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-   -   Long distance maximum reach broadcast Tv Antennas. (http://forum.tvfool.com/showthread.php?t=1907)

John Candle 21-Jul-2011 10:22 AM

Long distance maximum reach broadcast Tv Antennas.
 
Ideas and information. Maximum reach broadcaUse ash for a UHF broadcast Tv antenna. Mount a UHF Tv antenna pointedorn was. Depeind of UHF antenna , the antenna can be moveot. YES this has been done before.

GroundUrMast 22-Jul-2011 12:33 AM

10/22/2011: Sadly, JC got upset and vandalized his post... The gist of it was that one could recycle an old C-band satellite dish by replacing the microwave band feed-horn with a UHF dipole or similar element...


Original response:

I would expect a simple folded dipole or 'V' shaped whiskers located at the prime focus would be the easiest replacement for the C-Band feed-horn/LNB. Directors and reflectors not located at the prime focus would have little signal to act on.

ghz24 9-Aug-2011 7:23 AM

good use for a biquad
 
If you're looking for a good antenna to place at the focus of a large dish I'd suggest a biquad (with a reflector) because the large beamwidth will illuminate the whole dish. I've been working on a model to see what kind of gain is achievable.
Nice antennas in the links John. Ive been looking for reliable info on those tri-boomed yagis. Any other links?
BTW I'm pretty sure the wade helical antennas will actually be 3 dB lower than reported because of circular vs horizontal polarization unless you happen to be near one of the very few circular transmitting stations. But wow 24 - 3 = 21 that's still very large gain.
I wonder how flat the gain vs freq. graph is ( they always report gain at the best channel.

Dexter702 23-Aug-2011 10:23 PM

Can you get decent reception with an indoor antenna or am I going to have to get an outdoor to get consistent signal? I'm tired of paying ridiculous rates to my local cable provider and with Netflix and Hulu, I really don't want that much cable. Mainly I just want to keep my local channels for news, etc. I looked through the antenna reviews here but it is all kind of greek to me. Any suggestions on what I should buy?

ghz24 17-Nov-2011 1:53 PM

you'll get more help if
 
hi Dexter702
This is a discussion of deep fringe antennas to get help with reception or antenna selection start a new thread here
http://forum.tvfool.com/forumdisplay.php?f=7
you should include a link to your TV fool report
to get that start here http://www.tvfool.com/index.php?opti...pper&Itemid=29

ghz24 18-Nov-2011 8:10 AM

broadcast antennas I missed that
 
Maybe that's why JC got upset. This thread is supposed to be for broadcast antennas ? I didn't intend to hijack the thread (but if/since It's abandoned I will pick it up).
But I don't think that's it. Because I don't think the antennas he posted links to are broadcast antennas ( don't they use 50 ohm antennas for transmission ? ) and they were directional (as is a recycled c band sat dish)
I see he removed the links to the high gain wade antennas so I'll put those back cuz I think they should be here.

http://www.wade-antenna.com/Wade/WH14-51.pdf
http://www.wade-antenna.com/Wade/CSeries.pdf
http://www.wade-antenna.com/Wade/VHFLow.htm

There I'm pretty sure those were the ones he originally posted

BTW I've nearly completed modeling a 2 meter dish
I'll post a link to the model and a performance page. But here is a quick
overview across channels 14-52
Code:

Total gain (dBi)              Net gain (dBi)              SWR
max        19.28                max        19.1431516122      max 2.0347958365
min        17.24                min        16.9662580763      min 1.2860276345
                                       
Average Total        18.4936842105 (dBi) 
               
Average Net        18.2217478081 (dBi) 

Average SWR    1.6396934694


ghz24 18-Nov-2011 8:22 PM

2 meter dish
 
Here are the specs on the 2 meter dish and here's the model.
The finco p-5 and p-7 had a folded dipole driven three element yagi
(the p-7 had more directors I think) much like what john described
in his now mutilated post. Next I'll post a page on the p-5.
Then I'll try replacing the biquad on this model with the feed from a p-5.
I was actually hoping for more gain from this large of an antenna. I've seen
8bay whisker antennas that do almost this good with less wind area.

GroundUrMast 19-Nov-2011 12:21 AM

@ ghz24, I'm confident that your contribution and Dexter702's question are not the reason for anyone choosing to behave unprofessionally. Certainly, neither would justify such immature behavior.

Your modeling contributions and professional tone are quite welcome... IMO.

GroundUrMast 19-Nov-2011 11:50 PM

Quote:

Originally Posted by ghz24 (Post 13801)
Here are the specs on the 2 meter dish and here's the model.
The finco p-5 and p-7 had a folded dipole driven three element yagi
(the p-7 had more directors I think) much like what john described
in his now mutilated post. Next I'll post a page on the p-5.
Then I'll try replacing the biquad on this model with the feed from a p-5.
I was actually hoping for more gain from this large of an antenna. I've seen
8bay whisker antennas that do almost this good with less wind area.

