23cm SEPTUM FEED (Note:
Below describes my very first septum feed. For the latest new teqhnique:
http://kl6m.com/23cm/23CM-SEPTUM-FEED.pdf
)
More photos, with scalar ring:
http://kl6m.com/23cm/scalar.html
Return loss charts: cursor = 1296.0
MHz marker = 1147 MHz ???
I'm not sure why there seems to be a natural resonant point at 1147 MHz. This did
not seem to change when monopoles were lengthened.
Isolation before lengthening was about -16 dB. The plot showed a much deeper
isolation (>>20dB) about 40 MHz wide at about 1375 MHz. After lengthening the
monopoles isolation worsened to -13 dB. I tuned for maximum isolation and the best I
could achieve was -22 dB. At this setting the return losses were very bad, around -8
to -10 dB.
I plan to try some different lengths and perhaps some different diameters for the
monopoles. I am also questioning whether or not I should terminate the other port
during return loss optimization. Normal transmit operation would have the RX port
unterminated. Normal receive operation would have the TX port terminated in the
coaxial feedline all the way back to the amplifier.
Comments are welcome !!
1a-probe.jpg
61.16 Kb
Monopole probes
6mm diam. x 43mm
soldered about 3 mm
from connector |
1b-probe.jpg
59.24 Kb
Monopole probes
after resoldering
about 5mm above
connector |
1RL.jpg
66.67 Kb
1st measurement
Return Loss
Left port |
2RL.jpg
65.05 Kb
1st measurement
Return Loss
Right port |
3RL.jpg
43.36 Kb
Left port
Return Loss
retuned |
4RL.jpg
62.97 Kb
Left port
Return Loss after
lengthening. No
termination on
right port |
5RL.jpg
63.10 Kb
Left port
Return Loss after
lengthening.
Termination on
right port |
6RL.jpg
62.59 Kb
Right port
Return Loss after
lengthening.
Termination on
left port |
7isolation.jpg
68.90 Kb
Isolation between
ports. Max isolation
is occuring at
1375 MHz |
_septumparts.jpg
56.70 Kb
Fabrication of
parts completed
Ready for assembly |
quick70cm.jpg
39.83 Kb
New feed support
with temporary 70cm
using HD73 for polarity |
redoubt10-04.jpg
68.61 Kb
Mt Redoubt
As seen from our
living room window
5-Oct-04 |
23cm SEPTUM FEED - FINAL RESULTS
Final Return loss: Right port: -27 dB (1.09:1 VSWR) Left port:
-35 dB (1.04:1 VSWR) Isolation: -29.8 dB
I had excellent comments and suggestions from moon net folks. Most suggested that
I start trimming and try to find the best results. One person mentioned that their
final monopole length was around 48mm. Another mentioned 38mm. So I started at
48 and started trimming. When I got to 39.5mm I reached a maximum isolation of
almost 30 dB! So I backed up .5mm and soldered and bolted everything down and ended
up with the EXCELLENT results above!
Mission accomplished. THANKS!
