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

[Greg D]

Hi Art,

Yep, corrosion is a great source for harmonics.  I had a similar problem 
with AO-40, only mine turned out to be the relay contacts on the 70cm 
antenna's RHCP / LHCP relay.  Cycle them a few times and things quieted 
down.  But I only heard the problem when I was aimed at the big oak tree 
behind our house, which was odd because the 70cm transmit antenna was 
literally a few inches away from the edge of the 2.4 ghz receive dish.  
Never heard of a tree acting as a diode before.  Maybe the squirrels 
were up to something...

Greg  KO6TH


kc6uqh at cox.net wrote:
> 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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