9
votes
Accepted
Does a halfwave (or multiple) length of coax duplicate the load impedance of one end at the other end?
I have been told that 50 ohm coax is 50 ohm at both ends, and 50 ohms all along its length, and it is 50 ohms that is presented to anything to which it is connected, and the length of it does not ...
- 11.1k
6
votes
cut or lengthen to reduce swr on vertical wire antenna
If you're only measuring SWR at one frequency, or in a narrow range like the ham bands, you won't know until you cut it.
Mount the antenna in its final location as the SWR and resonant frequency will ...
- 9,804
6
votes
Is there a proper way to connect multiple radios via coaxial cable so they can be tested without going over the air?
My company built a system like this, to allow real radios to be used in a flight simulator. It had fixed and digital variable attenuators, so it could simulate exactly the effect on communication of (...
- 9,804
5
votes
Accepted
How can an HT antenna be half wave?
Judging by looks, it's a half-wave element with an autotransformer at the base. Nagoya says the antenna is 15.3 inches in length. Taking measurements from a photo, the bottom 2 inches is in that fat ...
- 11.1k
5
votes
Why does SWR of a dipole decrease the closer it is to the ground?
Shouldn't lower SWR generally indicate a better antenna placement?
No. Lower SWR generally indicates lower SWR. It doesn't tell you anything about an antenna's radiation pattern or efficiency.
...
- 11.1k
4
votes
Accepted
Why does SWR of a dipole decrease the closer it is to the ground?
I presume you are running a 50 Ohm system (radio & trasmission line), and while the characteristic impedance, in free-space, of a dipole is ~73 Ohms, at various distances from the ground, the ...
- 182
4
votes
Is there a proper way to connect multiple radios via coaxial cable so they can be tested without going over the air?
A run of coaxial cable, with an attenuator, is a perfectly good way to simulate an “over the air” connection. It is done all the time in labs.
(However, note that it does not automatically mean your ...
- 23.9k
4
votes
Minimal SWR at resonance
Why does minimal SWR DOES NOT indicate antenna resonance?
Well, because they're not the same thing.
Would SWR 1:1 be required to indicate antenna resonance?
No. A zero reactance indicates resonance....
- 11.1k
3
votes
What this E(EL) symbol does mean?
I haven't seen this notation before but it is almost certainly describing a matching section on a PCB - with two transmission lines connected together.
First is a line of 15.8 ohms impedance, 14.6 ...
- 9,804
3
votes
Does a halfwave (or multiple) length of coax duplicate the load impedance of one end at the other end?
If the impedance of the load is $Z_L$ and the characteristic impedance of the transmission line is $Z_0$, then the impedance at the input to a length $l$ of transmission line connected to the load is:
...
- 532
3
votes
Accepted
Understanding Coax Impedance when Connected to Reactive Load
50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with 50+0j load
That wording is incorrect. The characteristic impedance of your coax is a constant; it ...
- 14.9k
3
votes
Accepted
SMA Connector Impedance
Lots of questions here, let me try to cover them point by point.
A monopole is half of an antenna. A real antenna is a dipole. The monopole needs a "ground plane" to replace the missing ...
- 5,321
2
votes
Accepted
Do I need an antenna tuner for new mobile antenna
The HT needs 50 ohm impedence.
An antenna of this kind should be designed to have a 50 ohm impedance (when properly installed on top of a ground plane such as a car roof). It probably won't be ...
- 23.9k
2
votes
cut or lengthen to reduce swr on vertical wire antenna
The first consideration is that a 1/4 wavelength antenna has a wide bandwidth, it is not a high Q or high gain antenna. Don't worry about getting SWR as low as you can, it's not critically important ...
- 62
2
votes
Accepted
Off-center fed long wire antenna
Off-center fed antennas, fed between 25% and 33% of the antenna length, are vastly different antennas. First, presuming the overall antenna is one wavelength long, at 25%, you have a 3/4λ element and ...
- 644
1
vote
SWR reading problems
The process is a bit more complex - first you need to calibrate the internal SWR meter, then you need to read it on the antenna.
the manual says:
Calibrate for SWR (Standing Wave Ratio) SWR ...
- 9,804
1
vote
UnUn for VHF and UHF
Yes.
The matching section of a j-pole is an example of an impedance match device between coax and a monopole antenna. The contacts can be moved up or down the match to accommodate a wide range of ...
- 3,094
1
vote
Why does SWR of a dipole decrease the closer it is to the ground?
SWR tells you how well the radio is transferring energy into the antenna. While an antenna with a high SWR that transfers energy poorly might not work well, if what does get out goes where you want ...
- 5,321
1
vote
Off-center fed long wire antenna
Balun for common mode blocking can be put almost anywhere, but it is more effective at certain multiples of a quarter wave along the feed line. But you have to realize that if you don't put it at the ...
- 5,321
1
vote
Accepted
feeding a 20 meter 2-element yagi in an attic
There's a fairly simple approach to this, keeping the KISS rule in mind. Using a smaller type of coax (RG58, RG8) would work well since the run length is fairly short. The small amount of loss in the ...
- 62
1
vote
Hi SWR with End Fed HF Wire 9:1 UNUN
Remember an antenna using a 9:1 matcher is meant to use a tuner, whether in your radio or external.
The idea is to bring the impedance if a "random wire" down to a value your tuner can ...
- 139
1
vote
Balance of gamma / delta match
A half wave wire has a low impedance point at its midpoint. If you put two half wave wires at 90 degrees with respect to each other so the midpoints come close, but not in electrical contact with each ...
- 939
1
vote
Understanding Coax Impedance when Connected to Reactive Load
A couple of things are missing here.
If the antenna is not 50+0i then there will be SWR. If there is SWR, then loss in the coax is magnified.
If the impedance is not 50+0i, then the impedance along ...
- 5,321
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