Modifying Existing Analog Antenna

[texass44]

Hi All,

I get pretty good digital reception off my current analog antenna, 86% strength, 100% quality.

I do however suffer from intermittant pixellation when lights turn off/on etc.

Would it be acceptable to remove the Ch0-2 & Ch3-5a parts of the antenna to help reduce this ?

Will I somehow degrade my current digital signal ?

Thanks in advance for any insight !!

Cheers.......Tex.

[I am not a duck]

You can try. Nothing ventured, nothing gained.

Combinion antennas are designed (sometimes empirically) allowing for the interaction of the various elements that are used in their construction.

IMHO suggestions that antenna impulse noise sensitivity with these unwanted elements is not as good as an antenna without them is only valid if the performance parameters for the channels in question are the same for both antennas.

Save yourself the trouble and get a digital only antenna. Don't then be surprised if the problem is still evident, as the intermittent picture breakup you experience can be dependent on factors other than the antenna being used.

((little bit ot but can't resist the urge to use an image ) eg here's a rural installation using a crudster old antenna. Notice the 220Kv lines about 500m away that are arcing and carrying on, greatly disturbing am radio, yet there was no interference to digital reception as the signal to noise ratio is adequate to overcome impulse noise. Admittedly also the noise is side on to the antenna, which reduces pickup, however, there is a masthead amplifier, J40BF, between the 2 antennas.)

Edited March 26, 2007 by Island Antennas

[mtv]

As already mentioned, there may be other factors contributing to your impulse noise problem, such as the antenna coax being near power cables on your roof etc. Is your antenna mounted externally, or in the ceiling?

The location of the antenna may also not be optimum. Relocating an antenna to a better position can improve the signal to noise ratio, making the received signal more reliable. The only was to accurately find the best location is with a digital field strength meter which displays digital channel power and bit error rate. Any competent pro digital antenna installer should have one.

Antenna design can be complex, so for the best results you would be far better off installing a new antenna designed for only the digital channels in your area, (Which you haven't mentioned, other than being in Melbourne) rather than trying to modify your existing antenna, which may not have been designed to receive channels 11 & 12 in the first place.

[texass44]

Thanks for the feedback guys, it is much appreciated.

I'm in inner east Melbourne so get my signal from Mt Dandenog.

Antenna is external on the chimney. COAX disappears into the roof, into an amplifier (not sure of brand) then off to 4 outlets.

As I say, digital reception I think is very good appart from that intermittant stuttering/pixelation.

I hear what your say regarding a dedicated Digital Antenna.

I think I'll try and source a reputable installer in my area and just go digital all the way.

Thanks heaps.

Tex.

[mtv]

I think I'll try and source a reputable installer in my area and just go digital all the way.

Wise decision, Tex

The amp could also be contributing to the problem.

You could try forum member beeblebrox. I think he installs in your area.

[texass44]

Wise decision, Tex

The amp could also be contributing to the problem.

You could try forum member beeblebrox. I think he installs in your area.

Magic........Thanks for that.

Tex.

[bellotv]

((little bit ot but can't resist the urge to use an image ) eg here's a rural installation using a crudster old antenna. Notice the 220Kv lines about 500m away that are arcing and carrying on, greatly disturbing am radio, yet there was no interference to digital reception as the signal to noise ratio is adequate to overcome impulse noise. Admittedly also the noise is side on to the antenna, which reduces pickup, however, there is a masthead amplifier, J40BF, between the 2 antennas.)

Marc

What is the crudster? never seen one like that before

Texass44

BTW .my LPV345 test antenna had lost a few of the longest elements .When the new one arrived,I tested it with the new one and although the VHF elements had fallen off ,the gain was nearly 8dB lower on the UHF.In this case removing elements had upset the entire design of the antenna.

[digitalj]

Texass44

BTW .my LPV345 test antenna had lost a few of the longest elements .When the new one arrived,I tested it with the new one and although the VHF elements had fallen off ,the gain was nearly 8dB lower on the UHF.In this case removing elements had upset the entire design of the antenna.

If I was modifying a band 1-3 antenna, I'd cut the long elements back to band 3 size.

[wahroonga farm]

.....What is the crudster? never seen one like that before

Texass44

.... a very nice hi gain twin band log periodic .... hence the excellent noise immunity.

[bellotv]

If I was modifying a band 1-3 antenna, I'd cut the long elements back to band 3 size.

And what size would that be ?

[Theres Always Radio]

If you had a chance to sweep the antenna after cutting, you may find some severe notches in the response for there is always the desire to keep the mass of the antenna as low as possible and so a single element commonly has more than one role. These wideband antenna designers are very sneaky.

Cutting the elements down is most probably step one, so while your calculator is warm, you may then need to do some more calculations to reposition them on the boom but even that could be dissapointing.

None the less, lots of fun if its a hobby and rewarding if you have the time for lots of suck and see.

Cheers

James

[digitalj]

And what size would that be ?

obviously about the length of the shorter elements, assuming there's no UHF part to it.

[beeblebrox]

What is the crudster? never seen one like that before

Looks like an old channelmaster, I'll ask our resident antenna historian next time he comes in... with all those pesky phasing bars (10 sets I think I counted) i'm surprised it's not constantly being shorted by birds

[dig2all]

antenna design is a science, the cost of instrumentation to check and the skill to use it hardly worth it for 1 install. this old (you'r right b-brox) channelmaster is unlikely to be designed for channels 11 or 12, which puts it in the category of 'íf it works great, it it doesn't its too old to worry about.' breaking bits off won't make it better!