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Questions tagged [impedance-matching]

Questions about fixed impedance matching networks, the necessity of impedance matching, etc.

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4 votes
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Can the reactance on a transformer load, be "corrected" on the transformer primary, to improve transformer efficiency?

The following question is regarding the ability of a transformer, UnUn or BalUn, to be efficient, if the transformer (UnUn in my case), is feeding a load with reactance, and what can be done about the ...
Louis Seaman's user avatar
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2 votes
1 answer
61 views

Resonant 80m End Fed Halfwave Antenna With Counterpoise - Questions

Originally, I built an 80m EFHW, 130.5 feet long cut for approximately 3.58Mhz. I attached a 49:1 UnUn at the feed point 13 feet above the ground with coax back to the shack. I did not use a ...
Ron K5TDF's user avatar
0 votes
1 answer
41 views

Lumped Solution for Impedance Matching vs. Ferrite Transformer

Using a high-Q LC circuit to match impedance is more efficient than a ferrite transformer, however it is very narrow banded compared to a ferrite transformer. The statement above is...?
Louis Seaman's user avatar
  • 1,067
0 votes
1 answer
127 views

Input impedance of a shortened dipole antenna

I want to make myself a antenna for 40m and 20m wavelength band, but i don't have enough space for a full scale dipole, and even for more compact configurations like delta-loop or inverted v, so i ...
ZecosMAX's user avatar
  • 109
0 votes
1 answer
190 views

Circular polarization

I'm installing my first beam antenna. I have 2 connection points, one for vertical and 1 for horizontal. So far. I have not found a lot of information which would be better. To run them separately or ...
David Hamilton's user avatar
1 vote
1 answer
93 views

How do you decide on number of turns for twisted gamma match?

I'm looking at a 40MHz short transmitting loop (STL) with 6 rectangular loops: I need to fit within some design parameters and this gives the good radiation that I need in the near field. If I want to ...
Tunneller's user avatar
  • 111
0 votes
0 answers
86 views

High SWR at full height

I operate a low power FM radio station. I have always had issues with high SWRs. Recently I have purchased a new transmitter, new antenna, and new 100 ft cable from the same company assuming they ...
Jim North's user avatar
2 votes
1 answer
66 views

What is the apparent AC voltage source caused by a mismatched impedance on the antenna or transmission line?

From Understanding how antenna mismatch can damage a transmitter "The reflected wave appears to the transmitter's antenna port... as an AC voltage source... whose magnitude and phase depend on ...
SRobertJames's user avatar
2 votes
2 answers
508 views

Understanding how antenna mismatch can damage a transmitter

I know it's important to tune an antenna to the same impedance as the transmitter for maximum power transfer. But I've read that if you don't do so, you not only get less radiated power, but you can ...
SRobertJames's user avatar
4 votes
2 answers
390 views

Antenna tuning confusion - help!

In a recent discussion with a fellow ham about where to use a RigExpert antenna analyzer for tuning an antenna for minimum SWR, we couldn't decide if "antenna only" or "feedline+antenna ...
K4JUL's user avatar
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1 vote
1 answer
78 views

I would like to know more about designing broad bandwidth transformers and current baluns using binocular cores

Internet pickings seem mighty slim, would appreciate links to books, articles or websites. If there are good "how to" items that explain the design, that too. Thanks and 73s
Jimbo47's user avatar
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2 answers
113 views

SWR reading problems

Hey I'm new to using CBs I have a classic Cobra 29 I had it peaked and tuned supposed to be pushing about 60 watts also supposed to have everything set as far as my SWR however I am still only getting ...
Joe Lee's user avatar
  • 11
3 votes
2 answers
234 views

Does a halfwave (or multiple) length of coax duplicate the load impedance of one end at the other end?

Ignoring the possibility of multiple radiators and phasing harness(es), consider the following example: If I have a short inductor-loaded vertical antenna that I have not carefully matched to 50 ohm ...
always_learning's user avatar
2 votes
1 answer
181 views

UnUn for VHF and UHF

Is it possible to build an UnUn for VHF or UHF like in HF? Goal is to use a simple endfed wire or piece of metal as an antenna. EDIT: I meant "endfed halfwave".
microfox's user avatar
4 votes
2 answers
223 views

How can an HT antenna be half wave?

There's a model of HT antenna for the GMRS band by Nagoya (NA-771G) that's specified as a half wave. How can that be? An end fed half wave antenna needs a 49:1 impedance transformer to match with ...
Paul's user avatar
  • 781
2 votes
1 answer
94 views

What this E(EL) symbol does mean?

I can't understand what this E(or EL) symbol does mean. I know that Zo means impedance and I can calculate trace width according it, but what E symbol does mean?
Alatriste's user avatar
  • 131
1 vote
3 answers
1k views

Why does SWR of a dipole decrease the closer it is to the ground?

