Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Antenna analyzers, opinions please...
Antenna Newsgroup Denizens:
Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL |
#2
|
|||
|
|||
Antenna analyzers, opinions please...
I have only one comment which applies to most if not all of the amateur
level products, as well as a very high quality HP impedance meter I used years ago. I live about 15 miles from hilltops where the local AM, FM, and TV broadcast towers are. The signals from those stations are strong enough to overwhelm the broad bandwidth detection circuitry in the analyzers (and HP vector impedance meter) I've used, resulting in meaningless readings when connected to an antenna. I find that I grab my MFJ antenna analyzer for a host of jobs like measuring a ferrite core impedance, checking the length of a piece of coax, and so forth. But for me it's just about useless for the job of analyzing actual antennas. When I need to measure antenna impedance I dust off an old GR bridge and use a portable receiver for the detector in order to reject the strong ambient signals. Of course this isn't a problem for everyone, but it sure is for me and I don't think my situation is unusual for an urban environment. I've had to put common mode chokes on my thermometer thermocouple wire, my light meter connecting wire, scope leads, and even in audio circuitry to keep the RF out. But even one strong local station might be enough to upset a typical antenna analyzer. Roy Lewallen, W7EL On 8/23/2010 11:15 AM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL |
#3
|
|||
|
|||
Antenna analyzers, opinions please...
I've used Autek Research "RF" and "VHF" Analysts for some time and
they've served my purposes for antennas and testing. Also Heathkit, Diamond (VHF-UHF) and Daiwa power output & SWR meters in-line on coax. Not so important if one uses a Tansmatch or tuner with them built-in. W5MTV On 8/23/2010 1:15 PM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL |
#4
|
|||
|
|||
Antenna analyzers, opinions please...
Roy:
Thanks for your input on the effects of interference from other transmitters, especially BC transmitters, point well taken. I suppose one might add some kind of carefully designed passive filtering to the devices to 'notch' out offending BC stations, etc... But... that would be messy and complicated. Using a bridge with a tuned detector seems a much better approach. I do have an old MFJ Rx resistance bridge at hand, but I was looking for a little bit better accuracy. I must check e-bay, etc... for prices for a used bridge of the GR class you have. My current problem could likly be solved by using one of my (so-called) VSWR meters, but I felt I might like to get a little more metrological capability for a few bucks. I've never had a vertical antenna before and currently I'm laying out a radial field under a new vertical antenna. I just wanted to know when to stop laying down radials. I figure that I just need to measure the input impedance of the antenna Zin at my frequencies of interest and record the (hopefully decreasing) impedance values as I lay down more radials. My assumption is that Zin = Zant + Rg. where Zant includes the reactance and radiation resistance of the radiator element at my frequency of interest and Rg is the ground resistance. Hopefully Rg should decrease as I add raials. I intend to quit adding radials when the impedance decrease becomes 'negligible' ( In the sense of received S units [smile]). Thanks again! -- Pete k1po -- Indialantic By-the-Sea, FL "Roy Lewallen" wrote in message ... I have only one comment which applies to most if not all of the amateur level products, as well as a very high quality HP impedance meter I used years ago. I live about 15 miles from hilltops where the local AM, FM, and TV broadcast towers are. The signals from those stations are strong enough to overwhelm the broad bandwidth detection circuitry in the analyzers (and HP vector impedance meter) I've used, resulting in meaningless readings when connected to an antenna. I find that I grab my MFJ antenna analyzer for a host of jobs like measuring a ferrite core impedance, checking the length of a piece of coax, and so forth. But for me it's just about useless for the job of analyzing actual antennas. When I need to measure antenna impedance I dust off an old GR bridge and use a portable receiver for the detector in order to reject the strong ambient signals. Of course this isn't a problem for everyone, but it sure is for me and I don't think my situation is unusual for an urban environment. I've had to put common mode chokes on my thermometer thermocouple wire, my light meter connecting wire, scope leads, and even in audio circuitry to keep the RF out. But even one strong local station might be enough to upset a typical antenna analyzer. Roy Lewallen, W7EL On 8/23/2010 11:15 AM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL |
#5
|
|||
|
|||
Antenna analyzers, opinions please...
