On the 13th of May 2025, FM DXer Larry Horlick, VO1FOG in Newfoundland managed to log quite a number of FM radio stations from the Azore Islands.
The stations logged were in the range of 87.6 to 103.0 MHz and the distances were in the region of 2000 to 2600 kms.
It's very likely that the propagation mode was one hop Sporadic-E with some degree of tropo at one or both ends.
Most of the stations were logged in the period from 14:01 to 14:47 UTC although there are two from 15:21 and 18:14.
The power of the transmitters ranged from an EPR of 40-kilowatts down to as low as 50-watts.
This isn't the first time that Larry has logged the Azores but it's always interesting to see reports of stations from the Azores being heard in North America. It's also relatively early in the Sporadic-E season for such signals.
This is a selection of the radio stations that Larry heard...
Links... 1) The source of the above information is FMLIST.ORG 2) For more information on long distance paths on the FM band, see my 88-108 MHz page.
It's always interesting to read about how the low VHF band above 30 MHz was used over the years for various applications. In the United States in the decades after World War 2, they used doppler shift on the low VHF band to find the location of rockets that had been launched.
The antenna above is a helical antenna operating at 36.9 MHz which sent a radio beam up towards the rocket after launch. A series of similar receiving systems would then pick up the reflected signal which would be shifted slightly in frequency due to the motion of the rocket i.e. the reflected signals would have some doppler shift.
By examining the data afterwards, the exact position of the rocket at any particular time could be calculated.
The antenna shown above is at the White Sands Missile Range Museum in New Mexico. If we examine it closely then we can see that it has three turns so we can estimate the gain to be roughly 8dBd, have a beamwidth of about 60 degrees and is of course using circular polarisation.
The plaque on display reads as follows...
"36.9 Megahertz Helix Antenna Doppler Velocity and Position (DOVAP)
Reference Transmitter Antenna
Developed during World War II by the Germans as part of a V-2 guidance and control system, DOVAP traced the course of a rocket using the Doppler Effect caused by a target moving relative to a ground transmitter and receiving stations.
Unlike radar, Dovap did not allow scientists to "see" the rocket on a screen. Instead, it sent up radio waves, which were received and rebroadcast back to earth by the rocket. The returned waves combined with the original ground broadcast and produced a musical tone which varied with the rocket's speed - the faster the rocket, the higher the pitch.
DOVAP data was extremely accurate: it could place a rocket's position at 100 miles up within 50 feet. It could collect data at the extreme altitudes of 100 to 300 miles. Dovap's disadvantage was that it took 3 to 4 weeks to reduce the data.
The antenna is a helix because of its physical and electronic characteristics. A helix is simple to construct and operate, provides necessary signal gain and directivity, and can be operated in several modes or polarizations.
The DOVAP system provided trajectory data and ground guidance for most of the early rocket systems: Corporal, Sergeant, Honest John, Little John, Redstone, and Aerobee Upper Atmosphere programs.
This particular antenna was built in the mid-1960s near C Station. Like much of the early instrumentation used here, it was designed and built at White Sands Missile Range.
Erected by White Sands Missile Range Museum. (Marker Number 06.099.)"
Oguz, TA2STO in Türkiye has developed a new mode called LongChat to allow radio amateurs to communicate with each other.
It's described as follows... "LongChat is a low-power (QRP) / low bitrate text chat software application over ham radios connected to a PC. Chirp symbols with an audio bandwidth of 2400 Hz (300-2700 Hz) are generated on the PC side for encoding the messages. Baseband audio signal is then transferred from PC to ham radio for modulation at the selected mode. SSB, FM and other types of modulation modes can be used. Forward error correction codes are used to correct messaging errors
Current version is tested on ICOM-7300 and YAESU FT991A radios. Other radios are supported but not tested yet. Future improved versions will support higher data rates or lower S/N ratios.
Since the software is continually improved and data structures may have changed, newest version needs to be used for compatibility with all users. To ensure this, software will remind you to download and use the latest version when a new version is ready.
Specifications Usable data rate (net user data) is 7 ASCII characters per second at -12 dB signal to noise ratio. Eb/No (Energy per Bit to the Spectral Noise Density) is 5 db Measurement of received message SNR. Measurement of chirp frequency shift in SSB mode. You may download the software, user manual and brochure at the link below. https://drive.google.com/drive/folders/1NQwbeoHE3vPLORGN1krpSNHHI9brhDJh?usp=sharing "
***
Update May 2025: These are the recommended frequencies for the LongChat mode.
80 metre 3595 kHz
40 metre 7045 kHz (main) + 7055 kHz (backup)
20 metre 14095 kHz
17 metre 18095 kHz
15 metre 21095 kHz
10 metre 28095 kHz
6 metre 50295 kHz
2 metre 144.195 MHz
70 cm 432.095 MHz
QO-100 sat 10.489,548 MHz
***
As of late 2024, this is all very new and I'm sure a lot of people will have questions as to how good is it? Will it be better than modes like JS8Call? And more critically, will it get a critical mass of users to make it worthwhile?
I'd suggest that at the moment, it should be seen as something of interest to those who like to experiment with digital modes on the HF bands and want to experiment to see how it compares to other modes.
It also seems to be a 'work in progress' project but remember that the software for this mode is free and is being developed by one person. It'll be interesting to see how it develops.
TA2STO released the following video about it...
Update from TA2STO - 1st Dec 2024:
- Hi, I am the author of LongChat chirp mode. I started it a few years ago as a project for low power sensor applications. Then I wanted to try it as an experimental digital ham mode.
-LongChat is an encoder/ decoder. In general it should work on all modulations LSB, USB, FM, AM etc.
- I usually work with USB at lower band edges and LSB at upper band edge. It is easy to miss it when changing the modes. I guess I relied on IC7300 to disable transmission at band edges. IC 7300 does allow that though. I had no specific reason for using LSB. It works both on USB and LSB.
- I am preparing a new video to compare the power efficiencies of digital modes. I will post it when ready
- Newest version is 1.3.00 . Setup manual, version info and other things are also in the link above.
- LongChat is experimental and supports a number of radios. Untested radios are marked with * as the first character
- I am not an experience radio ham in operations and regulations. Maybe experienced radio hams can designate frequencies and protocols for test purposes.
- Since the signal is way below the noise level (-13 db) , there is yet no equivalent of a waterfall display like FT8, JS8 etc. This makes it harder to see the activity.
- You can view the waterfall in FT8 because it's minimum SNR is -4 db. and bandwidth is 50 hz . People quote -21 db as the SNR for FT8. This is the referred SNR if the bandwidth were to be widened to 2500 Hz. My next video will clarify these issues.
- Since there are no designated frequencies for LongChat, it is difficult to find some one for QSO
-There is also a criticism of LongChat not being open source . LongChat code has some new algorithms with IP value. If I open the source code to radio hams, people and companies with commercial interest will also have a free access. But I totally respect and mostly agree with the open source advocators.
- In short, LongChat is an experimental mode. My effort is to bring the SNR of LongChat to the limit dictated by the Shannon channel capacity theorem and make it the most power efficient mode.
- If people want to experiment with it, I am ready to support. I am not the best person to decide on the designated QSO frequencies, LSB or USB selection, protocols etc. If some of you want to do that , or perhaps open a group here or on google groups i.o, I would be happy to get involved.
Addendum: Matt, M0DQW released the following video which shows LongChat in operation...
