Same, but only just long long ago. The course was Microwave and Antenna
theory. Prof was a younger Pakistani who didn’t believe in deodorant and spoke
so softly your choice was watering eyes in the front or not hearing a thing in
the back. Midterm was a 200 point exam. I think I scored a whopping 25 -
which was the class average. Of course one kid had a 180. Dual major
premed and EE. Early admission to Johns Hopkins. Basketball all star. When
we asked him what he was doing in EE he said he wanted something to fall back
on if he didn’t get into medical school. Destroyed the curve for 4 years as a
backup plan. Couldn’t even hate him - he was too nice of a guy.
Wonder what happened to the guy…
Mark
> On Mar 6, 2020, at 3:30 PM, Ken Hohhof <af...@kwisp.com> wrote:
>
> It was a long, LONG time ago that I was an EE undergrad. And we had to take
> 2 courses called Static and Dynamic Fields. Not my favorite courses
> (remember these were the days of slide rules).
>
> For the final exam, the professor passed out a detailed drawing of a
> waveguide with all the dimensions, plus a blob of wet chewing gum stuck to
> one of the walls, and we were supposed to use Maxwell’s equations (?) to
> solve for something. He let the whole class sit there and sweat bullets for
> 5 or 10 minutes, and then said it was a joke and passed out the real exam.
>
>
> From: AF <af-boun...@af.afmug.com> On Behalf Of Bill Prince
> Sent: Friday, March 6, 2020 2:00 PM
> To: af@af.afmug.com
> Subject: Re: [AFMUG] PTP Microwave antenna question
>
> That's what I was thinking. Maybe a cockroach crawled inside the OMT?
> bp
> <part15sbs{at}gmail{dot}com>
>
> On 3/6/2020 11:40 AM, Ken Hohhof wrote:
>> You know the radio and antenna are good, and the adapter is dirt simple.
>> And it’s almost impossible to assemble wrong.
>>
>> That leaves the OMT. Or even just a bad OMT at one end. But that’s also a
>> piece of plumbing, probably a cast part. Have you visually inspected the
>> OMTs? Was somebody smuggling drugs inside OMTs?
>>
>> From: AF <af-boun...@af.afmug.com> <mailto:af-boun...@af.afmug.com> On
>> Behalf Of Mark Radabaugh
>> Sent: Friday, March 6, 2020 1:18 PM
>> To: AnimalFarm Microwave Users Group <af@af.afmug.com>
>> <mailto:af@af.afmug.com>
>> Subject: Re: [AFMUG] PTP Microwave antenna question
>>
>> Not a lot of options to put these together wrong. Line up the hangers and
>> it’s good to go:
>>
>> <image001.jpg><image002.jpg>
>>
>> Mark Radabaugh
>> Amplex
>> 22690 Pemberville Rd
>> Luckey, OH 43443
>> 419-261-5996
>>
>>
>>
>>> On Mar 6, 2020, at 1:56 PM, Steve Jones <thatoneguyst...@gmail.com
>>> <mailto:thatoneguyst...@gmail.com>> wrote:
>>>
>>>
>>> whats the OMT look like? That V/H pin puts the plate at 45?
>>>
>>> On Fri, Mar 6, 2020 at 12:48 PM Caleb Knauer <cknauer.li...@gmail.com
>>> <mailto:cknauer.li...@gmail.com>> wrote:
>>>> If that center part is press fit in slightly catawampus and not 100%
>>>> plumb then it could cause issues. Or the pipe isn't 100% either. But
>>>> kind of grasping at straws with that.
>>>>
>>>> On the C's I've bench tested with XPIC without antennas, it'll talk to
>>>> either one IIRC if you run 2/1 or 1/2 as I've played with it. It's
>>>> really not happy about it though. I'd have to confirm though, been a
>>>> bit.
>>>>
>>>> XPIC keys or settings wouldn't affect the raw RXL levels, it just
>>>> blows out your MSE if they're crossed. I've seen links where they
>>>> didn't turn on anything XPIC but set it up and it works, just kinda
>>>> janky.
>>>>
>>>> You could always mute one core on both sides and sanity check that way
>>>> too. If something is crossed, it'd show the right RXL one on core and
>>>> 30ish dBm down on the other core.
>>>>
>>>> On Fri, Mar 6, 2020 at 1:12 PM Ken Hohhof <af...@kwisp.com
>>>> <mailto:af...@kwisp.com>> wrote:
>>>> >
>>>> > You look at Mark's photo and think what could possibly be wrong, it's a
>>>> > round hole. How many ways are there to install a round hole, it's like
>>>> > the proverbial one car funeral procession.