I experimented with a 20m dipole made of a 1:1 balun connected to 2x ~5-meter lengths of copper wire, running parallel to the ground (by "ground" I mean "pavement", not quite the ...
JayPulsar's user avatar
1 vote
2 answers
328 views

Off-center fed long wire antenna

I want to feed a horizontal wire antenna (approximately 150' long at 50' or more above the ground) for multi-band HF operation with an off-center (25-33%) feedline. The element wire will have no ...
Allen's user avatar
  • 41
1 vote
2 answers
566 views

Is there a proper way to connect multiple radios via coaxial cable so they can be tested without going over the air?

Let me state up front that I am not an RF engineer, but I do have a EE background. I'm working with a group that has a collection of radios, VHF and UHF (military) that is licensed to use a VHF and ...
AnAnonymousParty's user avatar
1 vote
0 answers
63 views

How to determine if filter is well matched?

Hello i'm in process of creating band pass filters for my ham radio. I calculated the filter for 80m band basing on this website: And recreated it in reality: Then I started measuring it with ...
fifi_22's user avatar
  • 111
2 votes
2 answers
1k views

Hi SWR with End Fed HF Wire 9:1 UNUN

Good Day I understand every antenna set up is different, so I'm looking for advice on what I could change to alter my findings. The set up is new including the EFHFW - 20 which was bought off the ...
Simon Hefford's user avatar
2 votes
2 answers
415 views

Balance of gamma / delta match

A center fed dipole, with equal arm lengths, is a balanced device. If it is fed using a gamma match - does it change (the system) to be unbalanced?
Jan Hus's user avatar
  • 167
2 votes
5 answers
430 views

Minimal SWR at resonance

Why does a minimal SWR NOT indicate antenna resonance? Would SWR 1:1 be required to indicate antenna resonance?
Jan Hus's user avatar
  • 167
2 votes
1 answer
139 views

feeding a 20 meter 2-element yagi in an attic

I have an unused attic crawlspace in which I can potentially install a 2-element 20 meter yagi. I know that adding the reflector will drop the feedpoint impedance of the driven element below 50 to 70 ...
niels nielsen's user avatar
0 votes
3 answers
479 views

SMA Connector Impedance

I am new to antennas, and am trying to create a monopole that connects to an SMA female to transmit a 2.4ghz wifi signal. I know that the antenna needs to be a multiple of 3.1cm in order to have the ...
Saveer Jain's user avatar
2 votes
2 answers
798 views

Do I need an antenna tuner for new mobile antenna

I am looking to buy my first mobile antenna, for use with a 2m/70cm HT in the car. The HT needs 50 Ω impedence. I was looking at this antenna, but another ham told me that I need 1/4 wave or 5/8 wave ...
TSG's user avatar
  • 259
2 votes
3 answers
4k views

cut or lengthen to reduce swr on vertical wire antenna

Have tried measuring antenna wire using formula 234/frequency for 1/4 wave vertical but this gives high swr. How do I lower swr on a wire vertical antenna. Do I Cut or Add? wire'
Doug's user avatar
  • 21
1 vote
2 answers
125 views

Understanding Coax Impedance when Connected to Reactive Load

The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. So when the coax is connected to an antenna that is fairly reactive like $ 23-...
wbg's user avatar
  • 301
2 votes
1 answer
337 views

Yaesu FT817ND + (Bluetooth) CAT control + ESP32 microcontroller: reading SWR "programmatically"?

I am building a wireless control system for a magnetic loop antenna. The system uses an ESP32 microcontroller (that has Bluetooth and WiFi) that automatically drives the magloop capacitor by means of ...
Michele's user avatar
  • 31
2 votes
3 answers
248 views

Is a UHF connector any real disadvantage off the transmitter circuit board or at an antenna feedpoint?

I have a discone antenna intended for use in the 25-1300 MHz frequency range, but it uses a SO-239 connector. Now, we know that the so-called "UHF" i.e. the PL-259 male plug and SO-239 ...
natevw - AF7TB's user avatar
4 votes
3 answers
500 views

What is the difference between antenna input impedance and its radiation resistance?

I got to know that the input impedance of the halfwave dipole antenna is given as: Zin=1/Im* sin(β(H-|Z|)) where Im is the maximum current on the antenna( when excited with a 1 volt supply), H is the ...
Moulee's user avatar
  • 43
0 votes
1 answer
82 views

How do you create a DC-blocking ground-shunt that looks inductive in an "L" match?

We are optimizing an impedance match with s2p models for an LNA and found that an "L" match with a serial cap and shunt inductor will optimize to provide +3 dB of output, versus using serial ...
KJ7LNW's user avatar
  • 755
3 votes
4 answers
247 views

Is it worse to use an antenna tuner on an already-loaded short monopole?

If I had a good transmatch and wanted to use a spare CB antenna on the amateur HF bands, would I be better off bypassing its tuning coil completely? One ham pastime is using an antenna tuner to match ...
natevw - AF7TB's user avatar
7 votes
2 answers
4k views

Are "end-fed" antennas really more multi-band than dipoles?

