[TowerTalk] 80 Meter beam
David Aslin G3WGN
david at aslinvc.com
Sat Apr 1 10:07:38 EDT 2017
Grant, did you happen to also do a Pro/4 analysis of a 4-square over poor ground?
At my new QTH I'm not going to be able to get a beam higher than around 125ft for 80m, and that would be a 2-el wire inverted vee style since a Yagi is out of the question from a neighbour/town planning approval perspective.
Although the conductivity map of this part of UK suggests average ground, I'm getting some empirical data from the installation of electrical safety grounds at 3 points on the property. UK regulations require that these show less than 200 ohms resistance (!) and the electrician is finding he needs 5/8" ground rods 8ft or longer to meet that test (most homes in this country have 3/8" 4ft rods for safety ground at the service entrance). This suggests that locally I may have poor ground so a 4-square may not be my best choice. It would be good to compare the wire 2-el with a 4-square over poor ground. The downside of the wire beam of course, is that it will be fixed in direction.
All thoughts/comments welcome as I will only get one shot at building this station!
73, David G3WGN M6O
From: Grant Saviers [mailto:grants2 at pacbell.net]
Sent: 01 April 2017 04:20
To: john at kk9a.com; towertalk at contesting.com
Subject: Re: [TowerTalk] 80 Meter beam
I (try to) work 80m LP SSB to EU many winter mornings from Redmond, WA.
There are about a half dozen west coast stations that can often work them if they are there and 2 or 3 that can generate a pile up in EU.
The "biggest gun" is N7UA nearby in Poulsbo, WA who has some monster wire antenna I think at 240'. Height for horizontal polarization is everything on 80m to get the radiation angle lower. Next are a couple of 80m 3L beams in WA and OR. Then a couple of 4 squares, particularly one in the CA alkali desert which is about as conductive as salt water.
Even lower angles than horizontal antennas. As Jim noted, ground conductivity is everything with verticals/4 sqs. Then maybe several others and me with a 2L at 157'. The N7UA reported signal vs mine is often 10db or more and my location is pretty good.
Yes, you have to really want a beam for 80m as they are a major investment and can be a maintenance headache. My tower guy quipped, "put up a big one, and I'll see you twice a year."
Peak gains referenced to a dipole at 70' for a 5 deg take off angle (common EU to west coast) - EZNEC Pro/4 analysis I did for a club
dipole at 100' +2.8db
dipole at 125' +5.6db (this is where 80m dipoles begin to play well for my path to EU) single vertical average gnd +3.9db
4 sq average gnd +5.28db
vertical on the beach, 2 elv radials +13.4db - directive seaward (see my QST "Verticals on the Beach" article) 2L beam @ 157' +12.8db
4 sq over salt water +19db wow, that will hurt their ears!
Happy so far with my JKantennas 80m 2L beam and it covers 3.5 to 3.84 with switched inductors. Tower guy not called back. I do think I gained about 10db @ 5deg over my prior rotatable 80m dipole at 102', which was the plan. Of course gain is one indicator of often very important noise reduction. My DXEng 4 sq receive almost always beat the dipole at 102' and hardly ever beats the beam at 157'. The beam F/S is usually adequate to null the Chinese OTH radar coming from NW for EU LP to the SW. RDF is good enough on the 4 sq that it is close to beam performance which is what the calculated RDF numbers indicate.
My way back QTH in EMA dipole at 50' was a slam dunk to work EU, too bad I didn't save the QSL cards. HFTA puts the average arrival angles there at around 40 deg vs very little above 10 deg in WWA. As always it is location, location, location and then who you want to talk to.
I would add that there are some interesting wire antennas (what started this thread) with low angle gain such as phased dipoles, V's and delta loops that well done aren't mega investments.
On 3/31/2017 17:37 PM, john at kk9a.com wrote:
> You really have to want a rotatable 80m yagi as there are numerous
> challenges and expenses. I think a 4sq is about as good and it has
> greater bandwidth.
> John KK9A
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