10
votes
Accepted
Is "low loss" cable required for HF?
Your question seems as much about psychology as much as technical concerns. We mainly favor the technical questions, but I'll take a stab at the psychological aspects also. All of you, please feel ...
- 9,320
9
votes
Accepted
Tuner at antenna side versus transmitter?
There are a lot of topics in this question, so let's take them one at a time.
I figure the transmitter has a 50-ohm pure resistive output
Not necessarily. You're probably arriving at this conclusion ...
- 52.5k
7
votes
What are the implications of pulling LMR400 through EMT conduit with several 90 degree conduit body fittings
I am sure you will get many good suggestions for your situation.
The higher quality coax cables do have a specification for their minimum bend radius during install. For LMR-400 it is 1 inch (25.4 ...
- 18.6k
7
votes
Accepted
How do you solder/crimp a 90-degree BNC connector?
You strip the coax to fit, and solder the pin to the coax. Don't leave any wire sticking out past the pin. You don't and can't crimp it.
Here's a video I found of a similar connector.
If your iron ...
- 12.2k
6
votes
Accepted
What dictates ladder line max frequency?
1% here is just an overly precise way of saying "really small compared to the wavelength". The problem is that when the conductors are close together, their electrical and magnetic fields cancel; as ...
- 960
6
votes
Accepted
Why does ladder line generally have a lower loss than coaxial cable?
When the SWR is 1:1, the matched line loss of ordinary ladder line is lower than the matched line loss of ordinary coax because at HF, most of the loss is $I^2R$ loss, and the current magnitude is ...
- 1,684
6
votes
Accepted
Why do we talk about common mode current from an antenna, but not from a transmitter?
The short answer is that it can't.
A shielded transmitter, connected to an ideal piece of coax, does not generate common mode currents.
The inner and the outer of the cable look connected (and for ...
- 12.2k
5
votes
Accepted
Use a TV coax and balun for a poor-man's OCFD?
OK, let me try to answer this, but this answer may also be qualified as unqualified.
If you have a 50 Ohm receiver, and connect a perfectly (Z=R) 75 ohm antenna system, then your VSWR would be 1.5, ...
- 2,195
5
votes
Why isn't twisted pair used for feedlines?
Twisted-pair is just a special case of a balanced (untwisted) feedline. The twisting reduces crosstalk between the multiple pairs in the cable assembly but doesn't otherwise change the fundamental ...
- 52.5k
5
votes
Accepted
How to estimate ladder line loss?
For most feedlines, dielectric loss is very low, and at HF where ladder line is practical, negligible. So significant losses are due to resistance and associated Joule heating of the copper conductors....
- 52.5k
5
votes
Can coax be run through the center of a radiating element without currents being induced on the coax shield?
That is a great idea. In fact antennas of this design are quite common, and you probably have a much smaller antenna of similar construction on your Wi-Fi router:
Effectively, the lower dipole ...
- 52.5k
5
votes
SDR Transceiver over LAN
You can do this currently with any network connected SDR that is capable of streaming raw or IQ samples, and run an SDR application remotely from anywhere there is a network connection, over LAN, WiFi,...
- 13.6k
5
votes
Accepted
Is a 1/2-wave coax cable shorter or longer than the full-speed 1/2-wavelength?
Shorter. Like you said, the velocity of propagation is lower, which means that the wave travels a shorter distance in the same time, which means that the wavelength is shorter for the same frequency.
- 13.2k
5
votes
Coax in the wall, or around the house?
Three things that matter here:
Lightning! You need to ground the coax as it enters the house.
This is difficult if it comes in via a vent.
You should probably ground the antenna anyway, but you ...
- 12.2k
5
votes
Ladder line vs twisted pair: where do the losses actually occur?
You should also check out this answer to a related (but not duplicate) question over on electronics SE; in relevant part:
The main limiter of the bandwidth is from the attenuation, which increases as ...
- 4,658
4
votes
What type of solder is best suited for radio and electronic use?
