On 2/4/2015 1:39 PM, Jerry Stuckle wrote:
On 2/4/2015 2:02 PM, John S wrote:
On 2/4/2015 11:57 AM, Jerry Stuckle wrote:
On 2/4/2015 12:26 PM, John S wrote:
On 2/3/2015 2:17 PM, Irv Finkleman VE6BP wrote:
I haven't seen a post on this group since the 27th of January.
Was it something I said, or what?
Just gotta make sure this newsgroup is still working! :-)

de Irv, VE6BP

Hi, Irv -

I did not think you were interested in some of my research projects
because they are in the 70cm band. If it does interest you, let me know
and I'll describe my project.

Cheers,
John N1JLS

John,

There are definitely people interested in 70cm band projects. Please -
post away!

Thanks for your reply, Jerry.

History:

My thought was to have a remote transmitter for measuring rainfall. Yes,
I can buy one, but then I don't have a reason to do all this.

I decided to use a Silicon Labs si4420 device for both receiving and
transmitting. I would use the 70cm band and include my call sign on
every transmission. It would be inside the base of a very old tipping
bucket rain gauge using a 3-cell AAA supply. The trigger is a momentary
contact when the bucket tips, indicating .01 inches of rainfall.

Present:

Okay. Well, it turns out that the si4420 wants a 27+j136 balanced load
seen at its terminals. This is where the antenna investigation comes in.

So, I need to show a balanced input of 27+j136 from an antenna separated
from the chip with two traces of some impedance (TBD) to the chip. Some
lumped matching components can be used, but I have tried to minimize
them for home construction purposes. I don't have the room to put in
very many cm of micro strip transmission line.

My goal is to make it as simple as possible and be able to make it in my
shop by hand.

Thanks, Guys.
John N1JLS


John,

I've looked at similar chips with the idea of building an expensive
single-channel 440 Mhz FM rig. Not that the existing rigs aren't cheap
- just something to do.

You might want to look at a couple of PDFs on the silabs website:

https://www.silabs.com/Support%20Doc...Docs/an422.pdf
https://www.silabs.com/Support%20Doc...Docs/an421.pdf

The first is a datasheet on the 4420 (and others); the second has all
kinds of good information including PC board antennas (see figures 2.7
and 2.8).

Silicon Labs has a lot of good information on their website. However,
there's so much sometimes it can be hard to find exactly what you want


Thanks, Jerry. I have those documents and have read them. Good stuff there.