25 replies to this topic

[cyclone_27]

For 10 years now i've enjoyed an analogue TV in my tractor.
I'm only 1 km fom the transmitters, so the single was very good.
Just recently i installed a HD STB with and external powered antenna.
Most of the time the pictre is ok, but often the screen freezes and i'm thinking its from over signal, because if i turn off the external antenna (power) the picture comes back, then sometimes i have to apply the power again.

is there a device ( inline) or STB that will constantly adjust the input signal for a mobile application ?


cheers

[alanh]

Cyclone,
Does your tractor have spark plugs?
Your problem may be interference.
Is the reception reliable when the motor is not running?

All receivers have automatic gain control. If the signal is excessive, you can buy an attenuator for a few dollars. Insert it between the receiver and the antenna cable.

AlanH

[DrP]

cyclone_27, on Oct 30 2011, 10:42 PM, said:

Most of the time the pictre is ok, but often the screen freezes and i'm thinking its from over signal, because if i turn off the external antenna (power) the picture comes back, then sometimes i have to apply the power again.

In all likelyhood you are moving in an out of low signal zones (caused by several factors).  The same effect is seen when installers are fitting antennas on a roof.  Walk 10 feet to the left and signal can plummet, 10 to the right and its up significantly.

Tractors are almost exclusively diesels, which more or less negates the possibility of high voltage related impulse noise.  The electronics package in modern tractors (computer guidance etc) would be more of a concern.

That you can, at times, still get good reception with the antenna amp off (it acts like an attenuator when its off) suggests you are getting high levels at least part of the time and the amp is then pushing your receiver past its upper limit.  Having a professional with a digital signal meter look at what is going on as you drive along is probably the best option for you.  At least it'll point you in the right direction.  You might even find that an amplified antenna is not required at all.  Keep in mind that Australia's digital telelvision system was not built with mobile reception as a consideration and you may have to settle with less than perfect reception.

Edited by DrP, 31 October 2011 - 05:23 AM.

[cyclone_27]

DrP, on Oct 31 2011, 05:19 AM, said:

Australia's digital telelvision system was not built with mobile reception as a consideration and you may have to settle with less than perfect reception.

in a few days time i will try with the amp turned off.
Also the tractor is a 1997 diesel.
The problem with 'less than perfect reception" is the cliff edge.

I'm using the following antenna Digital TV mobile antenna ( it is powered)
Is there other non powered antennas on the market ?

cheers

[mtv]

Turning the power off to a powered antenna usually block signals.

Try using an unamplified antenna (eg: no amplifier at all).

DVB-T is not intended to be received whilst mobile.

Many people have enough trouble receiving it reliably with a fixed, directional antenna on their roof.

As you are close to the transmitters, your issua may be overloading signals caused by the amp and you may also be experiencing multipath/reflected signals as you move around, which can increase the digital bit errors in the data stream.

[alanh]

Cyclone,
Diesel engines do not produce interference.
The attenuator is not of any use if the antenna contains an amplfier.

Digital transmitters
ABNQ42
STQ43
TNQ46
RTQ49
SBS52

All horizontally polarised, 2.5 kW each, 1 km away.

Try a set of rabbits ears (indoor antenna) with each "ear" set to 113 mm long. The ear must be parallel with the roof, and the rods creating one continuous straight line. Put the antenna above the roof of the cabin by about 500 mm. Use a length of dry wood as the support. You may have to extend the antenna cable, you can either make your own or buy an extension antenna cable.

Tractor moving around a field is hardly a moving vehicle. The Doppler effect does not worry this system unless the tractor is moving at around 200 km/h.

AlanH

[mtv]

alanh, on Oct 31 2011, 01:18 PM, said:

Try a set of rabbits ears (indoor antenna) with each "ear" set to 113 mm long. The ear must be parallel with the roof, and the rods creating one continuous straight line. Put the antenna above the roof of the cabin by about 500 mm. Use a length of dry wood as the support. You may have to extend the antenna cable, you can either make your own or buy an extension antenna cable.

Tractor moving around a field is hardly a moving vehicle. The Doppler effect does not worry this system unless the tractor is moving at around 200 km/h.

AlanH

Indoor antennas will not be weatherproof.

