| Author |
Message |
    
Airplane1
Senior Member
Username: Airplane1
Post Number: 1319
Registered: 5-2004
| | Posted on Sunday, August 30, 2009 - 2:47 pm: | 
|
Anyone have one of these that could tell me how well they like it? I am contemplating getting the 7 band 3000 watt version for 80,40,20 and 6 meter.
I will be able to mount it at 40ft on my tower and the ends at about 10ft high each.
Thanks,
AP |
Tech237
Moderator
Username: Tech237
Post Number: 1215
Registered: 4-2004
| | Posted on Monday, August 31, 2009 - 10:33 am: |
|
Not sure about that actual one, but I have been using a home made OCF for a couple of years and it seems to work well..
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
|
Airplane1
Senior Member
Username: Airplane1
Post Number: 1320
Registered: 5-2004
| | Posted on Monday, August 31, 2009 - 11:01 am: |
|
I like the idea that it can be fed by coax and not ladder which I guess would need to be isolated from my tower which is the only place I can mount the apex. The ladder length and coax length for a G5RV wont work for me.
I can mount this with a plastic standoff and run my coax straight to it.
Unless I am wrong about the G5RV but I have no place to mount it the way it is supposed to be.
AP |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4632
Registered: 7-2004
| | Posted on Monday, August 31, 2009 - 9:30 pm: |
|
check eham reviews.....4.8 out of 5. not too shabby. 300 bucks for wire though..... |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1321
Registered: 5-2004
| | Posted on Tuesday, September 01, 2009 - 6:33 am: |
|
Yea, the cost is the killer here. I am going to look for a 6:1 balun and make a clone if the Buckmaster. I dont understand antenna design but I will be doing a ton of reading on the OCF and try to figure it out.
AP |
Tech237
Moderator
Username: Tech237
Post Number: 1217
Registered: 4-2004
| | Posted on Tuesday, September 01, 2009 - 9:40 am: |
|
I am interested to see how they get away with feeding it with straight coax, as the impedance of an OCF is way off of 50 ohms and varies widely depending on frequency - thats why the length of ladder is used to act as an impedance transformer.
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
|
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4635
Registered: 7-2004
| | Posted on Tuesday, September 01, 2009 - 10:21 pm: |
|
I am interested to see how they get away with feeding it with straight coax, as the impedance of an OCF is way off of 50 ohms and varies widely depending on frequency-probably most of the reason for the $300 cost....design & implementation of their 'custom' matching system (balun). |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1322
Registered: 5-2004
| | Posted on Wednesday, September 02, 2009 - 10:58 am: |
|
Here is a link if I am aloud to post it for good info on the OCF dipole.
http://blacksparrowmedia.com/misc_files/The%20OCF-dipole3col.pdf |
Tech833
Moderator
Username: Tech833
Post Number: 1728
Registered: 8-2002
| | Posted on Friday, September 04, 2009 - 3:29 pm: |
|
Feeding an Off Center fed Dipole with a current balun takes care of the common mode stray currents and also provides a phase stabilization advantage over simple coax feed.
The trick to the off center dipole is that assuming it is balun fed, either wire can become the 'hot' depending on the resonance required on a particular band. Since the HF ham bands are all harmonics of each other, this is really simple to accomplish.
For instance,
The beginning of 160 meters is 1.8 MHz. 1.8 x 2 = 3.6 MHz. which is 80m.
So, if 80 meters is 3.6 MHz. 3.6 x 2 = 7.2 MHz. which is 40m.
Re-center our band here a moment for 40m to 7.1 MHz.
40m is now 7.1 MHz. 7.1 x 2 = 14.2 MHz. which is 20m.
40m is 7.1 MHz. 7.1 x 3 = 21.3 MHz. which is 15m.
Back to 20m, at 14.2 MHz. 14.2 x 2 = 28.4 MHz. which is 10m.
So, for fun, let's say we have a 1/4 wave long antenna for 160m. That would be 130 feet long. that would be a 1/2 wave on 80m. That would be a full wave on 40m. etc. The reason one leg of an OCF is longer than the other is so you get a 1/4 wave multiple on one of the wires and a 1/2 wave multiple on the other. The 1/4 wave multiple has a low impedance, near 50 ohm, and will resonate while the wire that is the 1/2 wave multiple will have a high impedance and not resonate.
It is like having a folded fan 1/2 Zepp with a non-resonant counterpoise. The exception is that you would rotate the Zepp 180 degrees in the H plane each time you switch bands.
The reason the OCF was invented is because the multiband trapped antennas like the trapped verticals lose efficiency logarithmically as you go lower in frequency. The OCF can maintain comparable efficiency regardless of frequency, within design parameters.
