[amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink

Mon Jan 20 08:59:20 PST 2014

Greg,
I had a problem with 70cm jamming 2401 down link many years ago. The problem
turned out to be corrosion between the coax connector shell and the aluminum
antenna element. Cleaning up the connection solved the problem.  The
corrosion acts like a diode and will make enough 3 order products to trash
any receiver. Use liquid electrical tape or non-corrosive (doesn't smell
like vinegar) silicon seal to keep these connections dry and clean.
Art, KC6UQH

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of g0mrf at aol.com
Sent: Monday, January 20, 2014 1:23 AM
To: ko6th.greg at gmail.com; kq6ea at verizon.net; w4tas at gte.net;
amsat-bb at amsat.org
Subject: [amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink

Hi Greg.

Most decent VHF transmitters will already have a pretty good LPF on the
output to reduce the harmonics.

However, receivers these days tend to be DC-Daylight, so frequently need a
filter to prevent 'blocking' by unwanted high level signals. In that case
preventing the VHF coming into the UHF receiver can be important

Thanks

David

-----Original Message-----
From: Greg D <ko6th.greg at gmail.com>
To: Jim Jerzycke <kq6ea at verizon.net>; w4tas <w4tas at gte.net>; 'AMSAT Mailing
List' <amsat-bb at amsat.org>
Sent: Mon, 20 Jan 2014 3:47
Subject: [amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink

I know this has been answered before, but I forget.  Given one Diplexer, is
it better to put it on the Tx side to limit the 3rd harmionic going out, or
better on the Rx side to limit the VHF fundamental coming in?  
Tony's diagram shows the later; I would have thought the former would be
more effective (hitting the problem at its source).

Greg  KO6TH

Jim Jerzycke wrote:
> Yep, been using one of those for years!
>
> I have a Sinclair Labs unit that provides 100dB rejection outside of 
> the 2 Meter band.
>
> Jim  KQ6EA
>
>
> On 01/19/2014 07:32 PM, w4tas wrote:
>> I would also suggest a low pass filter on the two meter transmitter.
>> A diplexer will work well for this also.
>> This will reduce the third harmonic which is causing your problem.
>>
>> Good luck,
>>
>>
>>
>>
>> -----Original Message----- From: Jim Jerzycke
>> Sent: Sunday, January 19, 2014 2:09 PM
>> To: amsat-bb at amsat.org
>> Subject: [amsat-bb] Re: 145 MHz signal blocking 435 MHz downlink
>>
>> Buy a diplexer, and connect it as shown in the linked article:
>>
>>
>> http://www.amsat.org/amsat-new/articles/Mode-J/
>>
>> I also tilt both of my Yagis so they're 45* to the boom, which makes 
>> them 90* to each other.
>>
>> Yes, I lose some signal on terrestrial use, but ti helped cut the 
>> coupling, and desense, down quite a bit.
>>
>> 73, Jim  KQ6EA
>>
>> On 01/19/2014 06:56 PM, Gabriel - EA6VQ wrote:
>>> Hi all,
>>>
>>> I have a coupling problem in my station when trying to work FO-29.  
>>> My 2m
>>> signal is completely blocking the 435 MHz downlink, and so I can't 
>>> hear my signal off the satellite. I guess it must be something 
>>> related to the distance between the two yagis. (I use the 
>>> terrestrial horizontal yagis you can see at 
>>> http://www.dxmaps.com/jm19hn.html ). With mode-B satellites there is 
>>> no problem.  I have tried it with two different 435 receivers, and 
>>> it's exactly the same.
>>>
>>> Anyone has had this problem o have an idea of the possible reason?  
>>> And what
>>> is more important, of some way to solve it?
>>>
>>> Thanks for any possible help.
>>>
>>> 73. Gabriel - EA6VQ
>>> _________________________________________________________
>>> Web-Site: HTTP://www.dxmaps.com
>>> VQLog 3.1 (build 78): HTTP://www.vqlog.com 
>>> _________________________________________________________
>>>
>>>
>>> _______________________________________________
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>>
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>
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