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Re: Antenna pi-network matching High or low pass ??
On 7/22/22 2:00 AM, Diane BONKOUNGOU wrote:
Hi all, I am a beginner in RF system design and have some questions.Folks will chose high or low pass to meet spurious emission requirements. For instance, if your transmitter has 3rd harmonic, using a low pass matching network can help knock that down to below the (typical) -40 dBc or -60 dBcrequirement. As to why you might want to pass DC - AC coupled ungrounded antennas can build up static charge. If you don't have some way to discharge that static, then if the voltage gets high enough, you might have a spark (which generates broadband RF power) or a component failure (e.g. a capacitor exceeds its voltage rating). Some antennas though, are inherently grounded, so in that case, you don't care. |
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Re: Antenna pi-network matching High or low pass ??
You would want to pass DC through to your antenna if the antenna might have a pre-amp that needs the DC for power. Also in some cases, DC grounding the antenna is good practice for safety, like when dealing with radio detonators for fireworks, explosives, or just in the presence of fuel fumes. DC grounding means no static buildup.
SherpaDoug |
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At which point do we take the value of impedance to tune an antenna?
Diane BONKOUNGOU
Hello,
Hi, I am a beginner in antenna design and tuning. I want my antenna to have a resonant frequency of 2.45GHz for low-energy Bluetooth communication. And I want to know what to consider for the matching process. I have made some measurements with Nanovna of my antenna. I have a resonance frequency of 2.28GHz and at this frequency, I have an impedance of 47.8-7.06j. Can I take the value of this impedance at this frequency for the matching process or do I have to take the value of impedance at 2.45GHz? Where to take the value of impedance for tuning? Thanks. |
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Re: Antenna pi-network matching High or low pass ??
Maybe it easier to build the antenna that it has 50 ohms input then tune a mismatch with a network
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Dg9bfc sigi Am 22.07.2022 12:08 schrieb F1AMM <18471@...>:
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Re: Antenna pi-network matching High or low pass ??
F1AMM
If it is above all an impedance adaptation that you are looking for, it is easier to use an 'L' adapter. It will be low pass or high pass. You will choose it as impedance step-up or step-down.
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You can consider that a pi-adapter consists of 2 L-adapters one behind the other. For example on a classic pi: capacitor in parallel, inductor in series, capacitor in parallel, you cut (in your mind) the inductor in two. The one on the right is step-down and the one on the left is step-up. They are both low pass. A pi is especially of interest when the adapter must be fairly universal. This is not your case since you are going to measure your antenna with your nanaoVNA. The adaptation will be fixed (raise or lower). -- Fran?ois F1AMM -----Message d'origine-----De la part de Diane BONKOUNGOU Envoy¨¦ : vendredi 22 juillet 2022 11:00 |
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Antenna pi-network matching High or low pass ??
Diane BONKOUNGOU
Hi all, I am a beginner in RF system design and have some questions.
I have a PCB trace antenna, I need to tune it to 2.45GHz, this is for Bluetooth low-energy communication. I want to use a pi-network for the tuning process. I chose pi-network because it is selective and allows to set the quality factor Q of the circuit and the bandwidth (BW) of the antenna as Q=F/BW. -Can someone tell me when to choose the pi-network high pass or low pass for antenna matching? I have seen in the document "AN1275: Impedance Matching Network Architectures" by Silabs that the high-pass network allows high frequencies to pass through the antenna and the low-pass pi-network blocks the passage of high frequencies through the antenna, which also means that the matching network must allow DC current to pass through the antenna. What does it mean to allow DC current to pass through the antenna? In general, I know that the signal transmitted by the antenna is an AC signal. Could I feed (transmit) a DC signal to an antenna? Thanks, |
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Re: Common ground and 2-port measuring
On 7/21/22 10:37 AM, W0LEV wrote:
Jim, not just the UK. It's not the net Nazis. I could not access itIt's available in IEEE Xplore. Thanks for forwarding the paper, but I hope I can read it as its not theThe scan on the IEEE pdf isn't bad. Moire on the halftone figures. Drawings and text is sharp. |
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Re: Measuring characteristic impedance of shielded twisted pair
#nanovna-h4
#cables
#matching
Charlie, that's true although this isn't in a car , it's in a bespoke design I am doing and I am in control of the termination at both ends.
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Re: SMA to banana binding post
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-----Original Message-----
From: "Roy J. Tellason, Sr." <roy@...> Sent: Thursday, July 21, 2022 12:17pm To: [email protected] Subject: Re: [nanovna-users] SMA to banana binding post On Wednesday 20 July 2022 03:58:49 pm Jim Lux wrote: Some time back I acquired a cable with connectors on each end that resemble PL-259s, but are *much* smaller. Anybody know what these are, and what sort of equipment is likely to use them?True, the UHF connector isn't constant impedance, however, if you have a "Mini UHF" - Early analog cell phones from Motorola -J- -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: SMA to banana binding post
On 7/21/22 9:17 AM, Roy J. Tellason, Sr. wrote:
On Wednesday 20 July 2022 03:58:49 pm Jim Lux wrote:There's a mini-UHF that I've seen on things like land mobile VHF radio, and on older cell phones (instead of a TNC). Unlike the PL-259, it's actually designed for constant impedance. It's really more of a Mini-TNC, but it has that serrated edge on the jack, and a TNC is a smooth edge.Some time back I acquired a cable with connectors on each end that resemble PL-259s, but are *much* smaller. Anybody know what these are, and what sort of equipment is likely to use them?True, the UHF connector isn't constant impedance, however, if you have a Tessco |
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Re: Common ground and 2-port measuring
Jim, not just the UK. It's not the net Nazis. I could not access it
either. Something to do with no 'academic access" and, of course, not an IEEE member. I'm not sure even an IEEE member would allow access. Thanks for forwarding the paper, but I hope I can read it as its not the sharpest "copy". Dave - W?LEV On Thu, Jul 21, 2022 at 5:12 PM Dragan Milivojevic <d.milivojevic@...> wrote: Had no idea that the UK censors the internet. Good reason to get a VPN.-- *Dave - W?LEV* *Just Let Darwin Work* -- Dave - W?LEV |
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Re: Common ground and 2-port measuring
Had no idea that the UK censors the internet. Good reason to get a VPN.