>>>> >
>>>> > And I guess with an 820C + OMT, having H and V swapped shouldn't be
>>>> > possible, and even if they were, it would still work if you did the same
>>>> > thing at both ends. I wouldn't assume though that XPIC would straighten
>>>> > out an H/V swap, I don't think it's like MIMO on WiFi. XPIC assumes the
>>>> > antenna cross pol rejection does most of the work and it has to clean up
>>>> > what remains.
>>>> >
>>>> > I'm assuming you have the XPIC keys enabled, although that would
>>>> > probably create an alarm not the symptoms you are seeing.
>>>> >
>>>> > -----Original Message-----
>>>> > From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com>> On
>>>> > Behalf Of Caleb Knauer
>>>> > Sent: Friday, March 6, 2020 11:40 AM
>>>> > To: AnimalFarm Microwave Users Group <af@af.afmug.com
>>>> > <mailto:af@af.afmug.com>>
>>>> > Subject: Re: [AFMUG] PTP Microwave antenna question
>>>> >
>>>> > With XPIC it wouldn't matter that slot 1 was talking to slot 2 on the
>>>> > other side, it wouldn't know. At least I think anyways. Since it's
>>>> > just looking for RX on the frequency it's set, and it's on the same on
>>>> > both ends, and it'd still have XPD to separate the two. You could
>>>> > rotate one end 90 degrees to simulate on the office rig to test I
>>>> > suppose. Plus anyways if you can't get signal worth a flip on the
>>>> > office rig, even if it was a polarity thing, that short of a link should
>>>> > blast it through to something you'd see.
>>>> >
>>>> > Only thing I can think of is that something in that tube is not aligned,
>>>> > bad press fit or mill or something like that and the waves are getting
>>>> > blown out of phase or similar. There's not but one way to put it
>>>> > together, and 820c -> OMT takes it to circular and you have circular to
>>>> > dish.
>>>> >
>>>> > On Fri, Mar 6, 2020 at 12:30 PM Mark Radabaugh <m...@amplex.net
>>>> > <mailto:m...@amplex.net>> wrote:
>>>> > >
>>>> > > Odd thing is I don’t see any way to assemble this any way that would
>>>> > > swap polarity. Only way to screw it up would be internal to the OMT
>>>> > > itself. We are doing XPIC with this link which we have not done in a
>>>> > > lot of other places, so that is different.
>>>> > >
>>>> > > Mark
>>>> > >
>>>> > > On Mar 6, 2020, at 12:22 PM, ch...@wbmfg.com <mailto:ch...@wbmfg.com>
>>>> > > wrote:
>>>> > >
>>>> > >
>>>> > > V&H being swapped will always cost you at least 20 dB and if you have
>>>> > > them precisely aligned V&H I can see where 40 dB is reasonable.
>>>> > >
>>>> > > From: Ken Hohhof
>>>> > > Sent: Friday, March 6, 2020 10:18 AM
>>>> > > To: 'AnimalFarm Microwave Users Group'
>>>> > > Subject: Re: [AFMUG] PTP Microwave antenna question
>>>> > >
>>>> > >
>>>> > > OK, that says the antenna should be dual pol capable. So … is a
>>>> > > puzzlement. You’d expect a problem would cost a few dB, not 40 dB.
>>>> > > Unless H & V were swapped.
>>>> > >
>>>> > >
>>>> > >
>>>> > > Sounds like Cambium is looking into it, maybe they come up with some
>>>> > > ideas.
>>>> > >
>>>> > >
>>>> > >
>>>> > > From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com>> On
>>>> > > Behalf Of Mark Radabaugh
>>>> > > Sent: Friday, March 6, 2020 11:00 AM
>>>> > > To: AnimalFarm Microwave Users Group <af@af.afmug.com
>>>> > > <mailto:af@af.afmug.com>>
>>>> > > Subject: Re: [AFMUG] PTP Microwave antenna question
>>>> > >
>>>> > >
>>>> > >
>>>> > > It’s currently 2 single pol Horizons on a Dragonwave OMT mount that
>>>> > > combines the H&V to the round waveguide on the back of the antenna.
