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alanh

Antenna Design Basics + Amplification

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Yes I have clearly made a mistake in my comment. I did not see this pdf before I made that comment so I will give you that, but it doesn't change the gist of what was said.

It is funny you have pinpointed this particular thing though... No problem...

I will now be extremely alert and include some quotations of particular persons in the future :blink:

OK.

I am simple. As I have used this particular item the error was obvious.

There was also a sense of deja-vu, but I can't quite put my finger on it........ think I'll go on another holiday.

Marc.

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I know the sense of dejavu now.

New poster appears plugging Fracarro. (along with making sensible observations)

?Is he Poidahl/Peter/Pietro in another guise?

So would the good Herr Doktor Digital care to explain for me what his agenda is here? I wouldn't want to be misguided. :blink:

Marc.

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Marcj,

No guise here. Just want to give my 2 cents just like everyone else but I am tired of reading stuff that is just not true.

And no I am not any of the above persons you mentioned either. :blink:

And I do not know who poidahl is (i can't even pronouce the name), but I know who peter and pietro are and I can assure you I am not any of them in disguise.

However, Yes I have obviously dealt with them on a business level because I purchase my stock from laceys, OBVIOUSLY, but I can assure you I am not one of those persons. I did, however, go to uni with one of those persons but I will not say who :P

Bloody Typical...of course because I am plugging Fracarro you would be so suspicious to think that I am working for the aforementioned persons and I have an alterior motive...sorry to dampen your hopes :P

What about AlanH, is he working for GME Kingray maybe? He seems to plug kingray all the time???

Maybe he is taking a bit of payola on the side for plugging kingray on this site for so long!

Why are you not suspicious of him like you are with me? Absolutely Rediculous...

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Marcj,

No guise here. Just want to give my 2 cents just like everyone else but I am tired of reading stuff that is just not true.

And no I am not any of the above persons you mentioned either. :blink:

And I do not know who poidahl is (i can't even pronouce the name), but I know who peter and pietro are and I can assure you I am not any of them in disguise.

However, Yes I have obviously dealt with them on a business level because I purchase my stock from laceys, OBVIOUSLY, but I can assure you I am not one of those persons. I did, however, go to uni with one of those persons but I will not say who :P

Bloody Typical...of course because I am plugging Fracarro you would be so suspicious to think that I am working for the aforementioned persons and I have an alterior motive...sorry to dampen your hopes :P

What about AlanH, is he working for GME Kingray maybe? He seems to plug kingray all the time???

Maybe he is taking a bit of payola on the side for plugging kingray on this site for so long!

Why are you not suspicious of him like you are with me? Absolutely Rediculous...

Hi there Dok

I suppose you were once an excellent installer who has managed to climb up the ladder now right?

Everyone here is allowed to give his 2c worth of info...without an attitude and AlanH doesn't have one.

Cheers

PS: I suppose you use Unaohm as well right?

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Hi there Dok

I suppose you were once an excellent installer who has managed to climb up the ladder now right?

Everyone here is allowed to give his 2c worth of info...without an attitude and AlanH doesn't have one.

Cheers

PS: I suppose you use Unaohm as well right?

Hi there cofdmstuff

No actually I am still an installer!

And I do not have an attitude either. Maybe I'm a little raw and people can sometimes take that the wrong way because I say what I think but... thats life I guess :blink:

Maybe I might have to take diplomacy classes :P

P.S. Actually I have two instruments. One is a Rhoden Swartz and the other is a Kathrein.

And I have a HP network analyzer too.

Cheers

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Digital Docktor,

Firstly, I have no business connection at all with any manufacturer, wholesaler or retailer despite what you may have been told.

On overload I have mentioned this possibility in my Geographic Viewers' Posts where masthead amplifiers are only mentioned in weak signal areas. As for antenna basics this area is already covered. Measuring the signal levels to prevent overload is always a good idea. However there is nothing to stop a strong signal from local arcing from modulating a weak TV signal within the amplifier even to the point of clipping. Hence filtering.

I do not understand this technical term behind. There is nothing stopping you putting another filter in prior to distribution if there is a long cable from the antenna to the distribution point. The point is that filters should be prior to amplification to prevent intermodulation.

I have not been concerned about pricing provided the best result is achieved. That is a customer's choice.

Causes for BER to be poor.

Poor signal to carrier ratio. If the signal level through the antenna system is low and local impulse interference is high the BER will be high. If however the signal level in the antenna system is high then the local impulse noise will be a smaller proportion of the signal and will havel less effect on the BER

Momentary gaps in signal and poor shielding will let the impulse interference in due to poor cabling and connectors. The other factors I agree with.

