[wire_in_the_sky]

My Build

I built the Channel 7 10-element Yagi yesterday using a design from the VK5JDJ tool.

Another program you may like to use for a folded dipole Yagi calculation is Yagi Calculator from VK5DJ http://www.vk5dj.com/yagi.html
(I note that he just updated it in February with more features)
With it I get a folded dipole inside bend measurement of 820mm for 6.5mm material for 178 mhz.

There was no discernable difference in performance between the Yagi and my GH10n3 (as per Nikiml) for the target channel 7 station (WBBZ). And I lost CHCH, RF11. Hence, I did not proceed to install the Yagi and instead dismantled it. The Yagi was a remarkably inexpensive and easy build. I used a 12 foot 2x4 as a boom (cost $4.14), eight of the 10 elements were build from scrap from previous builds and then sat it on top of two concrete blocks on a flat roof. Hence, when the performance did not live up to expectations, I put it down to learning. I did however take the opportunity to tune up my one-year old GH10n3 and it is now performing as well as it ever has.

 

[300ohm]

There was no discernable difference in performance between the Yagi and my GH10n3 (as per Nikiml) for the target channel 7 station (WBBZ).

If the signal was there, you would have noticed the 4.2 dbi improvement, but obviously it just wasn't there.
It sounds like a heat fade issue, since summertime reception is more common.

 

[wire_in_the_sky]

At the time of the test, the signal was there - it was just below the lock level ("Channel Unavailable" on a Sony) as opposed to "No signal". The difference could be that at the test location, the Yagi was 10 feet lower in elevation than the GH10n3. - I wouldn't have thought that 10 feet would account for a 4.2 dBi difference.

 

[300ohm]

I wouldn't have thought that 10 feet would account for a 4.2 dBi difference.

For uhf fading, a difference of 10 inches can make a difference. Look here under Fading :
http://www.hdtvprimer.com/ANTENNAS/glossaryA.html#fading

 

[kgb]

HI VHF Yagi

CM 14 element HI VHF Yagi 	
CM 
CM 
CM 
CM 
CM 
CE
GW	1	9	0.378	-.308	-0.075	0.378	.308	-0.075	.01	'Wire 1, 9 segments, halve wavelength long.
GW	2	9	.378	-.308	0	0.378	.308	0	0.01
GW	3	1	0.378	-.345	-0.0375	.378	-.336	-0.015	0.01
GW	4	1	0.378	-.336	-0.015	0.378	-.308	0	0.01
GW	5	1	0.378	-.345	-0.0375	0.378	-.336	-0.06	0.01
GW	6	1	0.378	.345	-0.0375	.378	.336	-0.015	0.01
GW	7	1	0.378	-.336	-0.06	0.378	-.308	-0.075	0.01
GW	8	1	0.378	.336	-0.06	0.378	.308	-0.075	0.01
GW	9	9	0	-.4135	0	0	.4135	0	0.01
GW	10	9	0	-.4135	0.204	0	.4135	0.204	0.01
GW	11	9	0	-.4135	-0.204	0	.4135	-0.204	0.01
GW	12	9	0.470	-0.294	0	0.470	.294	0	0.01
GW	13	9	0.775	-.2975	0	0.775	.2975	0	0.01
GW	14	9	1.042	-.2925	0	1.042	.2925	0	0.01
GW	15	9	1.333	-.2875	0	1.333	.2875	0	0.01
GW	16	9	1.624	-.2765	0	1.624	.2765	0	0.01
GW	5	1	0.378	.345	-0.0375	0.378	.336	-0.06	0.01
GW	4	1	0.378	.336	-0.015	0.378	.308	0	0.01
GW	19	9	1.915	-.267	0	1.915	.267	0	0.01
GW	20	9	2.206	-.257	0	2.206	.257	0	0.01
GW	21	9	2.497	-.2475	0	2.497	.2475	0	0.01
GW	22	9	2.788	-.2475	0	2.788	.2475	0	0.01
GW	23	9	3.079	-.2475	0	3.079	.2475	0	0.01
GE	0
GN	-1
EK
EX	0	1	5	0	1	0	0	'Voltage source (1+j0) at wire 1 segment 5.
FR	0	0	0	0	180	0
EN

.
This is prety good Hi VHF antenna for ch 13 and is good up to ch 9. For lower channels it has to be re scaled. If anyone is interested I have sizes . This can be made 8 elements up to 18, but it is 10' monster.

 

[manuetdeo]

as i was reading this thread, i saw that you could use the stucco mesh as a conductor? is this true because i would be interested in build this huge bowtie and attach it to the side of my two story to see if it worked maybe hang it off the eave or something like that i just cant see making all those reflectors though.

 

[300ohm]

You mean you want to use the existing mesh that's in your stucco ?

