Andrew
  • Member for 3 years, 1 month
  • Last seen this week
  • Melbourne VIC, Australia
2 answers
10 votes
948 views
What is the appropriate length of an antenna for a handheld on 2 meters?
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13 votes

These antennas don't always contain a simple straight length of conductor, but rather usually have coils of wire inside, so the actual physical length doesn't mean that much. They are designed so that ...

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2 answers
7 votes
316 views
How to reduce VFO sensitivity to the hand capacitance?
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6 votes

As mentioned in the comment by henryflower, make sure that the shaft (and thus the frame) of the variable capacitor are grounded. You need to use rubber mounting grommets around the screws which bolt ...

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4 answers
5 votes
2k views
Do these look like amateur radio antennas?
5 votes

The cable strung between the two buildings has two parts, a strong wire probably made of stainless steel or similar, then you can see some form of cable, as Tommexus said it's probably fibre or ...

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3 answers
11 votes
3k views
How can I get rid of RFI coming from my house solar panel inverter?
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5 votes

See below a summary of what i did to remove most of the RFI coming from my house solar panel system. Problem = horrid RFI across the entire HF spectrum. It's only there when the sun's out. The RFI ...

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4 answers
2 votes
234 views
I'm looking for an effective beam antenna for both 20 meters and 10 meters
4 votes

Engineer999. The driven element of a yagi antenna is normally a half wave dipole, and it's true that a dipole antenna is resonant on multiple harmonically related frequencies. An ideal 10 m long ...

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5 answers
5 votes
420 views
Grounding a vertical antenna from a balcony
4 votes

Engineer999. While it might seem like a good idea to connect your antenna to the building ground wire, my experience has been that for those vertical antennas which are designed to operate without ...

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2 answers
5 votes
314 views
Can an oscilloscope be used as an RF voltmeter?
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One of the functions of an oscilloscope is actually to measure RF volts, just make sure to use the x 10 function to minimize loading on the circuit you are measuring, and keep in mind that some high ...

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1 answers
1 votes
62 views
Boom length of a Yagi antenna
3 votes

The boom is the center supporting section which holds all of the individual reflector, driven element, and director elements. The mounting bracket for larger yagi antennas is normally at the center of ...

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2 answers
4 votes
70 views
Mounting a hex beam on top of a high urban building
3 votes

The general rule of thumb is that for antennas the higher the better. The height above ground in this case is an absolute advantage. Your ability to put an antenna on top of a very high building is ...

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2 answers
5 votes
119 views
Is tuning at all useful for an antenna that is already resonant?
3 votes

This question is more complicated than it seems. If the antenna in question is only being used at one frequency, and at that frequency the SWR is already low, then in terms of obtaining a good match ...

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2 answers
1 votes
859 views
Yaesu FT-817 Won't transmit on 160m to 6m
3 votes

Tim, what you have said provides a few clues to the problem you are seeing. Assuming that someone has not accessed the hidden menu which allows factory alignment of the radio, your problem is not a ...

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3 answers
4 votes
786 views
What is the capacitors purpose on a balun?
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3 votes

Adding a capacitor to a balun like that is not standard practice and is probably a bad idea. A bulun is supposed to be a somewhat frequency independent device which cancels out common mode current and ...

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2 answers
3 votes
489 views
Is an antenna resonant at the frequency of lowest impedance?
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3 votes

Marcin, as you have alluded to, an antenna is resonant when there is no reactance present in the impedance seen at the feed point for the frequency you are using. There is no reactance because at ...

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2 answers
1 votes
88 views
Beam antenna changed directivity
3 votes

I would suggest that one of the transmission line connections to the antenna, probably the earth if you are using coax, has become disconnected at the antenna feed point, and it's just a coincidence ...

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3 answers
1 votes
165 views
Why half-wave dipole is the most efficient one in comparison to other electrical lengths of that antenna?
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2 votes

The formula in the question is taken from page 44 of a book called The Theory of Electromagnetic Wave Propagation by CH Papas. The text says that the formula describes the radiation pattern for a ...