You do not live in an area where the electricity company has many pole top fires caused by the arcing I mentioned every autumn. At one stage they lost power to a major city for more than a week! Just because you have not experienced it does not mean it does not happen. I would not expect Melbourne to have much of a problem with this because it is not on the ocean.

You should remember that the first radio transmissions were from spark gap transmitters which is what all arcing sources are. They have a wide bandwidth right up into the VHF band. The way they affect the BER is that the arcing signal is going to change the data being received. Error correction can only work so far. The measurement of BER would have to be instantaneous and not average values to pick these effects up.

Impulse interference is so bad this is why the ACMA made the decision not to allocate any digital transmissions below 174 MHz. (channel 6)

I would like to reiterate that I have recommended Fracarro products on my lists and would be happy to recommend any amplifiers which have filtered inputs to the channel combinations we use.

Finally you mentioned in another post that the Fracarro Log Periodic antennas have the CAI seal of approval. This is straight from the Fracarro Website. Unfortunately the CAI is an British organisation. The UK does not use band 3 for free to air TV. The European scene is so croweded with stations that band 4-5 antennas are mostly used. In Australia we have band 3 predominating, and the ACMA has selected band 3 & 4 only for capitial cities, band 4+ for high powered regional areas (where possible) and band 5 for low powered repeaters. We can optimise the antennas required. We also have a huge country where as in Europe congestion is a big thing and long distance is not considered.

We also use mobile communications, UHF CB and pagers in the European channels 21-28 which can also cause poor BER due to interference.

We also use vertical polarisation extensively which changes antenna requirements.

So do not blindly quote other countries' experiences that should apply in Australia.

AlanH

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AlanH and DoktorDigital

What's going on here gents. Lots of advice, diagreement and yet where there's agreement you are both wrong

Firstly I smell a rat here somewhere, I cannot conceive of someone have a piece of Rohde and Schwarz equipment and making such an abysmal effort in spelling the name.

One glaring error is that the fact is on amplification is that you don't always have to have the filter before first amplifier. You two have pressed the opposing view so often either you simply have no idea what you are talking about or limit your experience to what you can get from a Dick Smith or Jaycar catalogue.

Wake up you two, if you don't know what you are talking about, keep it to yourselves.

The poor sods whose only reference is this web site just need the facts.

James

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Alanh,

Hmmm...

On overload I have mentioned this possibility in my Geographic Viewers' Posts where masthead amplifiers are only mentioned in weak signal areas. As for antenna basics this area is already covered. Measuring the signal levels to prevent overload is always a good idea. However there is nothing to stop a strong signal from local arcing from modulating a weak TV signal within the amplifier even to the point of clipping. Hence filtering.

Actually masthead amplifiers are also used in Metro areas where the signal is extremely low such as valley like areas in the CBD (sydney melbourne brisbane). However, it should be mentioned that you should ALWAYS measure the signal at each and every job. If an installer is using a portable tv to check the signal, then they are not a professional installer and should go and do something else because it just gives our specialized profession a bad name.

The technical term BEHIND could be explained by:

Imagine you have a spike or another digital carrier, which could be referenced as interference (ie: 2MHz wide/bandwidth) and at a channel power of 50dBuV with CNR of 30dB referrenced to 235MHz. The actual placement or frequency of this "interference" is at 225MHz on the terrestrial band.

Now combine this "Interference" into a signal that is received from your antenna and lets use channel 12 Digital for this example..

Now tell me how to filter this "interference" with a normal filter???

I bet you can't - and no, you do not know where the interference carrier is coming from but let's just say it is some uni student playing around with some rf gear but you cannot tell him to turn it off.

Also because this is an example, you can not answer this by saying that you will call the ACMA and ask them to terminate this interference. This example is only to help you understand the point I am trying to get across to you.

I have not been concerned about pricing provided the best result is achieved. That is a customer's choice.

actually you said in the earlier post...

Putting the filter in a separate shielded box then makes is much more expensive

so I don't understand what you are saying here???

Then...

Causes for BER to be poor.

Poor signal to carrier ratio. If the signal level through the antenna system is low and local impulse interference is high the BER will be high. If however the signal level in the antenna system is high then the local impulse noise will be a smaller proportion of the signal and will havel less effect on the BER

Actually, what causes poor BER are many things but I think you are trying to say is LOW CARRIER to NOISE, NOT Signal to Carrier (maybe you made a typo here???). But Impulse Noise and Earth/system Noise (related to physics) are two different things here. Maybe you are tired today...

But...the fact of the matter is that the smaller the Carrier To Noise Ratio (that is the smaller the Carrier in Relation to the Noise), the worst BER you will have. Remember that the CARRIER is the messenger of data to the receiver. If there is not enough data (ie: large enough carrier in relation to the noise factor) then the receiver cannot display an image.

Impulse noise is different but will have the same effect as the "Interference" as stated above.

