In the early days of amateur radio if you wanted to work over great distances the required items were a tower (maybe 66 feet up), a beam antenna with a rotor and a high power amplifier. That's no longer the case. There are a number of ways of getting gain related to the modulation method. The satellites used to supply cable TV spread the 5 MHz video signal out to about 36 MHz. This adds process gain which allows a lower power transmitter in the satellite than would be required if a 5 MHz bandwidth was used.
There are many digital modes that take much longer to send a message than would RTTY or Morse code. By doing this they add process gain allowing a signal to be fully recovered even though it's up to 30 dB below the noise floor.
A classical problem is getting a message to the desired recipient without any errors in the presence of noise. In the analog world that was best done by minimizing the signal bandwidth and using a receiver with that same bandwidth. But, as the bandwidth is narrowed so is the amount of information per unit of time reduced.
Another concept is that it's better to transmit something than nothing. So modulation schemes that are always transmitting work better than schemes where the transmitter is turned off.
In the digital world there are new things that can be done. Multiple frequency-shift keying (Wiki) is an outgrowth of the development of dial-up modems (Wiki) where it was desired to send as much data as possible over a bandwidth limited to about 3 kHz. At the beginning 200 baud was that best that could be done, but ended up at 56,000 baud in that 3 kHz bandwidth. Later DSL (Wiki) would provide 6,000,000 baud over phone lines.
Continuous Wave (Wiki: CW)This is the oldest digital mode also knows as On Off Keying (OOK). This mode suffers from a number of problems. For example when the transmitter is turned off no information is being sent, so modes that are always transmitting are better. There is no synchronization in terms of the on/off edges or in terms or timing relative to the carrier.
Coherent CW (CCW)The idea is for both the transmitting station and the receiving station to have a precise clock and the start and stop edges of all the symbols fall at known points in time. This allows automated detection of CCW at lower signal to noise ratios than ordinary CW.
High Speed CWDuring WWII the enemy could use Direction Finding (DF) receivers to locate transmissions that were being made by spies. In order to reduce the time it takes to transmit a message High Speed CW sets were developed and later used as late as View Nam.
GRA-71 and and English version of the GRA-71 use a magnetic tape that is recorded manually and then played to the transmitter at about 300 Words Per Minute.
Amplitude Modulation (Wiki) has been around for a long time. Still used on the AM broadcast and shortwave bands (Wiki). The McKay Dymec DR33 receiver was optimized to produce good audio quality when receiving AM either on the broadcast band or shortwave band.
AM is used for aircraft ratios because it does not have the Capture (Wiki) problem of FM radios. That's to say that two signals arriving at an aircraft receiver with more than say 3 dB difference in amplitude will both be heard on an AM receiver. If FM was used only the stronger signal would be heard. So, AM will continue to be used on aircraft radios because of this vital safety feature, heading "doubled" transmissions.
The AM signal consists of a Lower Side Band (LSB), Carrier (CW) and Upper Side Band (USB) signal. A sideband receiver can tune into either sideband. Note when the audio stops the CW carrier is still present and has the effect of making dead air sound quiet.
Negative Cycle Loading
In a classical AM modulator the audio signal is amplified to have about the same power level as the RF carrier. The audio then increases and decreases the RF level. A problem occurs when the audio signal goes low enough to turn off the RF. This is called negative cycle clipping. The abrupt change causes harmonics to be generated and so must be avoided.
A way to get more talk power is to use a diode and series resistor connected to the modulation signal so that as it goes negative it will be loaded down to a lower voltage on the negative half-cycle than on the positive half-cycle where the diode disconnects the resistor which has no effect. That allows higher positive peaks while at the same time preventing clipping at the negative peaks.
This modification was made to a radio somewhere on these web pages but so far I have not remembered it's name.
Radio Teletype (Wiki: RTTY)Also knows as frequency shift keying (Wiki: FSK). Involves transmitting on one of two frequencies. This mode has been around for a very long time. Problems: If the shift is too wide the signal takes up more bandwidth than is needed relative to the keying rate. Minimum Shift Keying (Wiki: MSK) is better in this regard. The early demodulators required both Mark and Space signals in order to work and if one or the other was garbled the output was garbled. Frederick Electronics and I assume others offered advanced demodulators that would work with either Mark or Space signals.
Note that the transmitter is always transmitting something so more power is being used per bit than in a mode like CW where the transmitter has off time. In some cases this requires better heat sinking than other transmit modes.
