Some more antenna questions.

[AlmostHandy]

I'm going to try my hand at building an antenna. I've been doing a lot of googling and reading, and have a few questions I can't find (good) answers for. I think a lot of the pages I'm looking at assume that you know some of this basic stuff, so I'm I'm sorry if this is really long and boring, but I'm kind of CDO about giving details.

1. I'd like to start by building an antenna that covers the local Air Frequencies. I've heard the best way to do this is with a vertical dipole. I've found a couple of cheap outdoor baluns for tv sets, and I've read that this makes a good dipole. Is this ideal for the aircraft band, or should I consider a different design?

2. My second question is about a railroad specific antenna. The AAR frequencies are all clustered pretty tight, around 160.xxx, but it's been said that railroads are commonly using other frequencies, notably in the 45x.xxx - 47x.xxx ranges. Is there a dipole design work for both 160.xxx and 460.xxx? It looks like the multiple of 160.xxx is 480.xxx, which isn't too far from that 460mhz. How well will that work? Would using thick copper pipe instead of wire help to widen the bandwidth? (see #4)

3. Does the SWR of the antenna matter if the antenna is receive only?
If so, how should I go about finding an SWR meter? I haven't been able to find any dummies guides to SWR meters, so I have no idea what I'm looking for. Of course, the range of options is incredible. I've seen things like this cheap $15 model, but I know about the "You get what you pay for" way of business, so am wary if it will even work for my applications. What kind of specifications will my SWR meter need to have? Should I be looking for a local ham who will analyze my antennas for a 12 pack and some pleasant conversation instead?

4. I have read that the thickness of the wires is a factor in determining the bandwidth of the element in question. The thicker the wire, the wider section of the band it will receive, correct? How thick can the elements be? For example, when making a dipole, can I use 1/2 copper water pipe instead of wire?

4a. Concerning this Multiband Groundplane Antenna design; Do all three element wires need to be the same thickness? Can I use a thicker wire on the longer, lower band elements for a wider bandwidth, and a thiner wire on the 800mhz element for more specific tuning?
Do the ground plane radials need to be the same thickness as well?

5. And lastly, and this is a bit trivial, but it seems that when I'm done, the ground plane device will be quite lanky, and a little rickety. Besides using a piece of conduit to hold the whole thing up by the connector, (which I'm told must be thoroughly coated with some silicone to keep moisture out), what kind of protection should I use on the radials? Won't the copper corrode after time? Can I use some kind of spray poly coating to protect the wires, like Plasti-coat?

Thank you, everyone!
-Mike

 

[AlmostHandy]

Please? Pretty please?

I think I was a bit too wordy. Sorry about that.

But seriously, you don't have to answer all of them at once. Maybe I should have made separate threads?

 

[SAR923]

Buy a Radio Shack 20-176 ground plane. It will do well on the air band, VHF, and UHF. It will cost way less than the materials you propose and probably perform better as well.

 

[AlmostHandy]

Buy a Radio Shack 20-176 ground plane. It will do well on the air band, VHF, and UHF. It will cost way less than the materials you propose and probably perform better as well.

Perhaps, but buying it will be less fun than building it, and I won't learn anything new.

I've found a couple of books online that are really helping. The ARRL's 3 volumes of Antenna Compendium are on Scribd.com, so I've been reading as much of that as I can.

I've been focusing finding answers to the SWR questions. I can't find any reference to whether or not the SWR of the antenna matters when receiving only. Almost every article I have found on the subject is dealing directly with the CB band radios.

 

[blueangel-eric]

check this one out
http://www.radioreference.com/forums/showthread.php?t=109144&highlight=dipole+array

I built a 2 dipole array that is broad banded enough to cover 2 meters thru the RR band. works great. also seems to have some gain on the 450mhz band as well. it's a chore to built a phasing harness though. and the proper cable is harder to find these days. But just one dipole is still good. now i have a new digital camera i can go out tomorrow and take some pictures of mine and post on here sometime.

