DX'n Forum

[Tower Guy]

Originally Posted by smdp1

Now I haven't found this description, I would like to, but the link on the page leads me to something I can't read. I wonder what that DHR stuff is??

Try these links: http://www.mapability.com/ei8ic/inde...c/vhfrhom.html
http://www.mapability.com/ei8ic/inde...c/vhfrhom.html
Yes, a DHR has lots of gain, but it would be hard to rotate. Many hams who have build them intend to bounce signal off the moon. They must wait for the moon to be in the main beam.

So, if you want TV from one particular city, a DHR would work fine. If you want more than one city, it's not the best choice.

[scootski]

http://www.vhfman.freeuk.com/radio/23cmantennas.html

Scaleable to UHF TV...

Interesting !

[alphanguy]

KMIZ DT-22 might be a stretch at that distance.They're on a 1000ft stick with a directional favoring the NE.Ya never know though,you might get lucky.A large Band A,or two,or even four like I use would help.Here's a gain chart comparison

The thing that is so weird to me, is that at TVfool, it says that KOMU is the first Columbia station I should pull in, but I never get it, not evnen 5 percent of the time, while I get SOMETHING on KMIZ analog about 80 percent of the time, and about 25 percent of the time, mostly at night, it's a little snowy, but quite watchable. This is a direct comparison of what I have now, (I never laid it out concisely like this before, and I should have....) and what I'm going to switch to..... I would hope that this would be enough to push me over the top:

Currently have:
Radio shack lp-210 UHF gain-9.2
rotor
Radio Shack pre-amp 30 Db gain, 4.5 Db noise figure
85 feet RG6 cable run, gold connectors

Going to:
Xg-91 UHF gain-16.7
rotor
Channelmaster 7775 pre amp, 2.0 Db noise figure
50 feet RG-11 cable run, gold connectors
Can raise new antenna 15 additional feet above old one, if needed.

[Tower Guy]

Originally Posted by alphanguy

Channelmaster 7775 pre amp, 2.0 Db noise figure
50 feet RG-11 cable run, gold connectors

With the gain of the 7775 you will no additional advantage using that length of RG-11. Suggest that you stay with RG-6.

[alphanguy]

I had just thought that since I was trying for something so far away, every bit of signal I can muster would help... maybe not make the difference between pulling it in or not... but maybe the diffeence between making it stable 90 percent of the time, as opposed to 50 percent or whatever. I'm an overkill kind of guy, (I put metal hurricane ties on the rafters of my house when it was built... put them in with screws, everyone laughed at me. But I said, "Hey, in the case of a tornado.. that may be the very thing that saves the house.") So, I'll still go with RG-11 if it won't hurt anything. Nothing wrong with padding things a bit. However... I think I will use RG-6 for the short run from the amp power supply to the back of the set, RG-11 isn't exactly soft and supple, and trying to bend that crap around in the back of my entertainment center didn't sound like fun. And from what your'e saying, I guess I don't have to worry about the signal doing any "Bottlenecking" when it gets to the RG-6 for that last 3 feet.

[Bexon]

that it too easy

[Rick0725]

I installed rg11 from the 91 xg antenna to the grounding block to the distribution point inside. less than 50'. And I am only 12-19 miles from towers. Used rg6 from the hd8200p for vhf.

Improvement probably none but who cares. And the preamp is inside, not at the antenna, and used as a distribution amp.

I feel content now and that is all that matters.

go for it.

[smdp1]

Originally Posted by Tower Guy

Try these links: http://www.mapability.com/ei8ic/inde...c/vhfrhom.html
http://www.mapability.com/ei8ic/inde...c/vhfrhom.html
Yes, a DHR has lots of gain, but it would be hard to rotate. Many hams who have build them intend to bounce signal off the moon. They must wait for the moon to be in the main beam.

So, if you want TV from one particular city, a DHR would work fine. If you want more than one city, it's not the best choice.

If I built it, it would be for a specific channel in a specific city just to see if I could get it dependable....reading the article in the link you posted I noticed that he built his own balun...don't know if I want to tackle that yet, but might just to see what happens.

[Tower Guy]

Originally Posted by smdp1

Reading the article in the link you posted I noticed that he built his own balun...don't know if I want to tackle that yet, but might just to see what happens.

The balun he built was to handle the power of a transmitter. For reception only a low loss TV balun will work just fine.

The impedance of one Rhombic is 600-800 ohms. Two in parallel would be 300-400 ohms, which is very close to what is required for TV.

[donnyjaguar]

Here are some pictures of my home brew dual-UHF Rhombic. It does work, but there is room for improvement.

[scootski]

Originally Posted by donnyjaguar

Here are some pictures of my home brew dual-UHF Rhombic. It does work, but there is room for improvement.

Also read this for a true rhombic...
http://www.highdefforum.com/showpost...9&postcount=35
Right now, that antler is a basic Horizontal Loop.
Read the abover for effective improvements.

[scootski]

Originally Posted by Tower Guy

The balun he built was to handle the power of a transmitter. For reception only a low loss TV balun will work just fine.

The impedance of one Rhombic is 600-800 ohms. Two in parallel would be 300-400 ohms, which is very close to what is required for TV.

THAT is WHY you use the split-300 ribbon (split for 18")...
to get a better match...

[alphanguy]

I think I AM a fool.. and maybe I finally got a handle on how to work that site. When I was checking out my results, I wasn't clicking on the "Post transition"!! I also went and found my EXACT coordiantes, and used those instead of my address, and guess what? It now shows KMIZ as being the first Columbia station I can pull in, at LAST, I think I finally did it right, and the TVfool results are matching up with my real life experience. I did change my anteena height from 35 feet to 70, and it didn't make any difference in my results... so in my case, maybe where I'm at at 35 is just fine. I was freaked cause KMIZ wasn't coming up at ALL on the digital listings, BUT....their transmit power pre-transition is listed as 18.something KW, while after, it's listed as 50.00 KW...I guess I'm reading this right... that theyr'e not transmitting at full power yet? so the Digital KMIZ after transition is coming up with signal strength at -123, 2edge.... so i'll just get my XG-91, try it, and if it isn't quite enough... I'l jsut add another to it, and stack 2.... surely one of the 2 will get me results. Seeing 2edge instead of tropo listed for that station makes me feel more confident.

[smdp1]

if its listed as 18kw now and goes up to 50kw on post transition then yes its not up to full power, but 50kw still isn't much. Of coarse I am getting a station at 60 miles out solid thats only 41kw with 95% signal. If you are getting it at all now that could be enough to push it over the top for you. I'm really surprised that moving up to 70' didn't help....around here height is everything. Heck here 30' can mean the difference between blank screen and 80% signal on the same antenna....my neighbor moved hers up 4' and it made a big difference in hers.

[alphanguy]

I'm still going to play with the height when I get my antenna anyway. The tilt thing may help me, as I would be able to shoot over the tree tops with that. right now, i'm pointing directly into the trees. I could put the antenna on the other side of my house and shorten the cable run by 35 feet...but, the trees are denser on that side of the house, and the HUGE tree that is between my current antenna location and the transmitter, I'm almost 90 percent sure is dead... and will have to come down this year, really thinning things out on that side of the house. So I have a feeling that the extra 35' run would be worth it to shoot through the thinner part of the woods. I told you that I get signal on analog now about 80 percent of the time, and it's watchable about 25-30 percent of the time... TVfool shows the analog signal at 2edge -128. the digital after changeover shows it as 2edge -123..... so it looks as if the post changeover digital is going to be a little stronger, at least. Having an antenna gain increase of 7.5 Db over what I've got right now I'd think would make quite a difference.