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post #1 of 21 (permalink) Old 2018-01-02, 01:13 AM Thread Starter
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Newbie FF4

After lurking on the forums for a while, I decided to try my hand at building an antenna. I knew that it would need to be a strong antenna due to my TVFOOL report (note that this report is from before the recent database issues): http://www.tvfool.com/?option=com_wr...e6a4a418000073

The nice thing about my location is that all the good TV stations are located in pretty well straight lines away from my location. And there are very few vhf stations to try to reach. I still haven't decided if I really want to try to get them.

First antenna I made was a stealth hawk from Nikiml website. It worked ok for how simple it was. It received channel 41 (virtual 27) well. I paired it with the infamous RCA TVPRAMP1Z pre-amp that I got for $15 off Amazon and was able to get channel 36 (virtual 33) as well. Needless to say, that isn't really doing great as far as having lots of stations, even though both channels have 3 stations each.

So I built the GH0 from the Nikiml website out of 6-gauge copper wire and a 2x10. That was before I knew that would doesn't do well for antennas. I just made the base model and it did fine. I could receive channel 20 (virtual 21) with it. These results were achieved inside the house, as I was too lazy to run the coax outside.

Well, next I tried a yagi from the same site and got the same channels, so I decided to read some more.

After quite a bit of reading, I decided to make the FF4 antenna attached. It is based on the new version that holl_ands posted a little while ago. I kinda cheated with the reflector, as it is 4 feet by 4 feet piece of 2 inch by 4 inch fencing wire leftover from a fencing project, so it is way oversized, but I figured it couldn't hurt. The bowties are made from 6 gauge copper wire and the phase lines are 8 gauge copper wire. The bowties are probably a little shorter than the dimensions call for, and I probably made a few mistakes, but the results indoors so far have been encouraging.

I now get channel 33 (virtual 11) and channel 25 (virtual 2) in addition to channels 41, 36, and 20. Of course analog channel 29 has always come in, despite being in the complete opposite direction of where the antenna is pointed. Channel 45 was picked up by the scanner but would not play. This all was picked up inside my house, which has cement walls, pointed toward trees. I figure once I put it on the roof I shall get much much better results.

Now I know that the new FF4 drops it's gain off for the higher channels and that will hinder me from seeing much farther with that design, even though it still has decent gain up there. I would like to receive WPGH channel 43 (virtual 53) if possible (should be from what I have read), so I may make another antenna yet. Or maybe I will get lucky and be able to pick it up once mounted on the roof.

One question I have is, should I get a stronger pre-amp? I was thinking the KT-500 would be perfect for my location, seeing as none of my stations have a strong signal, so there should not be any overload troubles. However, I would like to thank everyone on this forum who has shared so much knowledge that has gotten me this far. I find it very enjoyable trying to make something like this that can actually work.
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post #2 of 21 (permalink) Old 2018-01-02, 02:57 AM
 
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Quote:
stronger pre-amp?
when gain of 1st stage is >10 dB, than noise factor of receiver is equal to noise factor of 1st stage

going to 20 or 30 dB do not decrease receiver noise factor, hence do not increase SNR at demodulator stage.

20+ dB gain preamp is needed for long coax line and to split signal on splitters

Last edited by Yurii Pylypenko; 2018-01-02 at 03:52 AM.
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post #3 of 21 (permalink) Old 2018-01-02, 12:07 PM
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Welcome to the forum, DoubleYou

Thanks for the photo and the earlier more accurate report. WYTV ABC real channel 36, virtual channel 33.1, seems to be missing from the new database report. (It is the custom to use the decimal form for virtual channel numbers to avoid confusion with the real channel numbers; stick with callsign and real channel number.)

If I have estimated your location close enough, this would be the current less accurate report:
TV Fool

I think you are doing quite well with you indoor antenna, but it should do much better outside. The trees will be a problem even if the antenna is outside.
Quote:
One question I have is, should I get a stronger pre-amp? I was thinking the KT-500 would be perfect for my location, seeing as none of my stations have a strong signal, so there should not be any overload troubles.
More preamp gain is not primary. The preamp can only amplify what is coming out of the antenna terminals. If the signal has a poor SNR, then the preamp will make it stronger but with a worse SNR because the Noise Figure of the preamp is added; GIGO. First comes putting the antenna where there is a good signal and using an antenna with enough gain. Only antenna gain can improve the SNR above the minimum required 15 dB; a preamp can't do it.
Quote:
I would like to receive WPGH channel 43 (virtual 53) if possible (should be from what I have read)
WPGH will require extra effort to capture, but I think it will be possible.

I see that WPGH Fox is also missing from a current TVFool report. Rabbitears.info says it will be moving to channel 20:
http://www.rabbitears.info/market.ph...&callsign=wpgh

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2018-01-02 at 03:22 PM.
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post #4 of 21 (permalink) Old 2018-01-02, 01:32 PM
 
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Quote:
If the signal has a poor SNR, then the preamp will make it stronger but with a worse SNR because the Noise Figure of the preamp is added;
it is not added, it is replaced by Nf ratio of LNA

Noise factor of multi-cascade receiver is a sum of 1st stage Nf plus 2nd stage Nf divided by 1st Gain and so on.
When gain of 1st stage is >10 dB, Ftotal =~ F1.


