Help needed with attic antenna selection

[freetvforme]

For current UHF real channels 14 to 51. 8.5"-9" should work fine.

I guess this would mean that the smaller the diameter, the higher the frequency. ??
Is there a calculator/chart that one could use to make the diameter in the middle range of the frequency of the channels in their area or is it that critical? The Radio Shack 15-1868 models I have now, have a 4.5" hold in the middle of a plastic triangle. I one set apart a while back to fix the male coax connector that was spinning and found that there was a thin wire in the middle of the loop that connected to the adjustment knob. I'm guessing that the wire circle itself was only around 6". Maybe the hole size doesn't matter in this design.?? https://www.radioshack.com/products/radioshack-indoor-hdtv-antenna?gclid=Cj0KEQjwx96-BRDyzY3GqcqZgcgBEiQANHd-nrhTXLQqbmG47NxV9ZzaP8xTWOeNIcxo9txXYBKQf3kaAqn28P8HAQ&variant=5716990021

I'm hoping to replace my cheap Chinese antenna before the end of the year and I don't think I'll be looking at Stellar Labs equipment now.

I would stay away from this model at least if I were you. I'd be interested in hearing what models you are considering.

In the mean time, I am going to stick with my rabbit ears and keep looking for either another model or perhaps one to build that can go in the attic.

Oh..and let's get rid of Soria! It seems every time I listen to the game, he is doing poorly. He was good the first time we had him but not since he has been back. It's all but over for the boys in blue this year.

 

[RF Steve]

Yes the smaller diameter the higher the frequency.
The old formula for calculating the length a full wavelength loop antenna is 1005/frequency= ft of wire. As an old radio man, that has always gotten me close enough when cut for the lowest frequency to be used, and fed into a 300,or 450 ohm load. Now days we have elaborate computer programs like 4NEC2 that have shown the 1005/f is a very flawed formula. Learning to use 4NEC is a very steep learning curve which I'm not ready to try at this point in time. Simple antenna formulas do not take into account wire diameter, and many other factors that go into antenna design.
The 1005/f is now superseded by more accurate formulas. In the newer ARRL antenna books the current formula is 1032/f.
Now if I did my simple arithmetic correctly using the new formula and my simple old radio man way of thinking that would result in a loop 8.39" in diameter for the current UHF band. Wire gauge of the antenna driven element becomes a very important factor when working with UHF frequencies.
I'm a simple old radio man.
I respect those who have learned to work with complex antenna analyzing computer programs, and find if the antenna is correctly built the results can be quite impressive. Free air space 4NEC2 models are not real antennas. Learning how to build them into working antennas can be a real challenge.

 

[RF Steve]

I went out and got the UHF double loop out of the the antenna scrap pile. I put it up on the test stand, and took a photo. The antenna worked quite well. 300 watt UHF translators from over 30 miles away were no problem. The strong VHF signals in this area were down in indicated signal quality, but well above drop out. The lower VHF signal levels from a UHF loop antenna are to be expected.
If the attachment works here is a photo.

Current TV Fool report.
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=e2cb4f55cbc969

 

[freetvforme]

Steve,

Thank you for posting the picture of your antenna and re-testing it. I have some old scraps of copper that used to run to a gas dryer that I think I will use to build one like yours. If that doesn't work, I will have to buy some heavier gauge wire than the 12 gauge I have on hand. If I understood you correctly, the 8.39" diameter would be for the lowest channel in the UHF band (14). Would I be better off selecting the lowest channel that is used in my area which would then make the diameter a little smaller?

Also, I don't think I am ready to tackle the understanding of the 4NEC2 models either. I'm just a guy looking to get a reliable antenna and willing to tinker around a bit to get there.

Thanks again for posting your double loop photo.

 

[RF Steve]

The 8.39" was just a very rough approximate calculation using a simple formula. Rough approximations using simple arithmetic are no match for 4NEC2 antenna modeling. Loop antennas fed into 300 ohm are very broad bandwidth. You will need a 300 to 75 ohm balun. The actual antenna I built a few years ago and got out yesterday is 9" loops built out of 9 AWG aluminum, because that is what I had to work with at the time. I did not have any 1/4" tubing and didn't want to waste any money on a simple experiment. The wire was old and a bit rough. I straightened, and strengthened it a bit by clamping one end of the wire in a vice and turning it with a drill. It's built on some scraps of PVC. I really would suggest following the dimensions used in the 4nec2 Antenna Sims by holl_ands. While I don't even understand everything I'm looking at when I open one of his 4nec2 files. I sometimes open them when I'm not real clear on the dimensions.
While I've built a couple 4bay antennas using mclapp's M4 dimensions. I'm currently using a couple of 2bay antennas they are not combined but separate systems one on the family's TV, and one on mine. I simply do not need a 4bay at my location. A well designed, and constructed 2bay will outperform a poorly designed,and constructed 4bay. I really don't understand the abundance of very poor 4bay plans that are on the net. When a well designed, and constructed 2bay is so much simpler to build, and get right. The double loop antenna should work at your location.
Build experiment have fun.

