Tv antenna back to back passive repeater

[kerinvalecomaudio]

I have a client in a very poor reception aera ,situated in a valley with a hill between him and the signal in a rual area aprox 25 kms from town with the nearest neighbour being 5 kms away and i have tried a very high gain
vhf ant and uhf ant and a amp with very little response also his neighbours have the same problem
I been advised to try two combine antennas back to back and put them on the hill 5 kms away from, his home and redirect the signal over the hill and if that doesnt improve it then add a tv amp between them
can anyone advise anything on this type of setup or sites where i could find the information on
thanks ian

 

[nbucska]

Around the 60-s I read a similar passive antenna in Germany
You need unique conditions to make it workable.

The active amplifier needs very good insulation -- suggest
cable between Rx and TX -- preferably on two sides of hill.
Even good directional antennas may not be enough to prevent
feedback. Travelling wave amp ?

With transposition it is easy task.
Do you have power ? or solar ? <nbucska@pcperipherals.com>

 

[kerinvalecomaudio]

thanks nbucska
I can set it up with solar power that is no problem
with your sugestion does that mean i would have to have the two antennas out of sight of each other (in other words one on one side of hill and the other over the other side and the amp in between).The amp i could use would be a stanard tv masthead amp .electrophone produce a tv amp with 20-40db gain so do you think this would be suitable.

 

[nbucska]

Correct-- out of site, if same frequency.

Transposing system is much easier. narrower band, more gain, less noise but single customer only. More harware but
easier and less unknown. ( Osc. remotelly controlled)
<nbucska@pcperipherals.com>

 

[kerinvalecomaudio]

can you please advise more detail on the transposing system

 

[nbucska]

Select frequency you can use -- perhaps need licence, too
( I have no FCC experience ).

Oscillator remotelly tuned -- so you need 2way communication.

<nbucska@pcperipherals.com>

 

[kerinvalecomaudio]

so the tv reception is carried by radio to his house,isthis correct?
at this stage i dont feel that he would go that far so we will have to trial the antenna version and see if it works
thanks very much for the information as i carnt find any anywhere else so i will try it hopefully this weekend or in the near future.
once again thanks ian

 

[nbucska]

In the 60-s I designed six repeaters up to 1400W -- but
since then I haven't been involved with TV. The requirements
became more critical, components improved etc.

A good antenna is a major effort, too.

Try to search e.g.

http://www.dogpile.com

for &quot;TV repeaters &quot; <nbucska@pcperipherals.com>

 

[kerinvalecomaudio]

thanks very much
ian

 

[nbucska]

I would be interested to learn what happened -- would
you please let me know?

 

[kerinvalecomaudio]

hi again
I havent had time to try it yet mainly because it has been
wet but i have been do some futher enquiries over here and here are some relys i received
1- The higher the gain of both antennas, the better it works. Works great on 10GHz with two 50 db gain dishes.
If you want to amplify the signal, then you can't have the gain of you amplifier exceeding the effective front to back ratio of you antennas at any frequency or it it will oscillate! Seperating the antennas by distance or placing the RX antenna on the side of the hill facing the TX and the other antenna on the other side of the hill will allow you to use much more amplifier gain.If you have a passive system only with UHF band 5 antennas and the nearest phone cell in the direction of the TV TX it will extend the range of you mobile phones into the valley!
I might comment further that the 5 km is a fairly long
distance from the passive repeater.You can calculate the received signal strength based on the losses over the
5 km and the antenna gains you have to see how much input you need at the antenna to get a good signal. If you find you need more than 120 dbuV you might need to use the Hills &quot;self help&quot; TX units (up to 2 watts) which are a
bit more expensive but may be the cost could be shared by several neighbours.
I calculate the free space path loss at 600 MHz over 5 km is 102db. If you had a 20 db gain antenna at both ends, and you need a minimum of 50 dbuV into you masthead pre-amp at the RX location, then you will need 50 + 62 = 112 dbuV into the repeater &quot;TX&quot; antenna. If you are receiving 80 dbuV
from the repeaters &quot;RX&quot; antenna, then you will need at least 42 db of amplifier gain in your repeater. If the two antennas at you repeater have a front to back ratio of 25 db each and they are aimed close to 180 degrees from each other it will work but you will need a couple of wavelengths
between their backs. A 1 m x 1m piece of galvanised mesh (say 25 mm x 25 mm squares) mounted on the mast between the two antennas (back to back) might work also.
As you can see from the calculations, with less antenna gain and front to back ratio, it is more difficult.
The more signal you can get from the originating TX at your repeater site, the easier it will be.
If you have a field strength meter, go and measure how much signal you can RX at you proposed repeater site.If you down load the tv_8.pdf file from