There is a BIG advantage to this type of antenna over the trapped verticals in that you have a full-length radiating element for every band without a bunch of coils in series. The trapped verticals are OK if you don't need good performance and want a small horizontal footprint. However, if you can string some wire, the OCF will give the multi-band ham a huge advantage over the comparably puny signals from trapped verticals.
The only downside is a sometimes unpredictable pattern. That can be overcome, in large part, by mounting the OCF higher above ground. |
Tech833
Moderator
Username: Tech833
Post Number: 1730
Registered: 8-2002
| | Posted on Sunday, September 06, 2009 - 6:27 pm: |
|
Using a trap vertical on the lower ham bands is like using a 2-foot Firestick on the CB band. An OCF on the lower bands is like having a full length 108" quarter wave on CB. It has no loading coils, it is a full-length radiating element. That is why they were researched and developed, as a higher performance multiband antenna alternative to the common trap vertical.
There is nothing wrong with using a trap vertical, especially if you have limitations and can accept the loss in efficiency on the lower bands as tradeoff for the small footprint. Same as someone in an apartment that cannot put up a quarter wave vertical CB antenna, but could get away with a 2-foot Firestick on the roof. It is better than nothing.
I am not putting down the trap vertical. I am saying that if you have the room, the OCF will give you a tremendous performance boost over a trap vertical, for the reasons I mentioned in my earlier post. |
Tech833
Moderator
Username: Tech833
Post Number: 1731
Registered: 8-2002
| | Posted on Sunday, September 06, 2009 - 9:19 pm: |
|
Since we are now drifting away from discussion of the OCF dipole and comparing antennas, apparently...
The Alpha Delta DX-CC is a great antenna, I agree. It is a 'parallel dipole' type of antenna (also sometimes called a 'fan dipole'), and takes a little over 80 feet of horizontal real estate to erect correctly. With three parallel elements on each side of the center insulator, it isn't the most stealthy, or wind resistant antenna there is for 80-10m, but it is a good performer. On 80m it is a little bit of a compromise due to the loading coils for that band. However, for 40-10, it is a full-length dipole, and performs the same as a dedicated mono-band dipole.
You can't really compare an OCF or a DX-CC to a G5RV since the G5RV is admittedly a compromise antenna to begin with. If we compare compromise antenna to compromise antenna, like a trap vertical, then the G5RV is a real contender. Comparing a G5RV (or a trap dipole) to a DX-CC or OCF dipole is apples and oranges.
Perhaps, if you would like to discuss various ham radio multiband dipoles, you should start a new thread so we can try and keep this one on topic. |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1324
Registered: 5-2004
| | Posted on Thursday, September 10, 2009 - 7:47 am: |
|
Lots of great info. I might be building a OCF myself, what do I got to lose and if it works I save big bucks over the cost of the Buckmaster. I have a spot on the tower that is 40 ft high and the tower is on the side of my garage. I will be mounting it as a inverted V with the ends at about 10 ft off the ground. It will be over the garage roof which is about 14 ft hight at the center with a aluminum ridge vent running the length of the roof (26)ft long. The long side will be running away from the garage tward the north east and the short side will run over the garage tward the south west.
This is the only way I can mount it because of a lack of trees or any other high mounting points in my yard, not space as I have enough space to mount about anything but I only have the 46 ft tower as the highest structure here.
Ok, my question is will the OCF react with the aluminum ridge went or will it be fine. I am estamating the short side to be 15 ft at the closest point to the ridge vent at the southwest most corner.
I cant wait to see how much better my receive is over my Maco V 5/8 which I use to listen on 20,40 and 80.
AP |
Tech833
Moderator
Username: Tech833
Post Number: 1739
Registered: 8-2002
| | Posted on Thursday, September 10, 2009 - 4:27 pm: |
|
Yes, it will react with your metal pipes, but not drastically. The OCF has a fairly low Q, so don't worry about it too much. |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1325
Registered: 5-2004
| | Posted on Friday, September 11, 2009 - 6:34 am: |
|
Thanks 833, I am hoping to get it up this month. Been listening on 80,20 and the maco does ok but I need something better, there is lots of acting there. Man do I gotta get my general, waiting for 10 meters to open is the pits. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4650
Registered: 7-2004
| | Posted on Saturday, September 12, 2009 - 9:22 pm: |
|
waiting for 10 meters to open is the pits-early autumn/late summer aided propagation on 50.148 150+ miles right into your neighborhood roger! 28' to the feedpoint between 2 squalos! and yeah, i hear that general is waiting for you! |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1386
Registered: 5-2004
| | Posted on Tuesday, January 12, 2010 - 10:14 am: |
|
Ok, let me bring this back for a moment. I want to know the best direction to place the legs of my OCF for DX over seas? North-South, East-West?
