Navtex 490 kHz LF-antenna signal amplifier

[JimB]

Where can I find the Navtex transmission protocol?

Try these:

NAVTEX services in waters around the British Isles

http://en.wikipedia.org/wiki/NAVTEX...s are transmitted using,as the SITOR-B format

.


JimB

 

[JimB]

Looks more like an American magazine project?

Look here:

https://worldradiohistory.com/UK/Practical/Wireless/80s/PW%201981%2003.pdf

on page 52.
This was the basis for my amplified antenna.

The entire balanced nature of the front end seems pretty pointless, and doesn't work well with the tuning capacitor, one side of which is designed to be grounded, so won't help the balancing

The idea of using a balanced circuit was to provide maximum flexibility as to the type of antenna which is connected. See the article quoted above.
In my case I simply used the antenna from the remains of a dead transistor radio.
The whole tuning capacitor is floating above earth, mounted in a plastic box, the degree of unbalance not a problem.

and then they even stick an external aerial directly on the end of the high impedance 'balanced' tuning coil, so heavily damping the coil, and completely unbalancing the front end.

The external antenna was my modification to receive a bit more signal from mainland UK while situated in the wilds of Hillswick in Shetland.
The external antenna is about 1 metre of wire, connected to the tuned circuit via an 18pF capacitor, please be assured that this does not heavily damp the tuned circuit.

The bottom line is (or was), the circuit fulfilled a need at the time, it may not have been perfect but any deficiencies did not impinge on the day to day needs of listening to the radio.

JimB

 

[unclejed613]

Where can I find the Navtex transmission protocol? I intend to eventually build my own RF receiver (with a cascode setup in the input stage) as well as message decoder using a controller.

https://github.com/search?q=navtex the search result brings up about 18 different navtex projects, mostly written in python.. all of them are source code archives, so you will likely find something there that you can use, or at least something you can adapt.

 

[earckens]

https://github.com/search?q=navtex the search result brings up about 18 different navtex projects, mostly written in python.. all of them are source code archives, so you will likely find something there that you can use, or at least something you can adapt.

Great! That helps a lot.

 

[earckens]

RF coils found here: https://www.box73.de/product_info.php?products_id=2417
I managed to tune them to 520kHz.