You do not live in an area where the electricity company has many pole top fires caused by the arcing I mentioned every autumn. At one stage they lost power to a major city for more than a week! Just because you have not experienced it does not mean it does not happen. I would not expect Melbourne to have much of a problem with this because it is not on the ocean.

How do you know where I live and where I have lived in the past. In one of my earlier posts I mentioned that I lived on some islands and other countries along the coast. So why do you say that I have not experienced anything ???

And

Impulse interference is so bad this is why the ACMA made the decision not to allocate any digital transmissions below 174 MHz. (channel 6)

well, this is a subject that posess great passion for in this country. In actual fact, just by putting 7MHz carriers in the VHF band just made life all the more difficult for everyone.

NEARLY the whole world runs on 8MHz channels (and no i did not say everyone) and where digital is concerned, MOST countries have allocated them in UHF @ 8MHz.

I don't know what it is but we always have to do things the hard way here in Australia...for what reason??? God only knows...

And as far as what other countries do, I have lived in many countries (I am 45 years old) and I can tell you that there are other countries that use Band 3 for FTA TV. If you like I can provide you with links to different sites if you want to be convinced or even better, google search the stuff and you can try and prove me wrong. Good luck... However yes, the CAI have approved the LP45N Log periodic, but that doesn't mean that the LP345 will not perform in a similar manner. I believe you understand what I am saying but maybe you don't like it because I am not talking about hills or something???

Finally, I will have you know that many countries use Vertical Polarization, including Italy, so don't be so quick to quote on other countries if you do not know anything about them.

Doktor Digital

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James T Kirk,

Mate, I never said I am perfect and I am the first to admit it...

And sure, I made a typo (Rhode & Schwarz) sure I forgot the "ch" and ??? what is your point here?

Can you give a constructive REASON why you think that if it is an error that you don't ALWAYS have to put the filtering behind the first amplifier?

Give us all an example of your reason and intelligence why this is the case!

Go on, please enlighten all of us... I am eagerly awaiting your interesting and enlightening reply !

(of course you must follow the same context of what was said)

P.S. And there is no rat here. Just a very interesting debate. No hard feelings, just trying to get to the facts...

Cheers :blink:

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DoktorDigital

Smelling a rat:

I looked at the quality of your written word, very few spelling mistakes and those that are there can be attributed to typo's. Then there's "Rhoden Swartz", spelt it as if you have never seen it written before, it just doesn't gel.

It is a point of particular frustration when I am challenged to explain something that if you had any real grasp of the subject you would know when to back off. However for the purposes of assisting those others reading here the reason is as follows.

The advice to place a filter before the amplifier is general and good advice that will give significant improvement in the huge majority of cases. It is also the safest option for installers with little experience.

There are however situations where the amplifier should be used first.

Classically these are situations where there is very marginal wanted signal levels and yet C/N (carrier to noise ratio) is reasonable and at the same time some local significant signals are present. In this situation if the filter is placed before the amplifier, the filter's insertion loss eats into the already marginal signal.

By originally placing a very linear low gain (10-20dB) amplifier stage prior to the filter and careful positioning of the receive antenna, these losses are overcome and the resulting signal will present the receiver with a better C/N ratio without the intermods the uninitiated might expect. This is no theory, it's in use and delivers superior results in this application.

James

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Docktor Digital,

I have not disagreed with you about measuring signal levels, and have recommended it in posts.

As for behind see the post on about Penrith. The interfering signal can easily be removed by a filter provided it is before any non linear circuit. Ie an amplifier. Afterwards its too late.

As for separate filters, it is much easier to add the small coils and surface mount capacitors with the amplifier on the same circuit board, than house them separately and it will perform better.

You are right about carrier to noise ratio. As far as this is concerned we are saying the same thing. If the carrier to noise ratio is low the BER will be high, however if the C/N ratio is large and the BER is high it is likely to be delayed signals & interference and reflections in the cabling.

As far as RF band width is concerned all transmissions in the Americas are 6 MHz wide, in Europe VHF is 7 MHz wide and at UHF it is 8 MHz. This then requires all receivers to have 2 SAW IF filters for dual bandwidth.

Here we have the same number of channels available as in Europe but we have 56 MHz for mobile communications.

If you look at the Geographic Viewers' Forums you will find viewers receiving signals over large distances 80 km is not uncommon.

The salt story is true.

AlanH

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James, you are just trying to wind me up. What alterior motive could I possibly have behind a spelling mistake? You are taking this totally out of context and you sound like one of those ignorant so and so's who say that they've been in the industry for 40 years, and they know everything...

Yet when I ask you a very simple question to give an explanation on why the filter before the amplifier is not important, you answer it with such a rediculous example. You obviously have no idea of how RF works and you should go back to school and learn before you open your mouth or write about such silly things.

