Today's Message Index:
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1. 05:55 AM - Re: Re: Grounding radio antenna and transponder antenna (Robert L. Nuckolls, III)
2. 05:56 AM - Re: Re: Grounding radio antenna and transponder antenna (Robert L. Nuckolls, III)
3. 06:38 AM - Re: Grounding radio antenna and transponder antenna (user9253)
4. 08:02 AM - Re: fuel transfer controller, revisited (wsimpso1)
5. 08:27 AM - Re: Re: Grounding radio antenna and transponder antenna (Robert L. Nuckolls, III)
6. 10:29 AM - Re: Re: Grounding radio antenna and transponder antenna (Charlie England)
7. 10:36 AM - Re: Re: fuel transfer controller, revisited (Charlie England)
8. 06:52 PM - Re: Grounding radio antenna and transponder antenna (Argonaut36)
9. 08:31 PM - Re: Daily Summary Missing? (farmrjohn)
10. 10:24 PM - Re: Grounding radio antenna and transponder antenna (user9253)
Message 1
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| Subject: | Re: Grounding radio antenna and transponder antenna |
At 10:57 PM 9/17/2019, you wrote:
>If the copper tape isn't soldered or otherwise
>electrically bonded to the rest of the metal
>ground plane (panel), then it's not doing
>anything productive. You could get what you were
>hoping for by using strips of aluminum; even
>something really thin like strips cut from
>aluminum flashing material. They could be
>riveted on one end to the aluminum doubler shown
>in the pics, and glued with clear 'sensor safe'
>rtv to the plexi, and screwed at the other=C2 end
>using the plexi mounting screws.=C2
>
>Having said that, the antenna still won't be
>centered in the ground plane. You could add
>strips going the other direction using similar
>techniques. The 'ideal' ground plane extends out
>from the base as far as the antenna height. As
>few as 4 equally spaced radial arms can get the job done pretty
effectively.=C2
Actually, there's a relatively simple experiment
that can be conducted. 4 radials ~1" wide, extending
from the antenna base and simply taped to the outside
surface of the a/c will emulate an excellent ground
plane. It does not need to be electrically bonded to
the airframe. Where it is in close proximity to the
airframe, there will be significant electro-static
coupling to the airframe. I'd make them 24" long or
so. Length not critical when so closely coupled to
the a/c skin. Here's a tape suited to the task of
temporary attachment to the airplane.
https://tinyurl.com/y3wrc7kx
I've used this stuff to run ribbon cable through
the baggage door seal, down the side of the fuselage
and past the entry door seal to bring investigatory
signals from the hell-hole of a Beechjet into the
cabin.
This tape would work fine for the experimental ground
plane installation as well.
>
>
>Having said *that*, are you sure your problems
>are purely transmission range? Tube/rag a/c are
>notoriously noisy in the cockpit. You may have
>as much a problem with *audio* signal to noise
>ratio as with transmission distance. Ability to
>accurately describe comm deficiencies is pretty
>rare, even for controllers. If you think that
>could be a possibility, we can expand on that.=C2
Excellent point! There was a list-thread on
this very topic way back when . Turns out
that transmission intelligibility was
completely dependent on the noise cancelling
quality of microphone . . . I'm embarrassed
for not to have recalled this.
Before hammering on the antenna installation,
do try another mic/headset combination. They
are not all the same . . . particularly
with respect to cancelling low frequency
'buffeting' kinds of noise common to airplanes
where creature comfort is rather far down on the
list of design priorities.
Is it just your transmitted signal that's
deficient . . . or both transmit and receive?
This brings up the point that few users
of two-way radios have the experience and vocabulary
to describe poor signal quality. For example,
you can have a strong radio frequency signal
that is dead quiet when not talking but the
audio is weak/distorted. This is ALWAYS an
audio/microphone problem. You can have
a marginal radio frequency signal (just
beginning to present 'popcorn' noises
when not talking and uncharacteristically
poor audio when adding voice modulation.
Then there's the truly weak-signal which
can be a combination of radio/coax/antenna
issued. Years ago, I asked a reader to
send me a recording of his received signal
as heard on the ground . . . his problem
turned out to be in the audio system causing
a badly under-modulated transmitter.
Charlie's memory jog suggests an
important avenue of investigation
that supercedes fiddling with the antenna.
Bob . . .
Message 2
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| Subject: | Re: Grounding radio antenna and transponder antenna |
At 10:25 AM 9/18/2019, you wrote:
>
>That copper tape does not do much good because it all goes in one
>direction. And it is questionable if it is making good contact with
>the antenna mounting plate.