 

[balm]

Boom correction

Im working on new #13 yagi model, using 5/8" tubing for the elements. I read that no boom correction factor applies if the elements are more than half the boom thickness above the boom...so I was considering if it matters what the element thickness is ?

 

[manuetdeo]

You mean you want to use the existing mesh that's in your stucco ?

in post 333 holl_ands said something about using to mesh inside stucco as conductors and i didnt understand it. i would readily hang about any design from my eaves if the wall would reflect as a testing place as since my sweet spot is about 11 feet off the ground not 20-30 ft above my house attached to my fireplace, i get much better results lower

 

[300ohm]

i would readily hang about any design from my eaves if the wall would reflect as a testing place

Yeah, that should be good if the wall is facing the station. Lots of people with aluminum siding facing the station report great reception using the siding as a giant reflector.

 

[balm]

bow-tie

I too am thinking of pursuing my Ch #13 challenge with a huge bow-tie using the house as a backstop, but I also want to enclose the sides, and it might be doable with the bowtie, but unsure about how to go about it, material, size, configuration...

My signals are only receiveable at 8-13 ft above ground, so this might be best option...I would partially use the wall, and add on a shield for the upper part on the tower...maybe use some fine mesh for the sides with framing....

I think it might be more practical to do this, instead of building a cage around the yagi hanging off the tower, or maybe even better than stacking 2 yagis horizontal at at least 5-10 ft apart......

 

[balm]

optimizing

To MINIMIZES Hi-VHF SWR (max 1.7) at expense of Hi-VHF Gain (5.7-8.1 dBi) and even worse Lo-VHF SWR, use following:
BowLength=27in, BowSeparation=26in, TineSeparation=13.5in,
FeedlineSeparation=3.0-in and ALL AWG10 wire size.

http://imageevent.com/holl_ands/multibay/hivhf2bay

Was considering if there is any room for more optimization on this model, assuming ONLY a single design channel #13 (210-216 Mhz).

Of course I would still need some sort of reflector. Ultimately I would like to place this model in some sort of enclosure like a Faraday Cage, but with one end open...

 

[Billiam]

Comparing Three VHF Hi Antennas

Which of these three antennas has the best gain figures for VHF Hi channels?

Channel Master Quantum 1110
Blonder Tongue BTY LP HB
Antennacraft CS 1100

I am aware that the front to back ratio on the 1110 is rated at an unheard of 35 db which obviously makes it the most capable to reject signals off the side and back. But for the moment I simply need to know which of these antennas is going to offer the best pure gain for VHF Hi channels.

At the moment I am not concerned with VHF Lo though it is possible at some point, that I may be able to DX on that part of the band.

 

[holl_ands]

The NO-Reflector Hi-VHF 2-Bay is ALREADY optimized for Ch13.

On the other hand, there is some room for improvement in the fol. 2-Bay
WITH Reflector version (e.g. swept forward bowties with bigger, curved reflector):
http://imageevent.com/holl_ands/multibay/hivhf2bayrefl

You should model Faraday Cage designs before you built it.....you could
very easily end up with a very poor design...

 

[balm]

OK. Thanks

I'm not sure whats most practical, to build a shield enclosure for a short yag (5 elements), or the VHF Bow-Tie

I didnt find much practical documentation for RF shielding of TV antennas, with one side open. So I have a few questions,

1. Is there specific amount of space bewteen the antenna elements and the walls of the shield, if so what, and what overall size should the shield be (I intend on keeping one end open facing the trasmitter) ?

2. If not using a 100% closed material, would fine mesh be good enough, if so what is the maximum size of the mesh openings ?

3. Is the antenna reflector (bow-tie or yagi) still required or can I use the back of the cage as the reflector ?


(EDIT: oops I think we were posting at the same time ! sorry bout that)

 

[rabbit73]

balm:

1. Is there specific amount of space bewteen the antenna elements and the walls of the shield, if so what, and what overall size should the shield be (I intend on keeping one end open facing the trasmitter) ?

The spacing between the antenna and the enclosure needs to be greater for a yagi than for a bowtie antenna because the yagi is a higher Q antenna. If it gets too close to the sides it will de-tune the yagi sooner than the bowtie. Let the anti-ghosting trash can antenna by Bill Naivar be your guide.

2. If not using a 100% closed material, would fine mesh be good enough, if so what is the maximum size of the mesh openings ?

Fine mesh might be good enough, certainly better that 1 inch mesh commonly used as a reflector, but not as good as solid aluminum sheet. You would need to make a test for F to B. The 1 inch mesh used for reflectors is based on keeping the opening less than 0.1 wavelength for minimum reduction of gain. I haven't seen any figures about mesh size to maximize F to B.

