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Question about interaction between separate rigs for Mode U/V sat ellite operations



Hi, Zack,

Thanks for your reply and suggestions.  I realize this may not be the
proper avenue to continue this discussion because "Ask the Doctor" is
basically a one-question-at-a-time forum, but wanted to inquire further
about my problem.  I also hope that you do not mind if I open it up to
discussion on AMSAT BB.  I can use all the advice anyone might have.

Taking your advice re: notch filters I stopped off at the local RS in Key
West on the way home from work last night and picked up a BNC T adapter
and short plug-equipped RG-58 jumper.  I attached the T to the input of
the 2M 3-el portion of my Arrow II crossed dual band Yagi, clipped the
RG-58 jumper to what I'd calculated (Vf of .66 and 234 as the denominator
of the freq/n equation for deriving physical length of a 1/4 wave) as the
1/4wave length for 432.15 (AO-7 uplink band center, worked out to be about
109mm,) left the far end open and connected it to one side of the T, the
feedline to the 2M receiver to the other side of the T and the male bottom
of the T to the Yagi as described above.  I fired the whole business up
and transmitting 2.5W PEP from the 70cm rig, still heard the interference
on the 2M receiver.  No reduction whatsoever.

Some things I noticed about the whole issue that I didn't lay out in
earlier email:

-It's not an issue in FM, only in phone and CW.  On CW, the interference
is a clicking sound on key make but not break and no tone heard.
-My HT, transmitting into the 70cm Yagi on 70cm FM, has no effect.
-No matter whether the frequency difference between my 70cm transmissions
and 2M receptions is, and regardless of changing one rig's frequency/mode
or the other during transmission, the pitch and quality of the
interference as received on the 2M receiver remains unchanged.
-There are "hot spots" on the 2M receiver's case where the received
interference signal is much stronger.  Of course, this is with the 70cm
mike in one hand, PTT engaged, with headphones from the 2M receiver on my
head and the other hand on the hot spot; I'm trying to duplicate the
operating condx during normal satellite use.  The hot spots are on the
mobile mounting brackets of the 2M receiver to either side and slightly
behind the front panel.  I touch those while transmitting and I cannot
hear anything in the headphones except the interference.  But I cannot
remove them during use because that same bracket is where the clip-on
linear amps attach.
-When I purchased the 70cm rig, used, it had a single wire dangling from
the case through a small hole drilled in it; it was the result of a mod
the first owner had installed to enable CTCSS because he didn't have the
Yaesu model and used an external CTCSS coder box.  Thinking the exposed
wire was radiating the interference from the location in the rig's
circuits to which it was attached, I clipped it at it's junction; I don't
care one bit about CTCSS for this rig; strictly weak sig stuff was why I
got it.

Anyway, that's the story.  If you have any other suggestions/advice, I'm
awfully glad to hear it.  Again, thanks!

Vy 73, Ray Fritts KA8SYX
Big Pine Key, FL

-----Original Message-----
From: Lau, Zack, W1VT [mailto:w1vt@arrl.org]
Sent: Monday, November 29, 2004 3:56 PM
To: rfritts@jiatfs.southcom.mil
Subject: RE: Question about interaction between separate rigs for Mode U/V
satellite operations


Hi Ray,
	Mike Tracy fowarded your puzzler my way.  Sorry for the delay in
replying--I was
on vacation last week.

	I suggest attempting to obtain another 2M receiver or another 70
cm transmitter.
The 70 cm transmitter could be an FM handie talkie.  This may allow you
to determine
whether the problem is the receiver or the transmitter.  As it stands,
it could be either.
You could need

	My guess is that the 2M receiver is the culprit.  The 2M antenna
is also resonant
on 70 cm, so it picks up 70cm signal with little attenuation.
Typically, receiver
input circuits are designed for maximum sensitivity--spurious responses
aren't unusual.
I suggest putting a notch filter for 70 cm--with a Tee connector add a
quarter wave open
stub cut to 70 cm.

http://www.ifwtech.co.uk/g3sek/swxfiltr/swxfiltr.htm
more complicated notch filters

73--Zack Lau W1VT


> -----Original Message-----
> From: Tracy, Michael, KC1SX
> Sent: Wednesday, November 24, 2004 3:16 PM
> To: TIS Unsorted
> Subject: FW: Question about interaction between separate rigs for Mode
> U/V satellite operations
>
>
>
> -----Original Message-----
> From: Fritts, Raymond C. (CONTR) (L)
> [mailto:rfritts@jiatfs.southcom.mil]
> Sent: Monday, November 22, 2004 10:52 AM
> To: TIS Unsorted
> Cc: 'ka8syx@arrl.net'
> Subject: Question about interaction between separate rigs for
> Mode U/V satellite operations
>
>
> Dear Doctor -
>
> I'm hearing transmissions from my 70cm allmode rig (Yaesu
> FT-790R MkII,) used to attempt uplinking to AMSAT-OSCAR-07,
> on my 2M downlink rig (Yaesu FT-290R MkII.)  I've tried a
> number of experiments, including the use of a homebrewed
> 432.1MHz Yagi physically separated from my 2M downlink Yagi,
> oriented to minimize interaction, running the rigs with
> different power supplies (batteries v. mains, separate
> batteries, etc.), physically separating the radios by a foot
> or so, separating the antennas, running the 70cm rig at 1/10
> the power, and/or into a dummy load.  Thinking that the
> problem may be caused by interaction between the 70cm and 2M
> elements on my Arrow II crossed dual-band Yagi, I even tried
> removing the 70cm elements and just used the 2M elements
> alone along with the homebrewed "cheap Yagi."  To a greater
> or lesser extent, the interference was still there no matter
> what I tried.  It intensifies when I have my hand on or in
> close proximity to my transmitting 70cm rig.  Over the past
> few months I've become increasingly familiar and successful
> at operating on the Mode V/U sat, Fuji-OSCAR-29, with no
> interaction whatsoever on that mode; I'm fortunate; I've not
> even experienced problems with desensing in the receiver.
> But this interaction between my 70cm uplink and 2M downlink
> in Mode U/V was totally unexpected, and it prevents me from
> finding my downlink signal, even when my pass predictions
> suggest that, for all of the predicted attributes, I should
> be in the ballpark and hear myself.  What is causing this
> problem?  Is there a cure?  If so, what must I do to correct it?
>
> Thanks very much, and 73,
> Ray Fritts, KA8SYX
> Big Pine Key, FL

[demime 1.01d removed an attachment of type application/x-pkcs7-signature which had a name of smime.p7s]
----
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