Saturday, 28 June 2014

HD-CCTV Cameras: Cheap quality live video for DATV

HD-CCTV Cameras: Cheap quality live video for DATV

In my quest for high quality DATV (Digital Amateur Television), I learned a lot experimenting with the HiDes DC-100-B-01 HD-CCTV DVB-T modulator/camera, the subject of an earlier post. With a good lens, it gives an excellent DVB-T signal at up to 1080P. It is a modified HD-CCTV SDI camera with a DVB-T daughter board modulator with a 50 Ohm BNC output that go to cable or to an amplifier then antenna.

Using the BlackMagic Design ATEM TV Studio, I could use SDI cameras. Box-style, HD-CCTV cameras, with inter-changeable "CS" mount lenses and SDI digital and analogue output cost less than $150 on eBay. A bargain! Most use Sony image sensors.

The cameras have a composite output that allows setting up the digital video even H.264 compression.

The catch! The purpose of HD-CCTV video is to allow high definition video to allow clearer inspection of suspicious activity. As such, and perhaps to avoid extra circuitry, they are not interlaced, with both 720P and 1080P. 720P is fine, it is a standard DVB-T format, but 1080P isn't and won't be recognised by the ATEM TV Studio. As such, it is only possible to use them directly on 720P, but at least at a range of frame rates.

The selection of lenses for HD-CCTV is important for quality at high resolution. The optical quality of the lens needs to be as good as, or better than the camera's resolution. Most CCTV lenses are for SD (Standard Definition) and not suitable for the HD-CCTV. The industry has standardised on this problem by using the term "Megapixel" for the optical high definition lenses.

HD-CCTV cameras use a "CS" mount, but with an adaptor, can use "C" mount lenses, commonly used for 16mm movie cameras. So it is possible to get quite good lenses for them.

DSLR cameras for live TV: not so simple!

DSLR cameras for live TV: not so simple!

In the course of setting up an amateur radio DVB-T transmitter, I have sought high quality video and audio.

The modern DLSR (digital, single lens reflex) cameras seem to be a good candidate as they are capable of recording very high quality video, have a wide range of relatively inexpensive lenses and have some auto-focus capability for use by a one-person camera operator. They are generally better than consumer-grade camcorders.

DSLR cameras are very popular with cinematographers, with an ability to do Full-HD and even up to 4K resolution (4K is used by cinema projectors). See sources such as Digital Filmmaker magazine

For DVB-T the maximum resolution is Full HD 1080i at 24, 25, 30, 50 or 60 fps (frames per second), and more commonly 720p at the same frame rates. The frame rates are related to the frequency of the electricity supply in the country, 50 Hz in Britain and Australia, 60 Hz in Northern America.

However, there are three problems using DSLR cameras for live TV video:

First, the video feed from the DSLR's HDMI port is fixed at 1080i 60 fps when switched to video mode and not recording. This is a problem when a different resolution is needed. There is no firmware fix for it at the moment. The only way to change it that I am aware of is to use a HDMI to HDMI Converter or Scaler. These start at less than $100 for a Chinese one on eBay and seem to be a suitable quick-fix. There is less of a problem scaling down resolution than changing the frame rate. The frame rate is usually changed by adding or deleting frames.

Second, the video feed is not clean from the cheaper DSLRs (<$3000), having all the camera information seen in the DSLR's LCD view-finder. These artefacts can be reduced to the auto-focus frames, but not eliminated. For some DSLRs, Canon in particular, third party firmware is available to give clean video, albeit making the camera a bit more difficult to use. Magic Lantern firmware is available for all but the most recent Canon DSLR cameras that can do video.

With Magic Lantern firmware, it is possible to use Canon DSLR bodies that cost about $300 and up. I am using a Canon M series (which is technically not a DSLR, but uses the DSLR firmware), with Magic Lantern beta firmware to get a clean live feed. I have a Canon 70D that has a very effective auto focus system, but the Magic Lantern firmware is still being developed for it.

