I have an Garmin Astro 220 GPS that uses the MURS frequencies, 151.82 - 154.60 Mhz. Using an online calculator I learn that the antenna should be 18.5 inches for 1/4 wavelength and 9.25 in. for 1/8 wavelength (based on the 151.82 Mhz frequency)

..I was considering buying an antenna on eBay but it is only 8 inches. (eBay item# one, eight, 1, 3, zero, two, 327, 578. Sorry for this workaround, the admins think I'm posting a phone number).

How much difference would this mismatch cause? Or is it a mismatch?

Thank you in advance for any help.
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In article ,
hunt4mac wrote:

I have an Garmin Astro 220 GPS that uses the MURS frequencies, 151.82 - 154.60 Mhz. Using an online calculator I learn that the antenna should be 18.5
inches for 1/4 wavelength and 9.25 in. for 1/8 wavelength (based on the 151.82 Mhz frequency)

.I was considering buying an antenna on eBay but it is only 8 inches. (eBay item# one, eight, 1, 3, zero, two, 327, 578. Sorry for this workaround, the
admins think I'm posting a phone number).

How much difference would this mismatch cause? Or is it a mismatch?

A lot of the "rubber duck" antennas on the market are not simply
quarter-wave whips. They include inductive loading, which allows the
antenna to be resonant (or close to it) even when it's physically
shorter than a quarter-wave.

The thin-whip "spaghetti-noodle" style generally uses a flexible-
wire whip, and a loading coil at the base (moulded into the BNC or SMA
connector).

Fatter "rubber ducks" often build the inductive loading into the
radiator itself... the radiator is a flexible wire spiral, wound
around a core of some sort (sometimes air, sometimes a supportive
structure such as rubber or plastic).

These "loaded" antennas are generally a good enough match to keep the
transmitter happy (if you have a transmitter... the Astro 220 appears
to be a receive-only device so this isn't an issue).

They tend to be lossy, though. The "short radiator which is
capacitive, resonated by a lumped or distributed inductance" tends to
result in higher current in some parts of the antenna than would be
the case for a true quarter-wave antenna with a decent ground, and
this leads to higher I^2*R losses.

Some short rubber duck antennas are very lossy... as much as 10 dB or
so worse than a full-length whip with a decent counterpoise. This
costs you transmit range and receive sensitivity... the price for
the physical convenience of having a short antenna that doesn't poke
people in the eye :-)

If you're going to need more dog-tracking receiver sensitivity than a
"duck" antenna provides, you'd probably want a full-sized directional
antenna... maybe a 3-element Yagi (search for "measuring tape Yagi"
for DIY plans). These aren't terribly field-friendly, of course.

"Dave Platt" wrote in message
...
In article ,
hunt4mac wrote:

snip
If you're going to need more dog-tracking receiver sensitivity than a
"duck" antenna provides, you'd probably want a full-sized directional
antenna... maybe a 3-element Yagi (search for "measuring tape Yagi"
for DIY plans). These aren't terribly field-friendly, of course.

Hi Dave.
I think this isn't a DF application. The Garmin comes with a dog's collar
that has a GPS receiver and a MURS transmitter. The collar receives the GPS
signals and transmits the dog's position (okay - technically it is actually
transmitting the position of the collar) using the MURS frequencies. The GPS
receives those MURS signals from the collar and displays the position on its
screen.
Can't see from the Quick Start Manual what is actually being transmitted by
the collar - the GPS data as received or the actual lat/long position.

It's not THAT clever - the collar doesn't include a long arm poop-scoop.

73 Ian.



--- news://freenews.netfront.net/ - complaints: ---

"hunt4mac" wrote in message
...
I have an Garmin Astro 220 GPS that uses the MURS frequencies, 151.82 -
154.60 Mhz. Using an online calculator I learn that the antenna should be
18.5 inches for 1/4 wavelength and 9.25 in. for 1/8 wavelength (based on
the 151.82 Mhz frequency)

.I was considering buying an antenna on eBay but it is only 8 inches.
(eBay item# one, eight, 1, 3, zero, two, 327, 578. Sorry for this
workaround, the admins think I'm posting a phone number).

How much difference would this mismatch cause? Or is it a mismatch?