By using a number of different forms of diversity the reception of HF RTTY signals could be radically improved. A common system was to use two receiving antennas, two receivers and two demodulators. If the antennas have different polarity and/or are separated by a distance that's a few wavelengths then the signals tend to fade at different times on the two systems and a combiner automatically selects the best signal so the output is the best of both signals. Another form of diversity is to use a common antenna but have the two receivers tuned to different frequencies that are both transmitting the same message. Another form of diversity is time. The MD-1142 sends a number of versions of the same message offset in time and modulation tone frequency. The idea is that fades only last a short time and the message can be reconstructed.
The CV-89A/URA-8A is a Military tube type FSK converter with a CRT type tuning indicator.
The CV-483/URA-17 is a Military solid state FSK converter with a CRT type tuning indicator.
The Frederick 1203 a solid state FSK Demodulator that works with either Mark or Space or both
The MD-1142 uses time diversity and multiple audio channels
PSK31 (Wiki)This is a digital mode that's optimized for human generated characters, very narrow bandwidth and the transmitter is always on.
"Weak Signal Propagation Reporter" Intended for propagation
analysis and/or antenna testing, does not include provision for
Official web page - http://physics.princeton.edu/pulsar/K1JT/wspr.html - software designed to be used with SSB HF radio and a computer sound card.
wsprnet.org - maps and logging
QRP-Labs - has a
relay filter bank as an option for their WSPR transmitter (6 Tx
frequencies) as well as a GPS receiver for keeping time, RF
frequency & Grid square.
WSPRlite - SotaBeams: UK based standalone WSPR single frequency transmitter- Classic SB or Flexi -
|WSPRlite Flexi beacon transmitter at base
of TCI-651 antenna
With Power Bank recommended for GoPro camera where my existing power bank did not work. SotaBeams says some power banks turn off if they don't see enough load.
The transmitter has microUSB for DC power and programming.
SMAf for RF out, a status LED and a start push button. A very simple setup. But the timing of the press and hold for start needs to be accurate to maybe 0.1 seconds, 2 seconds is far enough from correct to prevent proper reception.
|80 meters 3.570125 MHz
||40 meters 7.040104
Prior to using the WSPRlite it needs to be programmed using the
USB-micro port for both power and data.
That can be done using a standard USB-A to USB-microB cable and a laptop or desktop computer or a USB-microB to that matches your cell phone with OTG capability.
USB On-The-Go (Wiki) allows connecting two devices where one acts as the host. Intended for things like memory, keyboards, mouse, &Etc. Allows the WSPRlite app to both configure the beacon transmitter and to also start it at the exact time needed. But to remove the phone and keep the beacon transmitting requires a Y-cable.
|Turns out this does NOT fit the
connectors 6.81mm wide (Mini-B), but need to be 8.2mm i.e. the cell phone is USB-C.
|This is a USB-Bmicro cable - WRONG cable
for LG G6.
||<- This is a Cable Creation p/n: CC0756
Length" 0.2m (8")
eBay search term: "Micro USB Male to Micro USB Male OTG Cable Data Transfer"
The cable is asymmetrical and one end is labeled "Host".
The WRONG cable!
|Fig 1 Cables for OTG configuration &
Note USB-C at phone end and USB-Af going to "Y" USB-A cable.
|Although not marked on the Y-cable, one of
USB-A connectors only carries DC while the other
one will work for data. To test connect WSPRlite to computer using Y-cable and see which leg supports configuration. For this Y-cable the other leg does NOT support any data, only DC.
Note: the cable from the phone to the USB-A socket needs to
match your phone. Mine happens to be a USB-C connector,
but prior phones have used USB-Bmini and USB-Bmicro
|Fig 2 Set-up prior to tapping Auto-Start
||Fig 3 Counting down for auto-start to
||Fig 4 beacon has been activated
|Fig 5 Cell phone can be removed and beacon
gets DC from
The problem is that if the start transmission function is used
in the phone then the phone is powering the WSPRlite. When
the phone is unplugged the WSPRlite stops, so a "Y" cable is
needed to take advantage of the app auto start function.
The Y-cable sold by SotaBeams (web
page) seems to have a USBA socket and so is a two cable
I have on order (eBay title: "USB OTG Power Y Cable") It
has a USB-A plug for the power bank, a USB-A socket for the
existing WSPRlite power/programming cable & a USB-microB
plug for the cell phone. I'm guessing this is what the
SotaBeams cable is, so it will take two cables.
To determine if your phone supports USB OTG use the Android app "USB OTF Checker". The LG-VS988T does support it.
Part of the configuration is the Grid Square location of the
beacon. Here's a web
page to help with that. Note only the first 4
characters are used by WSPR.
When USB first came out it was a fantastic improvement on RS-232.
