Thursday, July 23, 2009

A Simple Low-Cost HDTV Antenna

Prior to the recent digital TV changeover, I was using several 7.25” ring antennas mostly made of thick copper wire. Since then, I’ve noticed that the reception was rather poor on some stations. I tried making a few of the bow-tie antenna’s that are shown on video and pictures around the web, but found them to be clumsily large for an indoor antenna, as well as hit and miss on a few dimensions.

While experimenting with a few shapes of formed metal rods, I came across a 16” by 4” steel rectangle that used a quarter inch rod. After connecting the split ends to a 300/75 ohm transformer (balun) and then to a TV input, I was amazed that all the local channels came in.

I’ve made a few others using copper wire and three-eight’s inch tubing, and they work great. With tubing, simply cut out a right angle section at each corner so that when bent inwards, it forms a 90 degree corner. Place a wooden or plastic dowel between the open ends at the connection. Coat hanger wire and thin copper wire will work, but not as well as material between one quarter and three-eighth’s inch diameter metal.

If this size does not work well, try an 8.25” x 8.25” square.

So far I've mounted the frames on wood or plastic with hot glue.

Here are the dimensions:

Wednesday, April 29, 2009

Review of PMP using a 2.5" SATA HD

The unit is advertised as a 2.5" High-Definition PMP SATA Hard Disk Enclosure with 1080i Component Video +Remote +RM/RMVB. I bought this during April of 2009 and at the time seemed to be the best of what was available in terms of resolution, connectivity, HD size, and capacity.

It's essentially a Personal Media Player (PMP) when hooked up to a monitor and the included 100~240V AC adapter or 12v car plug converter.

The $80 price is for a USB 2.0 hard disk enclosure that includes a portable media player with remote control. Output connectors support CVBS (composite video), VGA, and YPbPr (Component Video) for use with modern TV's, or a computer monitor in the case of VGA.

Additional inputs come in the form of an SD card reader and a USB slot. A mini-USB connector is provided for host PC interaction and operates independently of the additional inputs.

The user has to insert their own 2.5" SATA hard disk, and I added a 250GByte drive. The specification allows for drives up to 500GBytes.

Having spent a couple of weeks playing with this device, it seems I could write a book about its features and shortcomings, but as-is, this unit is not for the uninitiated.

My first challenge was to switch to an English language display--Chinese is the default. After several hours of trying numerous combinations, it switched! The manual is all but useless and their website at is only in Chinese.

The on-screen display is essentially pathetic. It seems that someone rushed a quick conversion of a limited Chinese character display to accommodate English. The next challenge came in the form of supported video. What many people do not know is that when the terms AVI, MPEG, MP4, etc are mentioned, these are containers for specific video and audio formats which can vary tremendously. So I then spent days trying to determine what formats worked as a lot of my video collection was in a number of formats. Also, I had a 1280 resolution video, which I quickly surmised to be too high. I eventually found a few formats that worked, as well as a 720 by 576 limit.

A very useful and free video converter is AVIDemux, and a chap at their site was extremely helpful. He pointed me to the most common formats of video containers, which are:

* MPEG-2 video + MP2 (TwoLAME) or AC3 (Aften) audio in MPEG-TS container
* MPEG-4 ASP (Xvid) video + MP3 (LAME) audio in AVI container
* MPEG-4 AVC (x264) video + AAC (FAAC) audio in MP4 or MKV container

I found their MPEG-2 requant and MP2 (TwoLAME) in an MPEG-PS container worked OK, as well as MPEG-4 ASP (Xvid) and MP3 (LAME) in an AVI container. One format that works directly are the main (non-protected) VOB's on a video DVD (as found in the VIDEO_TS folder).

You can download AVIDemux from

The next challenge came in the form of directory structures and the number of files contained therein. The unit supports NTSF that is nice for large files, but the unit won't look at anything above a couple of Gigabytes. It refused to play a 3GByte file, but breaking it down with AVIDemux worked OK. At times, some characters in directories or file names were simply missing, but I managed to improve this somewhat by limiting the number of directories at each level up to around ten. There's very limited room for character display, but when a file is highlighted with the remote, characters traverse to the left after a short while.

A limited description of a highlighted file appears to the right of the listing, and if there is anything missing from the audio or video format, it won't play. If the wrong combination is present (no clue given), that file won't play either. I've never seen anything in the thumbnail window.

Another issue was that I converted a large video into some 50-odd chapters (files). When I played the video, it was totally out of sequence, indicating the unit has a problem ordering files by name if the quantity exceeds some level. I didn't have a problem playing seven or so files in sequence. If a video contains multiple languages, it will try to play them all, so extra languages must be stripped before copying to the unit.

I haven't done much with connecting external media, but I read on one forum that someone tried an 8 GB MicroSDHC, with adapter, and it worked fine. One can apparently copy files to and from external media without connecting it to a PC. I've also yet to try audio files like MP3 or WMA, but this seems a waste when one can use a dedicated and more efficient MP3 player. The interface is awkward when selecting media from any available source and I found myself at the very root of everything most of the time.

The unit tends to run rather hot in PMP mode, so I made a couple of cooling-fin plates, one underneath and the other rests on top. I've even matched the curvature.

It would be nice to have additional features such as an effective menu structure, sleep mode and a media playlist. However, even though this unit needs some serious firmware development, I’m happy to be able to at least consolidate my video media into one source (with backup!).