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1500 questions
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votes
2 answers
Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?
A quick follow-up to this answer
... If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ...
I'm sorry to be so dense, but uh why is the risk of damage to the Tx due to an antenna mismatch…
VU2NHW
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9
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Hardened UHF Antennas
Minuteman missile silos used an interesting hardened UHF antenna.
What kind of antenna is this? Does anyone have a drawing with a cross section?
Edit:
Jay Moore added a picture to a different type of hardened antenna, the truncated cone in the…
Olg
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9
votes
5 answers
What limits a PIN diode or varicap from being used in a "Software Defined [Radio] Filter"?
A PIN diode varies its capacitance based on a DC bias, and a Varicap exhibits this effect even more clearly. What limits the use of "solid state variable capacitors" like these for dynamically filtering (low power/received) RF signals?
The question…
natevw - AF7TB
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9
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2 answers
Why is an RF ground not as critical as the other, and can they be used backwards?
I will give the magmount antenna as an example:
The vertical element to the antenna is very critical, cut to a certain wavelength, often added with some loading coils, or a little spiral to make everything perfect for the specific frequency.
The…
Skyler 440
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9
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1 answer
How effectively do modern transmitters protect against high SWR?
The following are fairly common knowledge:
Transmitting at full power with too much of an impedance mismatch can damage your finals.
If we do so inadvertently, modern radios drop the power significantly for self-protection.
Yet, it's still very…
Dominick Pastore
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9
votes
2 answers
How to effectively test and interpret the "working range" of a ferrite core with a signal analyzer?
I have a couple of ferrite beads that are advertised as effective for suppressing conductive noise around 150kHz. I'm trying to monitor their actual performance with noise filtering.
In my set up I have a ferrite core which I made a number of turns…
GHGC
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9
votes
2 answers
When would we ever want to use a voltage balun in ham radio?
In a world where common mode current is the enemy, and we're constantly doing what we can to avoid RF in the shack, why would we ever choose a voltage type balun over a current balun?
I understand that, in general, one uses a voltage balun to keep…
Paul
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9
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2 answers
Importance of Ferrite Size in Coax Choke Balun
The question is quite simple: When making a coax choke balun, does the size of the ferrite matter, and if so, why?
I have seen design notes that say to use a single FT240-43 toroid for powers up to 400W, and then to use two stacked FT240-43 toroids…
M1GEO
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9
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1 answer
Why are there no amateur allocations in the LF and VLF spectrum?
Amateur radio enthusiasts have slices of spectrum at every magnitude of spectrum MF and above, but in the US none are below MF.
Why are there no spectrum allocations below 160M?
Adam Davis
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9
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2 answers
Who enacts the FCC's rules and regulations?
I came across an old answer on this site which makes the claim:
It would take an act of Congress to change this [FCC Part 97] rule.
Is that correct? I was under the impression that United States Congress had delegated authority over civilian…
natevw - AF7TB
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9
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1 answer
Calculating the signal-to-noise ratio for CW (Morse Code) signals?
How is the signal-to-noise ratio for received CW and QRSS CW (and/or other ultra narrow-band DSP digital modes) typically computed? e.g. What noise bandwidth should be used to measure the spectrum power against the narrow CW "on" signal power?…
hotpaw2
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9
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1 answer
Musty smell in old equipment
I recently came into possession of number of old ham radio and a variety of old test equipment. Items from to 1960s to the 1980s. Several of the items have a strong musty smell. What can I do to get rid of the smell without damaging the items?
Keltari
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9
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1 answer
Antenna RX vs. TX
If I only want to receive radio signals and not transmit, are there any differences in the way I design the antenna I need to use, or is it the same either way? I was going to pick up a Realtek RTL2832U and use it as an SDR, but it has an antenna…
Jason Petrilla
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9
votes
5 answers
Is a Technician license enough to assist in times of emergency?
Is a Technician license enough to assist in times of disaster/emergency or do I need General or higher?
Timtech
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9
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2 answers
Are satellites Left or Right hand circularly polarized?
I'm thinking of building some helical antennas for satellite work. I want to know which way to wind them.
If satellites are spinning randomly, how can we know if they are left hand or right hand polarized or
Which way do I wind my antenna
Skyler 440
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