Topband: 160m inv vee questions

[Brian Pease]

I modeled an inverted-V last week.  If the feed is balanced, the total 
radiation pattern (Hor + Ver) is omni-azimuthal with a lot of upward 
radiation.  Directly broadside, the radiation is horizontal but off the 
ends it is entirely vertical.  For 160 to EU I would orient NE-SW.

On 4/1/2018 6:41 PM, Dick Green WC1M wrote:
> Hi all,
>
>   
>
> For many years I’ve had a trapped 80m/160m inverted vee with the apex at
> about 94’ on a tower that’s loaded with various yagis. The vee is oriented
> so that it’s broadside to the NE and SW (wires running SE to NW). The tower
> is on a steep hill, so the wire that runs to the uphill side is only about
> 17 feet off the ground, while the wire on the downhill side is about 27 feet
> off the ground (maybe more).
>
>   
>
> The traps are Rayco KW-80C, which is cut for 3.625 MHz, setup for two-band
> operation. On each side, the 80m portion above the trap is cut to 68 feet
> and the portion below the trap is cut to ~47’, for an overall length of ~115
> feet per leg.
>
>   
>
> As you would expect, the bandwidth on both bands is narrow. Since I operate
> almost exclusively on CW, and have an 80m delta loop with better radiation
> angle and bandwidth, I only use the 80m portion of the trapped vee for an
> SDR that monitors the band (due to switching limitations, the SDR can’t use
> the delta loop).
>
>   
>
> The lower wires have been trimmed to center the antenna at 1.830 MHz on
> 160m. The 2:1 bandwidth is about 40 KHz, and around 70 KHz between the 3:1
> marks. So the antenna is useful on most of the CW portion of the band. It
> hears OK when the atmosphere is quiet, but normally I use a 520’
> dual-direction NE-SW beverage for listening. As expected, the effectiveness
> of the transmit portion is limited. I’ve worked at least 100 countries with
> it, and in a typical contest I can work EU and SA/Caribbean if conditions
> are good. But I’m usually well behind the top stations in multipliers –
> maybe a little better than half what they have. Again, no surprise.
>
>   
>
> Recently I started thinking that maybe I should ditch the traps and convert
> the antenna to a full-size 160m inverted vee. The overall length and height
> of the ends above ground will be comparable. But when I compared the 160m
> inverted vee to the 80m/160m trapped inverted vee in EZNEC+, there was only
> marginal difference. They’re both cloud warmers at DX angles, and the SWR
> bandwidths were the same. I found this somewhat surprising, given trap
> losses and such. I would have expected a more noticeable difference in gain,
> angle and especially bandwidth. So, my first question is, am I reading the
> EZNEC+ results right, and there’s no real advantage to converting the
> antenna, especially in light of losing it for SDR use on 80m?
>
>   
>
> Second question came up while I was reading some articles about 160m
> antennas and came across one that said more radiation comes off the wires of
> an inverted vee than broadside. I was under the impression that inverted
> vees are omnidirectional, and if there was any directivity it would be
> broadside, like a dipole. I happened to orient my trapped inv vee so it’s
> broadside to EU (NE/SW) on the tiny chance there could be some directivity
> in that direction. But if the article is right, or if the radiation is truly
> omnidirectional, then I’m better off orienting the legs NE/SW (broadside
> NW/SE) because the slope of the land would allow for the uphill leg to be
> considerably higher off the ground (it would run mostly over flat ground),
> though it’s not clear to me what advantage that might confer. However,
> there’s a more definite advantage because the legs of the inverted vee would
> be much farther away from my beverage. Right now, one leg comes within about
> 20 feet of it. If I reorient the antenna it would be over 100 feet away.
> Comments?
>
>   
>
> Finally, another option would be to ditch the traps and one leg, and slope
> the other leg towards EU as a ¼-wave vertical on 160m (with lots of
> ground-mounted radials, of course.) Unfortunately, that would have to be the
> uphill leg, so the vertical would be somewhat flatter than if I could point
> it SW. Would such a vertical be superior to what I have now or the dedicated
> inverted vee?
>
>   
>
> 73, Dick WC1M
>
> _________________
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