Hi group,

I've been using a Tee-antenna for Navtex reception on 518 KHz for about
6 months now. Details are he
http://users.pandora.be/dirk.claessens2/NAVTEX/Tee-antenna.jpg

I'm very pleased with the results, the thing just works. Almost no
local QRM pickup, low noise. I was able to decode really weak Navtex
stations in Florida, Puerto Rico, Bahrein. ( I'm living near Antwerp,
Belgium).

But is this a really optimal antenna setup - given the obvious real
estate limitations of my back garden?

When I feed the antenna data into 4NEC2, the following data result:

Z = 241-j1812 Gain = -28.6 dB SWR = 278
I'm assuming that the mismatch is "solved" by the use of the 4:1 UnUn..

If I model a base loading coil of +/- 550 microH , the following
results:
Z = 165-j14 Gain = -26.9 dB SWR = 3.3

Question 1: Is installing a base loading coil worth the trouble for
receive-only purposes?

Question 2: Should I still use the balun?


Thanks for any advice.

Cheers - Dirk

Navtex-Fan wrote:
Z = 241-j1812 Gain = -28.6 dB SWR = 278
I'm assuming that the mismatch is "solved" by the use of the 4:1 UnUn..

Nope, not necessarily. Most 4:1 designs assume a resistive
load and do not handle reactance very well. A 4:1 device
might make the problem worse.

If I model a base loading coil of +/- 550 microH , the following results:
Z = 165-j14 Gain = -26.9 dB SWR = 3.3

As long as your receiver AGC has enough gain to overcome
the loss in the antenna, why worry? Internal receiver noise
is usually negligible compared to atmospheric noise at
518 KHz.
--
73, Cecil http://www.w5dxp.com

On 2007-12-28, Cecil Moore (75.23.42.181) wrote in
message


Navtex-Fan wrote:
Z = 241-j1812 Gain = -28.6 dB SWR = 278
I'm assuming that the mismatch is "solved" by the use of the 4:1 UnUn..

Nope, not necessarily. Most 4:1 designs assume a resistive
load and do not handle reactance very well. A 4:1 device
might make the problem worse.


Thanks for the reply Cecil,

Are you suggesting I should not use a unun at all?
I have also experimented with the commercial "magnetic balun" which has
a 9:1 ratio. The only difference I could tell was a _slightly_ lower
noise level.


Cheers - Dirk

Navtex-Fan wrote:

[...]

It would certainly be nice to see these fools behind bars ...

Instead of devoting time to finding renegade cb'ers, lets grab some of
these guys butts and put them where they should be!

JS

John Smith wrote:
Navtex-Fan wrote:

[...]

It would certainly be nice to see these fools behind bars ...

Instead of devoting time to finding renegade cb'ers, lets grab some of
these guys butts and put them where they should be!

JS

Oh yeah, I forgot, THREAD PLONK--BIG TIME!!!

JS

Navtex-Fan wrote:
Hi group,

I've been using a Tee-antenna for Navtex reception on 518 KHz for about
6 months now. Details are he
http://users.pandora.be/dirk.claessens2/NAVTEX/Tee-antenna.jpg

I'm very pleased with the results, the thing just works. Almost no local
QRM pickup, low noise. I was able to decode really weak Navtex stations
in Florida, Puerto Rico, Bahrein. ( I'm living near Antwerp, Belgium).

But is this a really optimal antenna setup - given the obvious real
estate limitations of my back garden?

When I feed the antenna data into 4NEC2, the following data result:

Z = 241-j1812 Gain = -28.6 dB SWR = 278
I'm assuming that the mismatch is "solved" by the use of the 4:1 UnUn..

If I model a base loading coil of +/- 550 microH , the following results:
Z = 165-j14 Gain = -26.9 dB SWR = 3.3

Question 1: Is installing a base loading coil worth the trouble for
receive-only purposes?

Question 2: Should I still use the balun?


Thanks for any advice.

Cheers - Dirk



Whoa ...

Sorry about that, had a virus and is was showing "all sorts" of strange
stuff till I ran the scanner and reloaded this ng thread.

My mistake, I apologize to the MAX :-(

I am throughly embarrassed ...

Warm regards,
JS

Navtex-Fan wrote:
Are you suggesting I should not use a unun at all?

Unbalanced antenna to unbalanced receiver with a
very large dynamic range may result in diminished
returns for your effort. But if you want to use it
as a learning experience, it might be worth it.
--
73, Cecil http://www.w5dxp.com

On Dec 28, 10:08 am, Navtex-Fan wrote:


Question 1: Is installing a base loading coil worth the trouble for
receive-only purposes?

I doubt it. As long as you hear an increase in noise when
you connect the antenna to the radio, "no signals",
it's good enough.

Question 2: Should I still use the balun?

I wouldn't bother if it's working ok as is.
MK

On 2007-12-29, John Smith () wrote in
message


I am throughly embarrassed ...

....And I thought *my* newsreader went bezirk... :-)

On 2007-12-29, (98.194.156.7) wrote in
message



On Dec 28, 10:08 am, Navtex-Fan wrote:


Question 1: Is installing a base loading coil worth the trouble for
receive-only purposes?

I doubt it. As long as you hear an increase in noise when
you connect the antenna to the radio, "no signals",
it's good enough.

I can clearly hear the noise level raise when I connect the antenna.


Question 2: Should I still use the balun?

I wouldn't bother if it's working ok as is.
MK

Ok - thanks