HF Antenna

V

VK3ZYZ

Guest
Today I decided to update my HF antenna.
There was a web site (I'll add the link later when I find it again) that told of an offset HF antenna that just about is the exact size for my block.
Tuned to 3.630Mhz, with the feed point at 1/5 the way from one end.
So, I set about trying it out.

First, a BALUN. This is similar to those I made for the RA event, but with only 6 cores in stead if 8( Jaycar only had 6 in stock ).
So it just fit into a smaller case.
BALUN1.jpg
You can see the filled in holes in the side I was going to use but the cores were in the way.



BALUN2.jpg
I ended up having the connections out the back. A piece of fiberglass board is screwed on the case for antenna wire and pulley cord attachment.

UV stabilized cord is to be used as the COAX strain relief and antenna hoist rope. This cord has fuzzy ends when cut so some dual wall heat shrink is put on like a boot lace end.
FixCordEnds.jpg

The COAX would be a bit heavy so strain relief is as below..
COAX_StrainRelief1.jpg

COAX_StrainRelief2.jpg

COAX_StrainRelief3.jpg
Dual Wall heat shrink is applied to hold the cord in place. This has hot melt glue inside so when it is heat shrunk, it is also securely glued.

Now, the COAX is screwed onto the BALUN and it too is sealed with dual wall heat shrink.
BALUN3.jpg

Next, the wire is hooked on.
BALUN4.jpg
BALUN5.jpg

A pole is now mounted to the front gate post.
PoleMounted1.jpg
PoleMounted2.jpg
PoleMounted3.jpg
I've added short lengths of PVC pipe around the 50mm steel pole to space it slightly away from the gate post because there are cable ties there already.

There are pulleys on eye bolts so the antenna can be raised and lowered easily.

Pulleys1.png
(done with a bit of brute force and ignorance)
Pulleys2.jpg

When I tried to raise the antenna, the cord jumped off the pulley so I had to take the pole down again and fix it :(
Plastic.jpg

PulleyFix1.jpg

PulletFix2.jpg
This addition stops the cord jumping off.

So, now I have a new HF antenna. I'm not convinced it is better and the SWR is suspect. With the pulleys, it will be easier to work on.
CenterPole.jpg
LongWire.png

This next Wednesday will be a good chance to see if it worked or not.
 
Last edited by a moderator:
V

VK3ZYZ

Guest
The web page...

And his comment...
My Windom is very lopsided. It is fed about 19.5% - 80.5%.


The position is very critical and must be very carefully adjusted to obtain the best SWR on all bands. At another QTH, you may need to vary its position slightly to compensate for local difference in terrain.





This very lopsided split (approximately 1/5 - 4/5) creates much more problems with Common Mode Current (CMC) than the classican 1/3 - 2/3 split and additional steps are required to deal with the CMC.
 
V

VK3YNV

Guest
Hi Denys,

I found a good design for a 4:1 current mode balun, https://vk6ysf.com/balun_guanella_current_1-4.htm

He is using the same Jaycar LO-1238 cores, but splitting the windings between two. I think using a current mode balun rather than a voltage mode balun might be important when the feed is off center.
 
V

VK3ZYZ

Guest
I pulled the old BALUN out...
Old Voltage BALUN.jpg

and rewound as a current BALUN...
New Current BALUN.jpg

Now I just need to see if it is any better.

While I was playing around, I put the Nano VNA on the ATU and measured the VSWR at a few points. As the ATU had a blank face, I thought a scale would be in order. My drawing skills leave much to be desired, so a Google search was an idea to find a ready drawn one.
The first picture that came up was a drawing protractor, so a quick trip to Office Works (and then another as I ran out of double sided sticky tape), procured a couple and with a bit cut out of the center with a hot wire, double sided tape and white paper later made a big improvement.
1 Protractor Scale.jpg


2 Protractor Scales.jpg

They are a bit rough but a lot better than what was there.