Third, a lesser problem is that the length of HDMI cables is limited to about 5m or less. There are HDMI repeaters available, but I have not tried using them for a live video feed and have had limited joy even running long (>10m) HDMI leads to projectors.

Most DSLR camera can record/feed audio as well as video. It is best to use an external microphone, either a shotgun type mounted on the camera or a microphone on a cable near the sound source.

An annoyance of using the HDMI output live, is that the operator cannot see the image. This is a problem with cinema cameras as well, but small focusing monitors are available that have a HDMI pass-through.

DSLR cameras have somewhat morphed into low-cost, high quality cine cameras, such as the BlackMagic Design's Pocket Cinema Camera. A small cinema camera that can use DSLR/SLR lenses, uses SDI output and costs about $1200.

In summary, modern DSLR cameras can be a quality video and audio feed for live TV via HDMI, but have some problems which can be overcome to some extent.

Thursday, 26 June 2014

DATV DVB-T BlackMagic Design ATEM TV Studio: Proof of concept

DATV DVB-T BlackMagic Design ATEM TV Studio: Proof of concept

An objective has been to get high quality video and audio, as well as TV production studio abilities for my DATV DVB-T system.

Production studio abilities includes the capacity to switch between multiple live TV cameras, recorded media and overlays, such as my call sign.

I originally experimented with software production systems, mainly aimed at network feeds, such as Vidcaster and Open Broadcaster. The commercial Vidcaster software has a virtual camera that can be the input video stream for a HiDes's device, such as the UT-100C via PC2TV. This required a fast PC, a HDMI video capture card from a DSLR camera, the Vidblaster software, the PC2TV software and the UT100C all working properly; a difficult feat many of us have stumbled on.

An alternative is to use a hardware production studio. The BlackMagic Design ATEM TV Studio is very suitable and a reasonable price, about $1000, given its capabilities. It is designed for broadcast TV and is a high quality device. The cost is not that much more than a capture card and the production studio software and does not require a particularly powerful computer.

See full specifications at:

From the picture, there are inputs for up to 4 HDMI cameras or media sources, up to four HD-SDI cameras and two channels of audio in addition to that within the HDMI stream. The device is controlled by a laptop/PC via a network, with the interface shown in the picture. One HDMI output goes to a monitor showing inputs, a preview of any of them, as well as the selected output. The other goes to the TX via HDMI (more on that in latter posts)

The following photos show my "proof of concept" setup with a DSLR camera, a HD-CCTV SDI camera, a Western Digital Live media player, control by a laptop, with the control monitor and output via HDMI to a TV, running 720p 50Hz HD video.

 The DSLR camera, a Canon M ($300) with a 50mm prime lens via converter, and a HD-CCTV camera ($150) with a very cheap lens. I have used a Canon 70D successfully as well.

The WD TV Live media player, streaming a movie across my home network from a computer in another room. (Chopstick is to lift to keep it cool!)

The BlackMagic Design ATEM TV Studio, rear side, showing cables and heat sink (it gets very hot).

The T430 laptop with the BlackMagic control interface.

The control display, a 16" HDMI TV, with sources in the lower 8 small panels, the cued preview in the top left panel, and the selected output in the top right panel, which is what would normally go to the TX, but for test purposes is going to a conventional TV via HDMI.

The final display on a 50" Full-HD TV.

All sounds so easy! Most of it is straight forward, the main catch being that all sources and the ATEM Studio must run the same video standard, such as 720p 50Hz or other "standard" TV format.

Briefly, the HD-CCTV cameras on do 720p and 1080p at either 50 or 60Hz. Unfortunately 1080p is not a standard broadcast TV standard and is not supported by the ATEM studio, but 720p is.

The DSLR cameras are more of a problem, outputting 1080i 60Hz and no way to change it with the camera. More on that in another blog as it not a simple problem.

Friday, 6 June 2014

Multi-band squid-pole dipoles and Yagi antenna: Feasibility?