3. Is the antenna reflector (bow-tie or yagi) still required or can I use the back of the cage as the reflector ?

You can use the back of the cage for the bowtie IF is gives the necessary F to B. The yagi should have its own reflector.

lithOTA is trying for max F to B for his co-channel problem:

Make a co-channel from the rear weaker
http://www.digitalhome.ca/forum/showthread.php?t=153344

Have you seen his thread?

I told him that his problem reminded me of your co-channel problem and made a post about your St-Anicet problem. Rather than repeat my thoughts here you can go to:
www.digitalhome.ca/forum/showpost.php?p=1412198&postcount=35

 

[balm]

hello rabbit73,

Excellent summary.

Even if you mount your antenna in a well shielded enclosure for the sides and back, you still must be careful not to pick-up any reflections in front of the antenna that come from the undesired co-channel signal.

Indeed, the only measure I could think of so far, would be to cover the metal boathouse in non-conductive materials, but likely still will not be sufficient attenuation

Another idea was to put the antenna, in front of the boathouse (such that it faces over the water, and such that the boathouse is not between the antenna and transmitter. And if I leave the antenna where it is, that is such that the boathouse is between it and the transmitter, then try aiming even slightly away to one side of the boathouse, I will lose what little signal there is.

I beleive holl_ands also mentioned that the ground in front of the antenna needs to be modeled if the antenna is enclosed, and close enough o the ground. For size reasons, I was thinking the bottom to have half the antenna with the house wall behind it (then, only the other half would be exposed to the wind "sail" effect on the tower. Thus, the bottom of the antenna would start around 5ft from the ground....

still at the stage of just thinking out loud....

 

[rabbit73]

Excellent summary.

Thanks

Putting your antenna inside the boathouse for a test might have seemed like an exercise in futility, especially when the weather was bad, but it told me that the WVNY signal was weaker than the tvfool report would lead me to believe.

Another idea was to put the antenna, in front of the boathouse (such that it faces over the water, and such that the boathouse is not between the antenna and transmitter.

If you put the antenna in front of the boathouse you will not receive the benefit of the signal boost from the additional signal reflected from the boathouse which adds to the direct signal.

And if I leave the antenna where it is, that is such that the boathouse is between it and the transmitter, then try aiming even slightly away to one side of the boathouse, I will lose what little signal there is.

Yes, you will lose the benefit of the reflection from the boathouse that adds to the direct signal which isn't strong enough without help. But, when you aim the antenna at the boathouse you also pickup reflections of undesired signals coming from the rear.

If you can mount the antenna at the optimum height and at a location that it doesn't "see" the boathouse but has a ground mounted reflector screen that gives some signal enhancement that replaces the signal enhancement that you were getting from the boathouse, you MIGHT improve the reception of WVNY.

Your reception problem is so difficult that you need to use every trick you can think of all at the same time:

1. The most sensitive tuner you can find
2. The highest gain CH13 antenna you can construct
3. Use a preamp with a low NF for the CH13 antenna
4. Grounding the coax to exclude unwanted signals
5. Shield the antenna for Max F to B and to reject local unwanted signals
6. Mount antenna at optimum height
7. Provide signal enhancement that adds to the direct signal
8. Make sure that no objects are in front of the antenna that will pick up reflections from the signals coming from the rear

....still at the stage of just thinking out loud....

Me too

 

[balm]

If you can mount the antenna at the optimum height and at a location that it doesn't "see" the the boathouse but has a ground mounted reflector screen that gives some signal enhancement that replaces the signal enhancement that you were getting from the boathouse, you MIGHT improve the reception of WVNY.

yes, but this isnt clear to me yet, since its very tricky on a 50 ft property & water on 3 sides

To not see the boathouse, would lead me back to the idea of stacking horizontally a pair of high gain channel cuts to reduce the beam width more (does this make any sense) or enclosing a bow-tie

But, for a ground reflector, that mimics the boathouse, I dont think there is any other place better to situate it. The only other place would be actually right in front of the antenna, and behind the cottage wall such that co-channel #13 is somewhat less received by this ground reflector....not sure at all, since the co-channel seems to get around most of the property & cottage.

In fact, the boathouse as is, is already lower than the house, and close to the antenna, so it should already be somewhat protected from co-channel #13.

For the antenna itself, I think this is a good starting point:

The metal would not only be needed for the reflector, but must extend around the sides to shroud the antenna from signals coming from the sides. You would still need to make sure that there were no objects in front of the antenna that would reflect the signals from the north into the front of the antenna. One example would be a 4-bay VHF antenna with a solid reflector and sides at least 1/4 wavelength deep. Yes, it would be big.

 

[threeflags]

On your DB8 clone, just stick about four 32 inch reflector rods on it, or attach a piece of 32 inch wide mesh to it for channel 9.

In relationship to the bowties, where on the reflector should one strap these rods? All on one bay or spread out?

BTW, how did you come up with the rod length?

Thanks.