 

[zz0468]

1. I'd like to start by building an antenna that covers the local Air Frequencies. I've heard the best way to do this is with a vertical dipole. I've found a couple of cheap outdoor baluns for tv sets, and I've read that this makes a good dipole. Is this ideal for the aircraft band, or should I consider a different design?

Look up information on the coaxial antenna. They're easy to make, and a balun isn't required. It, in effect, it's own balun. The TV baluns would work, if that's what you want to do, but there are better ways....

My second question is about a railroad specific antenna. The AAR frequencies are all clustered pretty tight, around 160.xxx, but it's been said that railroads are commonly using other frequencies, notably in the 45x.xxx - 47x.xxx ranges. Is there a dipole design work for both 160.xxx and 460.xxx? It looks like the multiple of 160.xxx is 480.xxx, which isn't too far from that 460mhz. How well will that work?

It would work just fine. Antennas used on their third harmonic present a decent match to 50 or 75 ohm coax. For your purposes, the frequencies are close enough. A viable alternative is to build a vhf dipole, then add a uhf dipole in parallel. so, each leg of the dipole would have a long element and a short element. Use your tV balun if you must, buit I'd just hook the coax up to it directly. A few loops of the coax leading to the antenna will decouple it from the coax shield.

Would using thick copper pipe instead of wire help to widen the bandwidth? (see #4)

Yes, but in a receive application like this, you're not going to notice the difference.

3. Does the SWR of the antenna matter if the antenna is receive only?

Yes and no. If it's really horrid, like trying to hook an end fed half wave to 50 ohm coax, there will be some signal loss. But realistically, an antenna cut for 150 MHz will hear 170 MHz just fine.

If so, how should I go about finding an SWR meter? I haven't been able to find any dummies guides to SWR meters, so I have no idea what I'm looking for.

For a receive antenna? I wouldn't waste my time unless part of the exercise is to learn. There are some excellent antenna analyzers aimed at the amateur market that are great for antenna experimentation. Check the ham radio supply places on the internet. An SWR meter itself requires a signal source, i.e. transmitter, in order to operate.

Of course, the range of options is incredible. I've seen things like this cheap $15 model, but I know about the "You get what you pay for" way of business, so am wary if it will even work for my applications.

It won't.

What kind of specifications will my SWR meter need to have? Should I be looking for a local ham who will analyze my antennas for a 12 pack and some pleasant conversation instead?

Many hams will do a lot more than that for less beer. It's a viable option.

I have read that the thickness of the wires is a factor in determining the bandwidth of the element in question. The thicker the wire, the wider section of the band it will receive, correct? How thick can the elements be? For example, when making a dipole, can I use 1/2 copper water pipe instead of wire?

Yes, thicker will increase the bandwidth, within reason. 1/2" copper water pipe makes excellent antennas.

Concerning this Multiband Groundplane Antenna design; Do all three element wires need to be the same thickness? Can I use a thicker wire on the longer, lower band elements for a wider bandwidth, and a thiner wire on the 800mhz element for more specific tuning? Do the ground plane radials need to be the same thickness as well?

What does the article say? If you're going to duplicate a published construction article, you really should duplicate the construction details as much as possible, or your results may vary wildly from the author's. This is especially true of antennas and other devices where the electrical performance is based on the physical dimensions.

And lastly, and this is a bit trivial, but it seems that when I'm done, the ground plane device will be quite lanky, and a little rickety.

I would agree with you there.

Besides using a piece of conduit to hold the whole thing up by the connector, (which I'm told must be thoroughly coated with some silicone to keep moisture out), what kind of protection should I use on the radials? Won't the copper corrode after time? Can I use some kind of spray poly coating to protect the wires, like Plasti-coat?

Yes, you can weather proof it. So long as the weather proofing material is non-conductive, it's unlikely to have any affect on the antenna's performance.

 

[AlmostHandy]

Wow far out. That takes care of just about everything I need. I'll start with the simple dipoles, and let everyone know how they work out for me.

I tell you, half the fun of all of this is planning, at least for me.

 

[AlmostHandy]

Ohh, Solid link, blueangel-eric!

That thing looks really ambitious. I'll have to build a few smaller ones first, before I can hang something that big in the yard.