Today's Message Index:
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1. 07:07 AM - Re: Transmitting with no antenna? (donjohnston)
2. 07:54 AM - Re: Re: Transmitting with no antenna? (Robert L. Nuckolls, III)
3. 08:14 AM - Re: Transmitting with no antenna? (Robert L. Nuckolls, III)
4. 09:38 AM - Re: Transmitting with no antenna? (Eric Page)
5. 12:56 PM - Re: Transmitting with no antenna? (donjohnston)
6. 01:00 PM - one-wire alternators- the subject that just won't die (Charlie England)
7. 01:00 PM - Re: Transmitting with no antenna? (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Transmitting with no antenna? |
edpav8r(at)yahoo.com wrote:
> Don,
>
> Just be sure the resistors you sourced are not wire-wound types. At a 10W rating,
most are. These are inductive and will make a very poor dummy load.
>
> Examples to avoid: http://bit.ly/1A3zd7U -or- http://bit.ly/1rImumj
>
> Bob's 2W-10W dummy load appears to be built with Metal Film or Metal Oxide resistors.
>
> Eric
>
>
>
> > On Jul 22, 2014, at 7:42 PM, "donjohnston" wrote:
> >
> > Using the logic of "if some is good, more must be better", I picked up some
10w, 100ohm resistors. :)
> >
> >
>
Yep... They're wire wound.
I can't get anything right lately. :(
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=427203#427203
Message 2
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| Subject: | Re: Transmitting with no antenna? |
>Yep... They're wire wound.
>
>I can't get anything right lately. :(
I was skeptical and disappointed when your conversation
with VAL suggested that 'your were probably going to be
okay' with the 10W resistors.
It would have been nice if the design I posted was
a little beefier . . . but getting resistors
with low inductance at VHF frequencies isn't a trivial
task. The venerable carbon composition resistor popular
to this legacy DIY task are not easy to find and not cheap
when you do find them. The 2W design proved to be the
best I could do with limited resources . . . although
suited to the task as long as you don't get into long-winded
test transmissions. As I recall, I produced that suggestion
as a test tool for proving that some appliance sensitivity
to transmitters was a function of energy radiated from
the antenna. Short transmissions would suffice.
If you want to acquire a more robust load, finding
suitable resistors then stacking fab-time
on top of the project is problematic. Suggest
you consider commercial-off-the-shelf products
like this:
http://tinyurl.com/k5w4vth
You'll need and adapter to attach this N-connector
load to your BNC-connector transceiver
http://tinyurl.com/mxjgusn
Hard to beat for price but it does take a bit of
time to ship them over the big pond.
Bob . . .
Message 3
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| Subject: | Re: Transmitting with no antenna? |
At 08:07 PM 7/21/2014, you wrote:
Alternatively, you could build this dummy load: http://bit.ly/1wSMtI1
...using 20 of these (buy 25 for the price break): http://bit.ly/1lnVgfM
Note: Do *not* substitute wire-wound resistors!
Eric
This is a time-honored and relatively easy methodology
for crafting a low SWR dummy load. Built one of these
when I was in high-school . . . my can was salvaged
from some painting project around the house and I used
Havoline motor oil . . . but as you can see, the time
to fabricate this thing is not trivial. Be sure to store
this thing rihgt-side-up . . . if it lays over then atmospheric
breathing will push oil past connectors that are not
liquid tight. The commercial-off-the shelf alternative
may prove more attractive.
Bob . . .
Message 4
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| Subject: | Re: Transmitting with no antenna? |
On Jul 23, 2014, at 10:13 AM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
wrote:
> This is a time-honored and relatively easy methodology for crafting a low SWR
dummy load. [SNIP] The commercial-off-the shelf alternative may prove more attractive.
Indeed. I always seem to forget that you can buy virtually anything cheaply on
eBay! For $19, the economics of building one yourself, in $ and time, make little
sense.
Eric
do not archive
Message 5
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| Subject: | Re: Transmitting with no antenna? |
nuckolls.bob(at)aeroelect wrote:
>
> I was skeptical and disappointed when your conversation
> with VAL suggested that 'your were probably going to be
> okay' with the 10W resistors.
>
> It would have been nice if the design I posted was
> a little beefier . . . but getting resistors
> with low inductance at VHF frequencies isn't a trivial
> task. The venerable carbon composition resistor popular
> to this legacy DIY task are not easy to find and not cheap
> when you do find them. The 2W design proved to be the
> best I could do with limited resources . . . although
> suited to the task as long as you don't get into long-winded
> test transmissions. As I recall, I produced that suggestion
> as a test tool for proving that some appliance sensitivity
> to transmitters was a function of energy radiated from
> the antenna. Short transmissions would suffice.
Uh... Val didn't say I would be fine with 10W resistors.
They said that the radios should be fine.
> In regards to circuit protection, the COM 2KR doesn't have any active protection
against keying the unit without a proper load attached. As such, you run
a small risk of damaging your radios keying them up without an antenna. However,
the radios are resistant to damage from being keyed without an antenna and
should be fine.
I'm going to redo with the proper resistors. I'm only tracking down an audio panel
switching issue. As such, I'm only keying the mic long enough to see if I
get a transmit indicator on the display. So about a half second whenever I hit
the PTT.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=427227#427227
Message 6
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| Subject: | one-wire alternators- the subject that just won't die |
Hi Bob,
Please forgive me, but I need a refresher on why one-wire (internally
regulated) alternators are no longer recommended for a/c; even banned from
'the Book'. I do remember (scratch that; know from experience) that if the
B-lead contactor opens while the alternator is under load, there can be a
'load dump' (high voltage spike) issue that can kill the electronics (the
regulator) in the alternator. Makes sense. But if the only way the B-lead
contactor is allowed to open is due to an overvoltage fault, does it
matter? At that point, it's a given that the regulator is already toast,
and the entire alternator will be swapped out to fix it. Given the very
high reliability of modern automotive alternators, and that the only time
the B-lead contactor would need to open under load is during a true OV
fault event, what's the compelling reason to keep the 'not recommended'
philosophy?
I've had a couple of different career paths involving running a soldering
iron & modifying stuff (both consumer and industrial electronics
maintenance), so I'm not 'afraid' to dig into an alternator to modify it
for external regulation. But I'm of the 'if it ain't broke, don't fix it'
school.
I'd like to be educated on what I'm overlooking in terms of risk, failure
modes (fire?), etc.
If it's reasonable to bring the one-wire alternator (with contactor style
OV protection)back into the mix, the next question will be about
integrating a backup dynamo style alternator without spending close to half
an Aviation Unit for the hardware. :-)
Many thanks,
Charle
Message 7
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| Subject: | Re: Transmitting with no antenna? |
>Indeed. I always seem to forget that you can buy virtually anything
>cheaply on eBay! For $19, the economics of building one yourself,
>in $ and time, make little sense.
But we won't talk about the things we do, buy,
read or just dream about . . . 'cause it's FUN!
It's probably cheaper than a gambling habit . . .
Bob . . .
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