>Here is a suggestion: Cut 4 pieces of coax each 22 or 23 inches
>long. Attach a ring terminal to the shield of each coax (not the
>center conductor). Connect one length of coax to each of the 4
>antenna mounting screws using the ring terminals. When the panel is
>mounted to the aircraft, arrange the coax ground plane so that it
>extends outward in 4 different directions. Elastic cord attached to
>the coax ends could help to position it.
>This experiment is worth a try and will not cost much except your time.
That would work too . . . the same tape could
be used to hold it against the skin.
Bob . . .
Message 3
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| Subject: | Re: Grounding radio antenna and transponder antenna |
I changed the length of the ground plane radials to 24 inches in my post above
to be the same as Bob's suggestion.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491391#491391
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| Subject: | Re: fuel transfer controller, revisited |
We went around a closely related topic on homebuiltairplanes.com a while back.
I have a similar system, and I am electing to simply run one of two Facet pumps
all the time to keep the header (main) tank full. The header (main) tank is
only vented back to the source tank through a duplex valve, so yes, it is circulating
fuel. I view having any additional switches, logic, timers, fuel level
sensors, etc in the loop as being less reliable than running one pump with another
in reserve. Having 150 miles worth of fuel in the header feels pretty good
too.
Thread is https://www.homebuiltairplanes.com/forums/threads/transfer-pumps-and-fuel-system-configuration.30820/
There are others on there that I started about details of fuel systems, but they
seem off topic for this thread.
Good luck
Bill
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491392#491392
Message 5
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| Subject: | Re: Grounding radio antenna and transponder antenna |
At 08:37 AM 9/19/2019, you wrote:
>
>I changed the length of the ground plane radials to 24 inches in my
>post above to be the same as Bob's suggestion.
The length won't be 'critical' in this case.
When crafting a free space ground plane for
a vertical antenna, the idea is to approximate
the 'perfect' ground plane . . . a solid conductor
radiating from the base of the antenna for a
long ways. Since an perfect (infinite)
plane isn't practical, the common approximations
take on the form of radial 'whiskers'
https://www.bing.com/th?id=OIP.frzhTHSL4nWMxO4KqsPwpAHaDU&w
In this case, they are just more antennas
brought together at the base such that their
impedances are paralleled. The more radials,
the lower the ground impedance, the better
the plane. These are resonant ground planes.
I.e. 1/4 wave in free space elements.
This technique is closely approximated
in composite airplanes with copper or
aluminum strips bonded to the inside
skin of the aircraft.
The DIY transponder antenna for composite
applications suggeseted a solid disk
ground plane with a radius equal to height
of the antenna.
Emacs!
This 'plane' looks like an infinite number
of radials joined at the center. But
unless the plane is in pretty much free
space with respect to surrounding conductors,
it's near-ideal characteristics are
degraded.
For the purposed of our 'experiment',
the proposed 1/4 wave elements will be in
closest practical proximity to a metal
airframe; no longer in free air and
certainly not resonant at the frequency
of interest.
So the exact length is no longer significant.
Instead we're looking for some electro-static
or capacitive coupling to the airframe to
combine with planar effects of the now-random
lengths of conductor. In this case, the
wider strips taped to the skin are more
desirable to increase the capacitive coupling
effects . . . but the suggested wire elements
may well produce the desired effect of compensating
for a suspected inadequate ground plane.
While the microphone performance issue is
worth examination, one of the 'grains of
sand' in this study says that performance
is degraded with DISTANCE from the other
station which discounts audio problems
(consistent irrespective of range) and
re-enforces the notion that there is a
signal strength issue.
Bob . . .
Message 6
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| Subject: | Re: Grounding radio antenna and transponder antenna |
On 9/18/2019 10:06 PM, Argonaut36 wrote:
>
> Thanks to All for the interesting comments and suggestions.
> In this post I would like to address the comments of Charlie on noise in the
cockpit. I need a little more time to write a second post on the antenna solutions
that have been proposed for testing (coax and external copper foil). I
may have a couple of questions.
> Yes, the problem is not just range. It is also noise. ATC says that my transmissions
are weak and with a lot of static noise, but still acceptable. As
I wrote in an earlier post, that is not the case if I go to Class B or C airspace
and I need to call from far out.
> My impression is that I receive better than I transmit. The noise level in the
cockpit is very high and when I press the push-to-talk button, the static noise
that I hear in the sidetone is louder than my voice.
> I use what is considered a very good noise canceling microphone that I periodically
replace. My understanding is that the noise wears out the microphone.
