9 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 ...
  • 8,942
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 ...
8 votes
Accepted

What happens in a low loss feed-line with a high SWR

For many modulations, the modulation is very slow compared to the propagation delay of the feedline. For example, SSB is typically limited to no more than 4 kHz. That corresponds to a wavelength of of ...
8 votes
Accepted

Why isn't twisted pair used for feedlines?

Balanced lines (of which twisted pair is a special type) really have an upper frequency limit; you can't use them to transport 1 GHz (well, you can, but the smallest variation in direction or distance ...
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 ...
  • 18.2k
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 ...
  • 940
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 ...
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 ...
  • 8,340
5 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: $$ -...
5 votes
Accepted

Why must twin-lead conductor spacing be small to avoid radiation?

Twin-lead transmission lines don't radiate because the opposite fields from each conductor cancel, but when the spacing is far apart this does not happen. First, let's consider the magnetic field ...
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, ...
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....
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 ...
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,...
  • 12.6k
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 ...
4 votes

Which is better in my situation: Balanced dipole, or as much wire as possible in the air?

I think in practice you'll find it doesn't make much difference as long as there's a common mode choke or "current balun1" at the feedpoint. In fact, if you get it off-center in just the right place ...
4 votes
Accepted

Connect Printed Yagi-Uda Dipole Array with Balun to coaxial cable correctly

I'm no expert on balun designs, but I think they mean to construct a folded balun, as follows. The coax's outer conductor is soldered to the same part of the antenna, but it is left on the coax, not ...
  • 23.2k
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 ...
  • 899
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 ...
  • 7,713
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 ...
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 ...
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 ...
  • 23.2k
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%...
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, ...
  • 4,508
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-...
  • 12.6k
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 ...
  • 9,552
3 votes

Balun and tuner configuration for multiband dipole

You might find some advantage to using a Slightly Off-Center Fed Dipole, as described in QST for September 2019. Feeding a single wire through a 4:1 step-down balun 45% from one end produces a usable ...
  • 7,713
3 votes
Accepted

Switching 450 Ω window line

Would soldering Power-Pole connectors to segments of window line create impedance problems? On HF, no. The significance of an impedance mismatch is proportional to its size in relation to wavelength. ...
3 votes

Use a TV coax and balun for a poor-man's OCFD?

Just Do It! :-) You should build it with those materials you have. What have you got to lose? I believe it will exceed your expectations.
  • 7,604
3 votes
Accepted

Is there a lower limit to the usable frequency for PCB 'stripline' feedline?

Microstrips should in theory work just fine at low frequencies, as Z0 is independent of f. The advantage of microstrip technology becomes clear at high frequency when it is practical, and often easier,...
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