Yagi vs Bowtie and other OTA Questions

[Rick0725]

not sure of the fox...send the engineer an email and ask the questions...they may be transmitting on low power...it will rest your mind.

btw...ingenious idea to use just the uhf portion of the antenna.

bet when they designed it, they just slapped on the vhf on the back of a yagi they already had.

fyi...tried the cm4228 at my place a month or so ago...wanted better...it wasnt...now its in the basement and I stare at it when I workout...so you may have made the right decision.

I hate ladders also.

 

[bhelms]

Question for Rick0725 - What's your take on RG-6/U QS for the OTA antenna vs. "regular" RG-6? You talk a lot about multipath issues. In my (limited) experience, some of that can be introduced in the downlead (?) Will the QS help prevent that? Due to my fringe situation I don't think multipath is much of an issue, but if there's no consequence in using the QS, I'll just do that from the getgo when I rewire/replace my OTA system this season.

Here's some related/interesting information - I recently looked at the connectors on my 25+ year old OTA installation in the house. I have my grounding blocks located inside at the point of entry vs. outside as that side of my house gets a lot of "spray" when it's a blowing rain. So they don't see much moisture at all. In the connector on the antenna side of the block, there was a build-up of a greenish contamination of some kind covering the exposed end of the foam and bridging between the ground part of the connector and the copper center conductor. Experience (telco equipment) tells me that this "salt" is a consequence of copper in the presence of moisture and voltage (pre-amp power), and it's variably conductive so it no-doubt has some negative impact on my signal. Interestingly, the connector on the equipment side of the block appeared completely "clean". I replaced the block and that one connector. Since the connector is inside, I'm curious where the moisture came from, and why it only appeared on one side of the grounding block (the cable and connectors are identical on both sides). While dressing the cable (QS) to replace that connector I noted that the aluminum foil was "crusty" with some kind of white powder (??) This is Tandy (RS) cable, presumably made in a factory they owned. (Many posts are now telling me to avoid the RS products, tho' my old VU-160 antenna has held up well.) I'm wondering if the coax itself is "leaky" and if moisture has penetrated that cable over time to cause this contamination. That would explain why it stopped at the ground block. Interestingly, there has been no real change in my OTA reception over the years - it has been only fair at best and weather/season-variable ever since I installed that system. I can receive quite a few analog channels poor to fair by spinning the antenna, some are UHF, two VHF channels come in quite well but with variable ghosting, and one new digital channel is received quite well (HD and 2 other subs, 15.1 to 15.3) from 35 miles away. So I'm not sure that replacing that cable will help me much.

I'm striving to receive the other UHF digitals I know should be available, per my other posts. I'm actually planning to replace/augment the whole thing with a UHF only system and in that installation I'll use premium cable, connectors, blocks, etc. I'm still not sure what antenna. With that link you provided to the $40 CM4228, I'll probably start with that one (do you want to unload yours?), but I'm not sure what preamp to use - CM7777? I know I need the best noise figure vs. highest gain; I will be driving a 75" coax run with it.

TIA and BRgds...

 

[fs2685]

With that link you provided to the $40 CM4228, I'll probably start with that one ...

FYI. Warren Electronics has had the $40 CM4228 on backorder for a couple weeks now. They were supposed to get a shipment this week, but I haven't gotten any update on my order yet.

 

[Rick0725]

I have not seen much difference with the quad shield coax. I would assume most of the multipath comes from the antenna down. but who knows its "voodoo" magic sometimes.

A good high quality rg-6 all copper... not steel with copper clad coax.... with 60% braid ...swept tested to 2ghz is fine. I sometimes scrapt with a knife to remove the plastic coating leftovers on the copper.

be careful not to purchase the coax for direct burial. it has a silicne coating that can leak to the copper and affect reception...have to scrape it away or use a solvent.

the white powder is the alum foil corrosion.

for longer runs (over 100ft) some suggest rg11. but you need special fittings and the solid wire is usually copper coated steel.