Setting antenna elements horizontally, whilst technically correct, become predominately directional, with the ends of the elements producing a signal null.

This will be more noticeable when turning the tractor (and subsequently, the antenna) at 90 degrees to the transmitters.

Doppler effect doen't enter this scenario, so there was no point in mentioning it.

A moving antenna is still a moving antenna, regardless of speed.

Moving an antenna in any direction, including up/down can have a significant influence on the quality of the received signals.

Whilts not theoretically correct, a vertically polarised antenna will provide better omnidirectional reception, but will be less efficient with horizontally polarised signals and 'may' add to reception issues, but may also naturally attenuate strong signals.

A long stainless steel whip (eg: 2-way radio) antenna formed into a horizontal circle, like a halo, 'may' work ok.

It's one of those things that can only be determined with experimentation.

Regardless of antenna used, I would not recommend using any amplification so close to the transmitters.

[bellotv]

While AlanH's advise is good with regards to a stationary set-up ,I'm with Col on this one.

I also suspect too much signal is the problem and you would be better off with an omnidirectional antenna with no amplification.

This is a tough call as you apparently have horizontal polarization.I'd try experimenting with a length of coax .Strip off the outer shields and leave about 120mm of center conductor sticking straight up like a vertical whip.( if it works ,seal it in silicon to keep the moisture out)

As Col says,it will be less responsive being vertical not horizontal but it will be more stable as you change direction.

I recall reading that during DVB-T testing back in the nineties that a car traveling at over 100km/h was able to receive signals without problems.Suspect your tractor travels a bit slower than this .

What the average field strength is like will depend on the countryside. If its very flat with no trees in the way then likely fairly constant but if undulating and with tree rows then you may very well be moving from one extreme to the other.

Considering that the likely distance from antenna to STB is only2-3 meters,there is no point in having any amplification (which is to overcome cable loses) .It would merely an extra noise to the signal,push the received high level signals into overload  or itself suffer from IMD and corrupt the signal

[cyclone_27]

bellotv, on Oct 31 2011, 07:26 PM, said:

While AlanH's advise is good with regards to a stationary set-up ,I'm with Col on this one.

I also suspect too much signal is the problem and you would be better off with an omnidirectional antenna with no amplification.

This is a tough call as you apparently have horizontal polarization.I'd try experimenting with a length of coax .Strip off the outer shields and leave about 120mm of center conductor sticking straight up like a vertical whip.( if it works ,seal it in silicon to keep the moisture out)

As Col says,it will be less responsive being vertical not horizontal but it will be more stable as you change direction.

I recall reading that during DVB-T testing back in the nineties that a car traveling at over 100km/h was able to receive signals without problems.Suspect your tractor travels a bit slower than this .

What the average field strength is like will depend on the countryside. If its very flat with no trees in the way then likely fairly constant but if undulating and with tree rows then you may very well be moving from one extreme to the other.

Considering that the likely distance from antenna to STB is only2-3 meters,there is no point in having any amplification (which is to overcome cable loses) .It would merely an extra noise to the signal,push the received high level signals into overload  or itself suffer from IMD and corrupt the signal

My tractor roof height is under 3m, but my property is hilly and i grow fruit trees which can be approx 3-5m tall.

I will give feedback with the amp off in a couple days.

thanks for all of the feedback

[Tazzy2Heads]

bellotv, on Oct 31 2011, 08:26 PM, said:

While AlanH's advise is good with regards to a stationary set-up ,I'm with Col on this one.

I also suspect too much signal is the problem and you would be better off with an omnidirectional antenna with no amplification.

This is a tough call as you apparently have horizontal polarization.I'd try experimenting with a length of coax .Strip off the outer shields and leave about 120mm of center conductor sticking straight up like a vertical whip.( if it works ,seal it in silicon to keep the moisture out)

As Col says,it will be less responsive being vertical not horizontal but it will be more stable as you change direction.

I recall reading that during DVB-T testing back in the nineties that a car traveling at over 100km/h was able to receive signals without problems.Suspect your tractor travels a bit slower than this .

What the average field strength is like will depend on the countryside. If its very flat with no trees in the way then likely fairly constant but if undulating and with tree rows then you may very well be moving from one extreme to the other.