 

[freetvforme]

Update: (I have had some other projects and some family issues to attend to which is why I have not been around for a while.)

I did build a loop antenna as a test but ended up using some aluminum craft wire I had on hand instead of the scrap copper tubing. My plan was to build the one from copper if the first one turned out well. The one with the aluminum craft wire did about as well as my rabbit ears so I lost momentum on the idea.

For the Stellar Labs antenna, I worked on the connections from the bow ties to the phase line and I think that was my problem. The cheap construction caused the wings to not make good contact. After I improved that situation, the antenna performed better.

I currently have that antenna on a 3-way splitter and one of those lines is split at the TV where one goes to the TV and the other to a DVR. For the most part, that seems to be working pretty well. I do get a random sound pop or drop out but the picture seems ok. The sound drop out is only for a split second and isn't enough to miss what was said. I have only noticed this on one of the channels. I'm guessing this is just interference of some kind as it happens on TVs hooked to 2 different antennas.

I also have my home made antenna in the attic which is one of those 4-bay bow-tie/whisker/coat hanger types. (There are about a million YouTube videos made on this with about a million different ways of making them.) This antenna feeds a 4 way splitter going to lesser used TVs.

This has been a very confusing project in that each TV I use seems to give different signal strengths from the same antenna. The one channel that is the best on one TV may be the worst on another. I would really like to have one of those meters to test the actual strength and best positioning without going up and down the ladder to the attic and testing channel strength. It's almost as productive as counting fish in a barrel.

I think I am in fairly good shape now but will probably always still be trying to tweak things. For instance, one run of cable has got to be fairly close to 100' and I am going to try and shorten that dramatically by installing a new outlet box and making a shorter path. (This is a challenge in my split level home with most ceilings finished.) I also may try and replace my home made antenna with another better quality antenna at some point down the road.

I do have one question though about my 2 antennas. Right now, I have them mounted where the sides are about 3'-4' apart. (As stated above, they are not connected and run to 2 different sets of TVs via 3 and 4 way splitters.) The reflector on the home made antenna is slightly above the bottom of the roof rafters on one corner. I'd like to move it away from that but that would require moving it closer to the other antenna. How close can 2 non-connected antennas be placed without interfering with each other? Or does that even matter since they are not on the connected?

 

[Fringe Reception]

Free,

In an outdoor situation, antennas should be at least three feet apart from each other to avoid interaction. However, in an attic they are already being affected by HVAC ducting, metal chimney and plumbing vent pipes and other unpredictable signal reflectors: the best advice is to experiment.

Regarding signal "strengths" your on-screen 'meters' report the quality of the received data streams and there is no standard: every different model tuner has different abilities to decipher and reassemble digital data and the rule is a clean stream of low signal-level data always beats a dirty or noisy stream of high signal-level data. I receive a channel from 75 miles away which is very weak, but my 'meter' shows its quality between 80 and 90.

Regarding replacing your antennas sometime down the road, be sure to check on your local Craigslist under Electronics, and search for antennas: if you find one of interest, ask us for our opinions before you buy. I have bought and sold about a dozen in my area over the last few years.

Jim

 

[freetvforme]

In an outdoor situation, antennas should be at least three feet apart from each other to avoid interaction.

Would an occasional split second sound pop/drop out on one particular channel be considered "interaction"? This occurs on TVs from two separate antennas which are not connected. I also don't recall having this particular issue when just using rabbit ears. A few times, I've had the TV signal meter running at the time this occurs and it does not spike downward. Perhaps there isn't sufficient time for the meter to drop since it is just a split second and the video isn't affected. ?? I guess I will have to experiment. If you have any other thoughts on what might be happening, I would love to hear it.

Thanks for your help.

 

[SplitRock Sam]

Desktop Support Services Technician

I have experience with other Monoprice products. ALL cheap crap. Failure is inevitable. Lifespan is multiple times less than brand name. For cable, I always use Belden. Granted, it may not be made in US, but the manufacturing standards are higher.