Multi-band squid-pole dipoles and Yagi antenna: Feasibility?

One source of thin fibreglass for use with the loading coils on the TET-Emtron antenna I have been working on is telescopic "squid" poles (used for catching squid). A 7m squid pole is in seven sections, a metre long, from 45mm to 8mm for the heavy-duty version. The poles only cost about $30 each. They are available from

Given that I was thinking of the TET Yagi elements using the tricks of vertical antenna to reduce length, I thought, why not go the other way and use telescopic squid-poles as rotatable dipoles or Yagi elements?

Telescopic elements are quite useful for me as my tilting mast tilts to the short end of a trapezoid, with only 3 to 4m for a boom, compared to 10m at the other end. With the mast right down, I can mount the boom and one side of a Yagi horizontally, rotate the boom 90 degrees to its correct orientation, then extend the elements on the other side of the boom as I raise the mast.

Squid-poles and wire dipoles or Yagi antenna have the advantage of being easy to dismantle, and could be used as a portable antenna.

One of the reasons driving this project that small multi-band beams are either not available or too expensive. TET-Emtron are currently re-designing their antenna, so there may be an option in the future.

Mono-band, full-size dipole or Yagi

The squid poles are long enough, at 7m for a full-size 20m dipole. Just mount two squid poles on a piece of rectangular aluminium and bolt it to the tube at the top of a mast. The antenna can be a piece of wire, or aluminium strips, held on with zip-ties and driven from the centre.

I tried coiling the wire around the poles, but that seemed to create an inductor and increase the SWR. Straight lengths of wire seemed to work best.

As I have a narrow yard, a two element Yagi with close-coupling and both elements driven, as per the TET design seems the best. So for a $100 or so, a 2 element, 20m Yagi seems possible. My local aluminium fabricator sells 50mm x 3mm tube for $15/m for use as a boom. The clamps are pretty much the more expensive bits.

Multi-band, full-size dipole or Yagi

Given that the squid pole is an insulator, it is possible to attach a number of different lengths of wire (or aluminium strip), cut to different wavelength. All conductors on each side are joined at the centre-end and can be driven, preferably with a balun or similar. The arrangement is not too dis-similar to a multi-band wire antenna such as those made by Alpha Delta, but are rotatable.

The conductors can be attached around the pole, or even extended down from it with spacers, like the Alpha-Delta wire antenna. It could be possible to suspend the Alpha-Delta wire antenna from the poles.

Again, two or more elements could be used to make a low-cost, light-weight Yagi.

Close-coupled, dual-drive radiator and reflector

A close-coupled, dual-drive radiator and reflector is used to increase the front to back ratio. Such a system is used in the pre-1985 TET antenna I have and in the Ca-Av Labs beams There is a PDF description of the drive system on their page. The drive is based on prior technology and a number of current and expired patents. The main patent seems to rely on using the lower velocity-factor of coaxial cable to make the boom length and feed system proportionally shorter.

Does it work?

I zip-tied a couple of squid poles to a piece of timber. I then used the insulated conductors from electrical wire, at three random lengths, strapped to the pole with gaffer tape. With the crude dipole sitting on a big plastic rubbish bin, I used my Rig-Expert AA-600 antenna analyser to see what was happening: three points of resonance, as expected.

Note the range on the analyser. In the first photo it is +/- 187 kHz, but in the second is +/- 6 MHz, thus showing resonance for the 3 pieces of wire. The lower frequency is probably more affected by the ground.

The RigExpert antenna analyzers are very good; the last photo is very impressive. I may do a post on it, once I have a better understanding of how to use it.

Shortened multi-band dipole or Yagi

While a compromise, it should be possible to use loading coils to effectively shorten the element length. Fully extended, the squid poles are 7m long but only 8mm at the tip. Not using the last two sections reduces the length to 5m, but gives about 20mm at the tip.

