Questions tagged [hf]

High Frequency is the frequency range 3-30 MHz. This tag may also be used for questions about the 160 meter band (1.8 MHz), which while not HF is often referred to as such due to its similar propagation.

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4
votes
2answers
101 views

Why a capacitor is needed in Fuchs antenna?

I tried to understand the physics of Fuchs antenna and there is one thing that I don't quite understand. This is probably a very silly question, but I spent a lot of time looking for an answer (books, ...
1
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1answer
67 views

EFHW works only on one band - what am I missing?

I tried to build a multiband EFHW antenna as described in articles by PA3HHO, PD7MMA, G0KYA and many others. I decided to start with a short 40/20/(15?)/10 meters version without any loading coils. ...
3
votes
2answers
88 views

House wiring as an antenna on HF and 2 meters?

The apartment I live in is a 1970s type without access to the outdoors. It does have a balcony. A 2m transceiver is the only radio which will enable me to reach the ham world. Would be possible to ...
2
votes
2answers
752 views

What is this burst transmission sequence across the entire band?

Fairly regularly on the 40m band I hear a quick blip of a tone, and when I look at the waterfall I see these brief transmissions all across the band that look like little dots. What is causing that?
9
votes
5answers
1k views

Will electrically joined dipoles of different lengths, at right angles, behave as a multiband antenna?

I haven't seen this done, (which, after more than a century of amateur and professional radio development, is probably a bad sign), but I had an idea the other day for simplifying the setup and feed ...
5
votes
3answers
273 views

What is the proper way to electrically wire in a loading coil to a vertical antenna?

I am trying to put together a vertical pole style antenna with a loading coil housed at the base using a plan very similar to the one described in this ARRL article. I am trying to understand how to ...
1
vote
0answers
59 views

Parasitic inductance of relay contacts

I need to switch a bank of filters operating on bands from about 2MHz to 30MHz. The parasitic series inductance of the relay contact system will have an effect on the performance of my system. ...
3
votes
3answers
146 views

How to splice RG-174 coax?

I'm pretty good at repairing broken regular coax, but I recently had an RG-174 cut and it's too small for me to solder the center wire and keep the braid away from it. What's a good way to do this? ...
1
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1answer
55 views

How to interpret VSWR results for an attic antenna

I have an Alpha Delta DX-EE antenna in my attic. The antenna is 40 ft long and my attic is about 5ft high by 55 ft long. There's a lot of other stuff up there--a chimney, Romex, Cat 6 cable, RG-6 ...
5
votes
3answers
74 views

How to measure wire for antenna leg | 40m inverted V

I am building the antenna for the first time and I have choosen to start with 40m inverted-v. I am almost done with the center insulator made of PVC piping elements, three eye hooks and SO 239 ...
5
votes
5answers
322 views

Loop antenna layout and radiation?

I've got, for the near term, limited resources to put up an HF antenna at my home. One of the options I can manage without excessive cost is a loop, which would enclose the house. I need to transmit ...
1
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2answers
103 views

Noise reduction

I live close to an AM transmitter broadcasting in the kW of power. My RTL SDR dongle gets very overloaded. Using 2 AM broadcast filters, I have mostly managed to stop the overloading, at least from ...
7
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4answers
153 views

Antenna options for a 10x20m property with a large metal roof?

I live in a house that sits in the middle of the city, in a lot 10x20m in size. The first 6x10m are covered by a metal roof with a rather low angle (IIRC only 50cm difference between the highest and ...
3
votes
2answers
75 views

Tips for HF Antenna with house near AM transmitter

My back garden is very small - about 500sqft. I also live near an AM transmitter and requires an AM filter. I would appreciate some general tips on the best approach to receiving HF signals (Ham and ...
3
votes
2answers
113 views

What are these antennas used for?

I noticed this antenna park in Heidmoosstrasse, Switzerland. What is it used for?
4
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1answer
246 views

What are Radio-location Services in the 1.9-2.0 MHz range?

I'm currently studying for the General Exam and in looking at charts of the new frequency privileges have run across a restriction I would like to have further defined. In the 160 meter band the books ...
3
votes
1answer
617 views

Where does the year 2019 fall in the sunspot cycle for HF propagation?

