[amsat-bb] Re: AO-51 V/S

Luc Leblanc lucleblanc6 at videotron.ca
Tue Apr 20 11:28:50 PDT 2010

On 20 Apr 2010 at 17:38, Bob- W7LRD wrote:

Date sent:	Tue, 20 Apr 2010 17:38:07 +0000 (UTC)
From:	Bob- W7LRD <w7lrd at comcast.net>
Subject:	Re: [amsat-bb] Re: AO-51 V/S
To:	Luc Leblanc <lucleblanc6 at videotron.ca>
Copies to:	eu-amsat at yahoogroups.com, amsat-bb at amsat.org

> Hi Luc and all 
>I am using a Transystem 3731AA downconverter.  Also an old Kenwood TS-700A for the tunable IF.  I have compared Keps 13LNC-PH 
downconverter against the 3731.
>The 3731 is virtually immune to desense to 2M tx as well as wifi etc.  However the Keps (pricey) is affected by the 2M tx.  Without the 
>noise blanker turned on in the TS-700 I get lots of snapping, popping from wireless phones, wifi etc.  The noise blanker in this old 700 
>is superb, better that the one in my 910!  Go figure!  Mind you this is all empirical evaluation using nothing but my ears.  I have heard 
>the filter in the 3731 is better than most.  I will be shipping some of my dc's soon to a fellow who can give a very accurate evaluation 
>on these devices.  Hope this helps Luc, see you on S band! 
> 73 Bob W7LRD 
Hi Bob

I have the same DC but my IF is on 123mhz and i got no desense at all on 2M but that's the 2.4Ghz RF your "snapping, popping" who i think 
is could be reducing the RF sensitivity of the DC. The AIDC was design to received MMDS TV where channels where isolated from each other 
and they was no other QRM on the original band this downconverter was design for. How he's performing on a band full of QRM that i don't 
know and it will be something to test to see if the DC keep his same sensitivity when is QRMed on 2.4Ghz.

Adding some sort of flitration is could be a way to reduce any 2.4Ghz desense if any and what the noise blanker does is to suppress the 
pops and clicks but he cannot reduce the overall QRM level. 

Our regular Ham receiver can be tweaked for the best reception possible but with a DC we are stuck with a static passband, no way to reduce 
the RF level and so on.

I don't know how wide the AIDC 3731AA front end was but to be able to receive TV signals it should be quite wide and he should pass a lot 
more than 15KC?


Luc Leblanc VE2DWE
Skype VE2DWE


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