|
Advice on antenna length
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. -- This post on narkive: http://narkive.com/uRfwtncD |
Advice on antenna length
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. |
Advice on antenna length
"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: --- |
Advice on antenna length
"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. |
Advice on antenna length
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) -- This post on narkive: http://narkive.com/uRfwtncD.5 |
Advice on antenna length
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. |
Advice on antenna length
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. |
Advice on antenna length
"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. |
Advice on antenna length
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? |
Advice on antenna length
"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. |
All times are GMT +1. The time now is 04:03 PM. |
|
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com