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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 09-02-2010, 10:04 AM
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Default New to HF, need some guidance on antennas...

Hey guys,

I just recently got my general license and an IC-718 and was looking into getting a better antenna. Currently I've been essentially using a random wire and its not really cutting it. Lately I've been looking at purchasing either a:

Comet H-422
NCG New Product Detail

or

a Comet HVU-8
Comet HVU-8 80/40/20/15/10/6/2M/70CM Vertical

Both of these seemed to have received decent ratings, and both of them are multiband, a big plus for me as I don't have much room to put multiple antennas at the moment. My big concerns are grounding, tuning, and mounting: three concepts I'm not particularly familiar with. As far as grounding goes, I'm aware that most HF antennas have to use ground radials, something I really don't have much room for. Would there be anyway just to use an 8' copper rod on either of these?

Second, as far as tuning and getting that SWR as low as I can, will I need an SWR meter, a decent antenna tuner, and to construct a good balun for the antenna? What are some good meters and tuners for a relatively low price?

And finally third, I'm thinking about mounting this on my chimney and I understand I'm going to need a rotator. Whats a good rotator to start with? What is the power source for these rotators? How much wire will I need for it?

I'm sorry if these questions are too elementary for ya'll, but I appreciate all your help!

Thank you!
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Old 09-02-2010, 10:55 AM
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The links don't provide any wind-load figures but both appear to be a lot of wind-loading for a masonry chimney. You might have better luck with some type of roof-peak mounting hardware (a saddle mount, a short mast and guys).

Most multi-band antennas are pretty narrow band. The shorter they are with respect to a 1/2 wave length, the narrower they are. You will need something to measure reflected power and a SWR bridge is going to be the cheapest way to go. Daiwa used to sell a really nice meter that displayed forward & reflected power and SWR at the same time. They were kind of expensive but you might be able to find one at a hamfest or on e-bay.

An antenna tuner will help reduce the amount of power reflected back into your transmitter. Almost all solid state RF amps have protection circuits that will cut back on the amp's power if the SWR is too high. It would be a good idea to have one if you will be using multi-band or loaded antennas.

You can make your own balum but you might be better off buying one. It will be cheaper and work better.

There is a lot of really good information in the ARRL Antenna Book. Get one and study it before making any major antenna decisions.
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Old 09-02-2010, 10:57 AM
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Thanks!
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Old 09-02-2010, 11:58 AM
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Both of those would make a fine choice as a new antenna. A few things to keep in mind though.

They are physically shortened (which means they are electrically loaded). Not necessarily a problem but it will result in some less efficiency.

The Comet H-442 would not require any radials. It has a very low wind load and MAY be ok for chimney mounting. Masonry chimneys do not do well with vibration and torsional loads. All of which an antenna produce in the wind. It would be very easy to put a steel pipe into the ground and mount the antenna onto that. That would also provide a better (read easier) method of grounding. Instead of having to run wires from your chimney, you would already have a direct path to ground. You would still have some work to do, but it would be easier.

You could also get by without a rotator. Rotors are expensive and add a whole new level of problems when it comes to the setup. While you would have a null on either side of the antenna, it will be performing like a dipole and would yield enough contacts that I doubt you really notice.

The other thing to look at is the wind survival rating. It is LOW. 67mph. Depending on where you live, that may not cut it. Especially if you have any ice problems. I know here, it would not make it a month, let alone years. We are consistently over 70mph winds for days at a time. So take that into consideration.

The Comet HV1 (or whatever) vertical would be my 2nd choice of those 2. And it would be near the bottom of any longer list as well It is extremely short (8 feet) which means it's efficiency will be LOW. It is not 1/4 wavelength on anything below 10 meters. I am willing to bet that side by side (although I do not own either), the H-442 would be the winner. You can fool with physics.

Good Luck, 73

WM
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Old 09-02-2010, 9:00 PM
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Given the information previously posted allow me to add my 2 cents.

What bands do you think you'll play on mostly?
Where do you intend to talk on each band? DX or ragchew locally?
How much horizontal room do you have available?