Typically LNA has Nf<2 dB, DVB-T2 tuners have Nf=4-5 dB
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post #5 of 21 (permalink) Old 2018-01-02, 02:03 PM
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The preamp NF is still added to the signal from the antenna which reduces the SNR of the signal, but the Total System Noise Figure is reduced because the tuner NF is buried in the amplified Noise Floor making it irrelevant and the distribution losses do less harm because they are after the preamp (they are a later term in the formula).

It is often called a trade, but it is actually a net gain in SNR because the System Noise Figure is reduced.

Here you can see that the antenna gain must make the SNR >15 dB + the preamp NF before the preamp can amplify the signal:





QED

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2018-01-02 at 02:41 PM.
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post #6 of 21 (permalink) Old 2018-01-02, 02:49 PM
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In the diagram in my previous post, you can see why antenna gain is more important than preamp gain. The antenna gain must make the signal strong enough to have an SNR of at least 15 dB, plus a little more gain to exceed the NF of the preamp before it can amplify the signal.

If you can not measure it, you can not improve it.
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post #7 of 21 (permalink) Old 2018-01-02, 03:39 PM
 
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LNA gain is not important at all, if it is >10 dB + coax cable loss.

LNA with 13 dB Gain and Nf=2 dB is better than LNA with 26 dB Gain and Nf=3
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post #8 of 21 (permalink) Old 2018-01-02, 05:51 PM
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Quote:
Originally Posted by Yurii Pylypenko View Post
LNA gain is not important at all, if it is >10 dB + coax cable loss.
Yes, that is correct. I agree if you mean coax cable loss after the LNA, but coax cable loss before the LNA, the balun loss, and the LNA NF directly subtract from antenna gain.

In the above diagram, using a balun with less loss and an LNA with a lower NF will reduce the System Noise Figure, making it possible to receive weaker signals if your ambient local noise floor is low.


If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2018-01-02 at 07:05 PM.
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post #9 of 21 (permalink) Old 2018-01-02, 07:42 PM
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DoubleYou

Here is the terrain profile for WPGH by TVFool. You will note that only 497 kW of 1000 kW ERP is sent in your direction because of the directional pattern of the WPGH transmitting antenna:

TV Fool

This is an extracted image from the above link:



This is another terrain profile for WPGH using different software:


If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2018-01-02 at 09:22 PM.
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post #10 of 21 (permalink) Old 2018-01-02, 07:49 PM
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The "New" FF4 appears to be the latest one I Re-Optimized for NEW UHF Band (470-608 MHz)....which turns out to use a FLAT Reflector Screen....which by DESIGN has significant Roll-Off above 608 MHz....it will come into it's own when Ch38+ are vacated...in early 2019 or perhaps earlier, depending on your location:
https://imageevent.com/holl_ands/mul...yscreenreflopt

Compare to the two FF4 versions (Standard and TALL) Optimized for Current UHF Band (479-698 MHz), where the TALL version has significantly higher Gain on the Upper Channels and employ Double Angle Reflector Screens:
https://imageevent.com/holl_ands/mul...dblanglreflopt

Note that each of these three versions uses a DIFFERENT set of Optimized Bow Tie Dimensions for Whisker Length and Bay-to-Bay Separation.....

Since there is ON THE AVERAGE about 13 dB +/- 7 dB Gain improvement moving from Indoors to Roof Mounted Location, you should TRY THAT before spending more $$$'s on a different Preamp that can only provide very limited improvement.

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #11 of 21 (permalink) Old 2018-01-02, 08:47 PM Thread Starter
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So, I gather from what you have said:

1. Put it on the roof
2. Don't worry about the pre-amp
3. The FF4 I made may not be the best at the moment to receive some of the stations that I could be receiving, like WPGH.


So I will mount it on the roof and report back later.
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post #12 of 21 (permalink) Old 2018-01-02, 11:16 PM
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I usually use the TVFool coverage maps, but the map for WPGH isn't available because of the defective database. The FCC Longley-Rice coverage map shows that Hemitage PA is outside the coverage area for WPGH:



This is a closeup of the coverage. To protect your identity, I have not marked your location. Red is the weakest listed signal strength; no color is weaker. You are on the edge of red:



Link for coverage map:
http://www.rabbitears.info/contour.p...=1516786&map=Y

Good luck with your project. Please let us know how it comes out on this same thread.

Best regards,
rabbit

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2018-01-02 at 11:44 PM.
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post #13 of 21 (permalink) Old 2018-01-03, 12:37 AM Thread Starter
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Thanks for the map. I still will try to get it, but we will see. I see as it goes up the hill from my place that it turns to yellow, hard indoor, so I think I might still have a shot if I can get it high enough. Might have to build an antenna with higher gain on channel 43.
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post #14 of 21 (permalink) Old 2018-01-03, 04:27 AM
 
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Zero margin (28 microVolt @ 12 dBi antenna) is at 335m above sea level. 340m is +4 dB
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post #15 of 21 (permalink) Old 2018-01-03, 04:50 PM
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Thank you for the interesting profile, Yurii.


If you can not measure it, you can not improve it.
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