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Author Topic: qrp base antenna  (Read 4342 times)
KC2ULJ
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Posts: 19




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« on: March 03, 2010, 03:47:37 AM »

hello, if you could only have one antenna for multiband
operation (40-10) would it be a vertical or g5rv mini or? Operating conditions ft-817 and ldg 817 tuner.New to qrp but loving it so far. Thanks for any input.kc2ulj
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WX7G
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Posts: 6131




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« Reply #1 on: March 03, 2010, 05:38:35 AM »

I think a good multiband vertical and the mini-G5RV will perform about the same. For example, a Hustler 4BTV and the mini-G5RV would both work well.
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W5ESE
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Posts: 550


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« Reply #2 on: March 03, 2010, 08:05:55 AM »

I would go with either a Center-Fed Zepp or a Horizontal
Loop fed with a tuned feeder (either 450 ohm window line
or open wire ladder line). You can also feed these with
300 ohm TV twinlead, although it will be somewhat lossier.

You can read more about the Center-Fed Zepp from the
ARRL at:

http://www.arrl.org/tis/info/pdf/9611073.pdf

73
Scott
W5ESE



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WB6BYU
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Posts: 13335




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« Reply #3 on: March 03, 2010, 09:05:16 AM »

Part of the decision depends whether you want to optimize performance
for 40m or 15m, rag chewing or DX, and on your soil characteristics and
available antenna supports, etc.

Generally I'd probably choose a horizontal loop resonant on 80m and
mounted at 90' or so among some trees.  But if I wanted to work my
buddy 100 miles away I'd lower the loop to 30' and size it for 40m instead.
Generally a high horizontal wire will outperform a ground-mounted vertical
unless ground conditions are very good:  I remember one ham in a logging
camp in Alaska who had a horizontal dipole up about 15 feet, and I kept
trying to talk him into trying a vertical because the camp was on a log
raft floating in salt water.

If you are considering a half-size G5RV, spend some time reading VK1OD's
analysis of feedline efficiency at http://www.vk1od.net/antenna/G5RV/index.htm.
You will have to decide how much power you are willing to lose in your
feedline on which bands.  One of the most efficient options is to feed it
with open wire line all the way from the antenna to the tuner in the shack,
and in that case there is little benefit in cutting it to any exact length (unless
you want the pattern aimed in a specific direction on a particular band.)
Any center-fed wire longer than about 40 feet or so can be pressed into
service on 40m, but the efficiency improves as it gets closer to a half wavelength.
The radiation pattern will be mostly broadside to the wire on 40m and 20m (unless
the wire is much longer), and will start breaking up into lobes on 10m (unless the
wire is less than about 45 feet long.)

So the "best" antenna depends on the preferred target location, the bands you
like the best, the characteristics of your site, how stealthy you need to be, the
effort you want to put into having a good signal, etc.  If you are going to use a
G5RV variant, choose an efficient feedline option.  If you are using a vertical,
use an adequate set of radials for it.  With other sorts of antennas, consider
the feedline losses - just because the tuner can match it doesn't mean that you
might not be losing 75% of your power before it reaches the antenna.
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KC2ULJ
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Posts: 19




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« Reply #4 on: March 03, 2010, 12:21:13 PM »

Thank you all for responding. I only have trees on one side of my property to hang wire in, hence the idea for the g5rv junior. The feedline looses are a concern. If I were to feed the longest dipole I can facilitate at approx 40ft could I use a 4:1 balun right outside the window of my shack (basement) to keep the ladder line out of the house as they are fixed windows? Thanks, Mike
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WX7G
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Posts: 6131




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« Reply #5 on: March 03, 2010, 02:06:36 PM »

A dipole fed with open line to a 4:1 balun and then coax can create a very high VSWR on the coax.

I would use the G5RV Junior because the VSWR on the coax is lower.
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WB6BYU
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Posts: 13335




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« Reply #6 on: March 04, 2010, 11:29:03 AM »

How are you going to get the coax into the station?  I'd transition from
open wire line to twinlead right outside the house (perhaps sheltered
under the eaves, or in the attic) then run the twinlead into the shack
and directly to the tuner.