Back to inside the house as the temp is dropping in my shed.
I will light the heater for the HAM club sked!
 
V

VK3YNV

Guest
Did changing the balun make any difference to the tuning?

Regards
Ray
 
V

VK3ZYZ

Guest
Yes. The tuning seems to be different.
But I did not use the VNA last time. Now I an setting the tuning as per the test on the VNA and ht Codan is actually outputting more power so I think the tuning was crook before.
When I get time, I'll spend a few hours with the VNA going over all the bands. the tuning curve shown on the VNA is quite steep and critical. But it is interesting to see the interation of the Cs and L moving the VSWR curve around.
 
V

VK3YNV

Guest
He has a you tube video as well, I'll see if I can find it. Found it.

In this video he stacks 2 LO1238 Jaycar toroids for each side for high power, so yours should be good for a decent power output.

 
V

VK3YNV

Guest
Yes. The tuning seems to be different.
But I did not use the VNA last time. Now I an setting the tuning as per the test on the VNA and ht Codan is actually outputting more power so I think the tuning was crook before.
When I get time, I'll spend a few hours with the VNA going over all the bands. the tuning curve shown on the VNA is quite steep and critical. But it is interesting to see the interation of the Cs and L moving the VSWR curve around.
I normally use the NanoVNA to adjust the Antenna Tuner, If you switch to bypass the tuner, it gives you a good picture of what's going on.
 
V

VK3ZYZ

Guest
What is your feedline Denys?
One of the coax cable I supplied for the RA event.
I thing the Codan is actually working better now the tuning is correct. I've yet to get back to spend time running through the bands to log the settings.
 
V

VK2RK

Guest
Today I decided to update my HF antenna.
There was a web site (I'll add the link later when I find it again) that told of an offset HF antenna that just about is the exact size for my block.
Tuned to 3.630Mhz, with the feed point at 1/5 the way from one end.
So, I set about trying it out.

First, a BALUN. This is similar to those I made for the RA event, but with only 6 cores in stead if 8( Jaycar only had 6 in stock ).
So it just fit into a smaller case.
View attachment 120
You can see the filled in holes in the side I was going to use but the cores were in the way.



View attachment 121
I ended up having the connections out the back. A piece of fiberglass board is screwed on the case for antenna wire and pulley cord attachment.

UV stabilized cord is to be used as the COAX strain relief and antenna hoist rope. This cord has fuzzy ends when cut so some dual wall heat shrink is put on like a boot lace end.
View attachment 128

The COAX would be a bit heavy so strain relief is as below..
View attachment 122

View attachment 123

View attachment 124
Dual Wall heat shrink is applied to hold the cord in place. This has hot melt glue inside so when it is heat shrunk, it is also securely glued.

Now, the COAX is screwed onto the BALUN and it too is sealed with dual wall heat shrink.
View attachment 125

Next, the wire is hooked on.
View attachment 126
View attachment 127

A pole is now mounted to the front gate post.
View attachment 129
View attachment 130
View attachment 131
I've added short lengths of PVC pipe around the 50mm steel pole to space it slightly away from the gate post because there are cable ties there already.

There are pulleys on eye bolts so the antenna can be raised and lowered easily.

View attachment 133
(done with a bit of brute force and ignorance)
View attachment 134

When I tried to raise the antenna, the cord jumped off the pulley so I had to take the pole down again and fix it :(
View attachment 137

View attachment 135

View attachment 136
This addition stops the cord jumping off.

So, now I have a new HF antenna. I'm not convinced it is better and the SWR is suspect. With the pulleys, it will be easier to work on.
View attachment 138
View attachment 140

This next Wednesday will be a good chance to see if it worked or not.
I had a similar problem with the rope jumping the pulley.
This how I fixed the issue.
Got some suitable plastic and narrowed the gap, so the rope can't jump out.
IMAG3430-20200909-101400851.jpg
 
V

VK3ZYZ

Guest
It is VERY annoying when the pulley at the top of the pole jams the rope!
 
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