The video cassette recorder (VCR) is gradually becoming very popular with TV DXers for keeping a permanent record of reception. One advantage is that distant signals can be recorded and played back to review specific items of interest, such as exotic rare signals or unidentified test cards or logos. The "freeze frame" or pause facility that is available on VCR machines will enable an unknown pattern to be examined frame by frame to enable identification. If a DXer has access to a second compatible VCR machine, it is possible to dub items of interest on to a the second VCR to build up an edited library of test card and other DX material.

Appropriate Type of Antenna

To achieve the best quality recordings, it is important to use a sensitive antenna and receiver system. A brief overview of antenna and receiver techniques will be discussed as follows.

Newcomers to the TV DX interest can start with relatively simple antennas, since signals propagated via Sporadic E can be strong. However, always attempt to make the antenna system as efficient as possible.

One word of caution - don't be tempted to use an FM radio antenna for DXing channels in VHF bands 1 and 3. The results will be disappointing. Always use an antenna designed to cover the appropriate channels.

Since signals received via Sporadic E often reach high signal levels, a simple folded dipole cut to approximately 100" can be used for 45-70 MHz band 1 DX. The dipole can be mounted vertically for an omnidirectional response, will not need to be rotated. If the dipole is mounted horizontally, it will need to be rotated 180 degrees, so it is facing broadside to the direction of the desired DX station. A horizontal dipole will also have slightly more gain with respect to a vertical dipole.

It is also worth noting that most DXers have found their domestic "garden variety" TV antennas are poor performers for DX reception.

To capture the weaker signals, a more elaborate antenna system is recommended. A 2 element wideband yagi array for band 1 can be quite adequate and takes up little space, while a 4 or 5 element yagi will offer greatly improved results in terms of signal level (gain) and directivity.

It is important to have the reflector element 125" in length, so it will receive down to NZ Ch 1 video (45.25 MHz). The dipole is usually 100" and the reflectors are cut to 80" for coverage up to Ch 2 audio (69.75 MHz).

Some DX enthusiasts use single yagi arrays for each band, while others use combined arrays covering bands 1 & 3 or bands 1, 2 & 3 (45-220MHz). An example of an excellent all channel antenna is the Channel Master CX 28 (28 element) log periodic array. This type of antenna takes up less space on the mast and requires only one coax line.

The CLP5130 log periodic 50-1300 MHz antenna is currently popular for DX TV and FM reception in Japan. The official web site for the CLP5130 can be found at: http://www.cd-corp.com/eng/ama/5130.htm     

It is not recommended that an all channel antenna, covering the entire VHF/UHF (45-860MHz) bands be used, due to its relatively poor signal gain. When possible, use separate TV antennas for VHF and UHF.

Yagi and Log Periodic arrays for band 1 are available from antenna installations firms in both Australia and New Zealand.

86-108 MHz antennas

A wide variety of antennas are now available for the FM band and Australian TV channels 3, 4 and 5. They range from a simple folded dipole to a 10 element yagi. Some examples of suitable band 2 antennas are the Matchmaster FM G8 (8 element) yagi, Triax FM-8, Hills 3-4-5, or Antenna Performance APS 13.

175-230 MHz TV antennas

Single band yagi arrays are available with up to 14 elements. As mentioned earlier, combination antennas are also available. If a combination VHF antenna is desired, it is wise to purchase a "deep fringe" antenna, designed for weak signal reception.

Rotating the antennas

Since sporadic E and tropospheric signals can come from almost any direction, it is desirable that some method of antenna rotation is provided especially when an antenna has several elements. Beginners can try the "armstrong method", which is a hand rotatable mast with a cross bar. Mechanical antenna rotators are also available from most amateur and TV installation firms.

TV DX receiving systems

Small screen portable TV sets are very popular with DXers and are also ideal for mobile/holiday use, as well as in the home.The set must have its tuners marked with the correct channels (Australia: VHF 0-11, UHF 28-69). Some sets have a continuous (varicap) tuning dial, covering VHF and UHF. Some examples of high sensitive portable TV sets are:

Toshiba C531 VHF/UHF 5" Colour TV: This particular TV has a sharp SAWF, hence is very selective. The D100 DX TV and Toshiba C-531 offer excellent results when used together.

