HFU HF Underground
Technical Topics => Equipment => Topic started by: Rafman on February 17, 2013, 1410 UTC
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I've been studying what to do for some better directional RX antenna(s)...
I've been studying the EWE but most design are long, mainly for BCB up to 160/80M...
Has anyone got a design/dimensions for a 7MHz EWE that works for them?
What height/length & rough termination value would be helpful...
Thanks,
Rafman
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I had a 7'x15'x7' made from lamp cord that worked great for 43 meters. The biggest performance factors I had was tuning it for the best rear null & S/N level along with getting the ground system dialed in. I also experimented with W8JI's idea of adding capacitance (I used a variable compression type) midway on the horizontal portion of the antenna to tweak the performance and it did help. Used a ICE 180A impedance matching unit for the interface.
I don't really have any fixed values other than using the 300:1 tap on the ICE interface and for the termination resistor I used a 1k potentiometer I adjusted by ear (~700 ohms if I remember from a meter check) - can't remember what the value of the variable cap was offhand, but like the resistor, I also tuned it by ear as well. As long as it's symmetrical with decent ground conditions you should be able to get good performance from tweaking the resistance side & getting the right interface value.
Edit: I should add that the 7'x15'x7' dimensions had more to do with the distance between two pine trees conveniently located than the 2x the vertical height formula and no regards to frequency either.
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Interesting, since I have seen designs from 3-5M High x 10-15M Long with termination values from 700 - 1.6k Ohms
Those designs seem to favor 3MHz-downward while I am seeking something that works at 7MHz downward & if it doesn't reach AMBC, I'm fine with that.
I got almost everything I'll need to build a few, including 100 of the 202 binocular cores :)
Thanks for the help!
Rafman
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One of my two antenna's is a EWE. I essentially copied Sealord's version as I wanted something small that wouldn't attract much neighbor attention. All the components are the same including the little variable cap in the middle and the ICE unit. When I first hooked it up, I tuned for maximum reception and was really pleased with how it worked. I didn't really fiddle with it much past that point as it was a huge step up from the 3ft indoor loop I was originally using back in '07. It's a nice quiet antenna if you are in a noisy environment.
If you are interested in any of the values, I can look them up for you.
Zane
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Well I have a little design update, leading to more questions:
I already have a 60' Rohn 25G tower at the house. What I am wondering is:
- Can I use the tower to deepen the null off the end of an EWE? [Tower will NOT be connected to EWE, just in close proximity & grounded]
- What spacing would I need to get away from the tower to get the best null [if any]?
What I have in mind is 3 [or poss.4] EWEs, facing 90~120 degs apart, almost forming a "turnstile" for directivity N-E-S-W & switched for obvious reasons.
As you can tell, I have yet to put up a single EWE antenna yet. Considering it was almost lightning gods' season when I got started researching, I dragged my feet & decided to build what I need [transformer/termination boxes] over Summer so I can sweep the install for next Fall's Listening Season.
In the meantime, my current Full-Wave 7MHz loop works just fine for my mainly exercise of pirate listening!!! IF I get itchy, a 2nd FW Loop might go up favoring E/W but only after June Field Day exercise. It is currently rolled up on my Radio Room floor waiting to stretch out & deploy!
Any help appreciated!
Rafman
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Sorry for the late response..
The little bit I understand about phased verticals is for the best null/s possible, the verticals themselves need to be identical. I would think the tower would have a negative effect due to coupling issues with the EWE, but you never know. DXE specs. 1/2 wavelength separation from other metallic structures to prevent pattern degradation with their systems, but that is for active elements and may not apply with a passive setup (I think a passive setup is more sensitive to this?).
Found this link from Koontz for a 4 directional EWE setup - there was also a couple of guys in the Netherlands who had a webpage using a similar system with (IIRC) computer ribbon cable in the switching design, but I can't find it now.
http://www.hard-core-dx.com/nordicdx/antenna/wire/ewe/ewe2.pdf
I just completely redid my 8 circle layout size due to both of my neighbors putting up new fencing (~6' tall) from the cheap 3' chicken/garden wire variety that had been there for years. The new fencing looks great, but it negatively impacted my reception pattern for pirate listening and I had to settle for 13850 spacing which seems to be working so far - even with less than 1/2 wavelength spacing between elements & fencing.