Hillsborough
Sheffield
S6 2LL
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Aerial Positioning Tests now has its own page
Also see
Tests of FM / DAB antennas and Tests of Aerial / Satellite Poles
Aerial test site on the moors above Sheffield, at an altitude of around 345m (1140ft).
Now that`s what I call “line of sight”, you can see for miles......
Over the years we have tested dozens different models of antenna on Belmont
(A / Wideband), Waltham (CD / Wideband), Bilsdale (A / K), Crosspool/Sheffield
(A / Wideband), Emley Moor (B), Stocksbridge (CD) Oughtibridge/Wharncliffe (CD).
The results are interesting to put it mildly, we rely on our own data now and more or less ignore manufacturers figures. This is particularly the case where they only give a (peak)
gain reading. Even if the latter is accurate, this figure can be misleading, especially with wideband aerials. What you really want is the gain graph, but many manufacturers won`t release this information, arrogant gits.
We tested the aerials against each other at the same time, in the same location,
and in actual reception conditions. We have also retested the same antennas and find
the signal reception can vary for no apparent reason (possibly the temperature, the
humidity or even differing -
In summer 2007 we decided to institute a major new test programme and identified a site
on the hills above Sheffield which would enable us to do this as it has “line of sight” off four main transmitters and three repeaters. Between them they cover virtually all the TV band frequencies. Some of the most significant data concerned the response of grouped
antennas above and below the designed for frequency band, this is particularly relevant for some Digital (i.e. Freeview) transmissions. As an example it proves that a B group aerial
(certainly the ones we sell ! ) will work perfectly well on CH 55, which is MUX6 off Sutton Coldfield transmitter, see the relevant graph.
At least two readings were taken -
every aerial (including many not published on this site), so some idea of the work involved can be imagined. I reckon I took around 8,000 individual readings, and that was just the 2007 tests ! Whilst it was very interesting to start with, it could became a hell of a grind !
The results are arranged in tables / graphs as follows :
Aerial Groups (the same model of aerial but all the different groups)
The C/D group aerials we stock
It should be noted that as antennas leave their designed for band their performance can become erratic and the further out of band you go the more pronounced this becomes.
This can give spurious readings, particularly in a spot where multiple TXs can be received, because the aerials directivity can become very poor and inconsistent. This is the main reason why we have not published some readings (e.g. C/D off an A group) as they are meaningless.
In order to make the results comparable all readings are in dBuV and are all relative
to a DM Log Periodic aerial. The latter has a pretty flat gain curve and thus is an ideal control antenna. Quite apart from anything else, wherever possible (i.e. in reasonable signal areas), Logs should be used as a matter of course, so the table(s) will show how much
gain you have to make your decision on antenna choice. Note how the Log performs pretty well (in terms of gain) against small/medium wideband Yagis at the bottom of the band(s) but falls behind as the frequency rises.
For those who are interested I reckon that, conservatively speaking, the gain of a DM log would be about 6 dB at the bottom of the band, then rising by about one dB in the middle, before dropping a little at the top end. These are the figures I used when calculating the absolute gain for the graphs. The absolute gain figures are conservative estimates,
though they are accurate relative to each other. Remember that all aerial test readings are approximate anyway, as far as I`m aware no lab will even guarantee accuracy better than
+/-
Note this is dBd, gain compared to a half wave dipole, NOT the (dishonest ? ) dBi....
Such are the signals available at 1140ft that even the Log was giving the signals shown in the table below. Bear in mind that the Yagi18s were giving up to 7 dBμV more than that
and the XB16s up to 9 more, that`s NINE ! Just to put it in perspective, one should be aiming for 60 to 80 dBμV (on analogue), and not more than that or cross modulation interference can result.
Differences in the test results of one dBμV on any individual frequency should be disregarded, manufacturing tolerances or a truck going over a hill somewhere between the test site and the TX could easily account for those ! Furthermore the response of any aerial is not linear, its gain curve will have bumps and dips in it. That said, a 1dB difference
across the whole band is significant, and an increase (or decrease) of two or three dB is
very significant. It should be remembered that 3dB is a 40% higher signal level, and such
an increase at the aerial (as opposed to through an amplifier) is very difficult to achieve.
Obviously if you live in a decent reception area these amounts of signal variation are not important, but if that`s the case, you should just use a Log Periodic anyway !
