Convert SBGH to DBGH using 300ohm's plans

[Billiam]

300ohm. Is it possible to stack your SBGH with a second unit? If not, do you have plans and a parts list to build your DBGH?

[300ohm]

300ohm. Is it possible to stack your SBGH with a second unit? If not, do you have plans and a parts list to build your DBGH?

Yes, thats what it was designed for. That why I have 2 pvc tees at the bottom corners and a pvc cross the bottom middle. Just build a duplicate, turn it upside down from the first one and add 3 short pieces of pvc (Ill get the lengths later) and voila, instant DBGH after adding the phasing lines.

Hmm, I just noticed that the bottom of the screen is already at 127mm (5 inches) which is the distance between the sets of elements in the original DBGH drawing. Adding the second SBGH to the first will increase this distance. The effect of this hasnt been modeled yet.

Since Im pretty well done playing and testing with this SBGH, I was planning to make it into a DBGH sometime this week. What Ill do, is to try to model the effect of an increase in distance between the two element sets on a DBGH made with my plans. If it turns out it hurts performance, Ill have to change the lower bottom section construction details. (which could actually make the costs lower, hmmm)

In the meantime, if you want to build this SBGH, just make it like I did. I only glued the cross tees, as they have been modeled and optimized at 100mm plus or minus 15mm, so they wont change. The rest of the the tees and ells are held together with tiny wood screws, so future adjustments are easy and cheap. My whole idea of building this way was so the antenna could be updated, just like Windows service pack 1, 2, 3, heh.

[Billiam]

300ohm. I'll look forward to your findings.

I have a friend that is also interested in this antenna and he and I will probably build a single for him and a double for me. We won't be doing this until at least September or more likely, October. I'd also like to wait until I see how the DBGH Generation 2 model turns out.

[Billiam]

300ohm. My friend is a broadcast engineer and he said your design is excellent and appears to be more sturdily built than a couple of other designs. We'll be building your single bay for him and possibly two of them for me to use unless the DBGH Generation 2 unit is unveiled by that time.

A question for you. I've read that you get more forward gain with the smaller mesh screen than large. Do you also lose some directionality if you use the larger mesh like you've used?

[stampeder]

Originally Posted by Billiam

My friend is a broadcast engineer

We have broadcast technicians and engineers as members at this site so please tell him he's welcome to join too!

[300ohm]

My friend is a broadcast engineer and he said your design is excellent and appears to be more sturdily built than a couple of other designs

Thanks. For a even more studier design, you can look at WSRYTV9 (hes from TV-9 in Syracuse, NY) a few pages back in this thread. Of course, with increased sturdiness comes more cost and more wind load. Its always a trade off.

A question for you. I've read that you get more forward gain with the smaller mesh screen than large. Do you also lose some directionality if you use the larger mesh like you've used?

Yes, I do. I chose 2in X 4in mesh for 4 reasons, cheaper, more available, less wind resistance and less F/B ratio on purpose so I can get strong stations from the rear.
I havent modeled it yet on this SBGH, but on a 4 bay whiskers type bowtie antenna, mclapp has and my guess is the SBGH will be in the same ballpark.
His figures 2in X 4in mesh versus 1 X 2 mesh are : At channel 52, .73db less forward gain. At channel 40, .44db less forward gain. At channel 14, .17db less forward gain. And it scales fairly evenly between ch 14 and 52, so you can extrapolate. Since my highest channel I want after February is 42, .5db or so less gain maximum is a good trade-off for me, Im not greedy heh.

So again its a compromise. If channels above 40 are important to you, then I would go with 1in by 2in mesh size or even smaller and then secure the antenna against high winds a lot more drastically.

[Billiam]

Spoke to my friend and he also wants the DBGH apparently to watch LPTV in his area.

That being said is it possible to stack the WSYR TV engineer's antenna? I took a look at it and it appears that it will easily weather the storms of Lake Ontario but I can't quite see how it can be stacked with another.

