rogersmithiii
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My favorite, HF homebrew antenna.
- Thread starter rogersmithiii
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ToddDubya
NES Member
I know an end fed setup as a flat top is supposed to give both vertical and horizontal benefits, so it stands to reason this would too, especially being more dipolish. I wonder if it favors the long or short side or they're equal.
This guy has some great thoughts on OCFD (aka "Windom" antennas) as well as a wealth of information on many other amateur radio topics. So far he has never steered me wrong. I've had several on line conversations in the past few years with him...check him out:
www.dj0ip.de
His stuff on OCFD antennas specifically:
Ham Radio Site - [HOME]
DJ0IP, NJ0IP, Spiderbeam, Antenna, Antenna Tuner, Matchbox, Balun, Rob Sherwood
His stuff on OCFD antennas specifically:
ToddDubya
NES Member
This could be a good project to build for Field Day, and I wouldn't mind having a quasi permanent antenna at my super secret squirrel location. I'll likely build a dual core 4:1 balun if I'm going to do it.
I'll have to find a good article that describes the number of windings, etc. I have some 140-43 toroids I can use. I use that size up to 100w and if they get hot I've never noticed. My Tx/Rx duty cycle is typically very low. In an enclosed box bigger cores might help, but I don't believe I have two 240-43s. I could be wrong, but two cores would be sharing the current so maybe they'd heat up less anyway.
I'll have to find a good article that describes the number of windings, etc. I have some 140-43 toroids I can use. I use that size up to 100w and if they get hot I've never noticed. My Tx/Rx duty cycle is typically very low. In an enclosed box bigger cores might help, but I don't believe I have two 240-43s. I could be wrong, but two cores would be sharing the current so maybe they'd heat up less anyway.
One thing DJ0IP mentions is that:
ALL of the companies manufacturing OCFD antennas commercially are still using the single core 4:1 Guanella, and under certain circumstances can incur severe common mode current problems.
The only exceptions I know of are Spiderbeam and DX-Wire, two German antenna companies.
This is not necessarily true...my OCFD made by Palomar Engineering is a hybrid balun with the 4:1 part having dual cores. The 1:1 Unun, which keeps common mode RF current off the feedline is, I believe, a single core. Both "baluns" are inside a weatherproof plastic box.
ALL of the companies manufacturing OCFD antennas commercially are still using the single core 4:1 Guanella, and under certain circumstances can incur severe common mode current problems.
The only exceptions I know of are Spiderbeam and DX-Wire, two German antenna companies.
This is not necessarily true...my OCFD made by Palomar Engineering is a hybrid balun with the 4:1 part having dual cores. The 1:1 Unun, which keeps common mode RF current off the feedline is, I believe, a single core. Both "baluns" are inside a weatherproof plastic box.
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ToddDubya
NES Member
How critical would y'all say this 10' length of coax is? I have 12' lengths, but no 10'. My gut is saying the horizontal part is doing the heavy lifting, but the point of the Carolina-ness is to have some vertical component. But is it radiating because of common mode current or is it actually part of the dipole? Maybe I just end up trimming the wires a little shorter?
Then again, the author says:
I made up a 4:1 this morning. It needs to be mounted in something, but at least that part is done. Probably should test it first.
Then again, the author says:
I made up a 4:1 this morning. It needs to be mounted in something, but at least that part is done. Probably should test it first.
They are very slow to ship though, or at least were back a few years ago. I ordered my OCFD from them and a month later, even with multiple emails unanswered, I sent them an email cancelling the order...I guess that's what it took because within 30 minutes I received an email from them confirming the cancellation. I called a buddy at HRO Salem that I used to work with when I worked there and he had one shipped that day and it was cheaper than Palomar and free shipping to boot. I had it the next day (I was still living in NH at the time).
I am running RG8x to it and running some power 700-800 watts (SSB) occasionally which might be OK but I have some RG-213 somewhere that I will eventually replace the 8x with.
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n1oty
NES Member
Although I have numerous Palomar products, I only bought one direct from Palomar, but it came quite rapidly. It was the OCFD that covers through 80 meters with their custom 5 kW balun plus the choke. I've got that up approximately 50 feet, fed with 1/2 inch Andrew FSJ-4 and often feed 1 kW into it. It plays quite well on most bands, although it clearly is best on 10 through 20.
