Many thanks to everybody for all the suggestions. I'll have a look at the filter designs.
There are some people that have suggested that the problem might be the 3rd harmonic from the 2m TX, instead of being overload by the 2m signal somewhere in the receiver. I'm also suspicious that this could be the case, but I did yesterday some tests that seem to indicate that the level of the 3rd harmonic is fine.
I tested with different antennas for TX and RX, with about 2 or 3 meter separation between them (my normal antenna is an arrow type antenna, with on coax for the 2m yagi and other coax for the 70cm yagi). Fist I connected the dongle to the 70cm port on the diplexer (and the antenna to the common port). With this setup I got a bit of desense as usual. Then, I connected the dongle to the 2m port on the diplexer. With this setup the desense is very big.
This makes me think that the problem is with the 2m frequency and not the 3rd harmonic, because the distance between the antennas and the 2m port of the diplexer should be more than enough to kill any 3rd harmonic.
However, it's possible that I am seeing two different effects with this: the 3rd harmonic when the dongle is on the 70cm port and overload from the 2m signal when the dongle is on the 2m port.
What do you guys think?
73,
Dani EA4GPZ.
El 16/04/15 a las 00:07, Daniel Estévez escribió:
Hi all,
My portable satellite station consists of a Funcube Dongle Pro+ for RX and a FT-817ND for TX. I use a diplexer in front of the dongle to avoid desensing, but still some of the 2m signal is getting in and causing desensing when working V/U birds. It seems to me that a 70cm high-pass filter in the receive chain would help.
Can anyone point me to some easy to build reference designs for this kind of filters? Power handling is not an issue, since this will only be used for RX. I'm mainly looking to something that I could build from things in my junk box, using air core inductors and ceramic caps (if this a sensible thing to do).
73,
Dani EA4GPZ. _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb