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I have a VisionPlus DVB-T card in my MythTV backend box. I'm currently getting alot of signal breakups using the (block of units = shared) roof antenna. Are there any good indoor antennas that may improve the situation?

(Another reason for this question is that I'd like to move my Mythbackend box to another room, which doesn't have a wall jack.)

Cheers,

Jon

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It depends on how close you are living to the transmitter.

The best choice would be to buy an outdoor antenna (gclark8 on these forums can suggest a good one to use) and put it inside.

I have used a DSE $15 indoor antenna to pick up UHF. I don't know how well it will pick up VHF as where I live, I can't get a good VHF signal using the rabiit ears.

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For anyone using rabbit ears (I still am for my FusionHDTV card), you may not be aware that adjusting the arm lengths will "optimise" reception for individual channels.

Longer lengths are required for lower frequencies (eg. ABC analogue) and shorter lengths are required for higher frequencies (eg. ABC digital and SBS analogue and digital).

Maybe George or AlanH could post the 'optimum' arm lengths for the capital city frequencies to help us all. Then mark the channel positions with a texta for future reference (until they rub off!).

My digital reception is fine on the PC using adjusted rabbit ears - though adjusting arm lengths for each channel change would be a PITA for channel surfing in the living room.

2i cents,

Ian

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OK its like this, rabbit ears is a half wave dipole, each ear 1/4 wave, so,

300/Frequency in MHz = wavelangth in metres

Divide that by 4 = length of each ear

so, for channel 9,

300/200 = 1.5M,

Each ear = 375mm

so for SBS/29,

300/536.5 = 560mm

Each ear = 140mm

and so on...

Best to set the angle of the ears at 45 degees to the horizontal, 90 degrees between the ears, rotate the base while watching the signal strength and quality on the box, quality is most important!!

Or you can buy a Fracarro LP345HV, its like having 13 rabbits. :blink:

Edited by gclark8
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George,

Have you ever seen an outside TV antenna which has its elements Veed vertically unless there has been a storm?

For horizontally polarised signals the ears must be horizontal, in vertically polarised areas hang the antenna so that the ears are vertical. There is no mixed polarisation in TV in Australia.

AlanH

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George,

Have you ever seen an outside TV antenna which has its elements Veed vertically unless there has been a storm?

Yes, G5RV and derivatives...  also LPV345HV fracarro in "no gain" or reference config.

For horizontally polarised signals the ears must be horizontal, in vertically polarised areas hang the antenna so that the ears are vertical.

Wrong, rabbit ears work best at 45 degrees.

There is no mixed polarisation in TV in Australia.

What about Canberra and wide bay??

AlanH

Has anyone seen a rabbit with flat ears???

If so, send it to Alan. :blink:

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George,

Vertically polarised antennas are used in many areas of Australia. Internal antennas need to be hung so that the dipole is still straight. If you then V it it will look like one type of log periodic rotated vertically. However, there used to be a double Vd antenna back in the 50s-60s. This went out of fashion.

I have used for horizontally polarised signals the internal antenna with the rods horizontal to produce much better picture. This is much more practical at UHF.

AlanH

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Thanks for the recommendations (and explanation!)

I should have added that (I'm hoping) this will be a temporary solution to last a few months until we move out of our unit, so I'm reluctant to spend a great deal on an internal antenna now, when I may be using an external one in a few months time.

I live in Greenwich (lower North Shore, Sydney) so I'm pretty close to the transmitters in Gore Hill and Artarmon. Our analog signal is pretty poor, which I put down to the block's shared antenna and anciant looking cabling. Given that situation, it sounds as though I may be able to use a bog-standard set of rabbit ears and get a reasonable signal.

I think I might just pay Dick Smith's a visit, and see how I get on. I shall make a point of buying a set who's ears can extend to 180 degrees! Obviuously, adjusting the ears when changing channel is going to be impractical - is it going to make that much difference?

Thanks again,

Jon

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  • 3 weeks later...
Or you can buy a Fracarro LP345HV, its like having 13 rabbits.  :blink:

Well, I have an update and a question. I thought I'd try some bog standard rabbit ears for $20.

On a clear day, I get the same signal strength and SNR readings from the rabbit ears as I do from the roof-mounted antenna, more or less (34% and 38% respectively for most channels; SBS is worse. Bear in mind that these figures are from tzap under linux, using a VisionPlus.) When it's raining, these figures get rather worse, and the signal is obviously very poor (plenty of pops and squeeks, pixelation galore, then MythTV dies.)

So I bought a Fracarro from Lacey's - an LP34HV on their recommendation. I have just quickly tried it out, and the figures are *worse* than the rabbit ears. I guess I've got something wrong! I'm running quad-shield RG6 to the PC. My question is: at the antenna end, should the cable's shielding come into contact with the body of the antenna, i.e. be clamped into the antenna, or should I clean it away and just clamp the sleeve.

Any other hints on maximising the signal from this antenna?

Cheers,

Jon

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I have found that i can not pick up any Digital signal using an indoor antenna and do not greatly recomend them. However if you live in a strong signal strength or have LOS then they are probably allright. It all depends onb your location. It will just take trail and error.

Try and work out where the transmitters are exactly located. If your lucky you can stand on your roof and see them. Thsi will help you direct your antenna, whetehr it be indoor or outdoor.

How do amplified indoor antennas compare in performance to non-powered? I would imagine there to be a big differnce.

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For those of us who can't stand on our roof and see the transmitters....one approach I have taken is to check out the ACA transmitter info and locations (they even give GPS coordinates) and then use the UBD on disk's distance calculator function to draw a line from your house/location the transmitter(s). The line drawn on the map can then be used to identify local landmarks that can be used as reference points for positioning the antenna in the right direction. Moving the antenna around and watching the changing strength, SNR an BER (at least on Nebula's Digitv) can give you further refinement

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