In order to give some idea of the gain of the aerials we also included in the tests a
46 element (it`s actually a 28 element....) Tri Boom Yagi which is very similar in
performance to a DAT45. We do not stock Tri Booms, I think they`re overrated....., but for those who know of them, the figures could be illuminating.
I didn`t test the DAT 75 because it was too unwieldy, but Televes report it as being about
the same as a DAT 45 at CH 21, rising to +1dB at 45 and peaking at +2dB by CH 62.
Incidentally this trend for extra directors to add gain at the top end of a widebands gain
curve (and less so at the bottom) was reflected in our own tests of other antennas.
It should be borne in mind that gain is not everything, which is why Logs are still one
of the best aerials despite being having relatively low gain figures.
Impulse noise rejection, directivity, out of band rejection, cross polar rejection and
front to back ratio and can all have significant effects on the quality of the received signal.
Having said that, gain is a function of the others (apart from impulse noise rejection) as it demonstrates that the antenna is performing efficiently. Indeed gain must be a function of the others. Why must ? Well an aerial is a passive device, the only way it can increase its gain in a particular direction is at the "expense" of gain in the other directions.
As an aerial`s gain increases, its acceptance angle (and its cross polar rejection come to that) decrease. They must do, there is no other way for the aerial to increase its gain.
Finally, all of the above is before you even start talking about wind loading considerations and/or build quality. Fortunately, we definitely know what we`re talking about when it
comes to the latter, there are no “Bacofoil” aerials here......
This table compares six Yagi 18s of the same model, but of all five groups plus
Wideband. Note, we don`t actually sell the Yagi 18 wideband (because the DY14WB outperformed it by a substantial margin) but the gain plot is included because it directly
compares aerials of the same model. Interestingly these grouped Yagi 18s performed
just as well as grouped XB10s, and since the Yagi 18s are cheaper, have lower wind
loading and are (arguably) more robust in construction, we do stock those.
The test methodology, and points to bear in mind when interpreting the results, are explained above. The figures are obviously for this particular model of antenna.
Other models varied in performance and this was particularly the case for gain outside the designed for band. As an example, the point above which significant gain fall off occurred,
for A group aerials this varied from CH40 to CH42, and for B groups from CH56 to CH59.
For gain within band, other tested 18 element A groups (which we don`t stock) gave
around 3dB (av) more than a DM Log, the other B groups gave 4 to 4.5dB and other
C/D groups gave 4 to 4.8dB.
I must confess to some surprise that the Yagi18 K performs as well as it does up to CH62,
but this was consistent over three sets of tests on three different days. It will be noted that the B group “beats” the K (on average) over the K band. However this is primarily due to its excellent performance in the B group, note how the B trounces the Tri Boom (e.g. DAT45), which is a larger and more expensive aerial don`t forget. The K is superior to everything bar an A group at the bottom of the band, and this is the area that is the weakest by far for all wideband (or semi wideband) aerials.
Note that the A group antenna is a huge 3.8dB up on the wideband (of the same size) for
the A group frequencies, it`s also a massive 3.2dB up on the (larger) Tri Boom antenna.
In fact such is the widebands inferiority that there is no such thing as a “High Gain” wideband aerial for the A group frequencies, or if there is I`ve yet to come across it.
The C/D`s performance was inconsistent, it was sometimes only on a par with the E and
the W/B, but sometimes it was in front ! It would have been easy to “massage” the results
to say what they should, but being supremely honest, I decided not to........
On the left is Ferrybridge power station and on the right we have West Burton.
Belmont is situated just to the left of the latter, except it`s a further 26 miles away.....
From the area of the site you can see an incredible 7 (seven ! ) power stations and these are marked with white pins on our TX map. From the NE to the SE they are :
Ferrybridge (24m to the NNE, opened in 1966, 2GW)
Eggborough (26m to the NE, opened in 1968, 2GW)
Drax (32m to the NE, opened in phases 1974 & 1986, 4GW, largest in Europe)
Thorpe Marsh (22m to the ENE, open 1963 to 1994, 1GW)
West Burton (32m to the ESE, opened in 1967, 2GW)
Cottam (34m to the ESE,opened in 1969, 2GW)
High Marnham (36m to the ESE, open 1962 to 2003, 1GW)
Incidentally I`ve been on trips round West Burton and Drax and they were mind blowing !
Also compare to :
The above table is a summary of the results, for the full results click here.
