[aprssig] Antenna separation

david vanhorn kc6ete at gmail.com
Thu Apr 27 08:40:45 CDT 2017


Well...  I don't have a lot of control over the vehicle length. It's a Ford
Transit Connect.  I can try to heat it up some.. :)

Vertical separation isn't going to be a thing either. It's 73" high and my
SG7900 is 62" high, topping out at 11' 4". The HF antennas are 86" so when
mounted, 13' 4".  Good thing they are all foldovers!
I will likely have at most a foot or two where the middle antenna can live,
in terms of front to back play between support ribs.

Back in the day, I made an argument for intelligent power control, but got
no traction.  So what happens is that any time you can't make the digi the
rig gets switched to "high" and there's no incentive to kick it back down
to low.  Basic industrial design says that you might as well not have the
power control feature since it will just get left in the "high" position.
Seems not too hard to have the power set to low, and if you don't hear a
repeat of your packet in N attempts, then kick it to high.  With additional
brainpower, then knowing the range to the digi, you can choose to lower
power again if approaching.. Wouldn't be fool proof, but it could be made
to work.    Are we still doing "wind speed = 0 means I don't have sensor or
there's no wind" and "temperature = 0 means I don't have sensor or
temperature is 0"?  Back in 2001 I showed APRS to Dr David Arnold of BSU,
and he immediately noticed that the baro sensors of various stations
indicated hurricane force winds in various directions, and commented that
it was probably 10 years from becoming useful for severe storm
applications.  :(

While making the drive up to a friends last weekend, an hour drive with a
4000' climb in the last 30 mins, I was remembering how I should be looking
at a plug-in electric.   Lots of different situations, and we all do what
fits best for our own.  I'd love to carpool, but my hours are
unpredictable. Bike is not a thing at 18 miles one way.

I thought about a notch filter for 4.39 on the 7000, but I don't think I
can make one that is narrow enough and small enough.



On Thu, Apr 27, 2017 at 5:12 AM, Ev Tupis <w2ev at yahoo.com> wrote:

> The issue you are dealing with is exactly why I strongly suggested that
> USA APRS move to 147.585 MHz during the "great QSY" from 145.79 MHz.  Many
> 2 meter SSB/CW operators with tall towers and living on hills (the very
> infrastructure that APRS needed) would suffer from self-QRM and likely
> abandon APRS if it moved *closer* to their operation.  That is exactly how
> it played out.
>
> Your issue is also fundamental overload, however the real-estate you are
> working with is significantly less.  You can't separate your antennas by 20
> vertical-feet. ;-)
>
> The safety of the radio is determined by the ability of the RXing radio's
> first amplification stage to absorb RF.  Without knowing what the radios'
> ability in that regard, there is no way to quantitatively answer your
> question.
>
> On the other hand, some empirical strategy can be applied, as the known
> quantity is the size of the vehicle and the RF outputs involved.  You
> control both.  Adjust both for best performance.
>
> Start by separating she antennas as far as possible, however also consider
> testing with the antennas in different vertical planes, too (even if they
> are closer).  To a vertically polarized antenna, vertical separation
> provides greater isolation than horizontal distance...however in a mobile
> environment, having the passenger compartment's "bump" in the way may
> mitigate that.
>
> Then, reduce power output to a point where you can still communicate (this
> is an FCC rule anyway, of course) and see if you can live with the self-qrm
> that remains.
>
> All of this results in a "most acceptable self-QRM" solution.
>
> Best regards,
> Ev, W2EV
>
>
>
>
>
> On Thursday, April 27, 2017, 12:03:49 AM EDT, david vanhorn <
> kc6ete at gmail.com> wrote:
> So, I'm about ready to push the button on this.
> I'll be limited by the location spots available, but I have one more
> question:
>
> I'm intending to have the FTM-350 running APRS, and the IC-7000 running
> voice on 2m/440
> I know I should mount those antennas as far apart as possible, but given
> the 50W output of each, what is the minimum separation for the safety of
> the radios?
>
> It's almost certain to end up with the 7000 V/U on the front mount point,
> FTM-350 on the middle, and the 7000 HF antenna on the back.
>
> I know the APRS will still punch holes in my reception on the 7000 VHF,
> but I'm hoping to minimize that. My main concern is not having the front
> ends damaged by the RF from the other radio.
>
>
> --
> K1FZY (WA4TPW) SK  9/29/37-4/13/15
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> http://www.tapr.org/mailman/listinfo/aprssig
>



-- 
K1FZY (WA4TPW) SK  9/29/37-4/13/15
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