[balm]

There are so many threads, but i would like to know what VHF-Hi only antenna, specifically #13, would give the maximum gain, commercial or DIY


the antenna chart mentions wade WL-7-13, winegard YA-17-13, antennacraft Y10-7-13,

and in the smaller ones, antennas direct C5, antennacraft Y5-7-13

how do these compare to VHF-Hi gain on the larger combo antennas, and GH w/ NARODS models?

so far my DIY #13 YAGI designed for 13 dbi didnt help me, so i was thinking of stacking 2 of them or 2 of the commercial antennas?

 

[hkaye]

A custom yagi for channel 13 will do better than a broadband antenna designed for channels 7-13.

What's your tvfool?

Here is an article on stagger stacking that might be useful -

http://www.anarc.org/wtfda/stagger.pdf

You can do a google search on stagger stacking for more information. This will only work on one specific channel. Stagger stacking will increase gain but also eliminate multipath or ghosting for that channel.

 

[balm]

thanks hkaye,

guess im out of luck then, as so far a single yagi (7 elements, 94") would barely offer any movement on my signal meter, and thats with the Kitztezh amp....im assuming because its a 2nd edge channel, and probably much weaker than the 3 db NM TVFool indicates...also the higher I go the weaker the channels get

i think the longer the Yagi the more complex the stacking gets, especially using the schedule40 pvc as boom...mine was built quite precisely, using 1.25" boom PVC with all #10 copper wire elements (model from "Yagi Calculator")

TVFool:

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d9fbe3eeb0522d1

 

[hkaye]

According to your tvfool you have another ch #13 almost 180 degrees in the opposite direction. I'm assuming you are trying to get WVNY. Can you get CJOH or atleast the audio of CJOH when you point the antenna at CJOH?

WVNY RF13 (22.1) @ -87.4db  118º
CJOH RF13 Analog @ -76.5db  291º

Looking at the power level rather than the NM in the tvfool chart and you'll see the analog station is actually stronger at your location by 10db. Noise Margins are calculated differently for analog stations than digital stations.

I would say that co-channel interference is your biggest problem and you'll need to get an antenna with a high f/b ratio to reject the CJOH signal. Your custom yagi with just one reflector might not be enough - a bigger reflector or more reflectors rods are probably required. Or stagger stacking two yagis to cancel out the other station.

But first I would use the tvfool interactive tools if you haven't already. Select the option to draw lines to the transmitters. Using Google satelite view follow the path to the transmitter and make sure there are no obstructions such as buildings in the way from your house to the transmitter. Follow the line carefully to WVNY for about 3km and do the same for CJOH. If there are more obstruction to WVNY than it just will get harder if not impossible to get that station.

 

[balm]

thanks hkaye, very informative,

i did not know about the power level relative to analogs....i never checked the reception of #13 analog with this antenna, and now unfortunately i dismantled the yagi, as it was constructed to "flimsy", ill try another one, but would like to avoid stacking as i dont have much room

what kind of reflector do you mean exactly, just add more reflector rods in the vertical plane, or like a screen behind the dipole...

ill check that on google earth, thanks

 

[hkaye]

The purpose of a better reflector would be to block signals coming from the reverse direction. For example, my tvfool indicates two stations at RF40-

CFTO RF40 (9.1)  @-89.4db 77º
CBLN RF40 analog @-77.5db 232º

Almost similar to your situation with an analog station with more strength opposite to the digital one I want to receive. Fortunately for me I live in a apartment building and the concrete walls of the building block the analog station so it doesn't interfere with the digital one I'm trying to receive.

If you have a big chimney or wall you could use to block the analog that might work also.

I haven't modeled any VHF antennas, but I do know when modeling UHF antennas that a screen reflector for my UHF antennas were too small and VHF signals would pass through them no problem. I'll try a couple of VHF models to see what it would take for a reflector to block the signals from the opposite direction.

