[nikiml]

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,

nikiml

 

[Dalek Prime]

Indoor or outdoor antenna? Anything blocking you? Can you get height? Are you feeding more than one tv set?

Without info like this, there's no telling what your needs are, including whether you actually need a pre-amp. That's just jumping the gun. Look to see what your neighbours get in Mississauga, and what their antennas are. The choices are broad as it stands. eg. GH, bowtie, LPDA, other. Any and all types may work for you equally, without knowing more, and the choice may be limited by your living arrangements eg apartment, etc.

 

[nikiml]

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.

 

[ericball]

You have three options:
1. Buy a commercial antenna like the Anntenas Direct 91XG
2. Build an antenna like the DBGH or M4.
3. Do the work to design one your self.

Note: many antennas a optimized for the new reduced UHF band which may make getting channels over 51 more difficult than TVfool indicates. You will probably also need a rotor unless the CN tower is in line with the Buffalo stations.

 

[Dalek Prime]

In free space it is then.

Heck, go for the DBGH, or combine a VHF and UHF LPDA, as the angle between Beefalo (just kidding, Buffalonians) and Toronto isn't so bad. That's the perfect setup in a perfect world.

Ah, erciball beat me to the punch.

Oh, and if you have a difficult channel you really want, use a yagi to pull it. And if you want to do something completely insane, use individual yagis for each channel, and cover your property with them... Not advisable though LOL! (Now you got me all giddy and laughing. Sorry.)

 

[nikiml]

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.

 

[Dalek Prime]

Why a custom? We named the best... Is this an early April 1st query? No offense, but by your standards, you want to design an omnidirectional antenna that sits on a pole miles high, and bends EM waves to it's will . Not very practical.

Seriously, with constraints, the combined LPDAs are your best bet. You won't get better than that. And if you do, I'll personally send in a Nobel nomination in your name. (All in good fun. No offense meant.)

 

[Xauto]

nikiml: You will not be able to get Ch.23 constantly. If the NM was +13.5 then yes but not with -13.5. You can have fun and try, but don't hold your breath.

 

[Dalek Prime]

"I am trying to come up with design requirements so I can design a new
custom antenna suitable for my area only."

Laws of physics are fairly universal, save a neutron star or black hole. No exceptions for Mississauga, or Hurricane Hazel, though she's a tough old bird.

Seriously, if you want to experiment and design, grab 4nec2 and go nuts with it. Mind, it doesn't share my humour. Depending on perspective, that could be a plus or a drawback.

 

[nikiml]

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.

 

[Dalek Prime]

Well, I think your question and specs keep changing, so I'll hush up and make way for the next support specialist. But you did ask for something that would kick your neighbours reception into the stone age, and now changed your mind. As well, you said you want to design something unique for your area alone. If I'm misreading you, okay. But everyone else who answered is reading you the same way. So I suspect it's the question that's nebulous and fuzzy.

Btw, I note in a picture that you do have a GH, and something to the side of it. Is that a Stealth Hawk? Either way, why would you want less now? Or minimal; not more, not less, as you say?

Anyone else want to give this a shot?

 

[PCmonkey]

Hi Nikiml,

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 interest...so for the far away stations you want lots of gain and for the locals you want reduced gain to prevent overload...correct?

If so, I think the first step would be to graph this. Maybe split it into major directions (CN Tower, Buffalo). Graph frequency vs expected signal strength. Look at the graph to see how gradual the signal strength numbers change - I think it will be nearly impossible to design a single antenna if you require gain notches at multiple frequencies...
Not sure if this helps...

T2

 

[300ohm]

The preamp will take of the losses after the antenna terminals (and help with weak TV tuner gain). For one thats about the best against overloading, get the Winegard HDP-269. Its also one of the lowest priced ones too.

 

[nikiml]

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 interest...so 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?

 

[300ohm]

And what would be the gain needed for channel 23 (NM -14db)?

If you had clear LOS to it, and -14 NM was just a matter of distance, roughly about 24dbi antenna gain for consistant viewing, as far as Ive gathered. Holl_ands would give you a better estimate.

 

[PCmonkey]

So here's my best guess:

I believe that the input sensitivity of a typical ATSC tuner is around -83dBm...
TV Fool lists the signal power of the various stations in dBm as well.

So to determine the needed gain of an antenna you need bring the signal up to a power level that falls within the sensitivity of the receiver (also need to compensate for some losses from the balun, connectors, etc.)

For example from my location:
TV Fool power estimate for WKBW-DT: -90dBm
My Antenna gain: 14dBi

Resultant signal output power from antenna: -90dBm + 14dB = -76dBm
Assuming there aren't significant losses in your system, then this should fall within the sensitivity range of your ATSC tuner (-83dBm).

Things to remember:
- decibels add (so math is easy)
- dBm = ratio of power in mW with respect to 1mW
for example: 0dBm = 1mW, 3dBm = 2mW, -3dBm = 0.5mW
- dBi = isotropic gain of the antenna.

EXPERTS - please correct me if I've messed up - this isn't my exact field of study

T2

 

[300ohm]

Resultant signal output power from antenna: -90dBm + 14dB = -76dBm
Assuming there aren't significant losses in your system, then this should fall within the sensitivity range of your ATSC tuner (-83dBm).

So for his channel 23, that would mean an antenna with 21.7 + dbi.

 

[PCmonkey]

>21.7 dBi sounds right - That channel is 160km away - I'd say that's going to be difficult.

 

[nikiml]

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.

 

[300ohm]

How tipical is the sensitivity you mentioned (-83dBm)?
Will preamp help here or a preamp will also have similar sensitivity?

Well, if your tuners internal amp is poor, the preamp gain will help boost it. If your tuners gain is already great, the AGC circuit is going to limit additional gain benefits. (I havent seen an AGC adjustment control on a TV in a very long time. It used to be common.)

what do you make out of the explanation in the tvfool signal analysis faq, just below the table:

Big difference between being able to detect a station versus getting a consistant strong lock on it. Thats why I added 10 to the figure (instead of 0).

So basically from what I understand :

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 10, then you should be able to lock onto that channel.