29 MHz - Revision history

G8GTZ: /* Introduction */

2025-12-07T17:19:49Z

Introduction

G8GTZ: /* Equipment for 29MHz DATV */

2022-12-19T14:44:58Z

Equipment for 29MHz DATV

G0MJW: /* Propagation Effects and multipath */

2022-11-30T22:53:55Z

Propagation Effects and multipath

G0MJW: /* Propagation Effects and multipath */

2022-11-30T22:48:38Z

Propagation Effects and multipath

G0MJW: /* Propagation Effects and multipath */

2022-11-30T22:43:08Z

Propagation Effects and multipath

G0MJW: /* Generating a low rate transport stream */

2022-11-30T22:40:07Z

Generating a low rate transport stream

G0MJW: /* Equipment for 29MHz DATV */

2022-11-30T22:19:01Z

Equipment for 29MHz DATV

G0MJW: /* Equipment for 29MHz DATV */

2022-11-30T22:18:07Z

Equipment for 29MHz DATV

G0MJW: /* Propagation Effects */

2022-11-30T22:11:48Z

Propagation Effects

G0MJW at 22:11, 30 November 2022

2022-11-30T22:11:09Z

@@ Line 2: / Line 2: @@
 The 2022 RSGB band plan http://rsgb.org/main/files/2022/02/220126_2022-Band-Plans_RadCom-web.pdf identifies 29000 - 29510 kHz segment as available for experimental wide bandwidth operation on a non-interference basis to other stations, including the amateur satellite service segment at 29300 -
-kHz.  In practice, this means we can experiment with reduced bandwidth DATV on 10m. The 10m band opens for worldwide DX around solar maximum, so theoretically and now in practice it is possible to transmit video worldwide.
+kHz.  It is recommended that stations use a center frequency of 29.250 MHz to avoid causing interference to the weak-signal satellite downlinks of OSCAR 7 and CAMSAT satellites.
 These pages are intended cover the experiments, noting they are experiments, that may require significant effort in construction of equipment, development of software and quite a but patience in order to participate. So far, signals have been sent across the Atlantic by several amateurs using very low symbol rates. There is much still to do to improve performance and reliability. If that interests you, you are in the right place.

@@ Line 32: / Line 32: @@
 A better option for receive may be to use an HF SDR, e.g. an Airspy, RFSpace SDRIQ/CloudSDR or an RTL dongle and decode the signal in a software package like GnuRadio or SDRAngel. Both of these software packages can also be used to transmit.
-Information on a simple 2m to 10m frequency transverter is [here]
+Information on a simple 2m to 10m frequency transverter is [[29MHz transverter]]
 Information on building power amplifiers for 29 MHz DATV is [here]

@@ Line 14: / Line 14: @@
 Despite the good signal strengths, none of these signals were decodable except very briefly whenever a single path became sufficiently dominant.
-The solution to multipath for digital audio broadcasting at HF and VHF and terrestrial television at VHD/UHF is to use a modulation mode, called Orthogonal Frequency Division Multiplexing (OFDM) where many narrow bandwidth signals are stacked next to each other. Each narrow bandwidth carrier is less impacted by multipath and clever algorithms can be used to compensate and even take advantage of the multiple paths to either increase bandwidth (as in MIMO) or improve the signal to noise ratio.
+The solution to multipath for digital audio broadcasting at HF and VHF and terrestrial television at VHD/UHF is to use a modulation mode, called Orthogonal Frequency Division Multiplexing (OFDM) where many narrow bandwidth signals are stacked next to each other.
-[OFDM IMAGE]
+[https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing Wikipedia - OFDM]
 Some form of OFDM is likely to be the best technique, but requires software development to enable it.