The OP question is copied directly from the the FCC amateur Technician test question pool. The answer is rosin core solder.
The question and its answer mostly sidesteps the question of solder ...
- 141
4
votes
Accepted
What is the actual loss in a feed line with high SWR?
Assuming no tuner losses, and assuming uniform loss throughout the line (which isn't true in practice, yet can be a practical simplifying assumption, more below), feedline losses in decibels are:
$$ -...
- 52.5k
4
votes
Use a TV coax and balun for a poor-man's OCFD?
TV coax typically has foam dielectric and very low loss. On receive it
does not matter if you use 50, 60 72 or 75 ohm cable. With short cables,
losses are also not important. The cheap TV balun could ...
- 1,019
4
votes
What is Electrical length in RF and how to electrically cut and measure the RF cable in degree?
The concept of "electrical length" begins with the concept of wavelength, $\lambda$ - the distance over which the value of a periodic phenomenon repeats, expressed as: $$\lambda=\frac{c}{f}$$ When ...
- 7,912
4
votes
Why does ladder line generally have a lower loss than coaxial cable?
It is well understood in the amateur radio community that ladder line, window line, etc. have lower losses per foot than say RG-213 or LMR400, particularly on HF frequencies.
Is it though? I'd say ...
- 52.5k
4
votes
How to estimate ladder line loss?
There is a program called TLDetails, available from https://ac6la.com/tldetails1.html, that will calculate the loss for many standard transmission lines. One enters the frequency, the type and length ...
- 1,684
4
votes
Accepted
Do I always need a tuner at both ends of the transmission line or is that only for certain types of antennas/circumstances?
It is not normal to have and use tuners on both ends of a feed line.
The purpose of an antenna tuner is to provide an adjustable impedance transformation. The reason we want that transformation is so ...
- 25k
4
votes
Accepted
What happens to the signal level if the antenna has high SWR?
Let's say the antenna impedance on a given frequency is 100 Ohm, the feedline is lossless 50 Ohm, the transceiver input impedance is 50 Ohm. Between the antenna feed point and the feedline SWR = 2, 11%...
- 52.5k
4
votes
Tuner at antenna side versus transmitter?
To make a long story short, if you are using 50 ohm coax with a 50 ohm radio, putting the tuner at the antenna is higher efficiency because it reduces losses in the coax caused by high SWR.
However, ...
- 6,960
4
votes
Tuner at antenna side versus transmitter?
I'll add that a tuner is used for tuning, and tuning, for a single or small set of frequencies is often done at the antenna, usually by adding or adjusting a loading coil or adding a capacitive top-...
- 13.6k
4
votes
Accepted
How do you calculate the impedance of a parallel-wire balanced feedline (ladder line)?
Yes, wire diameter matters. Assuming the two wires are round and of equal diameter, the impedance is $\frac{120}{\sqrt{\epsilon_r}} \mathrm{acosh}\,\frac{D}{d}$, where $\epsilon_r$ is the relative ...
- 13.2k
4
votes
Accepted
Can I use 14/2 UF-B wire as transmission line?
The ground wire doesn't cause any major trouble, because it's in the centre, at zero potential, as you say. It does reduce the impedance of the line though, because it effectively brings the two live ...
- 12.2k
4
votes
Wave bounce inside a resonant antenna
Now our antenna creates a standing wave.
Nope, not a wave in the "propagating wave" sense. That's the fallacy here: there's not a wave propagating forth and back.
What is standing is indeed ...
- 17.4k
4
votes
longest practical feed line length
There's no limit, really. Losses at HF aren't very high, and you're basically just trading cost for low-lossness. I'd go the other way around:
Write down the maximum TX power you want to work at. ...
- 17.4k
4
votes
450-ohm ladder line fact vs fiction
Here's some theory as to why this matters...keep this in mind and decide for yourself when you should worry.
All transmission line (coax too, not just ladder line) works by forming opposing magnetic ...
- 6,960
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