I am reposting this question about the year 2016 here. This is 2019. Are we now at the good or bad portion of the 11 years cycle? What effect are we seeing now? How large (strong/deep) is the effect ...
6
votes
3answers
189 views

Long range communication with just 1W of power?

Is it possible, and how can I setup communication between stations 1000km apart from each other by using just 1W of transmission power? By communication, I mean: It can be text based It can be very ...
5
votes
3answers
218 views

antenna in the rain

What kind of changes can be expected in the behavior (resonance, SWR, etc.) of a mobile vertical HF antenna between dry conditions and wet rainy weather? (assume a coax feed-line and low SWR in dry ...
3
votes
1answer
128 views

RTL SDR “dark region”

I'm new to RTL SDR, and I noticed there's a "dark region" (around 700-900MHz), and I haven't figured out why this is. My device's tuner is a Fitipower FC0012, where could I find the pinout and ...
5
votes
1answer
291 views

Why are the lower HF frequencies not working during winter day time?

Currently my location is Nepal. We use the ICOM f-7000 radios without the antenna tuner. We use the frequencies round about 5-9 MHz, for communication over distances between 150 and 400 km. During ...
5
votes
1answer
571 views

Do short waves pass through or reflect off concrete buildings?

I live in Moscow, Russia and use DIY indoor magnetic loop antennas to listen amateur radio. Recently I received quite strong signals from Italy (20m, IV3UTV) and Slovenia (40m, S51CK), both operators ...
3
votes
1answer
157 views

What is the minimum equipment necessary to get on the air with FT8?

To the extent that FT8 is a way to bring people into the hobby or re-ignite passion among those who haven't been on the air in a while, what's the easiest way to get someone on the air with this new ...
1
vote
1answer
61 views

BFO locked synchronous AM detection

I am fixing up an old classic Yaesu FRG7 general coverage AM/SSB/CW HF receiver. The BFO section is a rudimentry 455 kHz IFT configured as a carrier reinsertion oscillator that that is made to run USB ...
2
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4answers
437 views

What has happened to HF?

Has the HF spectrum become noisier over the decades due to man-made interference? Is this a reason why HF band activity appears to be declining?
3
votes
1answer
190 views

Understanding of NFC Reader Antenna matching

I have been designing a 20 x 20 cm square NFC reader antenna which looks like this: In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying ...
0
votes
1answer
105 views

NFC coil matching - Q factor improvement

I have been trying to match my NFC reader coil of size 20*20 cm with a three element circuit - one capacitor in series, another in parallel and one resistor in parallel. I have been using Texas ...
3
votes
5answers
292 views

How should I select an HF antenna for portable work?

I'd like to get started doing portable HF work and I'd like some information on antenna possibilities. My broad (and somewhat flexible) criteria are: By "portable" I mean it can be carried in a ...
6
votes
2answers
271 views

Why don't monolithic HF transceiver ICs exist?

HAM operators who build their own HF rigs typically do so using discrete components. However, for VHF and UHF rigs, an operator can make use of monolithic transceiver ICs on the market For example,...
5
votes
5answers
419 views

How important is the impedance and resonance of a receive antenna?

I'm very new to shortwave radio, as evidenced here: Can an antenna be too powerful for certain receivers? I want to build a longwire receive-only antenna for the HF frequencies. I've been using ...
3
votes
4answers
7k views

When will propagation on HF improve?

Will the propagation on the High Frequency bands come back up soon?? I am referring to the 3 to 30 MHz range.
3
votes
2answers
260 views

Not-too-distant saltwater ground

Problem I'm planning on mounting a vertical HF multiband antenna on the edge of my roof. Due to the presence of a paved walkway and some other similar property constraints, I have no room for ...
5
votes
1answer
140 views

What are these continuous sine wave tones I keep hearing?

I'm messing around on WebSDR and by just scanning through I sometimes come across these continuous tones in USB. One in particular was 28.800 MHz USB. I've picked them up on nearly every WebSDR unit ...
3
votes
3answers
293 views

Suggestions for mounting a mini-whip as high as possible

I've ordered two mini whip antennas from Ebay (Russia) for HF and MW. As power lines cross my city property in a L shape - the only way to get away from them is to go up. So I'm hoping that going 5-...
5
votes
2answers
229 views

How is it possible for an HF signal to go around the world when part of it must be in sunlight?