Using a 4 : 1 balun and a length of coax can lead to some quirky impedances
at the  tuner, not to mention that many 4 : 1 baluns are not optimum at high
SWR, a 1 :1  balun may be better in many cases, etc.  If you take that route,
keep the coax as short as possible and use relatively large, low-loss coax.
You may still have to adjust the feedline lengths a bit for convenient matching
on all bands.
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N9GGE
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Posts: 12




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« Reply #7 on: March 06, 2010, 06:40:59 AM »

I thought a G5RV-JR would be a good choice, and it was until winter came and 80m was the only band open in the evening when a lot of the QRP sprints take place. G5RV-Jr won't load up on 80. I had enough room, so last summer my friends took the Jr down and put up a full size 102' one. Now that the flux is finally picking up a little, the other bands may stay open longer next winter. Since you have a Z817, you might want to consider a random wire as a back-up. Not the greatest, but you would be surprised sometimes.
73 72
John
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W8BS
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Posts: 9


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« Reply #8 on: March 08, 2010, 03:00:38 PM »

A Mosley Pro-67B on a 70 ft tower makes a great qrp antenna.  :-)
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KC2ULJ
Member

Posts: 19




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« Reply #9 on: March 09, 2010, 01:17:09 AM »

hihihi, could I borrow it for a while?
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K2QPN
Member

Posts: 70




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« Reply #10 on: March 16, 2010, 04:49:18 PM »

Why not both. Two antennas are always better than one. I think you will find that the G5RV is better for shorter distances and the vertical is better for longer distances. For me, being a DXer, I would choose the 4TBV if I could have only one. I have worked QRP DXCC with a Hustler 7BTV vertical on 40, 30 and 20 meters.

73, Bob K2QPN
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WB5JEO
Member

Posts: 805




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« Reply #11 on: March 18, 2010, 07:15:11 PM »

I might add that IF you intend to work a lot of other QRP stations, consider that a separate low-noise receiving antenna is a possibility. It's not such a thing on higher frequencies and is more often something that low-band DX operators go for, but it can be useful on 40. Receivers can deal with weak signals but inevitably also amplify the noise, so gain is not so much of an issue. If you're after other QRP stations, low noise and sharp nulls can make the difference in whether you hear them or not. Beverages (if you  have the space) and the lesser performing magnetic loops are popular.
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WX7G
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Posts: 6131




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« Reply #12 on: March 19, 2010, 01:59:24 AM »

KC2ULJ, I have an FT-817 and an Elecraft T1 tuner on order. How do you like the FT-817?

The G5RV junior can be used on 80 and 160 meters by feeding it as a vertical. The LDG tuner should tune it on 80 meters and maybe 160. If it won't tune on 160 meters add series inductance at the tuner output.

At 5 watts the house AC wiring will suffice as a counterpoise. Connect the LDG GND stud to the AC socket GND. A banana jack will work plugged into the GND.

The three 160 meter contests during winter (ARRL, CQ, Stew Perry) are fun with QRP. With what you're contemplating for an antenna you can expect to make a couple hundred contacts in each contest.
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KC2ULJ
Member

Posts: 19




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« Reply #13 on: March 27, 2010, 03:55:13 AM »

Thanks again to everybody for all the help, I am liking the 817 alot,amazing little radio. I can hardly wait for better weather to do some camping and portable work. After several attempts I ended up with a 135 ft doublet fed with ladder line to a homemade 4;1 coaxial air bulun(qst)and a 3ft piece of rg8 to the z817 tuner. Seems to be working well. 73 w2waw (new call) pevious kc2ulj
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WB4TJH
Member

Posts: 192




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« Reply #14 on: January 22, 2011, 08:45:45 AM »

I have a 140 foot center fed dipole up 40 feet, fed with 450 ohm windowline and a DX Engineering 1:1 balun. I tune it with an MFJ rotary inductor tuner. It is a superb antenna from 80 thru 10, with qrp or qro. I doubt that any simple wire antenna could be more efficient or useful on all bands than this one. It is much, much better than a lousy G5RV. Period.
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