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1-10 of 13 messages
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Antenna for 40 and 80 meter
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by N7GCO on June 25, 2006
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I have a mini beam (TGM Communications Hybrid Quad) on roof tripod for 10 thru 20 meters but want to better my antenna system for 40 & 80 meters. I currently have a 80 meter dipole, but nothing on 40. The way my property is, I cannot really put out radials for a vertical or a tower (wet land issues). I might be able to roof mount an vertical antenna one on the opposite end from my mini beam. I also can get a dipole up around 45' using trees. Options I have considered are:
-BigStepper IR vertical on roof
-G5RV
-40/80 meter dipole
Other recommendations.
Opinions and advice would be appreciated.
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RE: Antenna for 40 and 80 meter
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by W3LK on June 25, 2006
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<<-BigStepper IR vertical on roof >>
Be prepared for at least two resonant radials PER BAND with this antenna mounted on a roof. 80m radials are pretty long. This antenna is much better ground mounted with a proper radial field.
<<-G5RV >>
Lousy choice for a multiband antenna, despite all the claims.
<< -40/80 meter dipole >>
Best bet as far as I am concerned. Separate 40 and 80 meter dipoles, fed by a common feedline is your best option, as far as I am concerned.
73,
Lon - W3LK
Baltimore, Maryland
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RE: Antenna for 40 and 80 meter
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by K3JVB on June 25, 2006
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I agree...
40 and 75-80 meter wire. Flat top or inverted v. At 45 feet it will play pretty well. Good contacts out to 1500 miles on 40. and 1000-1500 on 75. OR more with good band conditions !
Easy to tune...and can be kinda stealth. Some will call it a "fan" dipole as well.
I use one for 20-40-75 meters. I am in the middle of adding a 160 meter section , with coils.
You can also go with 450 ohm feed, and a good tuner.
good luck
JohnB
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RE: Antenna for 40 and 80 meter
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by WB6BYU on June 26, 2006
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A dipole is an excellent choice for getting started. Since
you already have an 80m dipole in place, just add wires
for 40m to the existing feedpoint and try to run them off
in slightly different directions than the 80m wires. (If
the ends of the 40m dipole are 5 or 10 feet away from the
80m wire there will be minimal interaction when you are
tuning them.)
If your primary interest is DX then a vertical would
probably be a better choice, but the dipole will give
good coverage around the US. (I put up a temporary dipole
at about 30 feet this weekend for Field Day and worked
Alaska, Hawaii, Maine and Florida with 5 watts, which
pretty much covers the whole US.)
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RE: Antenna for 40 and 80 meter
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by K3MOV on June 26, 2006
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Due to space constraints, I use a G5RV as my only 75 meter antenna. It is a flat top at about 35' and goes N / S. I run 500 watts with an Amritron ALS 600 and an LDG AT 1000 tuner.
On 75 I constanly work DX into Europe and South America with 5/9 reports. I have also worked quite a few stations in Africa, including South Africa and all of the recent DXpeditions. Frankly, I have no idea why this thing works as well as it does. Previously I used a Radio Works 80 Special which gave poor results. I keep toying with the idea of something "better", but inevitably return to, "If it ain't broke, don't fix it."
I'm not suggesting you try a G5RV, but rather that you don't dismiss it completely with out a try.
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RE: Antenna for 40 and 80 meter
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by N3OX on June 27, 2006
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It works as well as it does because you don't have a comparison antenna. "If it ain't broke, don't fix it" is a fine philosophy for your own station... if you're happy with the results, then great.
I don't think it's good advice to go with a G5RV because it seems to "work" though... maybe your G5RV is 15dB down from something else... matters very little for the EU big guns, but what about that 4X you couldn't hear? Would an extra 15dB help there?
All antennas "work" to make contacts. Not all antennas are equal. If you can only fit a G5RV at 30' in for 80m, well, it's better to have some capability on the band and have some fun working the loud DX than to not have an antenna at all.
That doesn't mean a G5RV at 30' is an acceptable antenna for someone who could easily put up something better, and I think it's bad advice for anyone who isn't limited in that fashion.
73,
Dan
N3OX
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RE: Antenna for 40 and 80 meter
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by G8UBJ on June 27, 2006
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If the soil has good conductivity (I assume wetlands has) you would be better with the vertical suggested.
I have the 5BTV and it goes very well on 30 and 40m ...80 is another story... but with a better ground who knows?
73 Rex (G8UBJ)
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RE: Antenna for 40 and 80 meter
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by K3MOV on June 27, 2006
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To N3OX: I pass my personal G5RV experience along frequently, not necessarily for the benfit of the original poster here, but for those who don't even bother considering a G5RV for 75/80 meter DX because they've been told that they simply won't be able to work any DX with it. I agree that in this poster's case substituting a G5RV for an 80 meter dipole will not improve his situation.
You mention that I do not have a comparison for the G5RV. Please take another look at my post and you will see that I took down a Radio Works antenna because of poor performance. I was only getting 5/4 or 5/5 reports from G3WXX and his gang whereas I am always 5/9 with the G5RV.
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RE: Antenna for 40 and 80 meter
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by WB6BYU on June 28, 2006
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I've seen similar DX results with a low dipole which
disappeared with the addition of a balun. The vertically
polarized current flowing on the feedline was providing
far more low angle radiation than the antenna itself.
In this case I suspect that much of the shield current is
flowing back down the outside of the coax from the point
where it joins the twinlead. That leaves more current
in one side of the twinlead than the other, so it acts as
a vertical radiator.
So it isn't so much the antenna design that is contributing
to the good DX signal, but the specifics of the installation
that mean the design is NOT working the way it was
intended. Adding a balun or choke at the junction with
the twinlead probably will greatly reduce the DX
signal. The doublet with ladder line didn't work
because it really was balanced. On the other hand,
to optimize the DX signal you could connect the coax
shield to ground radials and disconnect that side of
twinlead at the joint.
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RE: Antenna for 40 and 80 meter
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by K3MOV on June 29, 2006
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Dale, thanks for the info and possible explanation. I think my location probably helps as well. Most of the commercial TV stations in town have placed their antennas within a few miles of my QTH - definitely a good sign. Additionally, as the crow flies, I am only 90 miles from the Atlantic Ocean.
Maybe I am overstating the case for my G5RV. But I see posts on this site and others from hams whose opinions I value a lot suggesting that if you can't get a G5RV (or any type of dipole) up to 60 or 70 feet you're simply not going to work any 75/80 meter DX. And that just isn't so with my particular setup. 73, Tom
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