I believe most of us know about the ionosphere, and skywave propagation, but I'm kind of tripping up on the D-layer. If the ionospheric D-layer absorbs HF signals (40 meters, for example) during the ...
2
votes
2answers
311 views

Apartment antenna and rtl-sdr with upconverter

I'm just starter. I bought MFJ-1622 40-2M APARTMENT ANTENNA (I don't have access to the roof) I only have RTL-SDR with Upconverter (I'm on budget). I living on 10th floor and I will use it from my ...
2
votes
1answer
62 views

Alinco DX70 TH at 10W

Is it possible to make the Alinco DX70 TH operate at 10W PEP? The radio seems to be 100W and I read somewhere that you could switch it to 50W, but since my licence currently limits me to 10W, I'd like ...
6
votes
3answers
2k views

Is 20m noisy, or do I have a lot of local interference?

I'm making my first ventures into HF with a Yaesu FT-450D and a homebrew 20 Meter inverted-V antenna a local ham helped me set up. I've noticed that the 20 Meterm band seems to have lots of ...
5
votes
2answers
766 views

How to transmit images and video through a hurricane?

Background You're in the path of a hurricane, and the eye just passed over your head. There is no electricity (apart from your own generator or battery), there is no mobile network and there is ...
3
votes
1answer
105 views

How much leeway does an antenna tuner give me?

As far as I can tell, currently a 20m dipole has to be within a few inches to have a reasonable SWR without a tuner. How does this change with one? Does it depend on what tuner I have?
2
votes
5answers
330 views

What happens if an HF dipole is made longer?

Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?
5
votes
3answers
464 views

HF antenna design for high-altitude balloon

I'd like to put a WSPR or JT65-like transmitter on a high-altitude balloon, but lacking much experience with HF antennas, I don't quite know where to start. I'm thinking it will operate on 20 meters, ...
15
votes
7answers
7k views

What is the cause of this unusually long period of terrible HF band conditions?

I've been a ham for over 40 years, but never has there been such a prolonged period of such poor propagation. This has been especially the case over the past six months or so, and they continue to ...
2
votes
1answer
109 views

Signal on various frequencies, about 2.5k bandwidth, sounds like a broken motor turning: What is it?

There are a number of frequencies, where a certain type of signal can be heard. The characteristics is, that every occurrence takes about 2.5k bandwidth, and it is transmitted in a continuous way. ...
4
votes
2answers
154 views

Is using a DDS chip directly a viable way to transmit 2FSK and PSK on HF?

I'm thinking of building an HF transmitter for data (AX.25 or PSK31). Rather than using an IF stage, I'm thinking of generating the RF frequencies (or phases) directly with a Direct Digital Synthesis ...
9
votes
3answers
535 views

Stealth HF station setup advice

I need some advice on setting up my first HF station in a somewhat restricted townhouse community. If I had a detached house with a backyard I’d probably already have everything setup. But with this ...
2
votes
2answers
228 views

(HF) How to maximize probability of successful transmit given constrained packet duration? [closed]

I need a HF link that will be (mostly hah) operational 24/365. Edit: at least at local daytime. The link is supposed to transmit a controlling signal (just one bit) in one direction for quite a ...
4
votes
2answers
207 views

Very odd and wide 30m signal. What is it?

A local ham friend copied this strange, wide signal on 30 meters on his Flex 5000. Anybody know what it might be?
2
votes
1answer
657 views

How do I go about identifying an unknown digital signal?

I'm playing around with an SDRPlay. I'm using the CubicSDR app, and I'm tuning around the HF bands. I get to 5.650 MHz and I see this: This looks like a bunch of discrete RTTY signals. How would I ...
6
votes
7answers
4k views

Is a ground plane necessary for transmitting and receiving with a vertical (monopole) antenna?

I've read the post here: https://electronics.stackexchange.com/questions/77256/why-do-some-radio-antennas-require-a-path-to-ground-and-some-do-not which says The antenna system requires a "ground ...