I have also flown with a Bose headset; transmissions were better, but only marginally.
First, your experience with small-airport vs B/C airspace might not be
purely range. Have you tried small airport comm from the same distance,
and over similar (as in flat) terrain as the B/C comm? And do the B/C
comms have the same problems, once you get as close to them as you
typically are to the small airports? This might help determine whether
you truly have a range issue. But regardless, don't forget 'human
factors'. The small airport guys are typically not very busy, and can be
more 'focused' on listening. They're possibly used to dealing with
poorer quality than the big guys, since small airport fliers are often
not as dependent on perfectly performing equipment. The big guys, on the
other hand, are often incredibly busy, and if they have the slightest
problem with readability, may just tell you you're unreadable and to go
away. They're also unlikely to have the audio skillset to give a useful
technical description of what they're actually hearing.
OK, on to some random *generalizations*:
'Normal' noise levels in the mic's designed-for environment should not
wear out a mic. I've got headsets that are older than my >25 year flying
experience, almost all in homebuilts, that still have good mics in them.
Not saying that extreme noise can't damage a mic, but wearing it out
shouldn't be much of an issue.
Range can obviously affect transmission quality, especially with AM
(what we use for a/c comm). But background noise can often make more
difference than carrier strength (range). Others are much more qualified
to discuss the RF side of things, but I may be able to offer some long
distance help with the audio side of things.
Intelligibility is closely tied to 'signal-to-noise ratio'. We usually
hear (pardon the on-the-nose pun) the term used in electronics, where
the signal (audio) is measured as a ratio to the level of 'noise', which
is all the background hiss, crackling, etc that exists in all
electronics. But for practical, real-world applications, the entire
system must be considered. Ex: in a concert hall, the signal is the
singer's voice and the noise is everything else; audience conversations,
squeaking chairs, foot falls, even reverberations of the singer's own
voice bouncing around in the room. An extreme (though somewhat twisted)
example would be 'feedback' when the PA system's output gets back into
the mic and is re-amplified.
Now, how do we improve S/N in the concert hall? Turning up the volume
will make the singer easier to hear, and help mask hall noise, but
eventually the PA will get loud enough to cause feedback and then no one
will hear the 'signal'. So what to do? One thing is to lower the noise
level. Padded seats, carpet, noise absorbing panels on the ceiling &
walls, and even more important, telling your neighbor to save their
conversation till the concert is over. But one of the big drivers of
poor S/N is the singer him/her-self. If the handheld mic is allowed to
point out into the audience, feedback is more likely. If the singer cups
their hands around the mesh area of the mic, it kills the mic's
directional selectivity. If they sing into the side of the mic instead
of the end (assuming a typical handheld mic), or they hold the mic too
far from their lips, or sing too softly, then *their vocal volume is a
smaller percentage of the total sound the mic hears*. If the singer
messes up in the above ways, the sound guy's only way to make them
louder is to turn up the gain, but the mic hears everything, so noise
gets amplified along with signal.
The 'singer' issues are very similar to issues in the cockpit. Headset
mics are directional mics. Not a terribly common problem, but with some
headsets (particularly the in-ear models), it's easy to get the back
side of the mic facing your lips. This will give preference to noise
over voice. If the mic isn't so close to the pilot's lips it's almost
touching them (left or right edge of your mouth tends work best, to
minimize popping from breath), then like the singer, the 'hall noise'
will be a bigger percentage of what the mic hears. If the pilot speaks
softly, then 'hall noise' will be a bigger percentage of what the mic
hears. If the 'front' of the mic isn't pointed directly at the pilot's
lips... Are we getting the idea yet? If there's another mic in the a/c
that's plugged into the system, it will often go 'live' whenever the PTT
is pushed along with the pilot's mic. If that happens....
ETC ETC
Now, what to do that's 'fixing' stuff, instead of just 'technique'?
Reducing the ambient noise level in a tube/rag a/c is very difficult
unless we're willing to accept a lot of extra weight. But there are some
'tweaks' to the system that will likely help. One thing will sound
counter-intuitive, but does work (I just went through it with my
neighbor, who's flying the prototype One Design unlimited acro a/c).
First, check with the mfgr of your headset, to see if there is a gain
adjustment *on the microphone* of the headset. Many electret condenser
mics have a tiny gain adjustment screw in the body of the mic. If yours
has one, turn the gain *down* as low as you can get it and still have
your voice transmitted. The reason: Those mics actually have a tiny
preamplifier built into them. If the total volume (voice plus noise) is
loud enough, it can drive the preamp into distortion. When that happens,
we get fuzzy, garbled sound as the peak volume is clipped off.