On Aug 23, 6:15*pm, "Peter O. Brackett"
wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL i presently have 3 analyzers... an mfj269 which i use for taking up towers to check antennas when i have doubt about the coax or switch, checking tuning real quick on anything, and doing simple cable loss checks. then i have a minivna which i am still learning to use, but which has proved very helpful in tuning stubs and checking filters. it also does the tuning checks from the shack but requires a pc for operation so wouldn't be very useful up a tower. my third one is a home made tdr, just a decent scope and pulse generator set up to do tdr on cables from the shack end. indispensable for finding damaged cables, isolating bad connectors or relay boxes, etc. i wouldn't want to be without any of them right now. |
#6
|
|||
|
|||
Antenna analyzers, opinions please...
On 8/23/2010 2:53 PM, Peter O. Brackett wrote:
Roy: Thanks for your input on the effects of interference from other transmitters, especially BC transmitters, point well taken. I suppose one might add some kind of carefully designed passive filtering to the devices to 'notch' out offending BC stations, etc... But... that would be messy and complicated. . . . Yes, it is. I've done it, but a lot of care has to be taken that the filter doesn't have a significant effect on the impedance being measured. At best, it usually also restricts you to a relatively narrow bandwidth. It might be adequate for your particular purpose, however. But for the job you describe of evaluating a radial system, a simple homebrew resistance bridge is perfectly adequate. _Solid State Design for the Radio Amateur_ had some examples, and I assume its successor _Experimental Methods in RF Design_ does also. Roy Lewallen, W7EL |
#7
|
|||
|
|||
Antenna analyzers, opinions please...
On Aug 23, 4:53*pm, "Peter O. Brackett"
wrote: Roy: Thanks for your *input on the effects of interference from other transmitters, especially BC transmitters, point well taken. I suppose one might add some kind of carefully designed passive filtering to the devices to 'notch' out offending BC stations, etc... But... that would be messy and complicated. Using a bridge with a tuned detector seems a much better approach. *I do have an old MFJ Rx resistance bridge at hand, but I was looking for a little bit better accuracy. *I must check e-bay, etc... for prices for a used bridge of the GR class you have. My current problem could likly be solved by using one of my (so-called) VSWR meters, but I felt I might like to get a little more metrological capability for a few bucks. I've never had a vertical antenna before and currently I'm laying out a radial field under a new vertical antenna. *I just wanted to know when to stop laying down radials. I figure that I just need to measure the input impedance of the antenna Zin at my frequencies of interest and record the (hopefully decreasing) impedance values as I lay down more radials. * My assumption is that Zin = Zant + Rg. *where Zant includes the reactance and radiation resistance of the radiator element at my frequency of interest and Rg is the ground resistance. *Hopefully Rg should decrease as I add raials. I intend to quit adding radials when the impedance decrease becomes 'negligible' ( In the sense of received S units [smile]). Thanks again! -- Pete k1po -- Indialantic By-the-Sea, FL "Roy Lewallen" wrote in message ... I have only one comment which applies to most if not all of the amateur level products, as well as a very high quality HP impedance meter I used years ago. I live about 15 miles from hilltops where the local AM, FM, and TV broadcast towers are. The signals from those stations are strong enough to overwhelm the broad bandwidth detection circuitry in the analyzers (and HP vector impedance meter) I've used, resulting in meaningless readings when connected to an antenna. I find that I grab my MFJ antenna analyzer for a host of jobs like measuring a ferrite core impedance, checking the length of a piece of coax, and so forth. But for me it's just about useless for the job of analyzing actual antennas. When I need to measure antenna impedance I dust off an old GR bridge and use a portable receiver for the detector in order to reject the strong ambient signals. Of course this isn't a problem for everyone, but it sure is for me and I don't think my situation is unusual for an urban environment. I've had to put common mode chokes on my thermometer thermocouple wire, my light meter connecting wire, scope leads, and even in audio circuitry to keep the RF out. But even one strong local station might be enough to upset a typical antenna analyzer. Roy Lewallen, W7EL On 8/23/2010 11:15 AM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL- Hide quoted text - - Show quoted text - Hi Pete, If you are evaluating a radial field for a vertical, then the value you should be shooting for is 30-35 ohms, with no reactance. As you know this is 1/2 the impedance of a 1/2 wave dipole-70 ohms in free space. I have never done this, but an impedance below 40 ohms with little reactance should provide you with an efficient vertical. Once you get around this value, I guess there is nothing to be gained by adding more radials. What your analyzer tells you, as others have mentioned, depends on the rf in the area. Gary N4AST |
#8
|
|||
|
|||
Antenna analyzers, opinions please...
