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

[Jim Jerzycke]

Well, from my experience, every little bit helps.....

I first had the two antennas mounted horizontally on the cross boom, and 
had some interference/desense. Then I installed the diplexer, and it 
lessened. Then I put the 2 Meter bandpass filter on the transmitter, and 
it improved some more. Then I mounted the two antennas at 45* to the 
boom, making them 90* to each other, and it went down some more.

Short of hanging huge cavity filters on the antenna, and using a 20' 
cross boom, I don't think there's much more I could do!

73, Jim


On 01/20/2014 04:54 AM, Greg D wrote:
> The more I read about it, the more I expect that the right answer 
> depends on one's particular receive-side hardware.  If it's already 
> got good out of band filtering, then the hi-pass filter offered by the 
> posted diagram won't help, since it's aimed at reducing the 2m 
> fundamental overload.  For that, you need to use the 2m port on the Tx 
> side (Tx to Common, 2m port to antenna, leaving the 70cm port 
> unconnected).
>
> On the other hand, if the receiver pretty wide open, then the 2m 
> fundamental is the main problem, and the posted receive-side design 
> will eliminate it before it hits the receive chain.
>
> Yes?
>
> Greg  KO6TH
>
>
> Jim Jerzycke wrote:
>> Since I use a very good 2 Meter bandpass filter on my 2 Meter output, 
>> I use the diplexer AT the antenna, ahead of the preamp.
>>
>> Jim  KQ6EA
>>
>>
>> On 01/20/2014 03:41 AM, Greg D wrote:
>>> 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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>>>
>>
>
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