 

[holl_ands]

F/B and F/R Ratio specs for Commercial Hi-VHF antennas are only so-so (dBi = dBd + 2.15 dB):
W-G HD-7082P, F/B Ratio > 20 dB on Ch13 with 12.2 dBi Gain (111-in boom)
W-G HD-7080P, F/B Ratio > 18 dB on Ch13 with 13.2 dBi Gain (90-in boom)
W-G HD-8200U, F/B Ratio = 18 dB on Ch13 with 14.2 dBi Gain (168-in boom)
W-G HD-7084P, F/B Ratio = 17 dB on Ch13 with 13.0 dBi Gain (131-in boom)
W-G HD-5030, F/B Ratio = 15 dB on Ch13 with 10.3 dBi Gain (120-in boom)
W-G YA-1713, F/B Ratio = 14 dB on Ch13 with 12.5 dBi Gain (100-in boom)
W-G HD-769xP, F/B Ratio = 14 dB on Ch13 (for any size in the series)
Antennacraft Y10-7-13, F/B Ratio = 16.5 dBi with 11.6 dBi Gain in Hi-VHF band "somewhere" (120-in boom)
Unfortunately, most of the other manufacturers don't bother providing specs anymore.....

Pricey Professional Hi-VHF antennas are quite a bit better:
Wade WL7-13/S, F/B Ratio > 25 dB with 11.5 dBi Gain (96-in boom)

I modeled and compared several DIY Hi-VHF Antennas here:
http://imageevent.com/holl_ands/yagis
Comparison charts are included in K6STI results:
http://imageevent.com/holl_ands/yagis/k6sti

DIY K6STI's 5-ELEMENT YAGI:
Optimized for best F/R Ratio on Ch7-13, and has a F/B Ratio that is even higher than
the charted F/R Ratio (see chart below).
Shrinking all sizes by a factor of about 0.94 (seat of pants guestimate, not modeled)
would move the F/R Ratio peak so that it falls on top of Ch13.

DIY 13-ELEMENT YAGI WITH 2 REFLECTORS: User <kgb> posted a UHF Yagi design, which
has been rescaled for Ch13. However, I was unimpressed by either Gain or F/B numbers:
http://imageevent.com/holl_ands/yagis/hivhf13elyagikgb
Perhaps it needs an additional Reflector between the other two to improve F/B Ratio......

DIY ZS6BTE's 14-ELEMENT LPDA:
Exhibited an even higher F/B Ratio (equal to F/R Ratio) on Ch13:
http://imageevent.com/holl_ands/zigzaglpa/lpda/lpda14el

My DIY WEDGE ZIG-ZAG LPDA:
Simple DIY design for attic use also had high F/B and F/R Ratios:
http://imageevent.com/holl_ands/zigzaglpa/zigzagnoboom

STAGGER STACKING:
Can null out an undesired channel when it is in nearly the opposite direction
as the desired direction....which is the case for your two Ch13 stations:
http://www.tesc.com.au/stagger.htm
http://www.anarc.org/wtfda/stagger.pdf
http://www.simplicitytool.com/PDFs/Old Sitco/VHF_end_mount_stagger_stack.pdf
I haven't seen any good numbers on how effective this is.
It would be a simple, interesting project for 4nec2 modeling.....

 

[balm]

can you tell me why this model i( the one i built) isnt giving the designed (as per YAGI CALCULATOR) 13 dbi...

