tomnexus
  • Member for 6 years, 11 months
  • Last seen this week
  • Vancouver, BC, Canada
4 answers
5 votes
2k views
Do these look like amateur radio antennas?
13 votes

It looks like a fibre or telephone cable strung between buildings. It sets a good precedent for setting up your antenna though - if you can get access to the other rooftop at night, and a catapault or ...

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1 answers
4 votes
783 views
Why does Free space have the highest loss compared to other losses like atmospheric loss, feeder loss etc?
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12 votes

Free space loss is the power lost because it doesn't reach the receiving antenna. An example using an analogy is your eye, looking at the light from a light bulb. If you stand 10 metres away from a ...

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3 answers
8 votes
3k views
Were there any 6m handhelds produced ever?
10 votes

The Yaesu VX-5R had/has 50-54 MHz FM, 5 watts. Nice compact little radio! The VX-7 and VX-8 can also transmit 5 watts FM on 6 m, and 1 watt AM. None of the 3 will transmit SSB. It had a little ...

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2 answers
4 votes
256 views
What is proper procedure for asking for "distant" contacts on 2m FM on simplex?
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10 votes

One would usually call CQ DX, but on 2 m FM that would sound a bit odd. Also FM will be heard by many people close by, who will find CQ DX quite funny. You could simply call and explain what you're ...

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3 answers
10 votes
2k views
Can a 1:1 transformer be used as a protection from static electricity?
10 votes

A transformer can help and could also make things worse. I have some bad experience with this. The way that a radio is damaged by static is simple: Something charges up to a high voltage, and then ...

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3 answers
11 votes
2k views
What does the spark-gap do in a spark-gap transmitter?
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10 votes

The spark gap is a simple, low-tech way of generating high frequencies. It was the only way of generating them before valves and transistors were invented. As C1 charges up through R1, eventually the ...

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2 answers
9 votes
789 views
Can there be (long range) propagation of HF from satellites?
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10 votes

Satellites can and do use HF for communications. The first example would of course be Sputnik, which transmitted at 20 and 40 MHz. Amateurs use HF to communicate with satellites. According to Amsat, ...

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2 answers
5 votes
2k views
What is inside a 50 ohm termination?
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9 votes

It depends on the frequency range the termination is rated for, and the power handling required. High power and high frequency is very difficult. At HF, any old non-inductive 50 Ω resistor will do. ...

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2 answers
5 votes
159 views
Calculating satellite passes without an internet tracker?
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8 votes

The simplest might be to use an app. On Android, Heavens Above, a product of the 25-year-old website of the same name, stores the orbital elements of the satellites of interest, and does the pass ...

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1 answers
5 votes
127 views
How should two loopstick antennas be placed w.r.t each other to maximize transmission?
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8 votes

When they're very close together, aligning them end to end will give better coupling - think of them as coupled inductors or a transformer. You want the strongest magnetic field from one magnet, to ...

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2 answers
1 votes
208 views
Will transmitting on this antenna cause problems?
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8 votes

It won't work very well. antennas often work well if they're on a third harmonic of the transmit frequency This is calculating the third harmonic the wrong way around. A better statement would be ...

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1 answers
5 votes
444 views
How different is Q-factor of SMD inductor from regular one?
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8 votes

SMD chip inductors, compared to larger ones, will generally have: lower Q higher DC resistance higher SRF lower DC saturation current, if they're ferrite cored But read the datasheet and see if they'...

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2 answers
6 votes
4k views
Tuning/trimming a ground plane antenna
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8 votes

My trick is instead of cutting, rather extend the whip first, and see if the SWR gets better or worse. Extend it 1/2" with a bit of wire wrapped around it and sticking out. If the SWR gets better, ...

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1 answers
2 votes
70 views
Link Budget - Are there any restrictions in the formula?
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7 votes

The Antenna Gain in the formula is the far field gain - at an infinite distance, or at least far enough that the antenna is indistinguishable from an isotropic source or a dipole. When you're close to ...

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3 answers
2 votes
609 views
Do PCB antennas suit for NOAA and ADS-B?
7 votes

PCB is an appropriate and useful way of making antennas for higher frequencies, say from 900 MHz and up. My company made thousands of GSM antennas for window mounting (in the days of car-installed ...