@@ Line 12: / Line 12: @@
 [[File:Multipath1.jpg|400px]]
-The solution to multipath for digital audio broadcasting at HF and VHF and terrestrial television at VHD/UHF is to use a modulation mode, called Orthogonal Frequency Division Multiplexing (OFDM) where many narrow bandwidth signals are stacked next to each other.
+Despite the good signal strengths, none of these signals were decodable except very briefly whenever a single path became sufficiently dominant.
 [OFDM IMAGE]
-This is likely to be the best technique, but requires software development to enable it.
+Some form of OFDM is likely to be the best technique, but requires software development to enable it.
 ==Equipment for 29MHz DATV==

@@ Line 8: / Line 8: @@
 ==Propagation Effects and multipath==
-The F2 and E skip that provides good DX on 10m usually comes at the cost of multipath distortion. In practice this means our usual phase modulated signals (e.g. Quadrature Phase Shift keying (QPSK)) of above a few kHz bandwidth can't be decoded. Success so far has used relatively low bandwidth 18ks/s QPSK in a bandwidth of ~20kHz but even this is too wideband and does not deliver particularly good video.
+The F2 and E skip that provides good DX on 10m usually comes at the cost of multipath distortion. In practice this means our usual phase modulated signals (e.g. Quadrature Phase Shift keying (QPSK)) of above a few kHz bandwidth can't be decoded. Success so far has used relatively low bandwidth 18ks/s QPSK in a bandwidth of ~20kHz but even this is too wideband and does not deliver particularly good video. Here are three narrow band signals received by a networked radio in Pennsylvania. They are Gareth G4XAT, Rob M0DTS and Mike G0MJW. All were about 100W, with Mike and rob using beams and Gareth a vertical. The multipath distortion is very apparent, as is the difference in propagation paths.
-[M0DTS 10m DATV Image]
+[[File:Multipath1.jpg|400px]]
 The solution to multipath for digital audio broadcasting at HF and VHF and terrestrial television at VHD/UHF is to use a modulation mode, called Orthogonal Frequency Division Multiplexing (OFDM) where many narrow bandwidth signals are stacked next to each other.

← Older revision		Revision as of 22:40, 30 November 2022
Line 41:		Line 41:
	==Generating a low rate transport stream==		==Generating a low rate transport stream==

−	There isn't much bandwidth available on 10m which means relatively low symbol rates are needed, probably occupying no more than 100kHz of bandwidth, ideally less.	+	There isn't much bandwidth available on 10m which means relatively low symbol rates are needed, probably occupying no more than 100kHz of bandwidth, ideally less. This means we need to use the most efficient video compression readily available to us, at the time of writing this is H265 which can produce good video in 100kb/s and fair video in less. The ffmpeg software package can encode video and generate low data rates mpeg transport streams. Using ffmpeg requires a complex set of command line options that must be tuned to get the best quality. For example the following developed by Rob, M0DTS takes input from OBS and uses an Nvidia graphics card to generate a transport stream for a Pluto running Evariste F5OEO's firmware:
		+
		+	ffmpeg -f dshow -i video="OBS-Camera" -vcodec hevc_nvenc -g 8 -s 213x120 -bf 0 -pix_fmt yuv420p -b:v 10k -bufsize 30k -r 2 -preset fast -profile:v main -rc cbr_hq -rc-lookahead 5 -an -f mpegts -streamid 0:256 -metadata service_provider="YourCall" -metadata service_name="YourName" -max_delay 2500000 -pcr_period 80 -pat_period 0.4 "udp://192.168.2.1:8282?pkt_size=1316"
		+
		+	This is pretty complex and breaking this down is out of scope and might reveal many liberties being taken but it did actually work. Here is an example received trans-atlantic using SDRAngel.
		+
		+	[[File:SDRAngel1.jpg\|400px]]
		+
		+	The above parameters need to be tweaked for each required but rate, which will depend on the transmissions bandwidth, modulation and forward error correction.

@@ Line 26: / Line 26: @@
 Similarly on receive, the popular minitiouner used at higher frequencies does not tune down to 29 MHz. An upconverter is needed to translate the signal to an IF within the range of the tuner.
-Mike, G0MJW has developed a simple frequency transverter that can be used. Information is [here].
+A better option for receive may be to use an HF SDR, e.g. an Airspy, RFSpace SDRIQ/CloudSDR or an RTL dongle and decode the signal in a software package like GnuRadio or SDRAngel. Both of these software packages can also be used to transmit.
-A better option for receive may be to use an HF SDR, e.g. an Airspy, RFSpace SDRIQ/CloudSDR or an RTL dongle and decode the signal in a software package like GnuRadio or SDRAngel. Both of these software packages can also be used to transmit.
+Information on a simple 2m to 10m frequency transverter is [here]
 ==Software for 29MHz DATV==