OT a sign of the times

yes 75 ohm coax to 300 ohm balun

I wouldn't say mesh size - the best signal is with no mesh but horizontal parallel wires support on the outside edges with vertical wires is OK and a vertical wire in the center is OK too - but no mesh, no solid reflector works.

I have a large sheet size aluminum baking pan. It doesn't improve the signal but attenuates the signal

Well I've tried the solid pan at all distances . It is considerably larger than the dipoles and it has to be further away for any signal to get through but is not augmenting the signal strength at any distance.

I'm coming to the conclusion that this reflector is not a reflector at all but a director like a yagi antenna. This is also borne up by my geographical understanding - on the driven element side there should be an ocean out there somewhere not a TV station. I'm ~6 miles from the ocean and from looking at a map with my street orientation and house and antenna with respect to the street... Unless there's some large object out there like a water tower that is reflecting a signal from the wrong direction. There is a light tower ~30 miles offshore in the general direction, large aluminum square on stilts 50 from the surface.

They are so few and so valuable that plenty of copper plated ones were designed to fool people into paying big bucks for them - I had one of those at one time.

A 1943 copper cent was first offered for sale in 1958, bringing more than $40,000. A subsequent piece sold for $10,000 at an ANA convention in 1981. The highest amount paid for a 1943 copper cent was $82,500 in 1996.

Because of its collector value, the 1943 copper cent has been counterfeited by coating steel cents with copper or by altering the dates of 1945, 1948, and 1949 pennies.

The easiest way to determine if a 1943 cent is made of steel, and not copper, is to use a magnet. If it sticks to the magnet, it is not copper. If it does not stick, the coin might be of copper and should be authenticated by an expert.

To find out about coin experts in your area, you may call the American Numismatic Association at (719) 632-2646.

Steel, grain of wheat style, pennies were in circulation when I was a kid from the war years. Silver nickels too.

I can't swear to the date, but I do seem to recall that during some year in WWII, they made pennies out of steel because copper was needed for the war effort. I learned this about 40 years ago, when everybody was on a coin-collecting jag, and I do remember seeing some description of steel pennies.

Or, I might have dreamed it. I'd say the best route would be to check with a "real" coin person - if you have copper (or, actually bronze) pennies from

1943, they could be worth a fortune, or maybe you could get a couple of bucks for the value of the copper.

Good Luck! Rich

My comment was in jest. I really wish I had 1943 copper pennies :-)

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For the last time:  I am not a mad scientist, I'm just a very ticked off
scientist!!!

default Inscribed thus:

Mmm I would have thought that the (bowtie) dipole would have been a low impedance feed ! Do you have any source of pictures ?

Good morning from a cold, damp, snow covered UK !

Lets see if we can make some sense out of this. I assume that we are talking about an antenna like this which is a typical billboard type antenna. The signal is expected to come from the dipole side. This antenna offers a nominal 75 ohm match to 75 ohm co-ax. There is no balun on this antenna. 300 ohm ribbon is used between the elements as phasing lines. Termination is in the box in the centre. The reflector has a plastic molding supporting the ends of the reflector rods. The spacing between the rods making up the reflector are arbitrarily spaced at about 1/10 wavelength. In fact this antenna is almost a perfect scaling from the two meter antenna in the ARRL handbook, and very similar to the "144/148Mhz Cushcraft one" except that its much smaller.

Oddly enough I have a UK made version of the two meter billboard antenna somewhere stored in the garage. I bought it 15 or 20 years ago and never assembled it. I'll have to see if I can find it :-)

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Best Regards:
                     Baron.

default Inscribed thus:

Yes its the same here ! It seems to take an age to change.

One thing you can do if the beam width is a bit wide (about 130/140 degrees with a flat reflector) is to make the reflector twice as wide and then fold the extra outside edges towards the dipoles at about 45 degrees. Looking down on it should look like a flat pan... Excuse the art !

\ --- / \__|__/

I hope that it looks right. :-)

You will get much better results if you can get the antenna outside. At the frequencies that you are playing with, you will get reflections from walls, doors siding etc. Even your own body will cause things to change.

I'll not let the XYL see that last line. ;-)

I should have qualified that by adding UK ISP's...

At the frequency you are using a quarter wave length of 50ohm co-ax, corrected for velocity factor is all you need. Check out your ARRL handbook.

A compass and map can be an eye opener at times, particularly if you have a big obstruction in the general direction of the transmitter.

We've got our own wind at the moment thank you very much.. -16C here plus wind chill ! Brrrr

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Best Regards:
                     Baron.

Thanks Baron.

Thought I'd report back.

The thing is working beautifully. Reducing the space between the reflector and the elements from 10" to 8" made all the difference in the world.

I don't know that bending the reflector in on the sides would be advantageous. Right now I get all the stations the converter was able to find with excellent stability - and according to my research (and borne out by experimentation) the stations are positioned in a 45 degree arc.

I also conclude that it is more indicative of good signal quality if the on screen "meter" is stable and not changing much, rather than showing a high, but variable signal strength.

My wooden antenna supports wouldn't survive the elements so it has to stay indoors. BUT, I'm kinda fired up to experiment further.

