Here are some
notes I’ve received from others regarding this antenna:
29-Jan-2008 - From Martin Ehrenfried, G8JNJ:
I have now made a copy using 25mm
ferrite rings and 15mm copper water pipe as the inner cores.
The through loss curves when
terminated in 50 ohms seem to be very similar to your genuine unit. See
attached photos.
As another test I terminated the
input with a 50 ohm load and then measured the impedance of the secondary
winding with an Autek VA1.
|
Input 50 Ohms |
||
|
MHz |
R (ohms) |
J (ohms) |
|
0.5 |
8 |
-41 |
|
1 |
22 |
73 |
|
1.5 |
43 |
99 |
|
1.9 |
68 |
112 |
|
3.6 |
143 |
128 |
|
7.1 |
245 |
130 |
|
10.1 |
297 |
99 |
|
14.1 |
279 |
52 |
|
18.1 |
292 |
-24 |
|
21.1 |
252 |
-46 |
|
24.9 |
208 |
-59 |
|
29 |
193 |
5 |
So the secret seems to be that it's
a very lossy 4:1 balun !
I'm a bit mystified by the odd
construction though. I wonder if it was wound correctly in the factory. The way
the first turn of the secondary loops outside the ferrite core and then doubles
back on itself, before connecting to the output is very odd. It's almost like
someone made a mistake and then lost the rest of the surplus cable by folding
it up and stuffing it back inside the assembly.
Pictures sent by Martin can be viewed from these links:
29-Jan-2008
- From Hidehiko Koguchi, JI1AVY:
I am JI1AVY, Hidehiko (HIDE) Koguchi from
JJ1GRK, Takagi
So I think even he has never seen the
disassembled inside of CHA250. Your work must be the first ever in the world,
at least, which have been published.
I have just sent your PDF URL to JJ1GRK
(Hope Takagi OM would read it because he does not like to receive an
e-mail). And attached is a part of
JJ1GRK article. Although it is written in Japanese, you can find the figure of
MLB and its SWR charts. Attachment.
31-Jan-2008 - From
Martin Ehrenfried, G8JNJ:
I built a version of the CQ Ham
Radio balun design using some small, long, ferrite tube cores, and measured the
secondary impedance as before.
It's basically a 4:1 balun. The
first set of results is for the balun as shown in the diagram, the second is
the same balun with the feedback loop removed and the wire just pulled out of
the end where the loop is shown in the drawing.
The loop doesn't seem to do
much except reduce the performance at the LF end, mainly due to the
loss of one half turn. I thought it may have been some sort of 'neutralising'
mechanism to improve the performance at the HF end, but this doesn't seem to be
the case. Have you any ideas regarding its purpose, other than present the
cable at the desired end of the assembly ?
|
|
Jap balun with feedback loop |
|
Jap balun no feedback loop |
||||
|
MHz |
R (ohms) |
J (ohms) |
Z (ohms) |
|
R (ohms) |
J (ohms) |
Z (ohms) |
|
0.5 |
20 |
-50 |
54 |
|
33 |
-79 |
86 |
|
1 |
52 |
69 |
86 |
|
89 |
92 |
128 |
|
1.5 |
78 |
67 |
103 |
|
131 |
86 |
157 |
|
1.9 |
90 |
66 |
112 |
|
149 |
71 |
165 |
|
3.6 |
114 |
65 |
131 |
|
166 |
55 |
175 |
|
7.1 |
138 |
87 |
163 |
|
179 |
48 |
185 |
|
10.1 |
150 |
86 |
173 |
|
180 |
51 |
187 |
|
14.1 |
177 |
91 |
199 |
|
188 |
64 |
199 |
|
18.1 |
184 |
95 |
207 |
|
196 |
70 |
208 |
|
21.1 |
192 |
103 |
218 |
|
186 |
86 |
205 |
|
24.9 |
157 |
116 |
195 |
|
162 |
100 |
190 |
|
29 |
161 |
115 |
198 |
|
155 |
105 |
187 |
31-Jan-2008 - From
Martin Ehrenfried, G8JNJ:
I tried modifying the Comet balun
copy to remove the 'feedback' loop.