I don't think you would have any mismatch as the shorter antenna is probably
a 'rubber duck' type. It is sort of like a spring inside the rubber
covering and loaded to match the frequency. Many Ham handi talkies use this
type of antenna on 146 MHz without any problem.
The range is slightly shorter with this antenna, but for tracking dogs I
would not think the reduction in range would really matter. Doubt they would
be over 1/4 of a mile from you.

hunt4mac wrote:
Many thanks to Dave, Ian & Ralph for your helpful insights. I hadn't realized that the handheld unit is only receiving but that does make a lot of sense. I was advised it would be OK to turn on the receiver unit without an antenna...does that sound right ? (I just bought the unit on eBay, want to check it's operation & buy an antenna for the handheld, will go with the 8 inch, sounds like it should work well)
--
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http://narkive.com/uRfwtncD.5

In article ,
hunt4mac wrote:

Many thanks to Dave, Ian & Ralph for your helpful insights. I hadn't realized that the handheld unit is only receiving but that does make a lot
of sense. I was advised it would be OK to turn on the receiver unit
without an antenna...does that sound right ?

Yes.

On Wed, 22 Jul 2015 14:41:10 -0400, "Ralph Mowery"
wrote:


"hunt4mac" wrote in message
...
I have an Garmin Astro 220 GPS that uses the MURS frequencies, 151.82 -
154.60 Mhz. Using an online calculator I learn that the antenna should be
18.5 inches for 1/4 wavelength and 9.25 in. for 1/8 wavelength (based on
the 151.82 Mhz frequency)

.I was considering buying an antenna on eBay but it is only 8 inches.
(eBay item# one, eight, 1, 3, zero, two, 327, 578. Sorry for this
workaround, the admins think I'm posting a phone number).

How much difference would this mismatch cause? Or is it a mismatch?


I don't think you would have any mismatch as the shorter antenna is probably
a 'rubber duck' type. It is sort of like a spring inside the rubber
covering and loaded to match the frequency. Many Ham handi talkies use this
type of antenna on 146 MHz without any problem.
The range is slightly shorter with this antenna, but for tracking dogs I
would not think the reduction in range would really matter. Doubt they would
be over 1/4 of a mile from you.

Most, if not all, rubber duck antennas which come with the 2 meter
amateur radios are designed for the 150 to 160 MHz band,
the commercial radio between trucks and their boss.

I have measured dozens of them, all were out-of-band,
the ICOMs the KENWOODS the WEIERWEi and YAESu and and...

Never trust the content of a new box.

w.

"Helmut Wabnig" [email protected] --- -.dotat wrote in message
Most, if not all, rubber duck antennas which come with the 2 meter
amateur radios are designed for the 150 to 160 MHz band,
the commercial radio between trucks and their boss.

I have measured dozens of them, all were out-of-band,
the ICOMs the KENWOODS the WEIERWEi and YAESu and and...



What method did you use to determin the frequency range of the rubber duck
antennas ? I have several around here and may give it a try to see what
mine are.

On 7/24/2015 9:11 AM, Ralph Mowery wrote:
"Helmut Wabnig" [email protected] --- -.dotat wrote in message
Most, if not all, rubber duck antennas which come with the 2 meter
amateur radios are designed for the 150 to 160 MHz band,
the commercial radio between trucks and their boss.

I have measured dozens of them, all were out-of-band,
the ICOMs the KENWOODS the WEIERWEi and YAESu and and...



What method did you use to determin the frequency range of the rubber duck
antennas ? I have several around here and may give it a try to see what
mine are.

Forgive me for inserting myself here. I just wanted to ask what
equipment you might have for making the measurements?

"John S" wrote in message
...
On 7/24/2015 9:11 AM, Ralph Mowery wrote:

I have measured dozens of them, all were out-of-band,
the ICOMs the KENWOODS the WEIERWEi and YAESu and and...



What method did you use to determin the frequency range of the rubber
duck
antennas ? I have several around here and may give it a try to see what
mine are.

Forgive me for inserting myself here. I just wanted to ask what equipment
you might have for making the measurements?


For starters a HP 8924C ( service monitor with tracking generator) , return
loss bridge, wattmeters.

I just have not tried the rubber duck antennas to see what frequency I think
they may be for.