Baofeng

26 Apr 19
Gauri

50pcs Handheld 2 Pin PTT Speaker Mic for RETEVIS BAOFENG KENWOOD TYT WOXUN US – Buy – 50pcs Handheld 2 Pin PTT Speaker Mic for RETEVIS BAOFENG KENWOOD TYT WOXUN US

26 Apr 19
Gauri

50pcs 2-PIN Earpiece for Kenwood BAOFENG 888S Retevis H777 TYT 2-Way Radio – Buy – 50pcs 2-PIN Earpiece for Kenwood BAOFENG 888S Retevis H777 TYT 2-Way Radio

25 Apr 19
Gauri

5x Bone Conduction Tactical PTT Headset For Kenwood BaoFeng UV-5R Retevis Talkie – Buy – 5x Bone Conduction Tactical PTT Headset For Kenwood BaoFeng UV-5R Retevis Talkie

25 Apr 19
Ganymede

5x Bone Conduction Tactical PTT Headset For Kenwood BaoFeng UV-5R Retevis Talkie – Buy – 5x Bone Conduction Tactical PTT Headset For Kenwood BaoFeng UV-5R Retevis Talkie

25 Apr 19
Hackaday
This is an exciting day for me — we finally get to build some ham radio gear! To me, building gear is the big attraction of amateur radio as a hobby. Sure, it’s cool to buy a radio, even a cheap one, and be able to hit a repeater that you think is unreachable. Or on the other end of the money spectrum, using a Yaesu or Kenwood HF rig with a linear amp and big beam antenna to work someone in Antartica must be pretty cool, too. But neither of those feats require much in the way of electronics knowledge or skill, and at the end of the day, that’s why I got into amateur radio in the first place — to learn more about electronics. To get my homebrewer’s feet wet, I chose perhaps the simplest of ham radio projects: dummy loads. Every ham eventually needs a dummy load, which is basically a circuit that looks like an antenna to a transmitter but dissipates the energy as heat instead of radiating it an appreciable distance. They allow operators to test gear and make adjustments while staying legal on emission. Al Williams covered the basics of dummy loads a few years back in case you need a little more background. We’ll be building two dummy loads: a lower-power one specifically for my handy talkies (HTs) will be the subject of this article, while a bigger, oil-filled “cantenna” load for use with higher power transmitters will follow. Neither of my designs is original, of course; borrowing circuits from other hams is expected, after all. But I did put my own twist on each, and you should do the same thing. These builds are covered in depth on my Hackaday.io page, but join me below for the gist on a good one: the L’il Dummy. L’il Dummy As Al points out in the article linked above, a dummy load is just a resistive element that matches the characteristic impedance of the transmitter’s antenna connection. In almost every case, that’s going to be 50 ohms. The reason that the load needs to be as resistive as possible is that it needs to continue looking like a flat 50-ohm load no matter what frequency is applied to it. Any inductive or capacitive elements in the load will make it more reactive, changing the impedance as the input frequency changes. This could lead to RF power getting reflected back into the final amplifier transistors in the transmitter, possibly damaging them or destroying them altogether. Not what you’re looking for. That means our resistive elements need to be as non-inductive as possible. But, they also need to be able to dissipate a lot of power. The HT dummy load, which I’ve dubbed L’il Dummy, needs to handle the 5 to perhaps 8 watts an HT can output. Trouble is, power resistors in that range are often wirewound, and a coil of wire will have too much inductance. We’ll need to be clever in sourcing components. Looking down into L’il Dummy just before applying the torch. The RF Biscuit board is a handy little thing. The circuit for L’il Dummy is hardly worth a schematic – it’s just an SMA jack with a 50-ohm resistor across the outer ground and the inner conductor. I chose to build the circuit on an RF Biscuit board. This is an open-source design that enables all kinds of handy little RF circuits — attenuators, filters, and as in this case, dummy loads. The resistive element I chose was a thick-film SMT device capable of dissipating 35 watts – way more than enough for this job. That and an edge-mount SMA jack should have been all I needed to make a working dummy load. To my surprise, once I soldered the resistor to the RF Biscuit board, the dummy load was almost as good an antenna as the stock rubber ducky on my Baofeng HT. I was able to hit a local repeater through the dummy load without any issues. Clearly not a good design. To correct it, I put the whole thing into an enclosure made from 1″ copper pipe. Not cheap stuff, but not too bad, and I like the look of polished copper. Soldering the whole case together was a challenge that my big Weller soldering gun wasn’t up to, and trying to get everything heated up enough with a propane torch without overdoing the heat was a fun time. Testing on a Budget Now for the $50 question: does it work? I tested the resistance with a DMM and it comes out to just about 49 ohms, which is close enough in my book. But that’s DC resistance; what about impedance? I don’t have an antenna analyzer, so I trolled around and found a simple method for measuring impedance with only a function generator and an oscilloscope. My scope has a 20-MHz function generator built in, so I whipped up a quick test jig from a BNC jack and an SMA jack, connected in series through a leftover 1000-ohm resistor. L’il Dummy test setup. Measure the p-p voltage on each side of the series resistance connecting the function generator to the dummy, and do a little math. Applying a sine wave into the dummy load, measuring peak-to-peak voltages on each side of the resistance, and doing a little math is all that’s needed to characterize the impedance from 2.5 MHz to 20 MHz. The math is simple: with V1 being the voltage across the input, V2 being the voltage across the output, and Rref being the actual value of the series resistance, which I measured at 998 Ohms. And the results are pretty close to 50 Ohms, and flat across the tested band f (MHz) V1 (V p-p) V2 (V p-p) Z (ohms) 20.0 1.49 0.062 43.3 15.0 1.89 0.082 45.3 10.0 2.57 0.113 45.9 5.0 3.90 0.173 46.3 2.5 4.70 0.217 48.3 I wish I could measure it at VHF and UHF frequencies, but that will have to wait until I get a function generator that goes up to 400 MHz or so. I doubt very much that a $50 budget would cover that, though. Next Time I had intended to cover both L’il Dummy and its bigger, somewhat smarter brother in one article, but I still have some testing to do on Big Dummy. I’ll cover that next time, and after that we’ll move onto measuring the output of a cheap Chinese HT and perhaps building a filter to clean it up.
24 Apr 19
Globalmarketers