Phillips P45 VHF/UHF 4" B/W TV: Can receive DX on its own inbuilt rod antenna and also is lightweight for travelling. Features a varicap tuning dial for VJF and UHF.

National Ranger TR505DU VHF (only) B/W TV: This particular TV is extremely sensitive on band 1 and can receive Sporadic E DX signals quite well even just on its own inbuilt rod antenna.

Go to: TV and FM receivers, currently used by DXers for pictures and details of these sets.

All these models have long since ceased production, but can still be purchased second hand.

TV vision IF bandwidth

All modern TV receivers are designed with wide IF bandwidth stages, which are necessary in order to provide high definition pictures for domestic viewing under normal conditions. However, a narrow If bandwidth is essential when attempting to resolve extremely weak DX signals under difficult conditions.

Narrow IF bandwidth helps to display extremely weak signals, which are normally "lost in the noise", when wide bandwidth is used. By using narrow IF bandwidth, some DXers can detect low level signals from transmitters located 150-300 miles away, on a daily basis under normal reception conditions.

Selectivity

Single or Multi-system TV receivers, employing wide IF bandwidth will often suffer from adjacent channel problems, such as pictures floating over one another, (Australian Ch 2 over NZ Ch 3 or Australian Ch 0 over NZ Ch 1, etc). TV signals only 1-2MHz apart can easily be separated, when using a narrow IF bandwidth receiver system.

For several years the author has used a conventional VHF/UHF varicap TV tuner and 2 G8 selectivity modules connected to the IF input of a portable TV. This set up was very effective in separating NZ Ch 3 vision (62.250MHz) from the local Australian Ch 2 vision (64.250MHz).

For others not so inclined to modify and construct TV receiving equipment, a TV tuner unit, known as the D100, is available. The D100 is a self contained unit, which connects to a UHF TV and an FM (88-108MHz) radio receiver, to provide VHF/UHF TV DX reception with pictures and audio of virtually any TV standard worldwide. The vision IF bandwidth is switchable and variable, allowing reduced or semi-reduced bandwidth operation for weak signals and full bandwidth, when conditions allow. The benefit of such a system means that no modifications are required to your existing TV or radio receiver.

Recording DX TV FM Audio

There are several different methods to record TV DX audio, each of which have wide differences in sensitivity. The simplest method is to connect a lead to the output jack (earphone or auxiliary output connection) of a TV and connect it to the input of either a tape or video recorder. If a video recorder is used, it will record the audio on to videotape at fair sensitivity. It is worthwhile noting that the above two methods will not record TV sound signals originating from overseas countries using different TV systems. The reason being that most video recorders are only designed to receive the local TV system. In Australia and New Zealand, the majority of video recorders are designed to receive system B (5.5MHz) audio signals.

The sensitivity of the above two methods are only fair because of:

1) They both use the inter-carrier audio system, which relies on both audio and good strength video, being present at the same time on the TV receiver, which is by no means a certainty with distant signals.

2) The audio IF bandwidth of a standard video recorder or TV is typically too wide for weak audio signals (150-250kHz bandwidth).

The method used to receive extremely weak Australian and overseas TV video and audio signals is detailed in block diagram Fig A, B & C.



The antenna is connected to an optional low noise tunable mosfet preamplifier, which goes to a D100 TV tuner/converter. The output lead from the D100 at Ch 65 (UHF) is connected to the RF input of a Toshiba C531 5" colour TV, (or a similar type of TV), for vision reception. The second lead from the D100 is connected to a scanner at around 35MHz in wide FM mode for sound. If a scanner is not available, the second lead can be connected to an FM radio tuner at around 96-100MHz. The other end of the audio output lead from the scanner (or FM tuner) is connected to the audio input socket on the video recorder. The other end of the video output lead from the Toshiba C531 5" TV is connected to the video-input socket on the video recorder. Once all connected, the Toshiba TV needs to be switched to monitor, to eliminate the audio mute on the TV. Also, the video recorder needs to be switched on, so everything is working.

