Community Digest

Top new questions this week:

How to properly measure sensitivity of the receiver?

I have Kenwood TH-D72 2m/70cm HT. According to the manufacturer the sensitivity is "Less than 0.18 uV". I would like to check this, since the radio is not new and I'm not it's first owner. To do this ...

asked by Aleksander Alekseev - R2AUK 5 votes
answered by tomnexus 4 votes

Where to find HF channel models or statistics?

When designing a waveform for packet radio usage, it'd be helpful to know a few things, mainly distribution of coherency bandwidths distribution of coherency times Whilst such statistics are ...

hf doppler channel multipath  
asked by Marcus Müller 4 votes

no contacts with Rockmite

I finished building my Rockmite ][. It's running off of 3x 18650s, or 12v. I connected it to a MFJ-1840T and held the antenna horizontally in the air (also tried vertically) with my hand. I tried ...

antenna diy qrp  
asked by mh00h 3 votes
answered by Mike Waters 4 votes

Why EME with 100W and a single Yagi-Uda antenna is possible?

Recently I've been reading about EME and there was one thing that surprised me. Many sources claim that EME has path loss for 2m band about 252 dB. In the same time they claim (one, two): Recent ...

math eme  
asked by Aleksander Alekseev - R2AUK 2 votes
answered by hobbs - KC2G 11 votes

Do I always need a tuner at both ends of the transmission line or is that only for certain types of antennas/circumstances?

Last night was my first night on the air as a General licensee and at HF. I've got an IC-7300 with the built-in antenna tuner. I'm pretty sure I understand how to operate the radio, for the most part. ...

antenna feed-line antenna-tuner  
asked by NonYaBidnezz 1 vote
answered by Kevin Reid AG6YO 2 votes

UK Intermediate training a not qualified newbie

I'm 99.9% certain that this will be OK, but independent verification would be reassuring. I am an "Intermediate" licence holder in the UK. This means that I am authorised to design and build my own ...

legal united-kingdom  
asked by birdwes 2E0WZR 1 vote

How to use FE-5650A rubidium frequency standard?

I bought a FE-5650A rubidium standard reference from eBay in the hope I can readily use it: Unfortunately this is far from "reasily useable". First and ...

frequency oscillator  
asked by divB 1 vote
answered by dingensfredi 2 votes

Greatest hits from previous weeks:

Using my Baofeng UV-5R to talk to walkie talkies

I have a few walkie talkies at home and sometimes I connect my UV-5R to them to talk to them and act as another walkie talkie. At one time, I built a little simplex repeater out of it. Should I not be ...

united-states legal ht frs  
asked by Skyler 440 15 votes
answered by Adam Davis 16 votes

Calculating Antenna Length on the FCC Exam vs. in Reality

I have seen the following formulas for calculating half and quarter wavelength antennas: Formula for $\frac{1}{2}$-wavelength antenna (in free space): \begin{equation} \mathrm{Length~(feet)} = ...

antenna united-states antenna-theory math physics  
asked by Dan 12 votes
answered by Walter Underwood K6WRU 18 votes

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 ...

hf propagation space-weather ionosphere sunspots  
asked by Mike Waters 15 votes
answered by Brian K1LI 2 votes

How can I avoid accidentally transmitting with a Baofeng UV-5R?

I don't have $500 for a radio scanner. If I know the few (analog) frequencies that I would like to listen to, I think one can use the Baofeng UV5R (which doesn't cost much). The only problem is that ...

receiver baofeng  
asked by user4777 19 votes
answered by Chris 19 votes

Home-brew 10 meter walkie talkies?

"When I was in high school, we had 8 hams at once. (Probably rare) 4 of us built little 10 meter walkie-talkies and had great fun using them on Field Day, hiking or around town. It was ...

asked by Skyler 440 9 votes
answered by WPrecht 8 votes

Advantages of using Digital Code Squelch

I am trying to decide whether or not I should use a CTCSS (Continuous Tone-Coded Squelch System) or a DCS (Digital Coded Squelch) for my mini repeater I just set up. What are the advantages of using ...

rfi tone-squelch  
asked by Skyler 440 3 votes
answered by Trevor Johns 5 votes

How to find the front-to-back ratio given an antenna radiation pattern diagram?

I know that the front-to-back ratio is 18dB in the below antenna radiation pattern diagram, but I don't know how to read the diagram to obtain this result. How does one read and understand such ...

antenna math  
asked by Dan 6 votes
answered by Amber 8 votes
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