CE
GW	1	9	0.311	0.3165	-0.025	0.311	0.02	-0.025	1.29e-3
GW	2	11	0.417	0.32	0	0.417	0	0	1.29e-3
GW	3	11	0.67	0.3175	0	0.67	0	0	1.29e-3
GW	4	11	0.973	0.315	0	0.973	0	0	1.29e-3
GW	5	11	1.325	0.3125	0	1.325	0	0	1.29e-3
GW	6	11	1.719	0.3105	0	1.719	0	0	1.29e-3
GW	7	11	2.141	0.308	0	2.141	0	0	1.29e-3
GW	8	11	2.585	0.3065	0	2.585	0	0	1.29e-3
GW	9	9	0.311	-0.3165	-0.025	0.311	-0.02	-0.025	1.29e-3
GW	10	11	0.417	-0.32	0	0.417	0	0	1.29e-3
GW	11	11	0.67	-0.3175	0	0.67	0	0	1.29e-3
GW	12	11	0.973	-0.315	0	0.973	0	0	1.29e-3
GW	13	11	1.325	-0.3125	0	1.325	0	0	1.29e-3
GW	14	11	1.719	-0.3105	0	1.719	0	0	1.29e-3
GW	15	11	2.141	-0.308	0	2.141	0	0	1.29e-3
GW	16	11	2.585	-0.3065	0	2.585	0	0	1.29e-3
GW	17	11	0.03	0.345	0	0.03	0	0	1.29e-3
GW	18	11	0.03	0	0	0.03	-0.345	0	1.29e-3
GW	19	19	0.311	-0.3165	0.025	0.311	0.3165	0.025	1.29e-3
GW	20	1	0.311	0.3165	0.025	0.311	0.34	0.0125	1.29e-3
GW	21	1	0.311	0.3165	-0.025	0.311	0.34	-0.0125	1.29e-3
GW	22	1	0.311	0.34	0.0125	0.311	0.34	-0.0125	1.29e-3
GW	23	1	0.311	-0.3165	0.025	0.311	-0.34	0.0125	1.29e-3
GW	24	1	0.311	-0.3165	-0.025	0.311	-0.34	-0.0125	1.29e-3
GW	25	1	0.311	-0.34	0.0125	0.311	-0.34	-0.0125	1.29e-3
GE	0
EK
LD	5	0	0	0	5.8e7	0
EX	0	19	10	0	1	0
GN	-1
FR	0	1	0	0	213	0
RP 0 1 73 1511 90 0 1 5

 

[hkaye]

Unfortunately the software I use to model doesn't seem to be able to run card decks from other programs.

 

[300ohm]

(as per YAGI CALCULATOR)

Which Yagi Calculator, K7MEMs or the stand alone desktop Yagi Calculator ?

 

[balm]

300ohm,

the standalone calculator gives me 13 dbi (i assume this is RAW)

My nec file gives me 5 dbi, SWR =130...


im not sure where the modeling error is, the element dimensions are identical to those used in the calculator...

 

[300ohm]

Yeah, thats what I get too. Will have to investigate further.

 

[holl_ands]

Balm: In the Yagi above, the Simulated SOURCE is in the middle of the top element on the
Folded Dipole....which would be OK if you closed the GAP on the BOTTOM.

Alternatively, maybe you wanted to use a Simulated SOURCE wire to close the BOTTOM Gap????

 

[300ohm]

Heh, yeah.

Try this:

