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1500 questions
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2 answers

Practical 80m vertical wire antennas without radials?

We'd like to install an antenna for 80m at our club/contest station. Our club, OH2K, is housed at a school, and we can't fill the roof with a radial mesh. The roof is not metallic itself, either. We already have a horizontal dipole, but would like…
oh7lzb
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2 answers

Are "end-fed" antennas really more multi-band than dipoles?

Several "end fed" antenna kits (including the ARRL's for example) include wording suggesting that they are useful as multi-band antennas. But does feeding a wire antenna highly off-center with a transformer/balun/unun actually allow it to radiate…
hotpaw2
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How does a Large Loop Antenna work physically?

I am learning about loop antennas at the moment. I read that the response of a small loop Antenna is proportional to the rate of change of magnetic flux through the loop which causes a uniform current distribution in the loop. This would be…
kinu
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7
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1 answer

Can we use UHF/VHF ham bands for search and rescue missions?

Suppose that several licensed amateurs are part of a volunteer search and rescue team. The team is normally licensed and carries equipment to communicate on a variety of public safety bands in VHF/UHF during missions and training, and we are allowed…
crasic
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7
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7 answers

Why is 20m band waterfall showing signals every 50 kHz?

I'm very new to shortwave listening and just got to grips with my RTL SDR HF dongle. Last night while on the 20m band, there were signals exactly every 50kHz, starting exactly at 14.000MHz, then at 14.050 MHz, 14.100 Mhz and so on. Google said they…
rcx935
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1 answer

Is it ok to use a length of wire as an RX only antenna to test my new radio?

I have almost finished building my first shortwave transceiver kit (mcHF). Remarkably it's fired up and not gone up in a puff of smoke. The kit still needs some finishing off and I need to decide on an antenna solution, but in the mean time I'd…
rcx935
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Why ferrite-core transformers are wideband while air-core are not?

While experimenting with end-fed antennas I've made two 1:49 transformers. The first one has an air core, as shown in the article by John, M0UKD. This transformer doesn't even work as a transformer until you add a capacitor in parallel to the load.…
Aleksander Alekseev - R2AUK
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Simple circuit for acceptably clean CW in homebrew TX?

I'm working on a design for a home-brew 10 metre transmitter for CW. My oscillator is running cleanly, and I need to add a (small, probably 1/2 ~ 1 Watt) power stage to it, and I need to "modulate" the signal--i.e. turn the output on and off :) I…
Toby Eggitt
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Are there any active ham satellites orbiting that use the 5cm band?

I see that 5cm is available for satcom in amateur radio. Are there any active satellites for that? If so, what satellites and are their TLE's available?
KJ7NLL
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7
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4 answers

If I tie antenna wire in a knot, will there be damage to the wire?

I'm building HF kits 80m EFHW kit, and in the instructions it directs you to tie a knot in the antenna wire. I'm concerned of damage to the wire. I have found no source as of yet that indicates if damage will or will not occur. I am using their…
Erik Rusell
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7
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3 answers

What is a "direct sampling superheterodyne" receiver?

Browsing the specifications for the IC-7300, I noticed it says the receiver system is a "Direct Sampling Superheterodyne" with an IF of 36 kHz. I was confused by this, since I thought "direct sampling" means the received RF is amplified and…
Phil Frost - W8II
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7
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HF SSB etiquette when someone is working quick but not contesting and you're not sure they got you?

When someone is working quickly -- clearly trying to work a lot of stations -- but pretty clearly isn't contesting, what's the etiquette when they 73 you and end the contact but you're not sure they were talking to you? To be specific, I'm listening…
QuantumMechanic
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7
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1 answer

Efficient BPSK31 amplification

I'm looking at making a portable system that can transmit BPSK31. I have a limited power budget, so I'm looking at trying to make my final power amplifier as efficient as possible. From my understanding, you can't use a plain non-linear amplifier…
W5VO
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7
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2 answers

Doppler Shift Compensation in Inter Satellite Communication

I am currently doing a project in the area of optical inter-satellite communication (GEO-LEO). I am using a optical carrier of 281 THz, and the Doppler shift corresponding to it is ±7 GHz. I introduced this Doppler shift in the transmitted signal…
Seetharama
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5 answers

Why are an antenna’s nulls sharper than its lobes?

Why, for realistic directional antennas, are its nulls sharper (deeper, narrower, etc.), than the radiation pattern’s lobes (local angular maxima)? Is there some physics or mathematical geometry to EM fields that requires this to be true? Or is…
hotpaw2
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