modulation (AM) signals. The resulting SSB signals were several tens or hundreds of kilohertz wide, depending on the number of channels the radio circuit was designed to carry. SSB is also subject to noise, and like most baseband or analog communications designs, requires equalization at multiple locations in the circuit equipment. Cable TV (CATV) experiences this as well. The increased attenuation at higher frequencies is referred to as "tilt". CATV amplifiers are designed with a "tilt" adjustment that allows for the higher frequencies to be amplified more than the lower frequencies to compensate for tilt losses. Later, Long Lines was transitioned in part to Digital Radio, using full-duplex DS3 radios costing $50,000 or more to connect cities or sites along the route.

Add/drop telephony refers to a piece of gear or circuit where channels are picked off and either not replaced, or replaced with other information. Synchronous and Asyncronous circuits alike may be configured for add/drop simply by adding equipment. In the sense of Long Lines, the Add/Drop functionality was not added by equipment; it was a function of that switching office itself. Microwave channels could be received on one dish or horn, translated to a different set of frequencies, and transmitted out another horn in a different direction. Likewise, a copper circuit could terminate at the Long Lines facility and be converted to a microwave channel and "Added" to the network. In the reverse sense, a microwave channel could terminate at the Long Lines Office and be converted (Dropped) to a copper circuit leaving the Central Office (CO). In T-series circuits, individual circuits may be added or dropped out of the larger group present. Modern equipment like the Adtran Atlas can do this on the DS0 (56K or 64K circuit) boundaries from T3s or DS3s. Other equipment, made by manufacturers such as ADC-Kentrox, may add/drop a single or multiple DS0 channels from a T-series (T1, T1c) circuit to allow combining virtual circuits over a physical copper loop from the telephone company.

The use of digital radios by Long Lines and another companies in the long-distance markets was supported by the marketing the systems allowed the company to do. Many systems which switched to PCM coding for voice immediately met with quieter, noise immune circuits. But the common plague of digital electronics still pervaded the space -- if the circuit was up and correctly configured, it would be error free. If the circuit was down or incorrectly configured, it may take months before the actual cause of the problem is located and remedied. Handling audio in the digital domain also freed technicians from the tedious labor associated with individually aligning circuits and amplifiers as well as equalization requirements for each stage of the equipment.

Several manufacturers make full-duplex digital T1 (24-channel) modems which allow telephone circuits to be extended many miles beyond the initial termination point. One well known radio station uses this method to allow the sales, management, and studio staff to have access to a nearby larger LATA (telephone calling zone) without paying long distance. This sort of connectivity, along with the ability to add and drop circuits at will, allows one to selectively "dial up" one or more channels of voice or data to a remote endpoint. In the data world, it is quite easy to inversely multiplex a larger, faster rate signal into multiple slower channel circuits to achieve higher throughput. This has been used since the infancy of the internet and the Apollo Space Program for transmitting data, telemetry, and video across analog circuits.

One of the larger issues and concerns surrounding amateur radio is the use of shared tower space. Tower space is often at a premium, and is very difficult to find for cheap or free. Furthermore, there is a complicated issue with respect to the Part 15 bands, primarily 902-928MHz, 2.4 - 2.45 MHz, and 5.3/5.8GHz. Many of these bands coincide with amateur radio bands, in which amateur radio operators are granted the immunity from other operators in the band who -- being unlicensed -- must tolerate interference from licensed users of the spectrum: amateur radio operators. Where this turns into a conflict of interest is that the Part 15 band user may want access to the tower and may mount commodity video, data or other equipment on the tower which may cause interference to users in that band who are licensed or otherwise permitted use of those frequencies. Moreover, the Part 15 user is a for-profit enterprise and is paying rent for the tower, while the amateur radio operators, who claim a higher priority to the frequencies desired by the Part 15 operator, are not paying for rent. The simplest solution in the eyes of the site manager is to tell the hams to pack it and leave -- money talks. Hams are strictly forbidden from engaging in for-profit enterprising using amateur radio, so as long as that rule stands, ham equipment on towers will cost a large amount of money to setup and maintain. The solution, therefore, is to avoid frequencies which are shared with other users of the site or that might cause interference to other paying users of the site. This basically confines a ham to bands which are solely the domain of radio amateurs, or shared with federal agencies. 222-225MHz (1.25m) is one these bands, as is 420-450MHz (70cm).