>>>> > >
>>>> > > Mark Radabaugh
>>>> > >
>>>> > > Amplex
>>>> > >
>>>> > > 22690 Pemberville Rd
>>>> > >
>>>> > > Luckey, OH 43443
>>>> > >
>>>> > > 419-261-5996
>>>> > >
>>>> > >
>>>> > >
>>>> > > On Mar 6, 2020, at 11:19 AM, Ken Hohhof <af...@kwisp.com
>>>> > > <mailto:af...@kwisp.com>> wrote:
>>>> > >
>>>> > >
>>>> > >
>>>> > > We put 11 GHz 820C w/XPIC on existing Trango 3 ft dishes replacing
>>>> > > single pol ApexPlus ODUs and everything went as expected. I’d have to
>>>> > > look up the details but I think it worked because Trango used Remec
>>>> > > circular even with single pol except for 6 GHz. We should have
>>>> > > adjusted for best XPIC cancellation but instead we just made sure the
>>>> > > ODUs were plumb. But I think what we did was roughly the same as what
>>>> > > you’re doing, so it should work.
>>>> > >
>>>> > >
>>>> > >
>>>> > > We got a couple bad 820S radios last year, failed the RF loopback
>>>> > > test, but it sounds like you have pretty thoroughly verified it’s not
>>>> > > bad radios.
>>>> > >
>>>> > >
>>>> > >
>>>> > > Were the Dragonwaves single or dual pol?
>>>> > >
>>>> > >
>>>> > >
>>>> > >
>>>> > >
>>>> > > From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com>> On
>>>> > > Behalf Of Mark Radabaugh
>>>> > > Sent: Friday, March 6, 2020 9:37 AM
>>>> > > To: AnimalFarm Microwave Users Group <af@af.afmug.com
>>>> > > <mailto:af@af.afmug.com>>
>>>> > > Subject: [AFMUG] PTP Microwave antenna question
>>>> > >
>>>> > >
>>>> > >
>>>> > >
>>>> > >
>>>> > > We have installed a lot of Cambium 820C radios without much trouble.
>>>> > > Yes, the configuration takes some getting used to but we probably have
>>>> > > 46 links working and installed, so it’s not like it’s our first rodeo
>>>> > > configuring these things.
>>>> > >
>>>> > >
>>>> > >
>>>> > > And then we tried something new - reusing a 4’ Andrew Dragonwave
>>>> > > antenna in a XPIC configuration. We purchased the Cambium adapter
>>>> > > plate that clips onto the antenna radio mount and presents the 820C
>>>> > > mount for the OMT. Take off the dual Horizon radio OMT, add the 820C
>>>> > > and the RF signal is shit - in the -80’s from the mid 40’s. Reverse
>>>> > > the process and put the Horizon’s back on and the signal is fine.
>>>> > >
>>>> > >
>>>> > >
>>>> > > So we thought we had a bad 820C. It’s happened before. So we take
>>>> > > two different sets of 820C’s and test them one at a time swapping them
>>>> > > in for known good installed radios on working links. The 820C’s are
>>>> > > fine.
>>>> > >
>>>> > >
>>>> > >
>>>> > > Okay… we forgot to test the OMT's when we did that. So we try the
>>>> > > OMT’s in the shop - and they work fine.
>>>> > >
>>>> > >
>>>> > >
>>>> > > At this point the only thing left is the antennas themselves and the
>>>> > > adapter plate. The adapter plate is nothing more than a hole in a
>>>> > > aluminum bushing with a couple of small steps to match diameter
>>>> > > between the OMT and the antenna waveguide. Pretty hard to screw up.
>>>> > >
>>>> > >
>>>> > >
>>>> > > We have a pair of Dragonwave antenna’s in the shop that we can mount
>>>> > > all of this to and try here - and we can’t get a decent signal even
>>>> > > 20’ apart. I’m at a loss at this point. The only part that doesn’t
>>>> > > appear to work is the adapter plate - and there is nothing interesting
>>>> > > about it.
>>>> > >
>>>> > >
>>>> > >
>>>> > > How the heck can this not work:
>>>> > >
>>>> > >
>>>> > >
>>>> > > <image001.jpg>
>>>> > >
>>>> > >
>>>> > >
>>>> > > <image002.jpg>
>>>> > >
>>>> > >
>>>> > >
>>>> > > I can’t buy that the alignment of the antenna would need to be
>>>> > > adjusted. That makes no sense in my head. Am I wrong in that
>>>> > > assumption?
>>>> > >
>>>> > >
>>>> > >
>>>> > > Mark
>>>> > >
>>>> > > --
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>>>> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
>>>> > > <http://af.afmug.com/mailman/listinfo/af_af.afmug.com>
>>>> > >
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