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Anyway: !AvpPJnaZGO4PiHD2Qt_oLBZfweoD?e=dxDhWi On Thu, 21 Jul 2022 at 16:48, Ed G8FAX <ed@...> wrote:
On Wed, Jul 20, 2022 at 05:42 PM, Dragan Milivojevic wrote:site |
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Re: Common ground and 2-port measuring
On Thu, Jul 21, 2022 at 08:46 AM, Brian Beezley wrote:
Thanks Brian, information much appreciatedHave you used it with nanoVNA tests?I haven't, Ed, but N6LF has. What I like about this particular transformer is Ed, G8FAX |
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Re: SMA to banana binding post
On Wednesday 20 July 2022 03:58:49 pm Jim Lux wrote:
Some time back I acquired a cable with connectors on each end that resemble PL-259s, but are *much* smaller. Anybody know what these are, and what sort of equipment is likely to use them?True, the UHF connector isn't constant impedance, however, if you have a -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: Measuring characteristic impedance of shielded twisted pair
#nanovna-h4
#cables
#matching
Charlie N2MHS
CAN Bus in a car has term resistor and each end.
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On Thursday, July 21, 2022 at 11:52:24 AM EDT, Jim Lux <jimlux@...> wrote:
On 7/21/22 6:12 AM, Magicbean wrote: Hello - Totally new to VNA here...It should work fine.? That STP has a "reasonably well controlled" impedance, but i wouldn't be surprised by 5% changes.? It might be most useful to do the TDR type display, rather than a S11.? Then you can see the dips and peaks along the cable. (Fun experiment, tie a knot or kink it in the middle of the cable) No, that's not the right tool.? The NanoVNA is what you want. An interesting question.? The "resolution" in TDR type displays is determined by the frequency span. So 1 GHz gives you 1 ns (20-30cm) resolution. The unambiguous range is set by the lowest frequency. If you want to distinguish the "cable" from the "ends" (both at the VNA end and the termination end) you probably want the cable to be long enough that it's several resolution points.? The NanoVNA can go up to 900 MHz, so a 3-4 m piece should be long enough. Before you get into fixturing and all that, try it with a 2-3 m piece of 50 ohm coax, and see if you can distinguish the termination (i.e. do the cal with no cable, put the cable on, and then look at TDR with the short, open, and load at the far end) NanoVNA does that nicely. Whether you normalize or not depends on whether you need to have actual values, or if you're just doing a qualitative test.? If you get a reflection from the end vs no reflection, you don't really care what the value is.
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Re: Measuring characteristic impedance of shielded twisted pair
#nanovna-h4
#cables
#matching
On 7/21/22 6:12 AM, Magicbean wrote:
Hello - Totally new to VNA here...It should work fine. That STP has a "reasonably well controlled" impedance, but i wouldn't be surprised by 5% changes. It might be most useful to do the TDR type display, rather than a S11. Then you can see the dips and peaks along the cable. (Fun experiment, tie a knot or kink it in the middle of the cable) I do have a Siglent SSA3032X plus spectrum analyser for which there is a return loss bridge (RB3X25) but at around ?400. I'm not sure whether that would be useable for that kind of measurement, especially as the cable isn't 50 ohms.No, that's not the right tool. The NanoVNA is what you want. I assume the NanoVNA probably is suitable for measuring the 120 ohm pair and can probably offer more functionality even if some of the specs of the Siglent are rather better!? If so, what's the shortest length of twisted pair I could sensibly make measurements on? I have some 1m samples of cable which I would like to evaluate. The final cable runs will be in the order of 100m.An interesting question. The "resolution" in TDR type displays is determined by the frequency span. So 1 GHz gives you 1 ns (20-30cm) resolution. The unambiguous range is set by the lowest frequency. If you want to distinguish the "cable" from the "ends" (both at the VNA end and the termination end) you probably want the cable to be long enough that it's several resolution points. The NanoVNA can go up to 900 MHz, so a 3-4 m piece should be long enough. Before you get into fixturing and all that, try it with a 2-3 m piece of 50 ohm coax, and see if you can distinguish the termination (i.e. do the cal with no cable, put the cable on, and then look at TDR with the short, open, and load at the far end) BTW I know I can also fire a pulse down the cable and match with a variable resistor when the cable is easily accessible (and I might do that too) but I am interested to know if the NanoVNA would be useful for this and also, in some circumstances, I won't be able to get to the far end of some cables. Would it be necessary to normalise to something other than 50 ohms? Would I need any other components or equipment to do the test (apart form connectors to physically connect)?NanoVNA does that nicely. Whether you normalize or not depends on whether you need to have actual values, or if you're just doing a qualitative test. If you get a reflection from the end vs no reflection, you don't really care what the value is. I have some other applications for the NanoVNA too, so I will probably get one (I was thinking NanoVNA H4 although there seems to be a bewlidering number of variants). I'd just like to know if it is suitable for this measurement as well. Or... if I could do everything with a Siglent RF bridge, maybe that would be a better focus as I already have the SA. |
Douglas Butler
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