Some good stuff on the rest of the blog, too. found these charts...
for you connoisseurs out there who want nothing less than the Heliax... a 100 foot section, pre-assembled with "N" connectors, runs just over $25,000. You'll also need special adapters, special hanger clamps, and a system to pressurize the line with nitrogen (you'll have to change tanks periodically) or a dehydrator system. Figure closer to $30,000 for the complete installation... and don't forget to budget for the armed guard to fend off copper thieves.
I've seen these loss figures before with losses in dB, but not in percentages. Pricing rg6 vs rg11, for 50' terminated, rg 6 is $7.85+ shipping (monoprice), and rg 11 $36.50 shipped (Ebay). Looks like if you used RG 11, in some situations, it would be cheaper than rg6 + a pre-amp - and no amp noise! Hmmm...
I think they're embellishing a bit about the Heliax.
First of all, HJ series Heliax is air (gas) dielectric. It is, frankly, overkill for residential use of any kind. The reason it needs to be pressurized is that without a slight positive pressure, condensation will occur inside of the cable. For most people, foam dielectric cable is absolutely fine.
I have heliax on my tower for my ham radio antennas as well as a run to a vertical antenna out back. I use foam dielectric Andrew LDF4-50A (1/2") and LDF4-50A (7/8"). For the vertical I have Andrew Heliax LDF2-50A. The cost wasn't all that much, some of it I got for less than a buck a foot, about the price of good RG213. However since my antennas are used for both transmission and reception, very little of my transmit power is wasted on its 200' journey from my house and up the tower. The connectors are kind of expensive, some of them are over 10 bucks a piece but you can get NOS (new old stock) ones and if you're willing to use DIN connectors you can have these for a song. I used N connectors which is a good compromise.
I actually think that Heliax is tons easier to work with than RG213 or RG11 coax. The reason is that you can use common plumbing tools like a pipe cutter and hacksaw instead of having to get a special coring tool and the connectors have complete and accurate instructions on how to install. But I also have the coring tool for RG213. It works mostly well. No complaints.
They also use a solid outer shield and the foam is dense, which means that even if you submerge it in water the cable will not be ruined. Period.
However with regard to 75 ohm heliax, that doesn't seem to be as widely available as 50 ohm Heliax from the usual sources (ebay). But I do see that RF Parts carries it and sometimes your local cable company may have surplus cable ends that they will just throw away. (I say *may* because many of them are recycling them for scrap now).
The Gray-Hoverman antenna is well worth the effort to build. It does look like the one in the picture is over engineered, but it would last for years if erected outdoors. Below is a link to the one I built, and it is much simpler than the others I have seen and a lot cheaper to build. The only thing I actually had to buy was a $ 2.50 balun. One word of warning and that is that this antenna is physically large when compared to other UHF designs, but its large size also contributes to the high gain factor. How did you embed that picture? I have been trying to figure out how to do that too, but with no success.
to embed a picture, find the picture you want to embed, right click, select "properties". you can copy the URL by highlighting it and (CTRL-C) or right click and select "copy" from the menu. then select
and paste the URL into the dialog box.
I assume that's yours. Nice, minimalist. But since it will be visible from the road, I think I'd prefer the over engineered version!
Yes, that is my version of the G-H Antenna, and I live in a very mountainous area, and the addition of the side reflectors helps with Multi Path from the sides too. This is an experimental version, as the back plane depth is adjustable, and big differences in gain can be seen on a spectrum analyzer just by changing the depth of the back plane reflector assembly as little as 1/2 inch. I can see up to 6 db change, just by adjusting that aspect, which shows how sensitive it is to impedance changes.
The plans I used did not mention anything about the spacing between the reflector rods and the driven element, so I built mine as shown so I could find the optimum spacing between the driven elements and the reflector by making it adjustable by as much as 4 inches, and to enable it to be as effective as possible in combating Multi Path signals, and the side reflectors seem to make it less susceptible to side reflections. It has a very narrow beam width using the side reflectors, and is even more directional than other antenna designs I have seen due to that aspect.
I live in a Utah Valley, 75 mi n of salt lake, so all my signals from SLC are blocked by mountains, served by translators. Multipath is not a problem, but I have 1 set of translators 10 mi south, and another set 30 mi north. I am using an attic mount U-75 with distribution amp to feed 6 sets. I pointed the U-75 a few degrees east of the northern translators, and I get both sets (south set off the back side) This has been working ok, but I do get some dropouts now that the leaves are on the trees. I'm going to put the U-75 on the roof and see if that solves my problem (it should) but I'd like to build another antenna - on a rotor - so I can play around trying to get some others. I once got a lock on channel 20 from SLC (1edge) with the U-75 pointed south. Not much interested at the time, since it is a religious station, but they since have added some subchannels that might be worth tuning in. (old TV shows and kids programming)So i'll be playing around for a while.
While we're at it, I am looking for a small, easy to build, and cheap design to help get folks here off the cable, perhaps a small 1 or 2 bay. Suggestions or plans, anyone?
One thing I'd like to comment on (but that thread is so old so I'll do it here):
Posters on the Canadian forum have performed extensive modeling and testing with variant GH's. I'd trust their modeling and field testing. However, they are very protective of the patent for the GH. Tread carefully if you are going to market the antenna....
I don't think they've patented the antenna. I would be surprised if they did because patents cost money, and copyright doesn't have to cost anything. And since they (and we) are hobbyists I doubt that anyone spent the money to patent the design. What they have done is copyrighted the design under GPLv3. As such I don't think there's a problem so much with selling manufactured versions of the antenna as it is without disclosing the plans for it. The antenna design is licensed under GPLv3 which means that one can sell it, they just have to make the plans to build it freely available or at least provide a link to where they can find it, as well as a link to the GPLv3 license... I think that's the long and short of it.
That said, EV's build looks like the route I might go.