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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?
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6 votes

Yes it radiates. How much depends on the lengths of the wires. The point at which you connect the coax to the two-wire line is a bit like a dipole feedpoint, with about half the voltage applied to it. ...

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2 answers
3 votes
76 views
Impedance miss-match short vs long section?
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6 votes

Hams usually send just one frequency down a transmission line (as opposed to say high speed data like HDMI). So it's much simpler to analyse impedance down the line, than look at the reflections. ...

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2 answers
6 votes
202 views
How much attenuation (dB) from a balun is expected?
6 votes

If you do it right, the bead(s) shouldn't get hot at all, and shouldn't add much loss. The impedance of the bead(s) should be about 10 x the impedance of the dipole. The current on the feedline with ...

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1 answers
3 votes
190 views
Transmitted audio coming out through my speaker
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6 votes

The manual, on page 56 says: TX monitor allows you to monitor the on-going transmission sound. This is convenient when you want to check the modulation sound quality of the transmission. In FSK mode, ...

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3 answers
4 votes
428 views
Is testing SWR *practically* less important for 2m/70cm than HF bands?
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6 votes

I would say in practice it is less important because hams use different types of antennas for HF and for VUHF. At HF, the same antenna is often used for many bands. The bands have large fractional ...

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3 answers
3 votes
322 views
Use (TV?) Log-Periodic antenna for VHF
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6 votes

I'm sorry to say that's not a simple log-periodic antenna, it's a hybrid monstrosity to meet some particular need. Guessing from the element lengths: 136 cm each side would work at about 50 MHz, so ...

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4 answers
2 votes
180 views
Why do we talk about common mode current from an antenna, but not from a transmitter?
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6 votes

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 ...

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1 answers
4 votes
436 views
How do I design a dual band LPDA antenna?
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6 votes

You're on the right track, just cut the middle out of an LPDA and see what happens. The benefit of this design is that by eliminating the middle section of the antenna, you can get slightly more gain ...

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2 answers
3 votes
136 views
Do MRI machines use the ISM band, and do they generate audible CW signals?
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6 votes

Medical MRI looks for the nuclear magnetic resonance of hydrogen, at around 1 or 2 Tesla, at about 100 MHz. NMR is a phenomenon of the nucleus, not the atom, it is different to anything involving ions ...

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4 answers
1 votes
3k views
Is the ground on the back of the Icom IC-7300 an electrical or RF ground?
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6 votes

It's all of the above: an RF ground a 12 V power ground a lightning ground, for what it's worth a chassis ground to prevent "buzz" on the chassis if your shack 0V is not earthed The manual says to ...

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1 answers
9 votes
347 views
Why bother to have a high power base station when mobile units are generally low-power?
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6 votes

The link is actually balanced, because the base station receiver has diversity gain. 2G and 3G cellular systems use two antennas at the base station (for each coverage direction). They are either ...

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3 answers
6 votes
408 views
What is the reason/origin of conventional US repeater offsets?
6 votes

Repeaters need to receive and transmit at the same time. The offset needs to be large enough to make it possible for the filters to separate the transmit and receive frequencies. In my opinion 600 ...

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3 answers
5 votes
265 views
Transmitting Morse Code as Tone vs. Carrier
5 votes

As a mode for communication, as you say, it's pretty redundant and inefficient. I've never heard of it being used seriously. Occasionally people might hold a morse code practice class and transmit the ...

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4 answers
5 votes
1k views
Are there any cons of running shack on battery?
5 votes

Possibly an issue with your HF CB rig is that the output power will be lower at 12.1 than at 13.8 or 14.0 volts. I've seen on 100 watt ham rigs that the final amplifier runs directly from the DC ...

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1 answers
5 votes
236 views
Failing to detect Hydrogen line with 105cm dish
5 votes

The sawbird H+ looks like a nice LNA, do you have the H+ H1 version? The plan version seems to be for 1542 MHz, "center frequency of the module is 1.542GHz with approximately 80MHz of bandwidth (-...

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