Thanks,
AP |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4773
Registered: 7-2004
| | Posted on Wednesday, January 13, 2010 - 8:49 pm: |
|
if you run it north-south, it'll transmit most energy east-west off the long sides. you will be able to talk off the north-south ends, but at a reduced ERP. |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1387
Registered: 5-2004
| | Posted on Thursday, January 14, 2010 - 7:56 am: |
|
So the antenna radiates broadside! Thanks Pat.
AP |
Funtimebob
Intermediate Member
Username: Funtimebob
Post Number: 255
Registered: 5-2002
| | Posted on Monday, February 22, 2010 - 5:26 pm: |
|
there are 2 different ideologies on the OCF/Carolina Windom
Some people use the typical 33/67 split others prefer to do a 20/80 split after they figure out the length at a 1/2 wave.
I hear that the 80/20 falls better on different portions of the bands BUT you loose 30 meters.
Generally if the antenna is going to be mounted below 50 ft. a 4:1 current balun is normally used. above 50 ft. a 6:1......
Most web sites list an approx. 45/90 ft length for the two sides. should be able to find a decent 4:1 current balun, grab some quality copper weld and associated insulators for a LOT less than $300.00
This post was brought to you By Umpire Cologne.
73 KD8DEY
|
Airplane1
Senior Member
Username: Airplane1
Post Number: 1405
Registered: 5-2004
| | Posted on Tuesday, February 23, 2010 - 11:28 am: |
|
Funtimebob, you are right in saying I can do a ocf for much better than $300. I did not buy the buckmaster yet and am prob going to make my own and try it.
I just need a good water proof balun.
AP |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4807
Registered: 7-2004
| | Posted on Tuesday, February 23, 2010 - 9:21 pm: |
|
mfj913 about $27 from some ham dealers, have seen new for under $20 on ebay....not bad if shipping is reasonable. that, a couple insulators & 135' or so of #12 copper wire......you're probably at $75 or less.....
g-e-n-e-r-a-l.....g-e-n-e-r-a-l....g-e-n-e-r-a-l.. |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1406
Registered: 5-2004
| | Posted on Wednesday, February 24, 2010 - 10:06 am: |
|
I know Pat,
g-e-n-e-r-a-l.....g-e-n-e-r-a-l....g-e-n-e-r-a-l..
I have so much going on and if not then I am tired and want to sleep.
I got to get motivated. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4809
Registered: 7-2004
| | Posted on Thursday, February 25, 2010 - 12:00 am: |
|
aa9pw.com, qrz.com, eham.net.....take 1 practice test on each every day. if you have more time, take a 2nd. you may be surprised at how much you already know! and the ones you DO get wrong....think about 'em, i'll bet you really knew half of those....just thought a bit too much about 'em & 'guessed' the 'opposite' answer!
to 'test' the point, i just took a general practice on aa9pw. i have NEVER looked at the current general test, i took the last one. i took the whole test in about 5 minutes & did in fact get 8 wrong, and to prove my point, 5 of them i rushed through & did answer 'backwards'. the other 3, had i actually 'thought' for just a moment, i probably would have gotten right, too.
so you should be legal on 20 meters by....end of march  |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1407
Registered: 5-2004
| | Posted on Thursday, February 25, 2010 - 7:08 am: |
|
OK, I am going to do just what you said. I hope your right and if so what band would give the best chance of making a contact? |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4810
Registered: 7-2004
| | Posted on Thursday, February 25, 2010 - 11:05 am: |
|
depending on season & time of day, groundwave under 200 miles on 20m & 40m is fairly regular. 75m should be even easier, but i need to figure a way to get an antenna up that long.
remember, also, i've talked to some of the contesters on 2m & 6m through the reading area, in the 150-175 mile range quite a few times in recent months. and i'm just using stacked loops, probably zero gain over a dipole, definitely not much more. a beam on each end & ...... |
Airplane1
Senior Member
Username: Airplane1
Post Number: 1440
Registered: 5-2004
| | Posted on Friday, October 25, 2013 - 4:08 pm: |
|
Hi Pat and 833 and others. Been a long time but i got an ocf off of ebay for cheaper than the buckmaster and not much more than i could have made one for.
It has been up for a while now and running the short leg north east and long leg south weast, it works amazing.
Dxing all over the world.
73 |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 2355
Registered: 7-2004
| | Posted on Thursday, November 14, 2013 - 10:57 am: |
|
Hi Roger,
Sounds like your having a great time on your
ham radio/antenna...
Hopefully I will too someday soon!
CEF 375 (Jim)
Central PA. |