Do you think your unit can withstand the weather off Lake Ontario in the winter 300ohm?

Not too many channels over 40 in most of the locations I am considering. That should not be a worry.

[300ohm]

That being said is it possible to stack the WSYR TV engineer's antenna? I took a look at it and it appears that it will easily weather the storms of Lake Ontario but I can't quite see how it can be stacked with another.

Yes, his can be stacked too, just the same way mine can be. Just add a couple of small lengths of 1/2 inch pvc pipe to the tees at the end. But his has the same problem mine has, that is when stacked together, the distance between the last element stubs on the top SBGH and the first element stubs on the bottom SBGH exceeds the 5 inch (127mm) design of the original DBGH plans. So it hasnt been modeled before. Im in the process of modeling the effect of that now, but it will take a few days. Im going to try a 15 inch spacing first and then a 10 inch spacing.
WSYRTV uses 1/2 inch mesh in his plans, so I would think more snow and ice would stick to it outdoors.

Do you think your unit can withstand the weather off Lake Ontario in the winter 300ohm?

Yep, using the 10 gauge 2X4 inch fencing wire and 6 gauge copper wire for the elements that I did and u-bolted to a strong sturdy mast, no problem in a blizzard at all. The 10 gauge 2X4 inch fencing wire reinforces the 1/2 inch pvc frame a lot. (you can see how the fencing bows the pvc when tightly strapped, heh) Its sturdier than any commercial uhf antenna I can think of.

Even using common 14 gauge 2X4 inch fencing wire and 10 gauge copper element wire, it would be sturdier than almost all commercial units when u-bolted to a good mast IMO.

[300ohm]

To turn the SBGH per my plans in my sig into a DBGH, simply build another SBGH per the plans and add new 3 pieces, which Ill call pieces J, cut to 4 3/4 inches long and pushed into the 1/2 inch fittings 5/8 of an inch. (shown on top in the photograph above of my uncompleted bottom portion of the DBGH) Remember to drill weep holes in the bottom of the antenna to let any water out, or during a freeze you may get a nasty surprise.
This will result in a SBGH feedline to SBGH feedline of 45 inches (1143 mm) which is 2X the wavelength of about channel 23, which I feel is a good compromise for me based on my rough modeling of my 12 pair colinear rod DBGH. (To tweak for other channels, find 2X the wavelength of the frequency for that channel and adjust the sch 40 pvc and phasing line lengths accordingly. )
Also since my SBGH plans have the increased feed gap spacing of 93mm center of wire to center of wire, the phasing line spacing should be increased to 50-55mm too, also based on my rough modeling of my 12 pair colinear rod DBGH. I also found that the height of the phasing line above the elements is optimal around 10-30mm. (10mm is only slightly better than 30mm). And instead of the sharp bends, angling towards the gap size is just as well in all practical terms. What is very IMPORTANT, is that the phasing lines be exactly equal in length. So, using the above 45 inch (1143mm) distance between SBGH feedpoints and a phasing line gap of 50mm and 30mm height above the elements and using 10 gauge copper wire and compensating for the 360 degree middle loop and the 2 270 degree loops on the ends of the phasing line, (shown above in post #618) gives us 1143mm + 30mm + 30mm plus 7mm angular compensation plus (25.4mm + 16.51mm + 16.51mm total loops compensation) equals 1268.42mm (or divided by 25.4 = 49.94 inches, 50 inches rounded) total each phasing line to be cut.

So in summary, you will need to cut 3 pieces of 1/2 inch schedule 40 pvc at 4 3/4 inches each to join the two sections and you will need to cut two 10 gauge wires to exactly 50 inches each for the phasing lines.

I have not modeled the effects of joining or not joining the two sections of the mesh on the DBGH. Since that basically requires about 12 hours of straight computing time per run, I dont think Ill do that. Instead Ill try to determine the effects by old fashioned experimentation, heh.