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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5
votes
1answer
2k views

maximum acheivable range on CB radio by ground wave? [duplicate]

I have 10 watt CB radio system & 0.64 lambda monopole antenna , I think it has a 5 dBi gain . what is the maximum acheivable range by ground wave in an urban area ? If I want to increase my ...
3
votes
1answer
267 views

Recommendations for starting out with HF for an amateur

I'm a beginner who's nearly half a year from receiving my ham license in India. I want to start with HF radio and wish to build my own rig. Currently I have looked and multiple designs using the ...
3
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2answers
1k views

Longest achievable ground wave range on 40-meter bands [closed]

What is the longest possible range on the 40-meter band by ground wave? A reference said we can achieve 150 miles at 8 MHz with only a 100 watt transmitter. It also says on 160 meters, the ground ...
2
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2answers
906 views

High data rate on HF & MF bands

Is it possible to transfer data at a high rate, like 1-2 Mbps, on 0.5 - 30 MHz? From Shannon's Theorem, with a bandwidth of just 300 kHz it is possible to reach 1.5 Mbps. I want to use these bands ...
10
votes
4answers
562 views

Why are commercial SDRs so limited in operating frequency?

I spent a bit of time researching SDRs, mostly looking into the possibility of building an all-FPGA-based TRX. There are a lot of commercial ready solutions; some are cheap, some not, but they all ...
8
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3answers
1k views

Using ham radio bands for telemetry

If I built a machine that went far away, say a buoy, would I be allowed to use ham radio frequencies to transmit telemetry data back to its base station, if I used my call sign? This is for personal ...
3
votes
5answers
728 views

How does one know when band conditions are optimal and what factors to consider?

On many of the DX sites, one will find many variables for solar weather to include flux, A, K, sunspots, etc… I’d like to know how to read those and know what to look for. As I understand it, the sun’...
3
votes
1answer
1k views

recommended capacity bottom-hat clearance above metal roof

In a few days I'm expecting to mount a Cushcraft R7000 multi-band (HF) vertical antenna on top of a metal mast that will be attached to the outside wall of a large metal shed. The aim is to have the ...
1
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2answers
2k views

How to make a loop antenna for HF?

While researching this answer, I came across information that indicates that a many good Low Frequency/ Very Low Frequency antennas are loops, with high directionality and good overall characteristics....
23
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2answers
58k views

Which HF bands are best during the day and which are better at night?

I am rather new to HF operation and have recently purchased my first HF rig. I have read about bands being "open" and "closed" based on various conditions including time of day. As I have been ...
3
votes
2answers
2k views

What makes JT65 preferable for VHF, and JT9 for HF

Are the bands really that different in characteristics where JT65 works better for VHF, and JT9 for HF? The claim comes from the WSJT website: JT65 was designed for EME (“moonbounce”) on the VHF/...
3
votes
1answer
577 views

How to connect this Active Antenna Loop and 100MHz Upconverter?

I have bought the two devices in the image. The 100MHz Upconverter with a SMA connector is used to upconvert HF/MF signal for RTL-SDR to demodulate. I found that there is signal from the antenna (...
20
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2answers
3k views

Why do we use LSB below 10 MHz and USB above 10 MHz when operating SSB HF?

As a relatively new ham operator, I understand that it is customary to use lower-sideband below 10 MHz and upper-side band above 10Mhz when operating single-sideband HF. I'm curious how we got to such ...
2
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2answers
230 views

Technician Class HF Privileges in the USA

What are the current privileges below 30 MHz for holders in the United States of a Technician class license?
4
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1answer
328 views

How to avoid Bluetooth intereference?

I'm thinking about dropping a bluetooth module into my Softrock receiver so I can use it with my computers and portable devices wirelessly. The receiver runs from 1.8MHz to 30MHz, and the bluetooth ...
5
votes
5answers
2k views

Simple DIY AM receiver for 25/28 MHz

I'd like to build a simple AM receiver for 25 and/or 28 MHz to receive DCF77-formatted time code. It doesn't have to be extremely sensitive or selective - the local clock oscillator will keep time ...
15
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2answers
8k views

What does a noise blanker really do, and what are the side effects?

Most HF rigs have a noise blanker (NB) feature. It does reduce some types of noise (car ignition noise and such). How does it really work? I've read it has negative side-effects with strong signals, ...
3
votes
1answer
616 views

Why are loop antennas placed horizontally in HF

I am thinking of a large (circumference $\approx \lambda$) loop antenna at low (HF) frequencies. At higher frequencies the loops are used as quad antennas that have relatively high gain towards the ...
6
votes
2answers
111 views

During a radio contest, how do I determine if a station is “too faint” to be worth trying to contact?

Suppose I hear a station during a contest that is an eligible contact, but not necessarily a multiplier (worth points, but only a nominal amount of points). This station is relatively faint, (maybe 2-...
8
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1answer
155 views

How do I maintain my frequency during a contest?

Suppose I am operating a busy HF contest, and I have found an open frequency to call CQ. I make a number of contacts, and then suddenly another station starts to call CQ right on top of me. The other ...
10
votes
2answers
279 views

How do I find a frequency to call CQ on during a contest?

I know that in many contests, sitting on a frequency and calling CQ is a very effective strategy to rack up points. However, during very popular contests it can be very difficult to find an open ...
9
votes
5answers
26k views

Is there a simple, DIY, antenna suitable for HF receive only?

So the antenna I'm thinking about doing might be* way too large for my property. Is there another simple, cheap, DIY antenna I could try on my receiver? I know I'm going to want to hook it up and ...
4
votes
2answers
882 views

What impedance matching do I need between my 300Ω feedline and Softrock receiver?