While traps and loading coils could be used with a single conductor, it is probably easier to use multiple conductors and loading coils on the conductors needing to be longer than 5m, such as for 20 and 40m. With loading coils, it may be better to suspend some conductors below the pole, per Alpha Delta arrangement.

Capacitive hats, per TET, could be used to electrically shorten the elements, but they may be too heavy or difficult to mount.

Where to next?

I have two potential ways of making a small 2 element 40/20/15/10 Yagi, but only need one. Probably out of curiosity I will build both and try them. Tuning the antenna, especially with the close-coupling, dual drive most likely will be problematic. One immediate problem is how long to make the boom, more specifically to which band? A 1/10 wavelength for 40m is 4m, which should fit my yard, just... I probably want best performance on 20m.  Neither will be particularly robust, for storms or birds, but I don't mind too much.

To be continued...

Thursday, 5 June 2014

Computer monitors: Beyond Full HD- 1920x1200, 2K-2560×1440, 4K-3840 x 2160

Computer monitors: Beyond Full HD- 1920x1200, 2K-2560×1440, 4K-3840 x 2160

I have used a series of computer monitors with a resolution above Full High Definition: 1920x1080.

The obvious question is why? The highest resolution for most movies is 1920x1080.

The answer is simple; I don't watch movies on a computer but read a lot; web pages, books and magazines. The higher the resolution the better!

The high resolution gives a better quality display of a PDF document. PDF originally was a printing format and generally has a higher resolution than a computer monitor can display. Printers typically can print at 600 or 1200 dots per inch, about ten times higher than a video monitor.

LCD monitors produce their best display at their native resolution, anything less usually looks bad as there are not enough pixels to give a sharp image. Try lowering the resolution of your own monitor and you will see what I mean.

Ultra high resolution has been picked up by tablet manufacturers, particularly Apple, with "Retina Display". This is a resolution higher than the human eye can distinguish individual pixels. Retina Display is 326 pixels per inch for the iPhone/Mini iPad 2 and 264 for the later model iPads. The reason is simple, the displays look better!

I am writing this on a Samsung 28" U28D590 4K 3840x2160 (16:9 diagonal) monitor with screen dimensions of 620mm x 340 mm. The resolution per inch is 157 pixels per inch horizontally and 161 vertically. Despite the resolution, still a lot less than the Apple iPhone or iPad.

The Samsung uses a TN panel, older LCD monitor technology that does not have good contrast; 1:1000, and poor side-viewing. The poor side view is very important with a large monitor only 500mm from your face, as you look sideways to see the edges. The effect is bad enough to be nuisance in normal viewing. A poor-man's 4K monitor at about $700. It will be useful when I start getting 4K video. The resolution does improve the look of fonts in PDF documents, so the high resolution has some benefit.

I also have a Kogan 28" 2K 2560x1440 TCN monitor. While the resolution is lower, the contrast and angle view is better, but not brilliant. Quite a good monitor for about $450. The 2K resolution is a big improvement over 1920x1080 monitors for reading PDFs on screen.

An important caveat of the 4K and 2K monitors is that they need modern graphics to drive them. The best way is to use Displayport cable, but this is only possible with the Intel HD4600 graphics of the latest Haswell CPUs, I5 or I7. It is possible to use a graphics card on older machines, but they need a Displayport connector and the capacity to run 2K and 4K. The cost of the cards is over $200.

The 1920x1200 resolution are business monitors giving an extra 120 pixels vertically, still an improvement over 1920x1080 monitors for reading.

For watching TV I have a couple of Panasonic plasmas; great colour, contrast and good side-viewing. I would like to buy a plasma monitor, but they don't make them.

I am hanging out for OLED monitors (, similar picture characteristics to plasma, but without the problems of plasma. The technology is just entering the TV market. Hopefully in a year or so, high resolution OLED monitors will be available and affordable.

Cinematographers are using full-HD, 2K and 4K video cameras instead of film. Digital SLR cameras in video mode are becoming very popular as produce high quality, high resolution video, and are very cheap compared to film or cine-video cameras. Further, the DSLR lens are much cheaper than their cine equivalents but still very high quality, a function of respective production volumes.