These are the results. A graph is
also attached.
|
|
Comet copy |
|
Comet copy no feedback loop |
||||
|
MHz |
R (ohms) |
J (ohms) |
Z (ohms) |
|
R (ohms) |
J (ohms) |
Z (ohms) |
|
0.5 |
8 |
-41 |
42 |
|
12 |
-82 |
83 |
|
1 |
22 |
73 |
76 |
|
43 |
132 |
139 |
|
1.5 |
43 |
99 |
108 |
|
87 |
177 |
197 |
|
1.9 |
68 |
112 |
131 |
|
134 |
199 |
240 |
|
3.6 |
143 |
128 |
192 |
|
294 |
202 |
357 |
|
7.1 |
245 |
130 |
277 |
|
435 |
164 |
465 |
|
10.1 |
297 |
99 |
313 |
|
459 |
140 |
480 |
|
14.1 |
279 |
52 |
284 |
|
446 |
62 |
450 |
|
18.1 |
292 |
-24 |
293 |
|
438 |
18 |
438 |
|
21.1 |
252 |
-46 |
256 |
|
427 |
-66 |
432 |
|
24.9 |
208 |
-59 |
216 |
|
335 |
-20 |
336 |
|
29 |
193 |
5 |
193 |
|
321 |
-62 |
327 |
I still don't understand how this
works. The impedance match is miles off.
01-Feb-2008
- From Hidehiko Koguchi, JI1AVY:
Hidehiko
sent a translation for some of article in his previous message. I’ve reproduced it here. Please note:
This information is from the Japanese CQ Magazine. The articles were
written by JA6JCF (June 2005 issue) and JJ1GRK (August 2007 issue).
SWR measurements of a CHA250.
The SWR is less than 2.4:1 at all frequencies between
3.5Mhz and 54 Mhz.
This measurement was done in these conditions
1. Feed point 5m high.
2. Using MFJ-259B
3. Connected by 1m of 5D-2V (50?
Coax) between CHA250B and MFJ-259B.
Case A – MLB (Magnetic Loop Balun) with 5.5m element.
To test the difference with and without the “return loop” in the
winding.
The MLB consists of 2 of SC-05-200.
Each coil is 3 turns.
Note: SC-05-200 is the part
number of a ferrite core produced by NEC-TOKIN
The darker line is with the return loop, the lighter without it.
Having the return loop improves the SWR.
Case B – MLB (Magnetic Loop Balun) with 1.5m element.
Using the same MLB as in case A to test the affect of the antenna
element length.
The darker line is with the return loop, the lighter without it.
The SWR is not as good with the shorther element although it’s
still better with the return loop.
Case C – MLB with 5.5m and 6m element lengths.
Using the same MLB as in case A.
The darker line is the 6m element, the lighter the 5.5m element.
The 6m element gives a better SWR than 5.5m. The author also commented that element
lengths over 6m show a worse SWR.
Performance is sensitive to the element length.
08-Feb-2008 - From
Martin Ehrenfried, G8JNJ:
I made some measurements on my
copy. Some construction details can be found at: http://g8jnj.webs.com/61balun.htm
The first table shows the input
impedance with no antenna element connected. This was measured directly on the
input connector with no coax.
The second shows the impedance
presented between the input connector earth and the antenna connector. This was
measured with the shortest leads possible, and no antenna element connected.
Using similar information derived
from measurements on an actual unit it should be possible to characterise
the type of ferrite being used.
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28-Mar-2008 - From
Martin Ehrenfried, G8JNJ:
Martin has done a lot more useful work on this type of antenna. Details can be found here:
http://g8jnj.webs.com/cometcha250b.htm
http://g8jnj.webs.com/broadbandhfvertical.htm
12-Mar-2008
– From Marty KN0CK
Marty has also made a clone of this antenna. More details can be found at http://chat.qth.com/viewtopic.php?t=4455
Some pictures of Marty’s antenna can be seen here:
Matching
unit on antenna with cover removed
73’s
Iain