The FCC Rules, Part 97 limit the speed and amount of bandwidth that transmissions at or above certain frequencies may occupy. At the time of this writing, the following limits apply for 28MHz (10m) and up:

  • 10m: 1200 baud signaling rate, FSK may not exceed 1KHz
  • 6m: 19.6 kbaud signaling rate, 20KHz emission width
  • 2m: 19.6 kbaud signaling rate, 20KHz emission width
  • 1.25m: 56kbaud signaling rate, 100KHz emission width
  • 70cm: 56kbaud signalling rate, 100KHz emission width
What strikes my eye about this is the rate, specified as "symbol rate", particularly in bauds. A BPSK signal, operating at 9600 baud, transfers data at 9600 bits per second, at one bit per hertz of occupied bandwidth. QPSK on the other hand, transmits two data bits per symbol, doubling the capacity of the same 9600 Hz of occupied frequency. Switching over to QAM at higher densities allows for even more bits to be packed into a given space. Using QAM or QPSK requires linear amplifiers and different modulation methods to produce them. This adds complexity, however it extends the most precious resource we have -- limited bandwidth. By using 4/pi QAM on a 56Kbaud circuit occupying around 100KHz, 224Kbit/s of data may be transmitted using linear amplifiers. At these widths, duplexers may be used to fine-tune filters to keep noise out of the systems, as well as prevent possible interference from or to other stations on the same mountaintop. Additionally, being down in the amateur radio bands prevents a fight over who stays and who pays to use a given section of vertical real estate. Since the amateur radio operator isn't sharing frequencies with the unlicensed or commercial operator, this situation should not exist.

In short, we owe it to ourselves, as amateur radio operators, to explore dense data modulation techniques and apply them to amateur radio. We have had a thirst for bandwidth dating back decades; now we finally have commodity modems that make achieving those bandwidths possible using limited RF. Just look at Digital TV: 19 or 23Mbit/s in 6MHz. Twenty years ago, in 1990, that would have been astounding! And now we have that on ever single person's set top TV.

Improvized Power Loads

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Being something of a home-bound hacker without a lab other than my own equipment, I find it's sometimes necessary to improvise equipment using other stuff. After replacing batteries in a UPS, I needed to check everything out for loose connections, unusual sources of heat, and so on. It took a lot of effort to take the UPS apart, and I didn't want to have to take it back apart or have any issues inside that would crop up later.

When testing a UPS, or another other power generating device, a resistor is the best type of load to use. Since it's non-reactive, the impedance of the resistor equals its resistance across almost the entire spectrum.

Here's where we go crazy...

First, I tried the toaster oven. Fail. The toaster oven is 1400W. UPS is nominally about 1500 VA, which works up as a few short, because most computer UPSes are overrated in VA because most PC power supplies don't have a .99 power factor.  Good test of the overload capacity.

The portable heater didn't work out for one reason or another, 750 or 1500W. So I was left searching for something that would do the job. The microwave, at 1500W, was also out of the picture. The electric skillet was an amazing 1200W! Finally, I settled on the one obvious solution for some UPS runtime: the rice cooker / steamer.

The steamer's nameplate said 650W at 120V. This was a perfect load for the UPS, as it didn't exceed 1000VA or 1000W, allowing me some actual run-time with the UPS. Since the steamer works through phase change, the actual "output' of the device in steam wouldn't be very much. There would, however be a few cups of hot water in the bottom.

So remember the next time you need to do a test, what heaters you're surrounded with. Just because a heater is designed for 120V, doesn't mean you can't apply it at a lower voltage.

650W / 120V = 5.4167 A. 120V / 5.4167A = 22.154 ohms.

Likewise, were one to attach an 8-ohm speaker across the 120V line, it would need to dissipate 1,800 watts and would trip the breaker on a 15A circuit eventually.

120V / 8-ohms = 15A, 120V * 15A = 1800W.


If you really still want to buy power resistors, and there's no reason not to, you can find them cheaply at Surplus Sales of Nebraska and Fair Radio Sales. Be aware however, that above audio frequencies, impedance may become a factor as the device may start radiating. Just because you can match a HF transmitter to two steamers in series doesn't mean you should use them as an RF dummy load. Gordon West, WB6NOA famously demonstrated this by making contact with a fellow amateur radio operator across the world using a light-bulb as a dummy load.

Tower Work

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Do you have an abject fear of heights? Do you quake looking through a glass or metal floor above twenty feet? If so, you probably shouldn't be doing tower work. But if you are, here are a few other things you should be aware of:

If you need a rope to haul anything other than your tools, you need a ground crew.

Just because an antenna and/or bracket moves smoothly on the face of the tower doesn't mean you can lift it, or take it off the tower by yourself.

Never estimate the amount of time it will take to finish a task working alone. It will take longer, and eventually you'll find some point where you will need more power from the ground than you can exert on your own.

I'm going to update this as I go, so look for more lines to be added over time...

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