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
165 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
382 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
272 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
348 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
69 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
910 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
107 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
485 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
521 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
8k 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
110 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
169 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 ...
10
votes
3answers
596 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
233 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
218 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
778 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
5k 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 ...
13
votes
8answers
2k views

Why are Wullenweber CDAAs obsolete?

Wullenweber circularly-disposed antenna arrays (CDAAs) are large HF direction-finding antennas, sometimes colloquially referred to as "elephant cages", that were popular in the Cold War. They allowed ...
0
votes
2answers
709 views

what are the alternatives to LM387 and SA602AN?

I am building a 20 Mhz RF receiver out of the NASA radio JOVE instruction manual and they have recommended the use of LM387 as an audio amplifier. SA602AN as mixer IC:
2
votes
2answers
235 views

Highest Q loading Coils

The loading coils for electrically short MF and HF antennas that I have seen over the decades are all air cored. Ferrites have got better but air has not .Clearly a ferrite cored coil would be smaller ...
8
votes
2answers
2k views

How to do APRS in real wilderness?

I'm a relatively new ham (licensed a couple of years ago, occasional activity on 70cm and 2m, mostly repeaters). I'm looking to extend my ham experience and am interested in digital and packet modes. ...
3
votes
4answers
750 views

Is it normal for mini shortwave radios to not have any reception in a major city?

I'm new to radios. Just bought the mini Eton which has FM/AM/SW and while FM & AM work I have never received a single station on SW1 (5.9 - 10 MHz) or SW2 (11.65 - 18 MHz). Is that normal? Will ...
8
votes
1answer
2k views

What's the difference between “maximum usable” and “critical” frequencies?

In discussing HF ionospheric propagation, you hear about both "critical" and "maximum usable" frequencies. For example: Above the critical frequency, the ionosphere is unable to refract the signal ...
6
votes
2answers
7k views

Where year 2016 falls in the sun spot cycle for HF propagation?

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 during the peak and bottom of cycle? What will change in coming years?
3
votes
1answer
108 views

RF fading channel model?

What statistical or other descriptions exist regarding modeling of an HF-band RF fading channel? This is allow making (as in code my own software) lots of simulated test input signals for an SDR ...
2
votes
1answer
228 views

AN762 Amplifier Transistors

According to the MRF421 or MRF454 transistor datasheets, used in the AN762 HF amplifiers say that the transistors are "100% tested for load mismatch at all phase angles with 30:1 VSWR". Further, in ...
5
votes
4answers
4k views

What is propagation like when there are no sunspots?

Am considering getting my license again after raising kids, and wondering if there is any point in HF operation besides local chats — that is, what is propagation like when there are no sunspots?
3
votes
1answer
221 views

Are there many analog (AM) shortwave broadcast stations left?

I'm considering hanging a long wire this spring and trying to get my 13 y.o. son interested in radio as a Scouting activity. Has everything gone to DRM these days, or is it worth dusting off my HQ-...
3
votes
2answers
448 views

Antenna gain vs. radiation efficiency in 4nec2

I'm trying to evaluate HF antennas for low angle performance to pick from a list of designs that will fit in my limited space. I'm using 4nec2 to simulate them and compare the patterns. When your ...
8
votes
3answers
1k views

What is the origin, history behind “Ben's Best Bent Wire”?

Bens Best Bent Wire My uncle, who was a Merchant Marine in WWII used to tell me this. He was a ham, and said it would develop my fist musically. I was a small child at the time, and through his ...
5
votes
3answers
1k views

Running ladder line through window from inside shack to outside dipole antenna - what to watch out for?

For HF operating, I am considering running a ladder line from the ATU just inside a window, through the window (squeezing it between the window and the window frame; not actually through the glass), ...
7
votes
3answers
1k views

Why do I only hear broadcasts from 150 kHz to 29.999 MHz?

I am currently studying for my amateur radio license. Until I'm licensed, I'm trying to use a Sony ICF-SW7600GR receiver to listen in on amateur radio "phone" transmissions. No matter what I do, ...
3
votes
2answers
217 views

What are some shortwave radio stations I ought to reliably receive in New Hampshire?

I recently bought a Techsun PL-660 radio and it picks up virtually nothing on SW. I fear I may have a dud.
5
votes
2answers
3k views

Is there good antenna for 160m Band?