http://www.aba.gov.au/broadcasters/pdfrtf/tv_8.pdf

and search through it to find the EIRP and frequencies of the TV stations you are trying to watch then you could calculate the likely signal strength at you repeater location if it is a clear line of sight and you know the
distance.For example, at 600 MHz (middle of the UHF TV band) if you were getting the signal from a 1000 W EIRP (Effective Isotropic Radiated Power = TX power x TX antenna gain) transmitter and your repeater location is 20km from this TX and you are using an antenna which has 20 db gain, then you will get 63 dbuV of signal which means your repeater needs at least 59 db of gain which means it would be a bit difficult to avoid feed back unless the RX antenna
was on the other side of the hill to the TX antenna. Hopefully you will have more signal than that.
If it is a 100000 W TX 20 km away, then you will RX 83 dbuV at you repeater site (20db RX antenna)and only 39 db anplifier gain is needed so you might be able to set that up on a single mast. How much input signal is the question - measuring it will give you the best idea of what is possible.It would be possible for the two UHF channels using Jaycar LT-3182 antennas but you just won't have anywhere near enough forward gain at VHF.Don't waste you money on the LT-3155 they won't work. They qoute 4db to 9 db of forward gain at VHF which means at 200 MHz you would have to have a 6 Watt transmitter to cover the 5 Km if you had 9 db of gain or a 60 Watt transmitter if there is only 4 db of gain at those frequencies! Remember, most mast head amps can only output 120dbuV maximum which is 0.2 Watt (200mW). Also, there is no where near enough gain privided by the mast head amplifier you propose.To work for the UHF channels only, you would need 2 x 20 db gain satellite line amplifiers such as a SAT1700 ($24.50ea)from WES Components. (I have tested these on a network analiser and they have more than 20 db of gain down to 400 MHz even though they are specified for 950 MHz to 2050 MHz - they work well for UHF TV) You also need a power supply and inserter such as a PSK18 ($43.55) from WES Components. (The prices are from there 1999 catalogue)I might not be worth it for just two UHF channels - you need to evauate that.On 569 MHz at 3278688 W EIRP a direct signal 140 km away with an antenna with 16db gain would give you 78dbuV. 42db of amp gain into an other 16 db gain antenna then 5 km to another 16db gain antenna would give you 50 dbuV - the minimum I would recomend to feed a mast head amp.
The JAYCAR LT3182 (91 element UHF) which is specified as 15-19db of gain should be able to do this. For the 2 UHF channels. Up-converting the VHF channels to UHF and combining them is one way of getting them across the 5 km.
so maybe it isnt as easy as i thought
any comments would be welcome
thanks ian

 

[nbucska]

If you have a direct (passive or actice ) wideband system
then several users can share the cost. A transposing system
is simpler to make, but it is narrowband and you can
relay only one program at a time.
<nbucska@pcperipherals.com>

 

[kerinvalecomaudio]

ok i am trying to look into the self help setup to see if it will be better

 

[kerinvalecomaudio]

hi again
I haver been talking to a business over in west australia
and he came up with tghe idea of useing 2.4 ghz transmitters to retransmitt the tv signal from a video that is receiveing the tv station .but with futher talking with our australia communications authority they came back with the passive antenna repeater was the best way to go .so i will hopefully get a chance to setup it up and i will advise you of the results.
thanks again for the information ian

 

[kerinvalecomaudio]

hi again
I caught up with another antenna business and their sugestion is to run cable from the hill down to the house and have a inline amp every 400 meters and that doesnt require any licence and would have a greater sucess rate
over the repeater idea which if done properly would run proberly 10000.00 where the cable would run into 1500.00
includeing amps
.once again thanks for your input and i will let you know
what happens
ian

 

[jbartos]

Suggestion: What about launching a balloon high enough with an antenna and anchor it?