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. |
Advice on antenna length
Ralph Mowery wrote:
"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. If the rubber ducky is measured by itself, it may not show resonance at the right band of frequencies, however I wonder if it uses the handheld case as part of the system, in which case measurements might change to the anticipated range. Just a wild guess. Irv VE6BP |
Advice on antenna length
Irv Finkleman wrote:
Ralph Mowery wrote: "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. If the rubber ducky is measured by itself, it may not show resonance at the right band of frequencies, however I wonder if it uses the handheld case as part of the system, in which case measurements might change to the anticipated range. Just a wild guess. Irv VE6BP Using a RigExpert AA-1400 on various VHF and UHF antennas, what I have found is that lack of a counterpoise of some sort has a major effect on impedance and a minor effect on resonant frequency. -- Jim Pennino |
Advice on antenna length
In article ,
Irv Finkleman wrote: 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. If the rubber ducky is measured by itself, it may not show resonance at the right band of frequencies, however I wonder if it uses the handheld case as part of the system, in which case measurements might change to the anticipated range. Just a wild guess. That matches my own experience and experiments. An HT rubber duck tends to use the HT case, and (via capacitive coupling) the user's hand and body, as the "counterpoise". If you hook it to the end of a coax cable, or directly to a service monitor's test output, the "counterpoise" impedance will be rather different. Also, the HT duck is often operating in fairly close proximity to the head, with some amount of loading from that proximity affecting its feedpoint impedance. I've tested out a number of "ducks" by attaching them to an MFJ 256 or 269 antenna analyzer. They tend to shift apparent SWR quite a bit depending on whether I'm holding the analyzer or not, and (if I am) whether it's out in free space, or held near to my head as if on an HT in use. My impression is that most HTs have to be designed to tolerate a rather lousy SWR on the antenna port... because it often *is* lousy. Having an HT which burns up its final if you hold the radio wrong would tend to cause the warranty-repair department to start raising hell. |
Advice on antenna length
"Dave Platt" wrote in message ... If the rubber ducky is measured by itself, it may not show resonance at the right band of frequencies, however I wonder if it uses the handheld case as part of the system, in which case measurements might change to the anticipated range. Just a wild guess. That matches my own experience and experiments. An HT rubber duck tends to use the HT case, and (via capacitive coupling) the user's hand and body, as the "counterpoise". If you hook it to the end of a coax cable, or directly to a service monitor's test output, the "counterpoise" impedance will be rather different. Also, the HT duck is often operating in fairly close proximity to the head, with some amount of loading from that proximity affecting its feedpoint impedance. I've tested out a number of "ducks" by attaching them to an MFJ 256 or 269 antenna analyzer. They tend to shift apparent SWR quite a bit depending on whether I'm holding the analyzer or not, and (if I am) whether it's out in free space, or held near to my head as if on an HT in use. My impression is that most HTs have to be designed to tolerate a rather lousy SWR on the antenna port... because it often *is* lousy. Having an HT which burns up its final if you hold the radio wrong would tend to cause the warranty-repair department to start raising hell. I have played with some mobile antennas and mag mounts for 144 to 450 MHz and found the place it is mounted makes a lot of difference. That is why I wanted the person to describe how he is checking out the antennas to see if I could duplicat his results. Just as bending the ground plane elements of a simple 1/4 wave antenna can change the impedance a lot, I am sure many things will affect the HT antennas. Many vertical antennas ar designed to work with a ground plane in some way, especially the short ones. Not much of a ground plane with the HT so the hand/arm and most anything else around the HT will probably have a large effect. I would hope most HTs are designed to handle wide ranges of impedances without burning up or creating voltage spikes on the final transistor or module. I know some specs on RF power transistors state they can handle very large ammounts of SWR. |
Advice on antenna length
On 7/24/2015 12:47 PM, Ralph Mowery wrote:
"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. Better than my stuff. Envy occurs here. I have an HP vector voltmeter, a Fluke 6061A source, and a few accessories. It can be a pain to set up some measurements. I just have not tried the rubber duck antennas to see what frequency I think they may be for. Me neither. Might a be fun diversion, but my bet is that we can trust Helmut's input on this. |
Advice on antenna length
"Dave Platt" wrote in message ... In article , Irv Finkleman wrote: 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. If the rubber ducky is measured by itself, it may not show resonance at the right band of frequencies, however I wonder if it uses the handheld case as part of the system, in which case measurements might change to the anticipated range. Just a wild guess. That matches my own experience and experiments. An HT rubber duck tends to use the HT case, and (via capacitive coupling) the user's hand and body, as the "counterpoise". If you hook it to the end of a coax cable, or directly to a service monitor's test output, the "counterpoise" impedance will be rather different. Also, the HT duck is often operating in fairly close proximity to the head, with some amount of loading from that proximity affecting its feedpoint impedance. I've tested out a number of "ducks" by attaching them to an MFJ 256 or 269 antenna analyzer. They tend to shift apparent SWR quite a bit depending on whether I'm holding the analyzer or not, and (if I am) whether it's out in free space, or held near to my head as if on an HT in use. My impression is that most HTs have to be designed to tolerate a rather lousy SWR on the antenna port... because it often *is* lousy. Having an HT which burns up its final if you hold the radio wrong would tend to cause the warranty-repair department to start raising hell. ================================================== ============ With my dual-band Yaesu FT-530 HT, I used a rubber duck that was NOT for that radio. I was working through a repeater that was nearly line-of-sight. The other end of the QSO and I could barely hear each other and my poor, little HT got very hot very quickly. I was astonished and learned a very important lesson. "Sal" |
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