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Gain (curves), Again                                      (See Aerial Tests)

This page is strictly for the cognoscenti ( “the trade” ? ),

and those with an unhealthy interest in TV aerial performance.......

The gain curves are conservative estimates, but I bet they`re not that far out.........

One things for sure, they`re all accurate relative to each other, which is what matters !

Note these curves are in dBd, that is gain compared to a half wave dipole,

NOT (the dishonest ? ) dBi....

Typical Contract 10 gain curves

B group Contract aerial curves    (including Extending The Aerial Groups)

A group gain curves and comparisons

B group gain curves and comparisons

C/D group gain curves and comparisons

K group gain curves and comparisons

E group gain curves and comparisons

Wideband gain curves and comparisons

Just how much gain do you get from a 10 element Contract aerial ?

These were relatively good quality Contracts (they had baluns) and it cannot be

overstressed that some Contract aerials` performance can be very inconsistent,

and this is particularly the case outside of their designed for group, see below.

Note that the A group curve is that for post 1995 aerials, when the A group was extended

up to CH 37 from CH 34, see below. Thus the response curve for aerials fitted prior to this date would be about three channels down.

Testing decent quality aerials is all very well, but what about the cheapies that many people may already have up, or be put up by a tight arse aerial installer ?

Above we have two Contract 10Bs, and old Contract 18B (possibly 20 to 30 years old ?), two Contract 18Bs, plus the Yagi18B and the XB16B which we sell.

I was particularly interested to find out how much difference a balun made to the performance of an aerial and in the above tests the two Contract 10s are identical save for one having a balun and the other not. From those curves, and the others come to that, it can be seen that a balun does seem to have an effect on gain, particularly outside the aerials designed for band.

It will be noted that the gain of the old Contract 18B was dipping way before even CH53, which is the top of the B group.

Now, all of the aerial gain curves on this site (and in fact all published aerial gain curves....) are smoothed off for clarity, but the huge dip in the gain of the Contract 18B without a balun is of a different order altogether. This is typical of some Contract type aerials, beware.

Extending the Groups

Whilst on the subject of B groups when UHF TV transmissions began in 1964 the B group was

CH39-CH51, but it has since been extended up to CH53. During my research for a definite date for this a helpful contact at Ofcom found a guide to TV transmitters dated 1974 and that had the

B group up to CH53 so it must have changed prior to that date, possibly when BBC1 and ITV

started UHF transmissions in 1969 ? Furthermore the "Practical Aerial Handbook" of 1970

seems to confirm that because it reports that the Radio and Electronic Component

Manufacturers Federation have revised the aerial groups, Group B is now CH39 to CH53.  The same article also states that group C/D was extended down from CH52-CH68  to  CH48-CH68

The B group, and the E group, were also extended down to CH35 (from CH39) around 1995

when the planning for C5 transmissions (from 1997) was beginning. At this same time group A

was extended up from CH34 to CH37 because some group A transmitters (Crystal Palace being

the most obvious example) was having to transmit C5 on CH37, though somewhat confusingly

it`s actually transmitted from Croydon !

It must be said that extending aerial groups down a few channels is usually a bit irrelevant

because Yagi antennas generally work pretty well below their designed for bands, although,

as explained above, Contract type aerials (and any others without Baluns ? ) don`t  always work quite as well as decent antennas.

The story of C/D.   I`m sure you`ve often wondered what is the story behind the C/D aerial group,

I know I have and I don`t think I`m Autistic, well perhaps a little. My wife reckons all men have

Autistic tendencies and I think she could be right . The question is, can you actually be Autistic if

you take the mickey out of yourself for being Autistic ?

After pondering that psychological question we can now move on to the origins of the C/D aerial

group....... When UHF transmissions first started in 1964 the C group was CH52 to CH68 though

it was later changed to CH50 to 66.  However an additional D group (blue bung) was also added

which was CH49 to CH68. I have to say I can`t imagine there`d be much difference between

aerials of those three groups but there we go. Finally in 1969 the C and D groups were

amalgamated into one, the C/D at CH48 to CH68.

If you`ve found this site informative and, hopefully, interesting as well,

please help us increase the number of people reading it.

Also see B group Contract aerial curves, including info on the changing aerial groups.

Note that the dates of 1969 and 1995 are approximate.

1969 was the year that BBC1 and ITV joined BBC2 in being transmitted on UHF.

Channel 5 began transmission on the 30th of March 1997, but planning for this had started years

before this. A helpful contact in the aerial industry has informed me that the extending of the

aerial groups was being undertaken 18 months to two years before the actual launch of C5,

giving 1995. However aerials designed under the previous group designations would probably still have been on sale/being fitted months or even years after 1995.