Several "end fed" antenna kits (including the ARRL's for example) include wording suggesting that they are useful as multi-band antennas. But does feeding a wire antenna highly off-center ...
hotpaw2's user avatar
  • 13.4k
4 votes
2 answers
1k views

Measuring actual feedpoint impedance for a given frequency

Background I'm attempting to tune an antenna with my NanoVNAv2. I calibrated it using the included open/short/(50-ohm)load standards by screwing them directly onto the NanoVNA one by one and running ...
Bitbang3r's user avatar
  • 401
1 vote
1 answer
114 views

Current Transformers in Series versus a Single Voltage Transformer

I've read that the commonly used 49:1 (7t:2t) auto transformer for Multi-band End-fed Half-wave (EFHW) antennas has criticisms as not being very efficient. I haven't found any other designs that ...
wbg's user avatar
  • 301
1 vote
0 answers
97 views

S-Parameters Power amplifier impedance matching

I recently decided to conceive a 10W class 446MHz amplifier. I want to be able to amplify a 100mW signal into a 10W, for that i'm going for a two stages amplifier : SKY65162 to amplify the signal to ...
Wireless Learning's user avatar
3 votes
1 answer
263 views

Can you think of any reason my NanoVNA says my antenna has 1.2 SWR while my radio says it has off the scale SWR?

My radio is an mcHF kit that I just finished soldering up. It receives fine, but when I went to transmit it's giving off the scale SWR. I rechecked my antenna with my NanoVNA, and it shows 1.2 SWR at ...
rcx935's user avatar
  • 411
3 votes
2 answers
596 views

How do you calculate peak voltage given VSWR caused by impedance mismatch in a 50-ohm system?

I would like to choose a feedline that is safe for the wattage at a given VSWR to avoid coax arcing. How do you calculate peak voltage given a peak power in watts and maximum expected VSWR from ...
KJ7LNW's user avatar
  • 755
2 votes
1 answer
71 views

Whip/stub antenna sorting with SA using VSWR

I have an assortment of whip antennas for various RX & HT devices such as a 2M/70cm FT740, a Uniden race scanner 29-54Mhz/108-174Mhz/406-470Mhz/806-956Mhz, a similar Realistic Pro-32 scanner and ...
kjo's user avatar
  • 21
7 votes
1 answer
669 views

Why ferrite-core transformers are wideband while air-core are not?

While experimenting with end-fed antennas I've made two 1:49 transformers. The first one has an air core, as shown in the article by John, M0UKD. This transformer doesn't even work as a transformer ...
Aleksander Alekseev - R2AUK's user avatar
2 votes
3 answers
326 views

Ferrite unun transformer to match antenna resistance loads of <50Ω?

For LF/MF (2200m/630m), I am interested in the situation of a vertical antenna with capacitance hat top-loading, where the vertical antenna is VERY short compared to wavelength, and the antenna is ...
photosynthesis's user avatar
2 votes
1 answer
209 views

Reasons for an antenna tuner at the transmitter other than transmitter protection?

An antenna tuner colocated with the transmitter may be required to prevent transmitting into an SWR higher than the allowed specification for the transmitter, or if the transmitter might overheat or &...
hotpaw2's user avatar
  • 13.4k
1 vote
2 answers
524 views

How do you calculate the impedance of a parallel-wire balanced feedline (ladder line)?

I've looked around and maybe I'm just searching for the right terms to find the answer. I know that the impedance of ladder line has to do with the distance between wires: What is the generalized form ...
KJ7LNW's user avatar
  • 755
5 votes
5 answers
408 views

Antenna tuner at the transceiver output confusion

I am a bit confused. Let's take a HF transceiver for example. My understanding is that the output impedance of the transmitter is 50 ohms. The impedance of the coaxial cable feedline is 50 ohms, and ...
Engineer999's user avatar
1 vote
0 answers
233 views

Crystal Filter Impedance Matching

I downloaded a 2-meter receiver schematic using an IC for the dual conversion IF strip. The first 10.7MHz IF uses a crystal filter with a terminating impedance of 1800//5pF. The output impedance of ...
Thomas L's user avatar
  • 193
3 votes
2 answers
95 views

Impedance miss-match short vs long section?

Let's say there is a 50 Ohm transmission line coming from a transmitter, suddenly the transmission line is spliced into a 300 Ohm line. From what I've learned a partial reflection occurs at this point....
AllYourBaseAreBelongToUs's user avatar
3 votes
1 answer
259 views

Calculating SWR for a dipole

I have a dipole wire antenna that is tuned to 14.0 MHz so that it has an SWR there of nearly 1:1. Is there a mathematical formula by which I can compute the expected SWR for other frequencies? I would,...
Bill KG5RMJ's user avatar
1 vote
1 answer
1k views

Common-mode choke (CMC) hurting my SWR. Live with it? Drop the choke?

I have been using a Par EndFedz Mk2 Trail Friendly 40/20/10 though using the matchbox from an EndFedz EF-QUAD (with Vibroplex’s blessing) so I could transmit at more than 25W. On all three bands I ...
QuantumMechanic's user avatar
5 votes
2 answers
394 views

Is tuning at all useful for an antenna that is already resonant?

Say you have a resonant antenna that also has a tuner. Does this help at all? Can your antenna be "fine tuned" ?
NonYaBidnezz's user avatar