I will be assembling a Softrock Ensemble II HF receiver, and I know I'm going to want it on air as soon as I build it, so I'm challenging myself to build an antenna for it first. The plan is to do a ...
4
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2answers
198 views

How would one automate HF communications to a specific location?

There appears to be some significant interest in establishing a fool-proof* HF communications method for location to location communication regardless of current propagation conditions. Given that ...
1
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1answer
86 views

Preferred signal report format for Digital Voice?

When using FreeDV or other digital voice modes, what's the preferred signal report? The software has a single SNR number, but that fluctuates quickly. Since it's a digital mode, you either get the ...
5
votes
1answer
200 views

How to obtain raw data for Global Real Time foF2 Map

Note!!!!: I am not looking for help with how make a map using Google Maps API (that part is done). I need help with finding data. I am building a shortwave radio/HF listening log book online, and it ...
3
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2answers
1k views

Which HF transceivers feature a built-in Ethernet port for remote operation? [closed]

I would like to compile a list of HF transceivers that feature an Ethernet port (RJ45) for remote internet operation. It would also be interesting to add the supported operating system(s) for remote ...
6
votes
1answer
9k views

How to determine antenna height for given HF frequency and coverage radius?

I'm planning on setting up a low-HF antenna for near to mid-range contacts. In my particular case, ideally I would like to be able to cover a radius of approximately 1000-1200 km with good ...
17
votes
3answers
2k views

What is a “random wire antenna”?

Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system? From everything I have heard, the resonance of the antenna (...
4
votes
1answer
735 views

How can I generate a list of APRS IGates on 30m?

I am investigating using a Tiny Trak 4 with my portable HF radio to self-spot on SOTA activations via APRS on 30m. I usually self-spot via a text message. When I don't have any cell coverage, I can ...
9
votes
2answers
303 views

How does the South Atlantic Anomaly affect propagation in the HF bands?

At ~34ppt the Southern Ocean is significantly less saline than other major water bodies (Arctic Ocean excluded). The Southern Continent also shares proximity to the South Atlantic Anomaly - where the ...
9
votes
2answers
226 views

How are multiple-operator contest stations with one radio usually operated?

I am the president of a small school club. We plan an participating in the ARRL SSB Sweepstakes this weekend, which is our (new) club's first real multi-op contest effort. How do multioperator/club ...
28
votes
6answers
29k views

Can I reduce RFI/noise at the antenna?

Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands. When the power grid ...
10
votes
2answers
3k views

How to reduce RF in the shack when using vertical HF antenna (no radials)

What can be done to reduce RF in the shack (riding back along the coax) when using a vertical 10M antenna (without radials due to space constraints)? The antenna is an IMax-2000 at 32' elevation (20' ...
16
votes
4answers
18k views

What bands and modes will give me voice at 3,000 miles?

I pursued Amateur Radio primarily for local emergency communications and as part of my electronics education. My only radio right now is an inexpensive 2m/70cm HT which is good for local weather ...
3
votes
2answers
345 views

Do electronic ballasts for fluorescent tube lamps cause HF interference?

I am going to build a new home and I would like to use energy-saving fluorescent tube lamps in some rooms. Manufacturers are currently pushing electronic ballasts a lot in favour of switchstart series ...
9
votes
1answer
143 views

Antenna modeling on non-uniform terrain

I'm interested in modeling the radiation pattern of wire antennas for hf before I invest the resources necessary to erect the antenna. I'm familiar with tools such as 4nec2, but from what I can tell ...
0
votes
2answers
311 views

Can we build an open source firmware for the X1M qrp transceiver [closed]

There is a chinese transceiver the X1M, look at x1m.wikia.com and on google. That is basically an SDR but no one has worked to build open firmware for it yet. i think we have a great chance to build ...
12
votes
4answers
1k views

What is generally considered “too much” power for JT-65 on HF?

Recently, I have begun experimenting with JT-65A, mostly on 20 meters. I usually run about 5 watts with that mode, since I know that JT-65 is a weak-signal mode. Is that still too much power? What is ...
11
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2answers
322 views

What would propagation look like on Mars?

If we could get a few HF stations on Mars, what would the propagation look like? Thought shamelessly copied from this blog.
6
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2answers
955 views

Does a tube based HF transmitter need an antenna tuner?

With the adjustments on a transmitter such as a Yaesu FT-101E, is there any purpose for an antenna tuner, or can you accomplish the same thing by adjusting the loading and other controls?
23
votes
1answer
5k views

Is there a way to listen to live HF communications using the internet?

I'd like to be able to show people what a QSO sounds like without having my transceiver available. Is there a way I can listen to amateurs talking in real-time (or using Morse code) on the HF bands ...
7
votes
2answers
1k views

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 ...
17
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8answers
25k views

Should I chose a vertical or a horizontal HF antenna?

If I only have the budget for one HF antenna, should I chose a vertical or a horizontal antenna?
8
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2answers
834 views

Vertical antenna on HF?

What are some of the advantages and disadvantages of using a vertical antenna on high frequency? Are there any better antenna types that I should use?
2
votes
1answer
796 views

What antenna to use for medium frequencies in an apartment building?

I'm living at the 6th's and top floor of an apartment building. I have a balcony with a metal balustrade. Above the balcony there is a metal roof rail. I need an antenna which won't be noticed by the ...
9
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2answers
3k views

HF Digital Mode Band Plan for the USA

I recently started playing with the digital modes, but have been frustrated with the difficulty in finding where certain modes are commonly used. Is there a digital mode band plan for the HF bands, to ...
11
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8answers
4k views

What is the best time of day/Band to make a contact with Hawaii from the East Coast?

I need to get Hawaii for Worked All States, and live on the East Coast (Virginia). Furthermore, I have a poor antenna, and thus only the prime times of the day seem to really be opened for me. What ...