On 8/23/2010 5:38 PM, Gary wrote:
Hi Pete, If you are evaluating a radial field for a vertical, then the value you should be shooting for is 30-35 ohms, with no reactance. As you know this is 1/2 the impedance of a 1/2 wave dipole-70 ohms in free space. I have never done this, but an impedance below 40 ohms with little reactance should provide you with an efficient vertical. Once you get around this value, I guess there is nothing to be gained by adding more radials. What your analyzer tells you, as others have mentioned, depends on the rf in the area. Gary N4AST The actual value you get when the radial system loss is minimal depends on a number of factors, including the height and diameter of the vertical. I've also seen convergence to other resistance values when the ground was dry on the surface but apparently wet at some depth below. In that case, radial current can be significant at quite a distance from the antenna (as opposed to the exponential-looking decay you see in the current on radials buried in moist ground), making the system act more like a system of elevated radials. In those systems, radial length also plays a role in determining the feedpoint resistance value. The bottom line is that I don't trust a single value or its comparison to 36 or 40 ohms as being a reliable indication of efficiency. You either need to look for convergence of the feedpoint resistance as Peter proposed, or even better yet, look for convergence of field strength values at a fixed location as you increase the number of radials. Roy Lewallen, W7EL |
#9
|
|||
|
|||
Antenna analyzers, opinions please...
On Aug 23, 8:38*pm, Gary wrote:
On Aug 23, 4:53*pm, "Peter O. Brackett" wrote: Roy: Thanks for your *input on the effects of interference from other transmitters, especially BC transmitters, point well taken. I suppose one might add some kind of carefully designed passive filtering to the devices to 'notch' out offending BC stations, etc... But... that would be messy and complicated. Using a bridge with a tuned detector seems a much better approach. *I do have an old MFJ Rx resistance bridge at hand, but I was looking for a little bit better accuracy. *I must check e-bay, etc... for prices for a used bridge of the GR class you have. My current problem could likly be solved by using one of my (so-called) VSWR meters, but I felt I might like to get a little more metrological capability for a few bucks. I've never had a vertical antenna before and currently I'm laying out a radial field under a new vertical antenna. *I just wanted to know when to stop laying down radials. I figure that I just need to measure the input impedance of the antenna Zin at my frequencies of interest and record the (hopefully decreasing) impedance values as I lay down more radials. * My assumption is that Zin = Zant + Rg. *where Zant includes the reactance and radiation resistance of the radiator element at my frequency of interest and Rg is the ground resistance. *Hopefully Rg should decrease as I add raials. I intend to quit adding radials when the impedance decrease becomes 'negligible' ( In the sense of received S units [smile]). Thanks again! -- Pete k1po -- Indialantic By-the-Sea, FL "Roy Lewallen" wrote in message ... I have only one comment which applies to most if not all of the amateur level products, as well as a very high quality HP impedance meter I used years ago. I live about 15 miles from hilltops where the local AM, FM, and TV broadcast towers are. The signals from those stations are strong enough to overwhelm the broad bandwidth detection circuitry in the analyzers (and HP vector impedance meter) I've used, resulting in meaningless readings when connected to an antenna. I find that I grab my MFJ antenna analyzer for a host of jobs like measuring a ferrite core impedance, checking the length of a piece of coax, and so forth. But for me it's just about useless for the job of analyzing actual antennas. When I need to measure antenna impedance I dust off an old GR bridge and use a portable receiver for the detector in order to reject the strong ambient signals. Of course this isn't a problem for everyone, but it sure is for me and I don't think my situation is unusual for an urban environment. I've had to put common mode chokes on my thermometer thermocouple wire, my light meter connecting wire, scope leads, and even in audio circuitry to keep the RF out. But even one strong local station might be enough to upset a typical antenna analyzer. Roy Lewallen, W7EL On 8/23/2010 11:15 AM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL- Hide quoted text - - Show quoted text - Hi Pete, *If you are evaluating a radial field for a vertical, then the value you should be shooting for is 30-35 ohms, with no reactance. *As you know this is 1/2 the impedance of a 1/2 wave dipole-70 ohms in free space. *I have never done this, but an impedance below 40 ohms with little reactance should provide you with an efficient vertical. *Once you get around this value, I guess there is nothing to be gained by adding more radials. *What your analyzer tells you, as others have mentioned, depends on the rf in the area. Gary N4AST Hi Pete, long time since I've seen a post from you on this NG! Pete, I'd take Roy's route and use a GR impedance bridge. I've used the GR-1606A and the 1606B for the last 50 years. If you're not familiar with it it's been the standard impedance-measuring device for AM BC antennas for more than 50 years. It's accuracy cannot be beaten. These bridges were expensive when new, but they are available rather inexpensively now, and are stable as a rock. And as Roy said, they use either a millivolt meter or a tunable receiver as the detector. Using the receiver, interfering signals picked up with the antenna being measured are eliminated, thus not degrading the accuracy of the impedance measurement. The GR-1606A measures from below 500 kHz up to 60 MHz. The GR-1602 measures well into the VHF range. If you should try one I know you'll like it. Walt, W2DU PS--If you'd like to see the results of measuring W2DU's antenna impedances, I refer you to Reflections, Chapter 15, Tables 15-4, 15-5, and Fig 15-1, which is a graph of the data in the Tables. If you don't have a copy of Reflections you can see this data on my web page at www.w2du.com. Just select 'Read Chapters from Reflections 2'. |
#10
|
|||
|
|||
Antenna analyzers, opinions please...