I am trying to use DSLR cameras for my amateur TV, but only up to 1920x1080, still a big improvement on web or analogue cameras that most DATV amateurs are using. However, digital video and device inter-connection is quite complicated.

Small multiband HF beams- TET-Emtron revisited- 40/20/15/10m 2 element beam

Small multiband HF beams- TET-Emtron revisited

While I haven't posted much recently I have been chasing a few wild ideas.

I bought a few antenna from a deceased estate, including bits of a couple of TET and TET-Emtron HF beams.

TET 2 element 20/15/10 beam

TET 2 element 20/15/10 beams are quite innovative, especially considering they were first made pre-1985 with:
  • capacitive hats to physically shorten the element length
  • dual-drive, driving the radiator and reflector, 180 degrees or more out of phase. This doesn't increase the gain much, but does increase the front to back ratio, which is just as good.
  • close-coupling of radiator and reflector to shorten the boom length.

I had just the radiator of a version of the HB-23M, which is enough to use an antenna analyser to see what it does, albeit at ground level (which messes up capacitive hats and low frequencies). I have to make up the rest.

The traps, the rectangles on the elements, are two parallel R/C circuits tuned to 28 and 21m. Traps effectively short-circuit the antenna at that length. In a full size beam, the 10m trap is at 2500 mm (1/4 wave-length), the 15m trap at 3750mm, the 20m at 7000mm, and the half element/dipole is 10m long for 40m (yes, we are going for a small 40m beam!).

In the TET beam, the inner capacitive hat effectively lengthens the 10/15m section, even though it is only a bit over 2m long. The outer hat is to shorten the element for 20m.

My RigExpert AA-600 analyser, which is really neat, shows resonance at 10 and 25m, but not much at 20m- with the antenna at ground level, which messes up 20m the most. However, others have had trouble with it on 20m (include stuff from Norway.

It would be possible to improve the 20m performance by adding extra length and/or more capacitance. I haven't tried that yet.

OH5IY from Finland has worked with the TET-Emtron antenna: under amateur radio. He has drawn up a HB33M, including the details of the traps.

TET-Emtron 2 element 40/20/15/10 beam, yes, 40m!

When I was last into amateur radio, 40 years ago while at High School (see first post), a retired farmer come amateur had a full-size 40m beam. I have coveted having a 40m beam ever since, with little prospect until coming across bits of a TET-Emtron 40/20/15/10m beam, specifically the radiator main components. I just put them on the old TET mount to see what it would do.

It is common for vertical antenna to use different tricks, traps, loading coils and capacitive hats, to cover all HF bands, including 80m. A vertical is just a half dipole, with the other half reflected through the RF ground radials, which is why radials are important. It is possible to use the same tricks in a beam, just physically more difficult.

The TET-Emtron multiband beam uses 2 traps for 10 and 15m, in the first cylinder in the photo below. The second contains a 20m coaxial trap and a 40m loading coil in the second cylinder. Neat idea, but a fair bit of weight for small gauge aluminium; but it works!

My analyser shows resonance at 40, 20 and 15m, but not much at 10m. Good enough for me!

I had already made a second holder for the reflector. I have a 2m or 4m 50mm boom to mount them on. The next step is to make a reflector, essentially 5% or so longer than reflector. I have the reflector from the HB-23M to use as a guide.

I am contemplating how to do the phasing network, either aluminium, per the TET original, or use coax; the velocity factor shortens the distance needed. Interestingly, I had a newish VHF TV antenna that used the dual-feed; pretty innovative for garden-variety TV antenna- more engineering design than might be expected.

At the moment, I am waiting on parts to build the radiator. One of the most difficult to get parts is thin-wall fibreglass in the right size. A friend suggested a telescopic "squid-pole", so I bought a few; with a view to using them for other antenna- more on that later.

To be continued....