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Designing custom antenna for my very specific local needs?

2868 Views 23 Replies 9 Participants Last post by  jflarin
This is a question to all the OTA gurus on this forum.

I would like to design custom antenna for my location,
based on the numbers given by tvfool.

The weakest channel I'd like to get is 23 (ION) and for this I'd probably need a preamp.

By looking at the tvfool chart I've come up with a list of frequencies, azimuths and target gains.

My question are:

Are the target gains enough (with /without preamp)?
Are some if target gains to much if I am to use a preamp?
Could I go with less gain on any channel?

Chan	Network	Dist	Path	NM 	azim     target gain
	        (mi)            (dB)	(deg)    (dbi)
20	CBC	19.8	LOS	49.6	50	    0
18	Ind	26.2	LOS	46.7	-50	    0
40		19.8	LOS	44.4	50	    0
44	OMN	20.2	LOS	43.1	50	    0
64	OMN	20.2	LOS	41.6	50	    0
35	Ind	26.2	LOS	38.6	-50	    0
24	SRC	19.8	LOS	37.4	50	    0
32	CW	57.6	LOS	37.2	0	    0
65	GTN	19.8	LOS	34.9	50	    0
66	Sun	19.8	LOS	34.8	50	    0
53	Ind	19.8	LOS	33.5	50	    0
43	PBS	57.6	LOS	29.5	0	    1
14	Fox	57.5	LOS	24.2	0	    1
39	CBS	86.2	LOS	21.7	-5	    1
33	NBC	85.4	1Edge	17.5    0	    5
38	ABC	87.5	1Edge	12.9	-5	    8
26	Ind	87.1	1Edge	11.5	-30	    9
49	MyN	86.3	1Edge	7.7	0	    10
7	Ind	88.0	2Edge	-7.2	-10	    8
23	ION	100.2	2Edge	-13.5	10	    16
Thanks in advance,

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1 - 7 of 24 Posts
The questions are more or less theoretical.
Lets assume that there are no obstructions and that I can get the antenna to the height from the tvfool report.

I am trying to come up with a design requirements....
And beat all of the neighbours.
Thank you guys,

but my question is completely different.

I am trying to come up with design requirements so I can design a new
custom antenna suitable for my area only.
I am sorry, but you are just answering to different questions.
I am not trying to design an omni - just look at the gain targets I put.
I am not trying to do better than lpda, nor to design universal antenna at all.

I only want an antenna that is going to cover the minimum required.
And not do much better so I can have an amplifier without overloading.

My questions consern only that - what is the minimum gain required and what is the maximum gain allowed.

And those are the only answers I am looking for.
If I understand you correctly, it looks like you are trying to spec an antenna that has just the right amount of gain at the channels/frequencies of for the far away stations you want lots of gain and for the locals you want reduced gain to prevent overload...correct?
Yes. But I don't know what is the right amount.

If tvfool says channel 20 has NM of 50db what is the optimum gain that will recieve it but not overload the preamp?

And what would be the gain needed for channel 23 (NM -14db)?
Or for channel 7?
Thank you PCmonkey and 300Ohm,

I have few questions.

How tipical is the sensitivity you mentioned (-83dBm)?
Will preamp help here or a preamp will also have similar sensitivity?
Does this mean that I can have something like -20 dbi gain at 50 deg for channel 20 and still watch it reliably?

what do you make out of the explanation in the tvfool signal analysis faq, just below the table:
The most important number to pay attention to is the Noise Margin, in the "NM(dB)" column, for each of your local channels. These values tell you if you are above or below the detection threshold for each station and by how much. Since these values represent the amount of signal "in the air" at your location, you need to have enough margin to account for building penetration, cable loss, splitters, tuner sensitivity, and other factors specific to your setup. If you take the initial NM value for a given channel, add your antenna gain, subtract all the other system losses, and still end up with a value above 0, then you should be able to detect that channel.
I somehow hoped that if :

NM + antenna gain - preamp noise figure >0 (preamp means no cable loss)

it will be ok. I thought that the preamp will take the (>0) amount of signal and make it tv acceptable.
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