Considering that the likely distance from antenna to STB is only2-3 meters,there is no point in having any amplification (which is to overcome cable loses) .It would merely an extra noise to the signal,push the received high level signals into overload  or itself suffer from IMD and corrupt the signal

Hey 'Bellotv' What about a 'MK 2' model of your vertical antenna with a 120mm ground plane connected to the shielding of the coax ? I presume the tractor
roof is Fibreglass and a 1/4 wave antenna is a good omnidirectional antenna but needs a ground plane to work.
I think Tandy or Jaycar had a DTV reciever a few years back designed for mobile use with two antenna connections for the front and back mounting on cars
or on the mirrors of either side of Semi's like in the 27MEG CB days.
Tazzy.

[cyclone_27]

Tazzy2Heads, on Oct 31 2011, 08:14 PM, said:

Hey 'Bellotv' What about a 'MK 2' model of your vertical antenna with a 120mm ground plane connected to the shielding of the coax ? I presume the tractor
roof is Fibreglass and a 1/4 wave antenna is a good omnidirectional antenna but needs a ground plane to work.
I think Tandy or Jaycar had a DTV reciever a few years back designed for mobile use with two antenna connections for the front and back mounting on cars
or on the mirrors of either side of Semi's like in the 27MEG CB days.
Tazzy.

I've searched online, and all of the 'mobile' STB are SD only

[mtv]

cyclone_27, on Oct 31 2011, 08:46 PM, said:

My tractor roof height is under 3m, but my property is hilly and i grow fruit trees which can be approx 3-5m tall.

I will give feedback with the amp off in a couple days.

thanks for all of the feedback

Strong reflected signals and blocked signal path will be an issue.

Remember, you just can't turn off an amp.. you must remove it entirely from the cable.

In any case, you shouldn't be watching TV whilst the tractor is moving. It's dangerous and illegal in vehicles on public roads and probably the same on private property as well, just like driving on private property under the influence of drugs and/or alcohol is illegal and subject to the same laws and penalties as being on public roads under the influence.

[alanh]

All,
I suggested the horizontal dipole as a simple test of the available signal strength. The antenna inside his existing antenna is usually a dipole bent into a circle. The diameter of this circle would be half wavelength.
Once the signal strength was established then one of ears could be moved 90 degrees in the horizontal plane. Another option is to add a second rabbits ears to make a horizontal X.

As for vertically polarised antenna, you will lose around 15 dB regardless of direction. A dipole has a figure of eight pattern, are not perfect, so what is the signal strength when the dipole is in line the signal 15 dB drop?? Remember the receiver AGC can cope with a wide range of signal strengths provided the signal is not overloaded or given insufficient signal.

If the rows of trees are mainly in one direction then with the tractor in the line of the rows, adjust the dipole for maximum signal. Now the only drop in signal will be going from row to row.


AlanH

[mtv]

alanh, on Oct 31 2011, 11:01 PM, said:

If the rows of trees are mainly in one direction then with the tractor in the line of the rows, adjust the dipole for maximum signal. Now the only drop in signal will be going from row to row.


AlanH

That doesn't take into account the variable reflections and signal path blockages as the tractor moves around the hilly property.

[MarkTwo]

Are there any digital Tv systems designed for moving cars, say with a twin antenna system so that you can switch between antennas for the best signal? If you are only 1KM from the transmitters, it's a safe bet that the tuner in the set top box is overloading, and less signal might help.
An omni directional antenna, with some sort of attenuator, and you can be enjoying watching The Dukes of Hazard or I Dream of Jeanie while driving your tractor

Mark

[bellotv]

MarkTwo, on Nov 7 2011, 06:24 PM, said:

Are there any digital Tv systems designed for moving cars, say with a twin antenna system so that you can switch between antennas for the best signal? If you are only ........
Mark

Pretty sure GME Kingray used to sell a dual diversity  STB several years ago that had two antenna inputs feeding separate tuners that switched between the best output.

From memory these were only SD and were aimed at the maritime market.

[M'bozo]

bellotv, on Nov 7 2011, 07:15 PM, said:

Pretty sure GME Kingray used to sell a dual diversity  STB several years ago that had two antenna inputs feeding separate tuners that switched between the best output.

