New answers tagged

2

Yes, in my experience antenna measurements on a VNA are affected by external transmissions. They look like "noise" on the graph. Usually you can exclude them by eye - they're narrow and sharp while the antenna response is smooth. To make them smaller it helps to: increase the output power of the VNA reduce the measurement bandwidth turn on averaging. VNAs ...


2

The answer will depend on many factors. You've not given sufficient information to yield an answer, but the following concepts should help you arrive at your own answer. Firstly you must start with a link budget. The link budget determines how much power from the transmitter will arrive at the receiver. See What is a link budget, and how do I make one? ...


2

You can experimentally 'ball park' the location of the focus, visually, several ways, by using sunlight. One example -- some have temporarily attached (double-sided tape?) about a dozen one inch square mirrors in the dish, or reflective tape, from rim to center, and along say four radial lines from the center (if by the clock, at 12, 3, 6, 9 o'clock). Then ...


2

It depends on the gain of your receive antenna, your system noise temperature, and how much link margin you had in the first place. The moonbounce (EME) community use Sun Noise as a measure of their system performance, so the sun is certainly detectable by a modest amateur station. A quick Google search for "sun noise EME 144" yields this interesting ...


1

If you're OK with an approximation, the solid angle can be calculated with much simpler math. An isotropic antenna must radiate over a solid angle of 4π because it radiates in all directions. An antenna with a gain of (for example) 20 dBi has a gain of 100x, which means in the direction that gain is quoted, the power flux density must be 100x what it would ...


-2

AS A HAM FOR 59 YRS, 1. BYPASS THE INTERNAL "TUNER", AND USE A MANUAL (MATCHBOX, TRANSMATCH, COUPLER ETC) BOTH THE BOX ON UR DESK AND / OR THE ONE BUILT INTO YOUR RIG ARE NOT, ARE NOT, ANTENNA TUNERS. WHEN YOU CUT A DIPOLE FOR 7.25 MHZ AT 64.55' YOU HAVE "TUNED" THAT ANTENNA. CHANGE YOUR FREQUENCY, YOU MUST CHANGE THE LENGTH OF YOUR DIPOLE. - THATS TUNING. ...


1

I recommend trying solder first, as suggested by a couple of other answers. That should give you a good electrical connection as well as some mechanical strength. If it doesn't go as well as you planned, put some foil HVAC tape over the joint. You should have enough inductive coupling that you won't need to worry about the conductivity of the adhesive.


1

First, I'd say that using both the tuner for the antenna and your built-in antenna tuner probably didn't hurt anything, but was most likely unnecessary. You would have a bit more efficiency if you put your internal tuner on bypass. Of course if you adjusted the whip's tuner at a particular frequency, and then changed the frequency, then you might have had ...


3

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 that the transmitter can work into the (usually) 50 Ω load it was designed for. If you have an antenna tuner located (only) at the antenna, then this is the ...


4

I see what your problem is. That's a 1.4 meter long, based-loaded, telescoping, end-fed vertical antenna. It has significant losses on 40 meters. Furthermore, all end-fed antennas require a good RF return, such as a resonant elevated radial or counterpoise. Since you don't mention that, that indicates to me that very little of your signal is actually ...


0

I would suggest overlapping the edges and using a adhesive such as JB weld. after the adhesive has set you can sand or file the seam to smooth out any squeeze out.


3

For very narrow gauge, as in the sheet metal used for the waveguide in a microwave oven I think it's a process involving a roller disc inside the waveguide making spot welds at the closest interval possible and doing multiple passes until it's continuous. People reviewing TIG welders on YouTube routinely weld razor blades together. Any thin steel that's ...


2

For really fine control of soldering, use a soldering gun as a resistance welder. Just cut off the end of the heating tip, so that instead of a loop you have two big copper wires coming out of the gun. Press them onto either side of the joint and pull the trigger. The current passing through the metal will quickly heat it to the point where it will melt the ...


3

I'm no expert on sheet metal fabrication and hopefully someone will come along with a more confident one, but in general I would expect that soldering/brazing is the correct answer. (solder in reality would be hard to do, it running all over the place or being lumpy.) From what I have seen of soldering large metal parts (with a torch, not an iron), with ...


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