Global Isotropic Graphite report offers extensive information on fundamental Isotropic Graphite Market aspects and futuristic development plans. The latest news, Isotropic Graphite Industry trends, plans & policies and growth status is explained. The growth strategies, mergers & acquisition as well as new product launches are reflected in Isotropic Graphite Market Research Report. The market size, […]

24 Apr 19
Globalmarketers

Global Isotropic and Extruded Graphite report offers extensive information on fundamental Isotropic and Extruded Graphite Market aspects and futuristic development plans. The latest news, Isotropic and Extruded Graphite Industry trends, plans & policies and growth status is explained. The growth strategies, mergers & acquisition as well as new product launches are reflected in Isotropic and […]

24 Apr 19
YugaTech | Philippines Tech News & Reviews

Emergencies and disasters are things that can occur and mostly out of our control. Since most of them are unpredictable, there will be moments when we’ll get caught off-guard and just grab the nearest things to us, to save our lives. Even if they’re unpredictable, we can still do our best to prepare for them. […]

22 Apr 19
globalmarketersinsight

Global Special Graphite industry Outlook in global region – Investment opportunities, analysis, and forecast of Special Graphite market in global region. Global Marketers Published a Professional research Report on “Global Special Graphite Market Forecast 2023” includes the deep analysis of market status(2013-2018), competitive market analysis, scope, trend, stake, progress, and Forecast to 2023 The current […]

22 Apr 19
Gauri

50pcs Retevis 2Pin PTT Speaker Mic for Retevis Kenwood Baofeng 2-Way Radio US – Buy – 50pcs Retevis 2Pin PTT Speaker Mic for Retevis Kenwood Baofeng 2-Way Radio US

20 Apr 19
Gauri

20X 2-Pin Ear Bone Earpiece PTT Headset for Kenwood Retevis H777 BAOFENG Radio – Buy – 20X 2-Pin Ear Bone Earpiece PTT Headset for Kenwood Retevis H777 BAOFENG Radio

20 Apr 19
Gauri

100X Retevis 2Pin PTT Mic In-ear Earpiece for Kenwood TYT HYT Baofeng Retevis US – Buy – 100X Retevis 2Pin PTT Mic In-ear Earpiece for Kenwood TYT HYT Baofeng Retevis US

18 Apr 19
Gauri

50xSMA-F Female Short Antenna For Retevis H777 BAOFENG/Kenwood/Wouxun Radio US – Buy – 50xSMA-F Female Short Antenna For Retevis H777 BAOFENG/Kenwood/Wouxun Radio US

18 Apr 19
Gauri

50X2-Pin PTT/VOX Headset Earpiece for Kenwood/Retevis H777/Baofeng 888s Radio US – Buy – 50X2-Pin PTT/VOX Headset Earpiece for Kenwood/Retevis H777/Baofeng 888s Radio US

18 Apr 19
Gauri

20x Retevis Headset Earpiece Kenwood 2-Pin for Kenwood/ Retevis/Baofeng Radio US – Buy – 20x Retevis Headset Earpiece Kenwood 2-Pin for Kenwood/ Retevis/Baofeng Radio US

17 Apr 19
W 2 N P T

World Radio Network/World Friendship Net Announces “World Amateur Radio Day 2019” For the 5th straight year. Rochester, NY., March 11, 2019:  THE WORLD RADIO NETWORK and THE WORLD FRIENDSHIP NET today announced that for the 5th  straight year, we will be participating in WORLD AMATEUR RADIO DAY 2019 on VOIP/ECHOLINK on the “WORLD” CONFERENCE SERVER/IRLP […]