All posts by Nick
Below are all of Nick's postings, with the most recent are at the bottom of the page.
thanks Mike
behind tv all in one amps are useless, agreed.
I have seen masthead amps with 4 different sockets, each with a different gain. I assumed this was so you could connect to the most appropriate, rather than run 4 tvs where they would each state the same gain. Please clarify.
Now, assuming I am correct in stating that where there are 4 gain options, am I wasting my time putting the aerial at a convenient 6ft from the ground, [it still works] and connecting to the terminal which provides the best stable signal, and then transfer it to the roof? I am concerned that on the roof it might have preferred a lower gain socket, but I cannot keep taking the thing down to experiment.
| link to this comment |
Hardy, please tell me HOW you adjust this amp. I have not seen such, only the ones with 4 inputs, each with different gain specified.
Re stacked aerials, I have not seen these for many years. They were used prior to having high gain aerials, and were generally 18 element, folded dipole, no balun. Their problem was that the impedance was halved by joining two together, the net effect being little improvement over one aerial. So far as I am aware, this is why they designed directors in 'shallow x' form or triple boom types, so that all the directors fed one dipole.
| link to this comment |
thanks, Hardy,
Please confirm my suspicion that if I set the correct gain with the aerial conveniently at 8ft from the ground, it would not be appropriate when the aerial is on the roof.
| link to this comment |
Hardy, I am on the wrong side of town for Tacolneston, Sudbury comes in well but as described, easily knocked out.
With regard to boosters. Whilst on a good day, 27db is fine, but I have a feeling that on a bad day, ie when I am having problems, lesser amplification means I get knocked out less often. Is this possible?
Do you remember the J Beam aerials with square dipoles and reflectors? I have made one with three booms and it is wonderful. The reflector is small and hollow, so does not fall off. It used to be described as a slot aerial.
As far as I know, tribeams and shallow x aerials BOTH have large reflectors, unnecessarily so in my opinion.
Lately I have seen aerials with directors which look like hollow bottles, two per director placed neck to neck. Do you know these? Are they better?
| link to this comment |
thanks Hardy.
I would like to get Tac, but there are houses in the way. I can get a couple of the muxes now and then, but definitely not the weak ones, and only wanted them to get Al Jazeera which gave up its SD mux.
Many years ago J Beam were good enough to answer a few questions, telling me that I must not replace the square hollow reflector with something larger, as the reflector and dipole work on the 'slot' system, receiving a different aspect of the signal from other aerials....magnetic or something.
Why would the x shape give wider bandwidth? Those elements are very short, best suited to the c/d group in my opinion.
My home made is designed for channels 29-47. In essence it has group A dipole and reflector, both ex J Beam hollow, with three lines of group B directors almost parallel about 4 inches apart. Slight modification to balun.
| link to this comment |
Thanks Hardy.
Those shallow x's come in two versions, one being like two V's, the other is 4 separate short elements. I can understand the former being 'thick' but not the latter.
By 'grid' do you mean kooman array, ie full wavelength dipoles? I am not sure this would have enough gain and that is what I need or would have gone for a log.
I am experimenting with five rows of reflectors on my J Beam.
I will let you answer reception problems. There are so many of them since they forced us to go wideband, though Sudbury's channels are now closer than before. I hope they leave them that way and a shame they did not make it like that when they went digital.
| link to this comment |
Hardy,
would give up on trying to get the weaker channels from Tac, if I were you, specially if on high channels Where are you?
The aerial you describe for me is more or less what I am building. 5 rows of 8 group B directors. Group A square J beam dipole, but while keeping its total length as group A, I have 'squashed' it. It is now a rectangle, vertical, which conveniently makes its width group B. This extra height means I can get 5 rows of directors without them being only a couple of inches apart.
One reflector, about a foot square, netting. Despite J Beam saying it had to be a hollow square slot, like the dipole, that is what I am doing.
| link to this comment |
Hi Hardy, it is built and I am pleased.
On a 12 ft pole in the garden I had a single set of 8 group B directors, my squashed group A J Beam square dipole, no reflector. In broad terms, channel 29 right up to channel 44 showed 60% for signal quality and strength.
I have added 4 extra rows of directors and a mesh reflector behind. Signal strength on 29 near 90%, quality 75% On channel 44, less marked improvement, strength 68%, quality 75%
I cannot test channel 47 as it does not show on my set top box.
I am puzzled that the increase is greater on 29 as this is basically a group B aerial
No amplifier in line.
I have no idea how to tune a reflector so will leave the square grid.
Overall this is far superior to my my factory shallow x aerial
| link to this comment |
Hardy, many years ago when we had analogue and no way of knowing with any readings whether the signal was improved or worsened, I held an extra string of directors against a J Beam with only one. The picture improved, so I added two. Without doubt, extra directors above and below are more beneficial than one string of 16. This is the principle of tri booms.
Because my dipole is now 12 inches high, with the top and bottom strings two inches above and below that, the strings are 4 inches apart, and angled so that at the front they are six inches apart.
My reflector is 6 inches away. Maybe it should be closer, but as I do not know how to find the impedance of the dipole, I have settled on that as the directors may well have reduced it below 75 ohms.
I wish I knew how to make a similar one for wi fi, but no idea how to match the dipole.
| link to this comment |
Wednesday 22 August 2018 7:46PM
thanks, Mike