Radioworks Carolina Windom 40

VK7FMMM

VK7FMMM

Member
Hi All

Im running a ICOM 718 into an Antenna Tuner connected to a WINDOM 40 Meter antenna
The interesting thing is, the antenna via the Tuner can actually do a great job on 80 meters as well...
but not all the time....
there are several threads to my question so please have some patience with this....
Im running 75 ohm cable to the antenna.. more because it was available at the time and seemed to give a better SWR
Should I change this to RG58?
I have no choke in line but part of the cable is buried underground... should I still put a Choke in line regardless?
The Antenna is quite low around 8 meters off the ground [if that]
The reason I am not 'letting up' and just transmitting on it for 40 meters which is what it was designed for, is at one point during my tests.. I had a magnificent signal output on 80 meters with several stations.. now I cant seem to get back to it....since I have changed and fiddled with antenna lines etc
any simple advide re cable types etc would be useful

73's
VK7FMMM
 
When you say a windom 40 I assume that you mean a Radioworks Carolina Windom 40(?)

The CW40 like any 40m dipole has a top length which is around a quarterwave on 80m, so in effect you have an off center fed quarterwave on 80m.

The feed-point in the centre of the antenna would be around 150 ohms, so with the offset you may be seeing a feed-point impedance of maybe 400-800 ohms.

The CW40 (like all the Radiworks windoms) uses a 'line isolator' to block RF current on the outside of the braid (in theory), but even at the design frequency you will still see current on the outer braid of the coax back to the radio, and if operated well below the design frequency then I would guess that the line isolator will act like little more than a slight inductive load for the now 'hot' feeder.

So you may be not only loading up the top section on 80m, but the entire feeder!

RG58 is not the best cable to use, especially if the feed-point impedance is higher than 50 ohms, the 75 ohm feeder may well be better (I've used 75 ohm feeder with good results).

If you do change the feeder go for something more like either mini-8 (RG-8) or perhaps RG-213. RG58 can get VERY lossy VERY rapidly as frequency increases.

If it is a Radioworks windom then you should not need an additional choke since their 'line isolator' (supplied with the antenna) is supposed to choke out any RF anyhow.

Also, be warned about running Carolina Windows on bands or ranges outside of their design frequencies, a friend of mine tried that and burned out the top balun/transformer on his windom 40 while trying to run power on 80m :p

73, Mark.
 
Hi mate many thanks for the reply
Im doing further tests at present and will take your notes in review
some have said that testing needs to be conducted on the system for over two or three weeks with no change as conditions vary
this may well be something I need to consider as well

kind regards
and 73's

vk7fmmm Brett
 
I would attribute your good success that one time to good band conditions, and happening to find the right QSO at the right time (ie. the other stations were at an optimum distance for propagation at that minute).
Sorry, but this antenna will never be a good 80m antenna.
Even for the bands it was designed for, it may have excessive losses in its balun (I say this because most commercial Windoms use toroid baluns, which tend to heat up, saturate and convert precious RF energy into hot air for the local birds).
If you must use a windom, then build your own balun wrapped on a ferrite stick. It will have less losses.

The real problem with trying to use a wire that is 20m long and not fed at its end, is that you are feeding it with coax.
Changing from 75 Ohms to 50 Ohms coax will make no significant difference here.
The very best way to turn that wire into a good radiator for both 40m and 80m is to feed it in the middle with open wire feedline (either 450 or 300 Ohms).
Place the balun in the shack.
It can be (should be) home brew, made of just coax and pvc pipe.

Unfortunately you built-in tuner will notch match this on all bands.
You will need an external (any of the popular ones).
You will be rewarded with an antenna which not only tunes all bands, but also gets out well on all bands (ok, gets out "fairly well" on 80), even when just at 8m height.

73
Rick, NJ0IP
 
I dismantled a Radioworks Carolina Windom (40m one), that had been accidentally 'cooked' and donated to me, and I found that both the top balun and the 'line isolator' (as they call it), contained half inch diameter ferrite rods, about seven inches in length.


Mark.
 
Also, be warned about running Carolina Windows on bands or ranges outside of their design frequencies, a friend of mine tried that and burned out the top balun/transformer on his windom 40 while trying to run power on 80m :p
Click to expand...

I'm sure it was an 80 special!!..lol... :cool:

Tony - G6YWL
 
OK, so my memory is a little 'hazy' these days :rolleyes:

It was 80m special fried rice after the incident! :p

Just keep swimming, swimming, swimming...

73, Mark.
 
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