How Does That Work?

[securespark]

The aerial I had worked until some time last year, when there was a Freeview retune in aid of 5G, then I started getting break-up and pix.

A Freeview appointed bloke came and replaced the twig FOC.

The cables were not replaced.

 

[securespark]

I have identified the co-ax that feeds the garage amp.

Now I have two left to identify: an FM dipole and a TV twig.

One measures 1.18Ω.

The other measures 0.03Ω.

The resistance of the leads has been nulled.
The co-ax attached to each are very similar lengths, although not identical.
Is that cut and dried as to which is which?

I would say the TV aerial has a greater resistance.

 

[davelx]

Hard to say. In DC terms, folded dipole aerials are a short circuit. It's only at RF that they behave as they need to.

 

[securespark]

There is at least 16m of co-ax on each aerial.

 

[Harry Bloomfield]

I was always told them amps are waste of time, if you have crap signal to start then it just boosts the same crap signal, not sure how true that is, far better to initially pay more for a decent arial.

If it is a good signal, though weak, then they can work. Rather than an amplifier, I would suggest it is a 'distribution amplifier' - a device to maintain what is basically an a good signal, out to several sets. If you simply connected one drop from an antenna to multiple TV's each would end up with a fraction of the signal and it would be unbalanced, not be presenting 75 Ohm load to the antenna. The distribution amp gets around that, by boosting the good signal level and enabling proper impedance matching. It also avoids the need to have multiple antennas on the roof, one per set (if done properly), instead using a distribution amp.

 

[HERTS P&D]

Where's Chris?

Andy

 

[JohnW2]

If it is a good signal, though weak, then they can work. Rather than an amplifier, I would suggest it is a 'distribution amplifier' - a device to maintain what is basically an a good signal, out to several sets. If you simply connected one drop from an antenna to multiple TV's each would end up with a fraction of the signal and it would be unbalanced, not be presenting 75 Ohm load to the antenna.

Whilst that is all true, single-output 'boosters' do exist. Furthermore, even the multi-output 'distribution amplifiers' usually have an appreciable amount of gain between the input and each of the outputs, so do more than simply maintain the signal strength which would exist if the aerial were connected to just a single TV.

As we have both said, this can be beneficial if there is a 'weak but fairly clean' signal. Indeed, since any amplifier is bound to introduce at least some noise, if the amplification were only " 1:1 ", then there would actually be a deterioration in the signal-to-noise ratio - so the amplification provided is at least partially to compensate for the noise added by the amplifier.

Kind Regards, John

 

[Harry Bloomfield]

Whilst that is all true, single-output 'boosters' do exist. Furthermore, even the multi-output 'distribution amplifiers' usually have an appreciable amount of gain between the input and each of the outputs, so do more than simply maintain the signal strength which would exist if the aerial were connected to just a single TV.

Single output boosters are best located as close to the antenna as possible, sometimes mounted on the mast and powered via the coax.

Yes the distribution amps do boost the signal - my 8 way caused me to have to install a signal reducer, in the line to our latest TV, the signal was too strong and it constantly requested a retune as it picked up more distant, outside my area services.

 

[JohnW2]

Single output boosters are best located as close to the antenna as possible, sometimes mounted on the mast and powered via the coax.

Indeed so. The same would obviously be (functionally) 'desirable' for a multi-output ('distribution') one, but it would probably usually be considered to be impractical/inappropriate to have multiple feeds to individual TVs from a mast-top distribution amplifier!

Yes the distribution amps do boost the signal - my 8 way caused me to have to install a signal reducer, in the line to our latest TV, the signal was too strong and it constantly requested a retune as it picked up more distant, outside my area services.

That doesn't surprise me, since I've had to do similarly here - as I said, my aerial is easy line-of-site to the local repeater (probably only about 10 miles away), so that the signal strength is very high, even without amplification.

Kind Regards, John

 

[Harry Bloomfield]

Indeed so. The same would obviously be (functionally) 'desirable' for a multi-output ('distribution') one, but it would probably usually be considered to be impractical/inappropriate to have multiple feeds to individual TVs from a mast-top distribution amplifier!

They would usually mount the distribution amp centrally, to reduce cable run lengths. They can have distribution amps fed from distribution amps, is flats. One per floor, or per pair of floors.

 

[JohnW2]

They would usually mount the distribution amp centrally, to reduce cable run lengths. They can have distribution amps fed from distribution amps, is flats. One per floor, or per pair of floors.

Indeed.

Kind Regards, John

 

[securespark]

Hard to say. In DC terms, folded dipole aerials are a short circuit. It's only at RF that they behave as they need to.

On that basis, I have decided that the lower value must be the radio and the higher, the TV.

The cables and TV have now been re-sited.

 

[winston1]

Well, if that is remotely like a fair indication of how much power it actually 'draws' from the 230V supply, then that 0.3W (i.e. 3,333 hours for 1kWh) suggests that I probably wasn't far off when I suggested that the running costs would be "trivial"

Kind Regards, John

No that is the line power available to sent to a masthead amplifier via the coax. That is in addition to its own power requirements. Probably several watts including power supply losses.

 

[JohnW2]

No that is the line power available to sent to a masthead amplifier via the coax. That is in addition to its own power requirements. Probably several watts including power supply losses.

Fair enough.