CE
GW	1	9	12.244094	12.46063	-0.984252	12.244094	0.7874016	-0.984252	0.0507874
GW	2	11	16.4173228	12.5984252	0	16.4173228	0	0	0.0507874
GW	3	11	26.3779528	12.5	0	26.3779528	0	0	0.0507874
GW	4	11	38.3070866	12.4015748	0	38.3070866	0	0	0.0507874
GW	5	11	52.1653543	12.3031496	0	52.1653543	0	0	0.0507874
GW	6	11	67.6771654	12.2244094	0	67.6771654	0	0	0.0507874
GW	7	11	84.2913386	12.1259843	0	84.2913386	0	0	0.0507874
GW	8	11	101.771654	12.0669291	0	101.771654	0	0	0.0507874
GW	9	9	12.244094	-12.46063	-0.984252	12.244094	-0.787402	-0.984252	0.0507874
GW	10	11	16.4173228	-12.598425	0	16.4173228	0	0	0.0507874
GW	11	11	26.3779528	-12.5	0	26.3779528	0	0	0.0507874
GW	12	11	38.3070866	-12.401575	0	38.3070866	0	0	0.0507874
GW	13	11	52.1653543	-12.30315	0	52.1653543	0	0	0.0507874
GW	14	11	67.6771654	-12.224409	0	67.6771654	0	0	0.0507874
GW	15	11	84.2913386	-12.125984	0	84.2913386	0	0	0.0507874
GW	16	11	101.771654	-12.066929	0	101.771654	0	0	0.0507874
GW	17	11	1.18110236	13.5826772	0	1.18110236	0	0	0.0507874
GW	18	11	1.18110236	0	0	1.18110236	-13.582677	0	0.0507874
GW	19	19	12.244094	-12.46063	0.984252	12.244094	12.46063	0.984252	0.0507874
GW	20	1	12.244094	12.46063	0.984252	12.244094	13.385827	0.492126	0.0507874
GW	21	1	12.244094	12.46063	-0.984252	12.244094	13.385827	-0.492126	0.0507874
GW	22	1	12.244094	13.385827	0.492126	12.244094	13.385827	-0.492126	0.0507874
GW	23	1	12.244094	-12.46063	0.984252	12.244094	-13.38583	0.492126	0.0507874
GW	24	1	12.244094	-12.46063	-0.984252	12.244094	-13.38583	-0.492126	0.0507874
GW	25	1	12.244094	-13.38583	0.492126	12.244094	-13.38583	-0.492126	0.0507874
GW	26	3	12.244094	-0.787402	-0.984252	12.244094	0.7874016	-0.984252	0.048
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	5.8e7	0
EX	0	26	2	0	1	0
GN	-1
FR	0	1	0	0	213	0
RP 0 1 73 1511 90 0 1 5

 

[balm]

good, thanks for catching that!

with regards to the AD C5, has anyone tried modeling it and optimizing it for a single channel...

 

[300ohm]

Yeah, I did a 24" holl_ands loop with a mesh reflector behind it, and it comes very close to the the AD C5. Its wide band, but the gain is only about 7 to 8 dbi. Optimizing a loop for a single channel isnt going to do much, as a loop is naturally wide band.

 

[holl_ands]

Didn't modeled the AD C5 exactly, but did model a Dual Loop as well as a Loop with a Screen Reflector:
http://imageevent.com/holl_ands/loops/looprefl
Loop/Screen appears to be close to optimum for Ch13 without mods:
On Ch13, Raw Gain is 7.9 dBi with F/B=F/R=15 dB (a much bigger Reflector might help a bit.....)

That 9-Element Yagi with a Folded Dipole looks like a typical (so-so) K7MEM design:
On Ch13, Raw Gain is about 13.4 dBi with F/B and F/R about 14 dB (+/- 1 dB).

You also might want to consider whether adjacent Ch12 is degrading reception and whether
an antenna sidelobe null is available to suppress Ch12 while maintaining good gain on Ch13.
TVFool signal level predictions don't indicate that this would be a problem (Analog can be
tolerated at more than 40 dB higher levels than Digital), but the power levels might not be
correct and/or the propagation loss to your location might be different due to terrain factors.
Also, some tuners have much less tolerance to adjacent channel interference than others.....

 

[balm]

thanks for those suggestions,

re. #12, i might just try usng a #13 CM "Jointnna" ,do yo think that might be appropriate formy intended use

is there room for optimization specifically on #13 (especially gain) with the 5 element swept dipole yagi

wrt f/b ratio, i always thought so long as there was virtually 0 or less gain on the back, that was sufficent for most situations...the 9 elemet yagi i believe gives a 14 bi f/b ratio, does a higher f/b ratio actually help that much more in my case

 

[300ohm]

i always thought so long as there was virtually 0 or less gain on the back, that was sufficent for most situations..

With strong enough signals, you can get stations with a very high negative gain antenna, like a paper clip, heh.

 

[balm]

has this fracarro been modeled here and optimized for a single channel yet, i assume its too large for practical purposes...

http://www.fracarro.com/international/download/prodottitvsat/Aerials/BAND_III_wideband_BLV.pdf