Author Topic: Antenna ideas?  (Read 8175 times)

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asatrur

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Antenna ideas Reboot
« Reply #15 on: July 11, 2014, 03:39:51 PM »
Rebooting this based on a new situation.
I have moved my shack to on the 2nd floor of our house, so I looking at ways to mount my mag mount 2M antenna. before, I ran a cable out the window to where it was sitting on a table. Now out the nearest window is something like 20 feet of the deck. I am consider building a small pedestal out of treated wood and mounting to the side of the house right outside the house. There are trees, my soon to be tri-band pole, etc. that are much higher than this, so I am not too worried about lighting strikes.
Ideas?
Thanks,
Asa
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ghrit

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Re: Antenna ideas Reboot
« Reply #16 on: July 11, 2014, 04:26:54 PM »
Rebooting this based on a new situation.
I have moved my shack to on the 2nd floor of our house, so I looking at ways to mount my mag mount 2M antenna. before, I ran a cable out the window to where it was sitting on a table. Now out the nearest window is something like 20 feet of the deck. I am consider building a small pedestal out of treated wood and mounting to the side of the house right outside the house. There are trees, my soon to be tri-band pole, etc. that are much higher than this, so I am not too worried about lighting strikes.
Ideas?
Thanks,
Asa
You are going to need something to serve as a ground plane with the mag mount.  You might get away with steel gutters if you have them, but I would not count on it.  (A steel roof could be very good.)  I'll leave it at that for now, there are better ideas out there that someone else knows.
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Tevin

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Re: Antenna ideas Reboot
« Reply #17 on: July 11, 2014, 09:08:52 PM »
ghrit is 100% correct. A mag mount antenna sitting on a wood pedestal is literally only half an antenna.

If the cable will reach from your shack down to where you park your car, then stick it on the car. From a functionality standpoint, having a proper ground plane more than offsets the lower elevation.

You can get nice base antennas that have a ground already on them (or are designed to run without) for less than $100.

(You're an Extra, you should know this stuff already  ;) )

asatrur

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Re: Antenna ideas?
« Reply #18 on: July 14, 2014, 03:22:30 PM »
I should have been clear, I would cover the platform with sheet metal, so the magnet has a purchase point and hence the ground plane on it.
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Quiet1

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Re: Antenna ideas?
« Reply #19 on: July 14, 2014, 08:30:01 PM »
Or you could go with some J-pole / Slim Jim variant, which doesn't need a ground plane.  It just needs a place to hang, it could even hang from a broomstick outside your 2nd floor window.  All kinds of plans and pre-built ones on the net, but here are a couple of my favorites:

http://www.jpole-antenna.com/shop/2-meter-slim-jim-antenna/
Well-made, ready to plug-n-play, no meter needed.  A bargain at $42, about $50 shipped.

http://www.kn9b.us/slim-jim-antenna
Dead easy to make for maybe $5 in parts.  Be careful with the dimensions and it won't even need tuning (though it's probably smart to check the SWR before pushing 75w through it).  Also a good bug-out antenna, I've hit repeater 25 miles away with a 5w HT using this design.
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Tevin

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Re: Antenna ideas?
« Reply #20 on: July 15, 2014, 07:12:11 AM »
I should have been clear, I would cover the platform with sheet metal, so the magnet has a purchase point and hence the ground plane on it.

This ^^ will work but only if the the sheet metal is somewhat large in area, a few square feet at minimum.

Ideally, the metal would be round in shape and allow at least 1/4 wavelength of metal around the antenna. In these cases though you have to work with what you have.

As long as there is a substantial ground plane, you should be ok.

ghrit

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Re: Antenna ideas?
« Reply #21 on: July 15, 2014, 07:43:18 AM »
This ^^ will work but only if the the sheet metal is somewhat large in area, a few square feet at minimum.

Ideally, the metal would be round in shape and allow at least 1/4 wavelength of metal around the antenna. In these cases though you have to work with what you have.

As long as there is a substantial ground plane, you should be ok.
Perhaps not as ideal as a sheet metal ground plane, but you could also use an insect screen of a conductive metal.  Even stainless should work and be a whole lot lighter for your platform.  If you are going to build a platform anyway, there's no need for a mag mount, you could use something else bolted to the platform.  (Yes, that means unscrewing the whisker when moving it out to the car and putting it back on the mag mount --)
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Lamewolf

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Re: Antenna ideas?
« Reply #22 on: October 18, 2014, 10:34:19 AM »
Build yourself an 80 Meter Wire Dipole and use a 4:1 Balun in the Center. Put up a Pole to hold the Balun in the center of your Lot, as high as you can get it, and then let the ends droop down to 15 Feet out at the Property Lines. You can use regular 14 Gauge Stranded Wire, as it will not stretch enough to cause you any issues.  Then get yourself a Good MANUAL Tuner and use that to tune all the other Bands. I have used an 80 Meter on HF for decades, here in alaska and have very good contacts. Mine is 60Ft and strung between a tower and a Tree. Just say'en  Bruce in alaska AL7AQ.....

If he is going to use an 80 meter dipole on all bands, he would be better off skipping the coax feed with a balun at the center and just feed it with balanced feedline starting at the center of the antenna and coming to his entry point right outside the shack and put the balun there but use a 1:1 current balun, then a short run of good 50 ohm coax coming into the shack to the tuner.  This is what is know as an "All Band Doublet" that will work 10 thru 80 meters with a tuner.  If he uses the coax feed, things will be good on 80 meters and efficiency will be about 75% on that band only.  But there will still be a high SWR on the coax when force feeding it on other bands that will cause the losses to skyrocket. For example, by force feeding the 80 meter dipole on 40 meters, the losses in the coax feed will cause the efficiency to drop to somewhere around 10% which means he would be wasting about 90% of his power in the form of heat in the coax due to the losses.  But by using a very low loss balanced feedline such as 450 ohm window line, the efficiency of the same antenna on 40 meters will be somewhere around 90%.  The swr will still be present on the balanced feedline but the losses will still be very low simply because the balanced feedline is not effected by high swr like the coax is.  You just make up the difference in mismatch by using the tuner.  I know a lot of folks will say that this type of antenna is a compromise, but I would venture to say that they have never used such an antenna !  I know cause I use one all the time AND it works better than any coax fed dipole I have ever used and most of the time I run about 2 watts CW and have worked all over the world with it.  My signal reports actually started getting consistently better when I switched to a balanced feedline and the locals that I chat with on 75 meter when I do operate phone all thought I had bought an amp !