# Tag Info

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
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 ...
• 50.2k
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### 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 ...
• 50.2k
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 ...
• 13.8k

### 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
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
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 ...
• 1,646
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### 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
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• 7,713

### 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 ...
• 50.2k

### 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 ...
• 1,646
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### 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
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### 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%...
• 50.2k

### 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

### 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
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### 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

### 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
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. ...
• 50.2k

### 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