With connectors...the green corrosion (copper corrosion) ....cut back the coax a few inches. Go to a lowes and purchase electrical silicone ...comes in a tube...and put a squirt inside the the connectors then attach and tighten down with a 7/16" wrench...will inhibit this reaction some. the voltage pasing thru the cable to the amp contributes to the corrosion also.

Lowes also sells compession fittings and tools...takes some cash to get started for the tools but they work great.

coax preparer
compression tool
50- compression fittings.

like this connector much better than the older style. This is the fitting of the future.

the cm4228 is the internet popular choice...I was alittle disappointed...would like to unload mine probably locally

but please...this was my situation...the cm4228 is one of the best uhf antennas out there for the price.

 

[bhelms]

Tks again, Rick !! I also use the "scrape the center conductor" trick to hopefully clean it up a bit for better conductivity. I usually twist it in a pinch of steel wool for the same effect. (Careful to keep the steel "dust" out of where it doesn't belong!) This time I will use the silicone grease on all the outside connections at least, along with weatherboots on the exposed mast-mounted connections.

I was a bit surprised at the aluminum corrosion. I know that's a common reaction with alum., but I figured that being "sealed" in the cable would have prevented that.

I also looked at the tools at Lowes - seems like a worthy buy even if you only use the stuff infrequently. Case of "penny-wise, pound foolish", I guess, i.e., spend some good money up-front for best results in the long run.

I haven't decided on the antenna yet - still interested in the Winegard PR-9032 - similar performance (?) with less wind loading (??). I'd be really interested if someone has experience with both that one and the CM 4228 - anyone ??

Tks again and BRgds...

 

[Rick0725]

i am anxious to here how ralfyguy makes out with the 91xg he just purchased.

 

[ralfyguy]

I am anxious about it too. Well it'll take a few days for it to get here.

 

[mikekohl]

UHF signals are where you find them. This is especially true in hilly areas such as mine (SW Wisconsin), where you might not be getting a direct signal from the transmitter; bouncing off a hill or two before getting to your location. One common finding that I notice is that most antennas made in the U.S. have a 300 ohm connection, which requires a 75 to 300 ohm transformer. A lot of your potential mismatch at various frequencies, as well as corrosion problems, usually end up on both or either end of these 75/300 baluns.

Experience with European and Asian made antennas that have only a 75-ohm connection, how shown them to be far superior at providing quality signals for HD reception in our UHF band. You may or may not need a pre-amp. If your location has transmitters in several widely spaced locations in different directions, an antenna rotor is a cost-effective piece of vital equipment. A handful of degrees left or right makes all the difference in the world for peaking individual channels, which sometimes cannot be done with a single antenna pointing in one general direction.

Experimenting prior to installing is the only practical way to do a UHF installation.

 

[Rick0725]

One common finding that I notice is that most antennas made in the U.S. have a 300 ohm connection, which requires a 75 to 300 ohm transformer. A lot of your potential mismatch at various frequencies, as well as corrosion problems, usually end up on both or either end of these 75/300 baluns.

this is one of the reasons why I fell in love with the hd series winegard antennas.

no balum, a 75 ohm antenna.

I had my eyes on the blake uhf antenna JBX21WB ...same design as the 91xg.

http://www.atechfabrication.com/reception_solutions.htm

http://www.bobmerritt.com/dtv/dtv.htm

http://www.ultrasatellite.com/

http://www.blake-uk.com/

http://www.televes.com/



http://www.blake-uk.com/downloads/uhf tv aerials/high gain jbx leaflet.pdf

 

[NightHawk]

The 300 Ohm feedpoint is not without reason. Antennas themselves are a type of transformer, matching the feedline to the impedance of freespace, 377 Ohms. It would be impossible to design a good antenna with good broadband UHF characteristics and maintain a feedpoint anywhere near 75 Ohms over the entire UHF band. If your UHF antenna has an actual 75 Ohm feedpoint, compromises in its design are probably being made elsewere. Nothing is free.

It's more likely the antennas you describe have a balun you don't recognize in the form of a coaxial sleeve or quarter-wave stub. Directly coupling an unbalanced line to a balanced antenna element without the isolation provided by the balun is also a no-no at UHF.