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6 answers
2 votes
689 views
For a half wave dipole antenna, what's the value of the reactances that cancel out when the antenna is resonant?
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2 votes

A resonant dipole antenna can be likened to a series RLC lumped constant circuit where the impedance seen across the two terminals contains zero reactance at resonance, and where operation at a ...

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5 answers
4 votes
225 views
Do modern radios and power supplies require grounding for safety?
2 votes

If a radio is powered by 13.8V DC and it doesn't have vacuum tubes in it then it doesn't require a ground for safety. The ground in a radio is only required for safety when there are voltages in the ...

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4 answers
7 votes
1k views
How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?
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2 votes

After all this time no one has actually provided a complete answer to this question so after some investigation i have answered it myself. Thank you to those people who did give answers however. The ...

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3 answers
3 votes
103 views
If a sealed, non-airtight pipe is used as antenna element, how big of a problem is condensate trapped inside?
2 votes

Despite the intuitive feeling that water somehow might make a metal tube more conductive or something, for an antenna made from hollow mostly sealed tubular metal, regardless of which metal the tube ...

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1 answers
3 votes
113 views
How can i adjust the IF strip in a single conversion SSB receiver which has a product detector?
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2 votes

It looks like no one is going to answer this question and in the mean time i've found out was what wrong anyway so i am posting my own answer. Firstly after some more thinking it became obvious to me ...

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5 answers
15 votes
58k views
Good wire for wire antenna?
2 votes

Don't believe the many myths in circulation concerning which wire to use for an antenna. Most of the myths over complicate this very simple subject. In reality, it doesn't make much if any difference ...

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5 answers
4 votes
102 views
Antenna tuner at the transceiver output confusion
1 votes

In the special case where transmitter output impedance, transmission line characteristic impedance, and antenna impedance are all the same, for example 50 +j0 ohms, then everywhere on the transmission ...

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3 answers
9 votes
178 views
Will there be common-mode currents if a coax followed by a ladder line is terminated in a dummy load?
1 votes

The characteristic of coax that causes current to split up between the load or antenna and the outside of the braid is the fact that the braid has two surfaces, inner and outer. Ladder line has two ...

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3 answers
3 votes
133 views
SWR of 1.5 -- use internal antenna tuner or not?
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1 votes

For transmit, compared to a perfect SWR of 1:1, an SWR of 1.5:1 will give about 4 % loss of power radiated by the antenna due to reflections at the antenna / feed line junction. All other things equal,...

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2 answers
1 votes
38 views
Sealing connection between mobile antenna and mount
1 votes

Brass and stainless steel don't corrode hardly at all so you don't have to do anything in this instance. I would just leave as is and then every year or so clean out the accumulated rubbish with water ...

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6 answers
6 votes
339 views
If receive performance doesn't depend on SWR, then how can I tune my manual HF antenna tuner by band noise?
1 votes

As per Phil's answer, the idea that a matched system is most efficient from a system level perspective is undeniable. However, at VHF and UHF the receiver noise is well above the noise received by the ...

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1 answers
1 votes
149 views
Yagi performing far worse than a dipole
1 votes

It doesn't makes sense that a 6 element yagi doesn't work a good as a half wave dipole. Even a 6 element yagi with the worst design should still work better than a half wave dipole. I don't think the ...

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3 answers
1 votes
453 views
Wiring Cobra 29LTD CB for home use?
1 votes

Galaxy, there are a number of things to watch out for when connecting power to your Cobra 29LTD AM only CB radio. The power supply must be a regulated DC power supply, which outputs between 12 and 14 ...

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3 answers
1 votes
123 views
can I still hear a frequency if I can only tune in 5 kHz off?
1 votes

Jefferey, this is a very easy question to answer, and the answer is no. The Wallops Island telemetry transmitter is probably going to be a narrow band FM signal, and 5 kHz off is too far to be able ...

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3 answers
4 votes
332 views
Heathkit SB-102 Plate Current out of control
1 votes

Zeiss, the first step in fixing any radio is usually to check the power supply levels. If the power supplies are wrong then nothing will work properly. I would do that first before doing anything else....

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