It's been my experience that the parabolic really comes into it's prime as you enter the GHz+ region, At sub-GHz frequencies it's easier to build high aperture antennas in panel, curtain and Yagi forms. Your efforts reaffirm that notion. However, if very narrow beam-width is needed, the parabolic would still be worth considering.

ghz24 20-Nov-2011 3:29 AM

oops
 
I guess the antenna I thought had a folded dipole feed wasn't a finco but an antenna craft. maybe.

ghz24 20-Nov-2011 7:10 AM

still one the best antennas
 
Quote:

At sub-GHz frequencies it's easier to build high aperture antennas in panel, curtain and Yagi forms
That is true, but I do think a
parabolic has some qualities (over an 8 bay or similar antenna) that aren't
readily noticeable. Such as I think a parabola is more tolerant of hot/dead
spots than an 8 bay. If the 8 bay is half in a hot spot and half in a dead spot
the ~4 elements in the dead spot are parasitic and actually transmit some
of the signal back in to space (beyond the normal reflection of SWR).
Where if half the parabola is in a hot spot more of that signal is trapped
and loses less signal to the dead spot (IMHO)
This page explains the effect better than I can
http://www.hdtvprimer.com/ANTENNAS/16bay.html
under "Why this 16-bay antenna might not work".
Also SWR is very good compared to 8 bays I've seen models of
(SWR >3 near the ends of the band)
yagis rarely have flat response across uhf and curtains are pretty narrow band.
Opposing opinions welcomed

GroundUrMast 3-Dec-2011 12:46 AM

Quote:

...Also SWR is very good compared to 8 bays I've seen models of
(SWR >3 near the ends of the band)...
As I have started to work with 4NEC2 modeling software, I've seen how bandwidth narrows (ie. SWR increases more quickly as you move away from Fc) when more tuned elements are used in an antenna design. With a panel antenna, all the elements are of a common length so a sharper 'cut off' seems intuitive to me, just like a filter network. However, The GH designs demonstrate that a complex, moderate to high gain broadband solution can be produced. Presumably, the NARODs detune the 'filter' effect of the primary active elements.

I agree that for DIY dish project, a relatively simple, compact active element at the focal point of the dish would be compellingly practical.

No disagreement here... Ken Nist's work at hdtvprimer is appreciated.

ghz24 16-Jan-2012 3:02 AM

very E-Z parabola reflector
 
Built about 20 comparable models (different shapes and feeds but similar sized) and have found an lpda feed that makes a great feed for a parabola.
It won the gain and swr contest for all shapes I tested.

Quote:

At sub-GHz frequencies it's easier to build high aperture antennas in panel, curtain and Yagi forms
Not for long I have models that are very competitive with the best panels out there and they are easy to build you can follow the progress starting about here http://www.digitalhome.ca/forum/show...=96216&page=21

It is a work in progress

Alan909 22-Mar-2013 12:21 PM

What is a "LPDA FEED" ???

GroundUrMast 22-Mar-2013 6:41 PM

Log Periodic Dipole Array

Example, http://www.arcticpeak.com/antennapages/LPDA.htm

Alan909 23-Mar-2013 6:02 PM

Interesting, so I take it the LPDA Feed would work well with an old 7 ft parabolic c band dish if positioned properly???

ghz24 26-Mar-2013 8:08 AM

Hi Alan909,
Sorry so slow to respond had to review my data, I've been working on other projects.
Yes I would advise using the lpda to feed any center feed dish (not offset).
The lpda I used had a very high tolerance to focal point errors ,on most models there is a foot or more of "play" with very little change in gain or SWR in the ~470-695 MHz range.
It also exhibited a good SWR even when coupled to imperfect or even quasi-parabolic dishes.
I've yet to find a feed that gives better gain (on any dish).

One of its "weaknesses" is its pattern is taller than wider vs the biquads nearly perfect balloon shape.
So one could design a low wide dish that would favor the biquad some.

The model linked to above was an early model with lots of close horizontal wires (slow to run) it got 17.36 dBi net gain @ 521 MHZ with the biquad feed.
I made it 2 meters for convenience so 6.5 feet is a little less than your 7ft, but even wades 8 foot parabola only approaches the 20 dBi goal @ 521.
20 dBi is a pretty tall order at the lower frequencies.

I had never bothered to go back and put the lpda in front of that particular model (until last night) the lpda driven model gets 18.23 dbi net @ 521 MHz
You may be able to squeeze out that last 1.75 dB but...
If I remember right the first dish I saw get 20+ dBi that low was a 6 foot wide by 9 foot high square dish simplified to 12 flat panels.

The lpda I used was shamelessly borrowed from the 3rd post here with pretty complete assembly directions here

Stereocraig 26-Mar-2013 5:26 PM

So, when designing a quasi parabola like the Kathrein Scala, it it important to keep the H dimension proportional to the V dimension, or is it even critical past a certain width?

Example being: If I want to go 10' tall, can I keep the 3' width, or would I need to increase it to about 5'?

ghz24 27-Mar-2013 9:52 PM

Scalas don't scale well
 
I set aside the scala (like) models temporarily due to strange (and interesting) results. I built them as an intermediate step to the chevron type due to the tendency to beam split/spread above a certain width. I had a dusty 10 foot tall model sitting forgotten in my parabolas folder (I don't remember what focal point was ) I polished it up to find the answer you asked.
According to how the models optimized.
All figures are in dBi of raw gain @ MHz.
Your 10 foot high example can get 19.46 @585 and 16.82 @ 470 (reflector width 49.524 in.) and also could get 18.25 @ 470 if the reflector width is extended to 61 in. if you go with the 61 in. reflector gain @ 585 drops to 18.89 and 17.48 @695.
A 6.5 foot model I had from the comparisons optimizes @ 585 to a reflector width of 46.728 in. (gain of 17.42)
It seams that optimum width depends mostly on the frequency.
Selecting a different focal point when you build the reflector could alter these results some but the general tendencies should still apply.
As you push the reflector width to the extreme, beam width increases but gain stays mostly constant at about 3 dB down from max gain..

Stereocraig 27-Mar-2013 11:39 PM

Thanks, GHZ24.
Just playing around at this point.

Interesting to know though, that the focal point offers so much leeway.


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