The other Palomar items I purchased at HRO. I keep a couple of spare baluns and a couple of spare chokes on hand. I also have a Palomar OCFD of lesser power rating that I drag out to Ohio on vacation.
UJay
NES Member
A resonant yagi?
A fan dipole to cover multiple bands is next.
I used a Carolina Windom for many years, which worked well until the 'top' balun lit up like a flair at high power. So stick to <500w and should be OK.
I ended up using, and still have, a couple of the radioworks windoms- We used a full-size 160m one for field day the last few years.... Looks like radioworks is gone, but the web archive still has the info. They were truly great and the vertical element on 20 kicked ass. The 80m version was the best performer, and would consider that size for your builds.
UJay
ToddDubya
NES Member
Well, I got the 4:1 into a box and ready to go. If the weather cooperates I'll see about getting it in the air and tuning the wires.
www.northeastshooters.com
What did you do in the shack today?
I have always wondered if this forum had a "What did you do..." thread like others on NES. A search appears to show that it does not. So I will start off... Today in the shack I began manufacturing coax jumpers using RF Industries RFU-508X crimp connectors on Ventev/Terrawave TWS-240 cable...
www.northeastshooters.com
You DO know that antennas put up in crappiest weather work the best, right?Well, I got the 4:1 into a box and ready to go. If the weather cooperates I'll see about getting it in the air and tuning the wires.
What did you do in the shack today?
I have always wondered if this forum had a "What did you do..." thread like others on NES. A search appears to show that it does not. So I will start off... Today in the shack I began manufacturing coax jumpers using RF Industries RFU-508X crimp connectors on Ventev/Terrawave TWS-240 cable...
Inversely proportional rule here.
ToddDubya
NES Member
Yeah, I'm hoping for snow/ice. And since I'll have to tune wires, wind.You DO know that antennas put up in crappiest weather work the best, right?
Inversely proportional rule here.
ToddDubya
NES Member
Well, it wasn't an ideal setup but I did the best I could in the yard. I cut the wires a little long to start and never bothered trimming them. The SWR dip on 40m was 2.5. I don't remember the others, but they weren't great either. Trying to get the dip in a good spot wasn't worth it for such a high SWR. I'll leave it for another day.
I had it about 20' up at the balun point, and the wires sloped to about 8' at the ends. That's the best I could do in the trees out behind my house. Maybe if I could get the ends up higher it would improve. I don't know how people navigate through all the branches when they setup antennas.
I did try moving the choke balun (1:1) from about 10' down to right below the 4:1. That didn't seem to have any impact on SWR or the center frequency of the dip.
Oh well, maybe it'll work better another time.
I had it about 20' up at the balun point, and the wires sloped to about 8' at the ends. That's the best I could do in the trees out behind my house. Maybe if I could get the ends up higher it would improve. I don't know how people navigate through all the branches when they setup antennas.
I did try moving the choke balun (1:1) from about 10' down to right below the 4:1. That didn't seem to have any impact on SWR or the center frequency of the dip.
Oh well, maybe it'll work better another time.
The best thing I've bought for getting rope high in the tree is a pneumatic launcher. It puts a 2oz fishing weight over a 100' tall tree with ease. I bought it on ebay last year but it looks like they aren't selling it any longer. They still have the weights but no launcher. I wonder if some ambulance chasing lawyer told them it is "too dangerous".
ToddDubya
NES Member
I guess my problem is always that I'm in the trees, not going from one tree, across a clear field to another tree. I can get the center pulled up, but now the two legs of the dipole have to get up to the center point and woven through all the other trees and branches to a point I can tie them off. And the center of this thing is heavy with two boxes of toroids hanging off it, so I have to support the center for sure.
Ahhh... that does pose some issues. I've been trying figure how to erect a fullwave 160 loop but I don't have trees in the right place. I definitely have the room but nothing in the right places. I'm actually thinking about approaching the power company out here and see if they would sell me four 60' utility poles (and how much they'd be).
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