I want to try this idea using PVC for the support and cross fittings by Brian Mileshosky, N5ZGT

Unfortunately my Adobe Acrobat won't let me see the whole thing, but I like the construction technique Easy, cheap, "uptown" design, and weather proof/resistant.

From what I can see: The boom is PVC with cross fittings (not usual plumbing stuff but a large hardware store should have them) and slots cut in the fittings with hose clamps holding the pipe sections.

Do you think using 1/2" galvanized steel tubing (called EMT Electricians Metal Tubing here - thin conduit tubing) would be bad? I could always spring for aluminum if it makes a difference. I figure zinc isn't a great conductor - but then anodize is an insulator and anodized aluminum is a material of choice.

Using thick tube should make the antenna more broadband, right?

That, mast and maybe a small JEFET or MMIC amplifier. . .

Anyhow, thanks for your help.

Take care bob

Hi Bob,

default Inscribed thus:

I did wonder if you might :-) Its nice to know how you are getting on ! Anyway I have an interest in antennas myself.

Good ! I'm glad that its improved signal strength for you.

Yes ! What happens is that it reduces the strength of signals coming in from the sides. You can take this to extremes and wrap the reflector around much further so that the edges are further forward, in front of the line of the dipole. Think parabolic dish but only in the vertical plane. If done well, it can double and triple the antenna gain by narrowing the width of the beam in the horizontal plane.

If you have the skills you could make an active field strength meter and get an almost instant indication of signal strength.

You would be surprised just how robust it can be. I once made a two meter (144/146Mhz) transmitting antenna from two bamboo canes, a brush stale, copper wire and fishing line. The brush stale broke after a very large bird crashed into it whilst chasing a pigeon !

I'll get back to you after I've had a look at that.

I can turn PDF's into Jpegs/Giffs if I need to...

PVC drain pipe is a useful material for antenna. As is 6mm PVC rod.

Avoid steel if at all possible ! Aluminum is the material of choice. Anodised is fine if you don't need to make an electrically sound joint, otherwise you will have to grind or sand the anodising away where the connection is to be made.

Not so much that you would notice ! The diameter can become important as the frequency rises.

For the time being don't worry about amplification of the signal. Get the antenna right first. You might find that you don't need it. Anyway it can give rise to other problems. But thats another story.

No problem. You're welcome. :-)

--
Best Regards:
                     Baron.

Hi Bob,

I had a look at that PDF. There is some good info there. Particularly if you look at the radiation patterns. In particular the ones for just a dipole and the one with a dipole and reflector. Essentially they show you the radiation pattern for the antenna that you have just built.

I have a suspicion that the antenna that you are thinking of building is the three element yagi. If it is, please don't waste your time on it. You will be disappointed by its performance in comparison to the one you have just built !

--
Best Regards:
                     Baron.

You guessed it. Lots easier to build, make weatherproof, less expensive, less awkward (neat, compact, lower wind loading) etc..

AND I could easily raise it almost 30 feet higher, where the trees are a bit thinner. The downside is 30+ feet of coaxial losses.

In contrast, it would be more expensive to come up with a bow tie that is rugged enough and long lived. I can count on high winds, and the occasional falling tree limb, pine cones not to mention long leaf pine needles (they seem to have a real penchant for affixing themselves to any kind of screen wires suspended in air)

In total would it still be a net loss?

Regards bob

default Inscribed thus: Hi Bob,

Whilst I see where you are going, I promise, a three element yagi will not provide the performance that the four element billboard will give you.

You are right, you have to subtract the co-ax losses from the antenna gain figure.

The only real hazard that I see there is the falling tree limb. I doubt that any antenna construction could survive that.

Regretfully "Yes" !

You could put a director in front of each of the four dipoles of your billboard array and have effectively the same gain as four of the three element yagi added together. ie 6db more gain. As a rule of thumb each 3db is a doubling or halving of gain depending which way you are going.

As an example, if a single antenna has a gain of "one" then two antenna will have a gain of two. The two antenna has a combined gain of 3db over a single one. Four antenna will be 3db over two antenna or 6db over a single one.

So a single three element yagi will be approximately -6db compared to your billboard array. Notice the "-" sign. In practice the difference is only about -4db.

If you look at the radiation patterns I mentioned, you should see that antenna gain is created by confining the signal pattern in some directions to the advantage of others.

The horizontal pattern of your billboard array is a very much reduced signal from the rear, as you have already discovered, and a narrowing of the pattern at the front.

--
Best Regards:
                     Baron.

For 10m at UHF frequencies and good coax, loss will be 1db or less not a big deal.

The 4 element bow-tie phase array gets its gain mostly by having a larger aperature, the Yagi-Uda, or the similar log-periodic is a directional antenna. IIRC your desired stations are spread over a 45 degree angle.

the bowtie is probably the better one for this application unless you are troubled by multipath reception.

OTOH a 3 element yagi is probably not very directional.

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?? 100% natural

Empirically that seems true enough. I connected a long piece and carried a dipole around looking for hot locations and never really saw any problem with losses in the line.

I miss the good old days of analog TV. You could look at the screen and see multipath, or ignition noise, or a noisy power line connection or arcing, or some idiot who bought one of the $69 vacuum toob linear amplifiers and connected it to his CB rig.