I recently purchased an Advanced Receiver Research 2M pre-amp to use when operating on the LEO SSB satellites. I purchased the SP144VDG (24 db gain, <1 NF). They don't offer the lower gain, higher noise figure 2M pre-amps anymore.
I tried setting it up this weekend and when the pre-amp is on and I'm transmitting on the 70cm band, I'm getting a lot of audio distortion. When I tried this during a pass, my audio on 2M was barely readable because it was so distorted, but with the pre-amp off, I sounded fine.
I'm currently using a 2m/70cm Arrow antenna mounted on a portable Yaesu G5500 Az/El setup. When I spoke with ARR, they suggested it was a desensitizing situation and it may be due to the 2M and 70CM antennas being so close to one another.
Can anyone help or suggest some things I could try to eliminate this situation? Separate antennas? Some kind of filter before the pre-amp? The pre-amp sounds great when turned on, but right now it can't be used when I'm transmitting at the same time on 70cm, which doesn't help.
Thanks, Dave N2TEB
On 10/03/16 17:10, David Mennerich wrote:
I recently purchased an Advanced Receiver Research 2M pre-amp to use when operating on the LEO SSB satellites. I purchased the SP144VDG (24 db gain, <1 NF). They don't offer the lower gain, higher noise figure 2M pre-amps anymore.
I tried setting it up this weekend and when the pre-amp is on and I'm transmitting on the 70cm band, I'm getting a lot of audio distortion. When I tried this during a pass, my audio on 2M was barely readable because it was so distorted, but with the pre-amp off, I sounded fine.
It sounds like the active devices in your 2m LNA is getting crushed by the output of the 70cm transmitter.
You could try "A Simple Desense Filter for Mode-J Satellites" in reverse: you want to put the preamp and radio on the 2m side and leave the 70cm side unconnected.
http://www.amsat.org/?page_id=2136
N0ZGO
Hi Zach - I checked out that article and to my surprise I had a Comet CF-416 duplexer sitting in my box of radio parts down in the basement. I did a quick test of the setup down in my basement and was able to easily reproduce the desensitization scenario. Then I changed the wiring and ran from the antenna to the duplexer to the pre-amp to the radio. No more desensitization!
I will fully test this out the next time I set up my portable satellite station - hopefully this upcoming weekend.
Thanks to all of those that replied to me - I have other ideas I can experiment with as well based on your emails, but I'll start with this one and see if it works for me.
73, Dave
On Mon, Oct 3, 2016 at 6:26 PM, Zach Metzinger zmetzing@pobox.com wrote:
On 10/03/16 17:10, David Mennerich wrote:
I recently purchased an Advanced Receiver Research 2M pre-amp to use when operating on the LEO SSB satellites. I purchased the SP144VDG (24 db
gain,
<1 NF). They don't offer the lower gain, higher noise figure 2M pre-amps anymore.
I tried setting it up this weekend and when the pre-amp is on and I'm transmitting on the 70cm band, I'm getting a lot of audio distortion.
When
I tried this during a pass, my audio on 2M was barely readable because it was so distorted, but with the pre-amp off, I sounded fine.
It sounds like the active devices in your 2m LNA is getting crushed by the output of the 70cm transmitter.
You could try "A Simple Desense Filter for Mode-J Satellites" in reverse: you want to put the preamp and radio on the 2m side and leave the 70cm side unconnected.
http://www.amsat.org/?page_id=2136
N0ZGO
participants (2)
-
David Mennerich -
Zach Metzinger