They did, it was this one.

I had one on appro for a fixed reception site problem, but due to received signal issues it didn't happen so I returned it.

Edited by M'bozo, 08 November 2011 - 04:52 AM.

[cyclone_27]

M'bozo, on Nov 8 2011, 04:52 AM, said:

They did, it was this one.

I had one on appro for a fixed reception site problem, but due to received signal issues it didn't happen so I returned it.

Ok, i removed the inline amp and connected to antenna directly to the STB.
Depending where i am, the antenna is blocked by higher trees, and i get no signal.
If i'm at a higher location and the trees are smaller, and i can see the TV tower, i pick up a signal.

[alanh]

Cyclone,
With the amplifier disconnected do you get reliable reception when you can see the transmitter? Does it matter if you are moving?
With the amplifier connected is there any locations where you get stable reception? eg behind the trees?

AlanH

[Tazzy2Heads]

cyclone_27, on Nov 8 2011, 01:46 PM, said:

Ok, i removed the inline amp and connected to antenna directly to the STB.
Depending where i am, the antenna is blocked by higher trees, and i get no signal.
If i'm at a higher location and the trees are smaller, and i can see the TV tower, i pick up a signal.

I think it's time for some good ol' Aussie farm tractor technology! Bad signal antenna mast pumped up, good signal, antenna mast down.( All while stopped for lunch of course)

[DrP]

Given that TV reception while moving about in a complex environment is always going to be a case of pushing .... up a hill, perhaps the idea of watching live TV should be dispensed with.  Record something overnight and watch it with one of the numerous media players that can be connected to a TV these days.  From what I can see of the guide, daytime TV isn't much chop anyway.  Primetime is where the interesting stuff runs and unless the OP is driving his tractor around the fields at night...

Plus with a media player you can easily pause or even stop the playback when you accidentally run over the farm hand.  Missing parts of the show as you apply first aid or call the meat wagon would surely be annoying.

Edited by DrP, 09 November 2011 - 06:46 PM.

[cyclone_27]

alanh, on Nov 8 2011, 07:28 PM, said:

Cyclone,
With the amplifier disconnected do you get reliable reception when you can see the transmitter? Does it matter if you are moving?
With the amplifier connected is there any locations where you get stable reception? eg behind the trees?

AlanH

With the amplifier disconnected do you get reliable reception when you can see the transmitter? Does it matter if you are moving?only when the antenna is in view of the transmitter, once i'm behind trees (fruit) the signal is lost.

With the amplifier connected is there any locations where you get stable reception? eg behind the trees?
when i'm behind trees the amp connected is the better option.
I'm behind trees for approx 80% of the time

[cyclone_27]

DrP, on Nov 9 2011, 06:44 PM, said:

Given that TV reception while moving about in a complex environment is always going to be a case of pushing .... up a hill, perhaps the idea of watching live TV should be dispensed with.  Record something overnight and watch it with one of the numerous media players that can be connected to a TV these days.  From what I can see of the guide, daytime TV isn't much chop anyway.  Primetime is where the interesting stuff runs and unless the OP is driving his tractor around the fields at night...

Plus with a media player you can easily pause or even stop the playback when you accidentally run over the farm hand.  Missing parts of the show as you apply first aid or call the meat wagon would surely be annoying.

my tractor driving is 80% at night (prime time) and i watch tv when there is no one in view (if i'm approaching the shed etc it is off)
I also have widespread wifi setup on the farm, but none of the FTA stations show live tv online.

[Tazzy2Heads]

cyclone_27, on Nov 15 2011, 08:01 PM, said:

my tractor driving is 80% at night (prime time) and i watch tv when there is no one in view (if i'm approaching the shed etc it is off)
I also have widespread wifi setup on the farm, but none of the FTA stations show live tv online.

Hi 'cyclone 27'

How about a VAST Satellite ' travellers 'card and a self tracking Marine dish on roof ?It would make the neighbours look !

Tazzy.

[mtv]

As I have said before, it's dangerous (and illegal) to watch TV whilst driving a vehicle or operating machinery.

It's a very foolish thing to be doing, risking your life and possibly lives of others.