I live in Japan. Japanese houses are very narrow, but I want to try 160 m band. Is there good antenna for 160 m band? I want to operate HF (160m~10m) bands. Now I use vertical antenna (40, 30,20,15,...
5
votes
1answer
216 views

Does a low amount of atmospheric noise reliably indicate a lack of propagation?

We know that the primary source of interference at HF is atmospheric noise. Thus, all else being equal, the strength of heard noise is a fair indicator of RX system performance (such as in adjusting ...
6
votes
3answers
1k views

How to stop interference on shortwave radio when connecting to a computer

I have a Tecsun PL-600 and when I can receive clear signals, and they come through just fine on headphones, and through the speaker. If I'm trying to receive RTTY or fax, when I connect the radio to ...
3
votes
2answers
959 views

Dipole versus ungrounded end fed for HF RX

I've built a 2 meter ground plane antenna that works pretty well for RX and has a decent SWR on 2 meters with my Alinco. However, I'm experimenting with SDR quite a bit and would really like to build ...
12
votes
3answers
463 views

What are the relative bandwidths of the amateur bands?

While I was operating on 40 m for Field Day, I noticed a higher SWR than when I first set my antenna tuner for the band. This happened, of course, because I was in a different part of the band, but I ...
8
votes
2answers
635 views

Can there be (long range) propagation of HF from satellites?

HF transmissions from the ground can be reflected by the ionosphere leading to very long distance propagation. Satellites in low Earth orbit (160 km to 2,000 km) fly within the ionosphere (60 km to ...
4
votes
1answer
140 views

Calculating effective SSN (sunspot number)?

I am doing research on how SSN-like parameters affect HF radio signals. As I can see, effective SSN is a parameter that is derived from SSN or using other parameters. Does anyone know how to calculate ...
2
votes
1answer
938 views

Do I need a Balun for a single band QRP antenna?

I have a little MFJ QRP CW 20m rig that I plan to turn into a portable kit for SOTA peaks. I have everything figured out except for the antenna. I am wanting to make a dipole. However, I was wondering,...
2
votes
4answers
1k views

What should I look for in a modern portable shortwave radio?

I'm looking to buy a shortwave to listen to either solely at home or perhaps if possible in a vehicle when traveling. What should I look for when looking them over? I recall many years ago the ...
13
votes
2answers
2k views

How does selecting the opposite sideband when receiving CW on HF reduce interference?

I am studying for my FCC General Class license, and question/answer G4A02 reads as follows: Q: What is one advantage of selecting the opposite or "reverse" ...
3
votes
1answer
464 views

Trap dipole tuning up on the wrong band

I'm building a trap dipole for the high HF bands, 10 / 12 / 15 / 17. So far what I've got in the air is: The 10 meter section (4.92 meters, 16.14 feet, resonant at 29Mhz) The 10 meter traps (...
3
votes
2answers
172 views

Setting up an HF Schedule

I want to make a contact with a ham who is far away (>10,000km). How would I intelligently plan a scheduled contact to maximize possible success? Assumptions: Both stations have optimized their ...
4
votes
2answers
352 views

What is the difference between Yaesu noise blanker (analog IF) and Icom noise blanker (perhaps digital)

What is the difference between the Yaesu (say FT DX 5000) and Icom (say IC 7700) noise blankers? I understood that the Yaesu NB is an analogue one while Icom uses a digital solution.
4
votes
1answer
119 views

How can I establish a wireless link between my PC and TenTec 506 / chipKIT UNO32 using USB port?

I have a TenTec 506 HF transceiver that uses a Digilent chipKIT UNO32 microcontroller. My PC running Teraterm (serial connection) or the MPIDE monitor is connected to the microcontroller's mini B USB ...
1
vote
1answer
133 views

International Broadcast - database programs? [closed]

In my search to identify the stations I can (barely) hear on my small shortwave setup, I discovered the HFCC. They have a tool that takes your location and UTC time, and provides a list of stations ...
2
votes
2answers
254 views

Air conditioner duct as counterpoise?

Many suggestions on the Internet for a "starter" HF long wire, suggest running a wire in the attic. My (South Australian) roof has a 30 degree pitch, and what little space remains contains air ...