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



Hi Ray, KA8SYX

>From your story of the "hot spots" it seams that your 2 meter coax cable
is connected to an antenna wich dipole has not a good balun so that in
this condition the radio frequency flows also over the external surface
of the braid of the coax cable wich in turn functioning as an unwanted
antenna pick up a lot of signals from everywere even from the case of
your FT 290 R

Please disconnect the 2 meters coax cable from the antenna dipole and
replace the 2 meters antenna with a good 50 ohm termination and see if
the interference disappear or not.

If  you are still receiving the interference than connect the 50 ohm
termination directly to your 2 meter receiver and see what happens
particularly looking if the "hot spots" if they are still present have the
same strenght with your hands engaged as before.

Hopefully the above simple procedure will permit you to identify
step by step a little more about the source of your problem.

Best 73" de

i8CVS Domenico

----- Original Message -----
From: Fritts, Raymond C. (CONTR) (L) <rfritts@jiatfs.southcom.mil>
To: 'Lau, Zack, W1VT' <w1vt@arrl.org>; 'amsat bb' <amsat-bb@AMSAT.Org>
Sent: Wednesday, December 01, 2004 4:21 PM
Subject: [amsat-bb] 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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----
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