It turns out the RS-232 was an agreement to NOT have a standard. The pin assignments (Tx on 2 or 3?), number of pins (9 or 25) in the connector and sex (pin or socket), type of handshake (hardware, ACK/NAK,, none), parity bits (none, 1, 2, even or odd) are not fixed, so in order to get two devices to talk in "RS-232" you need a custom cable or a stock cable (straight or null modem?), BAUD rate (select from a long list or auto determined) and a bunch of adapters to get it working and settings on the computer to match. That all went away when USB was introduced because there was USB-A where the desktop or laptop computer had a USB-A socket. The one and only cable had a USB-A plug to a USB-B plug and the other device had a USB-B socket. But then people wanted video and USB was to slow so, Firewire came out as something different. That didn't last long and USB got faster and then the "B" connectors started changing. Now there are B, Bmini, Bmicro and C connectors and various number versions of USB like 2.0, 3.0 &Etc
So, USB has become an agreement to not have a standard. Just like RS-232 you need to specify which flavors of USB cable you want. This allows retailers to sell cables without specifying the connector and instead specifying what models of phones they fit. Of course this is accompanied by a price 10X higher than what you would pay for the generic cable.
After using time.is web page on
my cell phone, I started getting signal reports.
It's also important to start on an even minute, which I may have done by accident.
The time to send one frame is just under 2 minutes.
"Press the button 2 seconds after the start of an even minute.
It turns out that the time shown on my WIN7 desktop computer
was off by 1.8 seconds and my LG-VS988T cell phone does not
display seconds on the clock.
The desktop clock was fixed by using Dimension4 software. Now the desktop computer agrees with the UltraLink WWVB receiver and time.is web page.
I added the ClockSync app to the cell phone but unless you root your android phone it can NOT set the system clock. But it does have a seconds display. This is because the Android system forbids apps from changing the system time or date, probably because if you could do that, then you could keep trying the demo version by setting the clock back to when you loaded the app.
home page - Vimeo:
|Distance (km)||Call||Spots count||Last seen|
|646||W7OWO||12||2018-06-22 17:02 to 20:26|
|246||KM6I||2||2018-06-22 18:06 to 18:26|
|174||KK6ZIZ||7||2018-06-22 17:02 to 18:20|
|173||KP4MD||4||2018-06-22 17:02 to 18:26|
|155||KPH||20||2018-06-22 17:02 to 20:14|
Digital Voice (eHam, ARRL)The military uses Continuously Variable Slope Delta (CVSD) as a method of converting voice into a digital signal. This is the signal that is sent over the wires of the TA-1042 Digital field phone. For use in the KY-57, KY-58, or KYV-2 Secure Voice Module the CVSD data is enciphered prior to sending and then descrambled at the receiving end. This is a symetric system with the same key used for both sending and receiving.
I started looking into what it would take to make a digital voice interface to work with the military radios that have "wide band" capability, i.e. the VHF and UHF radios. The CVSD chips used in the early military voice encryption units are now obsolete. There was some amateur radio work done using the AD73311 CODEC, but it has a 16 bit word output with a framing pulse. This makes it very hard to send over the air without also using some type of VOCODER chip to reduce the bandwidth. By using a CVSD type of codec the output is just a single bit data stream with no framing required, making it relativity easy to send and receive.
I recently saw a nice distinction made between voice scrambling and voice encryption. The implication was that scrambling involves mixing up the audio and sending that audio, whereas enciphering implies using a digital data stream to carry the voice message. From what I've read it's possible to reconstruct any mixed audio scheme, but very much more difficult to break a digital cipher.
The KY-38 came out during the latter part of the Vietnam era and worked with the PRC-77, so probably used a digital enciphering method rather than an analog scrambling method, but this is all speculation since not much has been published about it.
Frequency Hopping (Wiki)One way to make direction finding difficult is to have the transmitter change frequency frequently. Note that the hopping itself may not provide any security since a simple crystal radio that had a wide band input would detect all the transmissions. This is the case no matter in what order the frequencies are changed. So voice encryption is needed in addition to the hopping and that's what is done in the COMSEC part of the SINCGARS radios, externally with a KY-57 for the early radio and internally in the later radio.
Spread SpectrumAlthough Frequency Hopping is a form of spread spectrum, the term is used more often to describe what is called a direct sequence (Wiki). This is where the data signal is mixed with a spreading signal with a data rate considerably higher than the data signal rate so the the final signal that's transmitted has a bandwidth larger than what would be used for just the data. For example the C band satellite television system spreads the normal 4.5 MHz video signal out to 36 MHz thus adding process gain to the system allowing much lower transmitter power in the satellite. The Magnavox Procom hand held radios have a very long range for a low power radio because of the spread spectrum signal. The GPS satellites use spread spectrum and the signal falling on the Earth is so weak that it is below the background noise level.
The Black Box uses pulse modulation but it's transmitted spectrum looks very much like spread spectrum. I assume that there's a receiver optimized to receive this signal. But none of the receivers I know about will receive the signal.
