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1-4 of 4 messages
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Page 1 of 1
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R7 performance
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by AB8BC on September 8, 2000
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hello gang. I have a Cushcraft R7. Had a question about performance. It's not one of the better performers I've had but it's all I've got at this time. Question is, can I improve performance on 20 meters? It tunes ok in that band, but should I add some ground radials? If so, how long, how many and what type of wire and ga.?
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RE: R7 performance
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by K0RS on September 10, 2000
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The Cushcraft "R" (R5, R7, R7000) series verticals have never been known for their stellar performance. Check some of the owner's comments in the review section here on eHam. They have traded convenience (small footprint, several bands) for reduced efficiency. The best bet is to stick with the manufacturer's suggestions for installation. You may find added radials actually DECREASE the performance of these antennas, as they were designed to operate without them. Extra radials could raise the "Q" of the antenna and make its SWR response even narrower than it already is. This could increase the possibility of damaging a trap, an infamous weak spot, when operating off resonance. For improved performance on 20m, try a simple quarter wave vertical (about 16' tall) with several radials under it. For better multiband performance in a vertical, a Butternut HF6 or HF9 is hard to beat. The Butternut verticals have no traps and through an innovative design use all (or nearly so) of the antenna to radiate on each band.
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RE: R7 performance
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by LA1SJA on September 25, 2000
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Agree with K0RS.
Some additional remarks.
On 20 meters you can build a wire-based "monobander" vertical in a single afternoon at fraction of the
cost of any model in the R-series or its competitors, and chances are that it will outperform most of the commercial multiband verticals for low-angle DX stations.
That is, - provided your local ground is in the range "medium / average" or better.
Ref. ARRL Antenna Handbook.
If you live on "bad RF ground", no vertical will serve you really well, but those with elevated radials are
usually the best.
This is a $ 10 solution with a tree (or a $ 100 solution with a quality glass-fibre fishing rod):
Find a tree (or a fishing rod) that is 9,5 meters high. String a 1/4 wave wire cut for 20 meters down from the top.
Drop 3 1/4-wave wire radials evenly spread down from where it ends and towards ground at 30 degrees angle.
The lower ends of the 3 radials will each end up approx. 2 meters above ground.
Continue from there at the same angle with ropes to ground, trees or even to your house.
Feed it with coax.
If you have the patience to cut all wires carefully, it will end up closer to 50 ohms than to 30.
This is simply a dedicated 20-meter version of the time-proven GP-antenna.
The better your ground is, the more you will hear of DX, and the less of nearby stations..
For bad ground it is the other way around.
Unless your QTH is surrounded by high buildings you should start hearing some real DX again.
For local ragchew, move it as high up as possible, (DX normally goes away though).
In comparisons over a long period, this antenna seems consistently to win over my R7 with a considerable signal margin, - exept for the very rare occation.
I have tried this approach with "monobanders" on the 7 highest HF bands, and they all outperform my trap-based multibander, at least for DX.
If for practical reasons you prefer a multibander, you might try the Butternuts.
(Think of it; - 9 HF monobander GPs spread out on a salt water beach.
160 to 10 meters.
Perfect ground (!).
Most of us with just have to dream about expeditions like
http://pages.prodigy.net/k2kw/story.html
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