The audio sensitivity will improve if a narrow IF bandwidth of around 110-150kHz is used by the scanner or the FM tuner's IF (Intermediate frequency 10.7MHz) circuits. The author uses an Icom R7000 VHF/UHF scanner with Murata SFE 10.7 MHY-A ceramic 110kHz wide FM IF filters to improve TV audio sensitivity and selectivity. The advantage of this approach is that any overseas audio TV signal can be received, regardless of the vision spacing. The scanner or FM tuner acts as a tunable audio IF, thus capable of receiving all TV audio systems.

HS Publications (7 Epping Close, Derby, DE22 4HR, England, Phone: 0011-44-1332-381-699), sell the D100 TV tuner/converter. This tuner uses a MOSFET varicap tuner covering 45-860 MHz. It also features variable IF bandwidth to improve selectivity. The D100 also converts the TV audio to 95-100 MHz, for use with a FM tuner. TV audio can also be received on 36 MHz using a scanner. A excellent combination is a D100, and Icom R7000 modified with MURATA SFE10.7 MHY-A, 110 KHz filters. The output frequency of the D100 is at UHF. Veteran TV DXer Bob Cooper uses a D100. This tuner is used extensively in Europe, and has received positive reviews from DXers.

HS Publications TV FM DX equipment catalogue (PDF version).

DVD Recorders

Even though there are several DVD recorders now available at relatively affordable prices, their suitability for recording TV DX signals is yet unknown.

The 2003 Panasonic RDR-GX3 is capable of recording weak TV signals with excellent results. The later model Panasonic GX300 is likely also suitable for recording TV DX.

Video Recorders

There are now a large variety of VHS Video Cassette Recorders (VCRs) on the market, which have their own individual advantages and disadvantages for DX reception. One important ability is the VCR's capability to lock on to weak video signals. This is the same situation when purchasing a television. If possible, before purchasing a VCR, try to tune in the weakest signal available, record it, then play it back to see how well the signal locks horizontally and vertically.

It is also important that the VCR does not mute weak signals. Some VCR's have a switchable mute that can be turned off, when weak signals are being recorded. Other VCR's have no mute at all. Any VCR or TV that has a mute that can't be switched off, (a mute will make the screen totally black or blue on blank stations), is not advisable to purchase for recording TV DX, as the mute will block most of the wanted DX signals. Most Panasonic VCRs don't have any picture mute, hence are ideal for recording weak signals.

VCRs that don't mute weak signals are as follows:

1) The National NV-G16
2) The Panasonic NV-L20HQ
3) The Panasonic NV-L25HQ

4) The JVC HR-J635EA
5) The Panasonic NV-FJ600

Since all VCR's now have a VHF/UHF varicap tuner fitted as standard, they can form the basis of a basic DX receiver system for beginners.

By simply connecting an outdoor DX antenna to the VCR's RF input and then selecting the appropriate band, such a recorder may be used to record TV DX signals, when used in its E to E mode (ie: monitoring the output from the VCR tuner on the TV receiver. (Fig D). Recordings can also be made directly off-air, but as mentioned earlier, overseas TV audio, with different systems, can not be recorded.

diagram showing VCR connected between antenna and TV


By using a scanner, it is possible to detect the presence of TV signals, long before they are strong enough to produce an image or sound on a TV set.

When a Sporadic E opening is in progress, the scanner can be used to determine what video frequencies are present. The next step is to tune in the signals on the VCR and store them in pre-set memory locations, (eg: Memory 1 - NZ Ch 1 45.250 MHz; Memory 2 - Aust Ch 0 46.250 MHz; Memory 3 - ChE 2 48.250 MHz; Memory 4 - ChC 1/ChR 1 49.750 MHz, etc. After all the available signals are stored into the memory, it is advisable to keep a record of memory location/channel pre-sets.

Recently (August 2001), I purchased a Panasonic NV-FJ600 NTSC and PAL VHS VCR. The weak signal locking is excellent. There is no mute on weak signals. I strongly recommend that TV DXers consider this VCR.

Copyright © 2009 Todd Emslie