On 80 & 40 meters I would string up an inverted vee from the chimney.
There's no "real" wind loading on the chimney with this.
You'll much prefer the performance of the dipoles on these bands compared to a vertical with no groundplane.


On 80m, you're looking at around 60 feet each side of center (if mem serves me well).
Hang the 40m dipole from the same center insulator / balun as the 80m dipole.
Separate the two antennas by a foot or more using some homemade spacers.
Hang the distant ends using a small pulley & rope.
This makes it easy to trim the ends for best tuning in each band.

On 20m, it depends on what you plan on doing.
Verticals generally offer a lower angle of radiation than a horizontal dipole.
DX'ing would probably be better with a vertical.
You'll want a tuned counterpoise if you mast mount it high above ground.

If it's ground mounted, you'll want at least a few buried radials of appropriate length.
At & above 20m, 3 or 4 quarter wavelength radials for each band the antenna covers will work ok.
The length of buried radials is not terribly critical although it's better to err on the long side of the formulas.

If the vertical covers 40 & 80m, more buried radials works much better unless your soil conductivity is excellent.

For anything at or above 20m, it's a toss-up & depends more on where you want to talk mostly.
The choices come down to yagi / quad, vertical or dipoles.

I would not mount a multiband yagi / quad on a chimney.
Multiband verticals might even be too stressfull for a chimney.

This is not all inclusive & ...now you know.......as little as I do.

BC
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Old 09-03-2010, 1:45 AM
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Wow this is alot to take in to consideration. What about this one? Its a little pricey but its seems somewhat simple and despite the fact that it does present alot of compromise it seems like mounting it wouldn't be too difficult:

Wirelessness!: New Antenna!!
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Old 09-03-2010, 8:46 AM
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I don't know that I would give this reviewer much credence. I stopped reading when he said that it was unfair to compare this vertical to a dipole. I mean come on! Fair? Is he writing a review or is this a sporting contest?
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Old 09-03-2010, 9:30 AM
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Quote:
Originally Posted by jackj View Post
I don't know that I would give this reviewer much credence. I stopped reading when he said that it was unfair to compare this vertical to a dipole. I mean come on! Fair? Is he writing a review or is this a sporting contest?
"As expected the Comet performs better than the homebrew." With a "lower noise floor" AND "getting signals where there were no signals before"? I agree with Jack, this is a jacked-up review. We don't know what bands he's working, or anything else. dBd = decibels of gain over a dipole, it's a common and useful comparison.

Having said that, for your first HF antenna, build a dipole. A spool of wire is cheaper than most verticals. You can build one for a single band, or for multiple bands. Keep in mind, if you go with a multi-band antenna (homebrew or store-bought) you will compromise performance on each band, as a trade-off.

Have fun!!
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Old 09-03-2010, 10:51 AM
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Ya, that review was not so great. That gent clearly has the ability to sacrifice performance for ease of install. Being quieter than a dipole (despite being a vertical which are widely known as being far noisier than a horizontal dipole) does not make me think "amazing". It makes me think a lot of loss.

The fact that there are no radials needed and the coax plugs into a black matching coil makes me think there huge voltages seen at the feedpoint. Resulting in lost power (watts) and eventual failure. Whenever I see an antenna like this and they limit the power to 200ish watts, I get scared. A cheap dipole can easily handle 1500 watts. What are they protecting by limiting power?

Remember, there is no free lunch in the antenna world. You cannot fool physics with money.

73

wm
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Old 09-03-2010, 11:24 AM
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Let me add my .02 cents with this...

I didn't see if you were using a tuner with your radom wire,
I live in a one bedroom apartment with NO ACCESS to the roof, what I have done is run an 18gauge wire out my window to a tree 100 feet away and added an AH-4 tuner from ICOM and use it with my IC-7000.

The tuner is grounded to a cold water pipe which services the HCAV unit on the roof and does not run into anyone units.
The tuner is mounted to a piece of 3/8 plywood below the widow and does not damage the wall or anything, this window also hold my wireless weather satation.

I would never mount any type of antenna to a brick chimeny, that is just asking for prolbem in any kind of windload
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