You say that you analysed all my previous posts and how the majority of the spelling is correct, yet you have failed to understand what was written and the context of the discussion.

If you had read properly, you would have understood what we were talking about and that is completely different to what you have mentioned here. And still, you have no idea what you are talking about. But I like a challenge, so I will back my comments up with fact! Not like you do

Here is why...

If you have two carriers (but each carrier is a DIFFERENT service ie: Channel A & Channel B ) on the same frequency, there is no way you can take out the un-wanted channel with the type of filtering you described.

The only way you can eliminate the unwanted channel is by positioning the antenna so that it receives the least amount of the unwanted carrier. As to what you are saying, its absolutely crap! There is no way you can filter out that channel (IF ON THE SAME FREQUENCY AS DESCRIBED ABOVE) by inserting a filter after an amplifier stage of any gain. By Amplifying the particular Channel (ie: the full 7-8MHz bandwidth where BOTH carriers are present) all you are doing is just that...AMPLIFYING BOTH CARRIERS !

Still don't believe me...ok, just set up two analogue modulators (reason for analogue is because Digital modulators are out of most people's budget) and set BOTH modulators for channel 50 (681.25MHz).

Now connect the RF output of One of the modulators to a 2 way splitter (in reverse) and connect the output (which was the input) of the 2 way splitter to your spectrum analyser and view the actual TV picture (which the modulator is obviously connected via A/V to a video source different to the second modulator).

Now without taking your eyes of the picture, connect the RF output of the SECOND modulator to the Second port of the 2 way splitter (in reverse) and turn the modulator on and see what happens to the picture now.

This is with analogue! and you can imagine what happens to the data in digital. (This of course is just an example but I believe gets the message across).

Now try and use that silly filtering example that you made before to fix the picture...I bet you cannot!

Now who looks silly?

Also, CNR, In Digital scenario, is not the most important factor. You can have a fantastic CNR and channel power but if you have an interference behind the wanted carrier, your BER will suffer.

Also CNR measurements are referenced to another frequency which has NO carrier, but just noise present.

And if you have carrier A that has a CNR of 40dB and carrier B (which is behind carrier A so to speak) which has a CNR of 25dB (if you could measure it that is - or turn off the transmitter that is transmitting carrier A), then your true CNR would be 15dB by rights.

And although BER and CNR are mathematically related, doesn't mean that if you have a good CNR you will necessarily have a good BER.

You just don't know what you are talking about and suggest you go back to school to learn RF and English and stop trying to baffle people with bulldust. Your example makes absolutely no sense whatsoever!

So if you want to continue to make a fool of yourself, keep tit for tatting... But I CHALLENGE YOU TO PROVE WHAT YOU SAY IS CORRECT! Good luck :blink: Otherwise give it a rest! :P

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AlanH...this could go on forever... :P

Just a quick one before I stop posting on this subject...

I agree with you about filtering MUST be BEFORE the amplifier so we are saying the same thing but in a different way. It's just good ol james.t.kirk that can't get his brain around the concept. Not sure he ever will :blink:

Same goes for Carrier to noise, we are saying the same thing.

And yes, in the USA is 6MHz just like Japan, all the way through all bands (of course NTSC). And Europe is 7MHz VHF and the Superband (PAL). But 8MHz in the Hyper/external Superband and UHF so no gripe with you there either.

And yes I agree that viewers are receiving channels from 80km away is also possible. I never said it wasn't. Even further with the right antenna and optimal atmospheric conditions...the ionosphere can do marvelous things with RF in the right conditions!

But, although your salt spray example could be real, it is not the reason why everyone that is near high voltage powerlines experience pixelation.

Anyway...

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DoktorDigital

Not even close my friend. Try another forum to wind people up. Knowing you cannot filter out in band interference with a filter is pretty basic. Try reading what was written and with experience over time you may learn how to describe it technically.

James

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James,

hehehehehehehehe...Very poor comeback...try telling us how to ACTUALLY filter it out rather than a meaningless reply like that... :blink:

It just shows that you are full of BS and nothing constructive to say!

Go on, I challenge you to tell all of us how to filter the second carrier WITHOUT removing the number 2 input and putting a filter AFTER the splitter or imaginary amplifier...Try to PROVE me wrong instead of just saying I don't know...I want to know how to do it because you are such a knowledgeable person...

GO ON we are all waiting :P:P:P

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DoktorDigital

I didn't come down in the last shower sonny, stop trolling and wearing out your keyboard with very long explanations of what the technically savvy can pass on in a few lines.

By the way, who were you last week before you decided to try DoktorDigital?

On the other hand, if you are genuinely unable to grasp what I have already described fully in very simple terms, then I apologise because there is little I can do for you!

James

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