Next, find the mic gain or mic volume adjustment on your comm radio, and
turn *it* down as low as you can go, and still get your voice out there.
Even if you have to speak 'with authority' into the mic. Remember the
'too soft' singer? If you speak louder, your voice is a larger
percentage of what the mic hears. Now obviously, you need enough audio
to properly modulate the RF carrier, but you'll likely be surprised at
how much you can turn these setting down and still hear yourself. As
long as you sound ok in your sidetone, you're likely going to be ok with
modulation. (RF guys feel free to step in here.)
The last thing returns to technique, in the form of 'compensation' for
a/c deficiencies. When comm is critical, pull the power back. This was
the last step in getting the One Design mentioned above into the 'clear
communications' category. By reducing the throttle setting, the cockpit
noise goes down significantly, improving signal to noise ratio. (Could
this be a factor in small vs large airport operations, where you're
likely at reduced power close to the small airport but still at cruise
power when far from the large airports?)
Sorry for such a long 'epistle', but hopefully there will be some useful
info buried in there.
Charlie
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Message 7
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| Subject: | Re: fuel transfer controller, revisited |
On 9/19/2019 10:01 AM, wsimpso1 wrote:
>
> We went around a closely related topic on homebuiltairplanes.com a while back.
I have a similar system, and I am electing to simply run one of two Facet pumps
all the time to keep the header (main) tank full. The header (main) tank is
only vented back to the source tank through a duplex valve, so yes, it is circulating
fuel. I view having any additional switches, logic, timers, fuel level
sensors, etc in the loop as being less reliable than running one pump with
another in reserve. Having 150 miles worth of fuel in the header feels pretty
good too.
>
> Thread is https://www.homebuiltairplanes.com/forums/threads/transfer-pumps-and-fuel-system-configuration.30820/
>
> There are others on there that I started about details of fuel systems, but they
seem off topic for this thread.
>
> Good luck
>
> Bill
Hi Bill,
I think that technique has a lot of merit in a lot of situations, but as
I mentioned in another post, my plane is acro-capable, and I need to
preserve the ability to *know* that the auxs are empty for acro. Another
factor is that in this plane, two of the three auxs will almost never
have fuel in them (only for extended out/back legs with no refueling).
I'm trying to keep the fuel-delivery tank as close to 'as designed' as I
possibly can, and still be able to use auto style fuel injection and get
aux fuel to it.
Thanks,
Charlie
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Message 8
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| Subject: | Re: Grounding radio antenna and transponder antenna |
Reference is made to the following comment of Bob in a recent post:
Quote
Years ago, I asked a reader to send me a recording of his received signal as heard
on the ground . . . his problem turned out to be in the audio system causing
a badly under-modulated transmitter.
Unquote
When the radio was almost new, it failed and I flew for a while with a loaned radio
(identical) and then I got the replacement radio (also identical) that I
have now. The three radios worked exactly the same and for this reason I did
not consider the radio itself being the source of the troubles. At the time I
flew with the other radios, however, I had different antenna, coax and harness
that could have masked issues with the radio.
Going back to the alternative antenna configurations that have been proposed, could
Bob please answer the following questions:
What is the recommended 1 copper foil tape and where I can buy it?
How is the tape terminated at the antenna? Does it stop at a certain distance from
the antenna or right at the antenna?
Does the recommended 2" white vinyl tape leave adhesive residue on the paint? Considering
that testing will probably require only a single short flight, could
perhaps a less strong tape that does not leave residue be used?
Thanks
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491405#491405
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| Subject: | Re: Daily Summary Missing? |
Well, my account must have fallen into limbo. When I try to unsubscribe, the email
distribution tool says it is sending a link to my email address to confirm.
That email never arrives, and the unsubscribe is not successful. I have checked
in the spam folder as well, and tried with different browsers with the
same (non)results. Curious. John
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491409#491409
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| Subject: | Re: Grounding radio antenna and transponder antenna |
https://www.talkbass.com/threads/where-to-buy-copper-foil-tape.437391/
-
https://www.homedepot.com/p/Corry-s-15-ft-Slug-and-Snail-Copper-Tape-100099017/100662157
-
https://www.amazon.com/Freely-Copper-Foil-Conductive-Adhesive/dp/B06XQ9T2WN/ref=pd_lpo_sbs_229_t_2?_encoding=UTF8&psc=1&refRID=ZR2J0MDFBA4CF5HH5S0Z
-
The antenna could be removed, the copper tape stuck on, then re-install the antenna.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491410#491410
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