MIL-STD-188-110A/B/C (Wiki, MARS) Interoperability And Performance Standards For Data Modems (Tactical Data Link: TADIL, Link 11)
110A-1991: 75bps through 2400bps coded and 4800bps with no FEC or interleavingMIL-STD-188-141B/C Interoperability and Performance Standards for Medium and High Frequency Radio Systems
110B-2000: 9600bps coded in a 3Khz channel and
110C-2011: from 3Khz up to 24Khz in increments of 3Khz channels while providing user data rates up to 120,000bps coded hroughput with multiple HF Independent Sideband (ISB) channels.
STANAG 5066 Profile for HF Radio Data Communications (Data Link Protocol (DLP) (5066-ARQ))
STANAG 4197 - Edition 1, Modulation and Coding Characteristics that must be Common to Assure Interoperability of 2400 b/s Linear Predictive Encoded Digital Speech Transmitted over HF Radio Facilities
FED-STD-1015 - Analog to Digital Conversion of Voice by 2400 bit/second Linear Predictive Coding (LPC)STANAG 4198 Edition 1, Parameter and Coding Characteristics that must be Common to Assure Interoperability of 2400 b/s Linear Predictive encoded Digital Speech
STANAG 4203 - (Edition 3), Technical Standards for Single Channel HF Radio Equipment
STANAG 4285 - Characteristics of 1200/2400/3600 bit/s single tone MODEMs for HF radio links,
FED-STD-1052 Appendix B Telecommunications: HF Radio Modems (Data Link Protocol (DLP))
STANAG 4415 Characteristics of a Robust, Non-hopping, Serial-tone Modulator/Demodulator for Severely Degraded HF Radio Links
STANAG 4481 - Edition 1, Minimum Technical Standards for Naval HF Shore-to-Ship Broadcast System
STANAG 4529 - Characteristics of single tone MODEMs for HF radio links with 1240 Hz bandwidth
STANAG 4538 - (Edition 1) Technical Standards for an Automatic Radio Control System (ARCS) for HF Communication Links
STANAG 4539 C3 (Edition 1), Technical Standards for Non-hopping HF Communications Waveforms
STNAG 4591 - Edition 1, 600 b/s, 1200 b/s and 2400 b/s NATO Interoperable Narrow Band Voice Coder
STANAG 5065 MSK waveform
Link 11 MIL-STD-6011 (Wiki) -> Link 22 (Wiki)
U-229 AUDIO/DATA connector pin out.
DS-101 Smart Fill Devices (Wiki)
DS-102 Common Fill Devices
See Fill on the Crypto Machines web page
OtherThere are a lot of digital modes in addition to those mentioned above. Some are for transmitting text and some are for transmitting images. For example see:
Worldwide Utility News (WUN) -
Harris 5710 & 5720
These are modems in a box that support many of the military data modes.
4365338 Technique for high rate digital transmission over a dynamic dispersive channel, Harris Corporation, Dec 21, 1982, 375/230, 375/254 - referenced by 121 other patents - optimized for HF data - uses known preamble
4599732 Technique for acquiring timing and frequency synchronization for modem utilizing known (non-data) symbols as part of their normal transmitted data format, Harris Corporation,
Jul 8, 1986, 375/346, 375/367, 375/355 - referenced by 184 other patents - makes use of I & Q processing - preamble type known information is interleaved with the data so the receiver can dynamically re-equalize.
The CV-89A/URA-8A is a Military tube type FSK converter with a CRT type tuning indicator.
The CV-483/URA-17 is a solid state FSK converter with a CRT type tuning indicator.
The Frederick 1203 FSK Demodulator
The Frederick 600A BER test set
Digitech also made a modular rack mount Digital Data Generator
FS5000 cold war embassy secret coms 2-way HF radio set
PRC138 ALE capable HF manpack radio
Micom ALE capable HF vehicle radio
GRC-109 HF radio works with GRA-71 high speed Morse transmission (but not receive high speed Morse)
In order to test any digital mode you need a test signal and a way to evaluate how it gets through the modulation - demodulation system.
Test equipment for early RTTY equipment was designed to test the mechanical RTTY machines and has special functions for them. These machines were used in a current loop configuration where all the equipment was in series. Included was a power supply of around 100 Volts and the current was adjusted for typically 60 ma and later 20 ma.
Digitech made a modular rack mount Digital Data Generator and analyzer
The Frederick 600A BER test set uses RS-232 levels rather than the older current loop type of interface.
When testing a communication path that will be used for encrypted messages the bandwidth of the test set needs to match that of the encrypted signal. For testing both wire line and radio systems utilizing the VINSON protocol the F91120 test set is suitable.
page created 31 July 2001