I've been pretty satisfied with the AIM 4170. Check this out.
http://arraysolutions.com/images/Tun...m_Vertical.pdf 73, Danny, K6MHE On Mon, 23 Aug 2010 17:53:33 -0400, Peter O. Brackett wrote: Roy: Thanks for your input on the effects of interference from other transmitters, especially BC transmitters, point well taken. I suppose one might add some kind of carefully designed passive filtering to the devices to 'notch' out offending BC stations, etc... But... that would be messy and complicated. Using a bridge with a tuned detector seems a much better approach. I do have an old MFJ Rx resistance bridge at hand, but I was looking for a little bit better accuracy. I must check e-bay, etc... for prices for a used bridge of the GR class you have. My current problem could likly be solved by using one of my (so-called) VSWR meters, but I felt I might like to get a little more metrological capability for a few bucks. I've never had a vertical antenna before and currently I'm laying out a radial field under a new vertical antenna. I just wanted to know when to stop laying down radials. I figure that I just need to measure the input impedance of the antenna Zin at my frequencies of interest and record the (hopefully decreasing) impedance values as I lay down more radials. My assumption is that Zin = Zant + Rg. where Zant includes the reactance and radiation resistance of the radiator element at my frequency of interest and Rg is the ground resistance. Hopefully Rg should decrease as I add raials. I intend to quit adding radials when the impedance decrease becomes 'negligible' ( In the sense of received S units [smile]). Thanks again! -- Pete k1po -- Indialantic By-the-Sea, FL "Roy Lewallen" wrote in message ... I have only one comment which applies to most if not all of the amateur level products, as well as a very high quality HP impedance meter I used years ago. I live about 15 miles from hilltops where the local AM, FM, and TV broadcast towers are. The signals from those stations are strong enough to overwhelm the broad bandwidth detection circuitry in the analyzers (and HP vector impedance meter) I've used, resulting in meaningless readings when connected to an antenna. I find that I grab my MFJ antenna analyzer for a host of jobs like measuring a ferrite core impedance, checking the length of a piece of coax, and so forth. But for me it's just about useless for the job of analyzing actual antennas. When I need to measure antenna impedance I dust off an old GR bridge and use a portable receiver for the detector in order to reject the strong ambient signals. Of course this isn't a problem for everyone, but it sure is for me and I don't think my situation is unusual for an urban environment. I've had to put common mode chokes on my thermometer thermocouple wire, my light meter connecting wire, scope leads, and even in audio circuitry to keep the RF out. But even one strong local station might be enough to upset a typical antenna analyzer. Roy Lewallen, W7EL On 8/23/2010 11:15 AM, Peter O. Brackett wrote: Antenna Newsgroup Denizens: Apart from the professional 'lab grade' (and undoubtedly very expensive) devices made by the likes of Agilent, there are on the amateur market several antenna analyzers that are more reasonably priced. I'm currently considering the purchase of such a device, and so... I'm interested in hearing opinions, pro-con arguments, and/or receiving pointers to reviews of such devices. All thoughts and comments will be appreciated, unbiased or not. Thanks! -- Pete k1po -- Indialantic By-the-Sea, FL |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
MFJ Antenna Analyzers hints, tips | Antenna | |||
Spectrum analyzers | Antenna | |||
Antenna/RF Analyzers anything other than MFJ? | Antenna | |||
Opinions on Antenna | CB | |||
Vector Network Analyzers | Homebrew |