Posts

FM Band notch filter with coax cable

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Usually the case is that we are close to a radio station transmitter(for repeaters) transmitting with some kilowatts, or near an airport and this is causing problems!!! In such case you need to have a filter cutting out these bands. The filter described here is for the VHF Band (2m) and it is really easy to construct. You will need the following:
Coax cable (good quality LMR-240,400,600)T connector ,bnc or n-typeSignal generator & spectrum analyzer so you can tune your filter to the desired frequencyA plastic electrical box to use it as enclosure (if you wish) I personally wanted to create a Notch Filter for a near by Radio Station that transmits on 94.5Mhz. So after some quick calculations:
The Wavelength of 94.5Mhz is 3.17m LMR-240 VF = 84.0
So for the 1/4λ coax stub: 1/4*3.17*84 =  66.57cm
For the 1/2λ coax section between the 2 stubs: 1/2*3.17*84 = 133.14cm = 1.33m
Personally i constructed a one stub filter which has great results with low insertion loss! Please see the plot …

TYT MD-398 Review

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The review for this handheld radio will be a quick one! First of all to sum up DO NOT BUY THIS RADIO if you are an amateur radio operator

Pros: Robust constructionSplash proof10w tx power outputBig batteryEasy to programCons: One timeslotLow tx power 4wBulkyNot amateur radio materialBad modulationProduces high BER even when you are 5m from the hotspot(when other radios are perfectly fine) If you want to spend money on something better go a offer the value of this radio to someone who needs them because if you buy this radio is like throughing your money to a dumpster. For some people that think that there might be a solution to the one time slot thing, there is not!!! This radio only trasmit in one time slot TS2. You cannot use it on a repeater because you will produce a mess!!! Finally this radio is not support by the DMR community so you will not find information nowhere. Even TYT says do not buy this radio if you are an amateur radio operator!!!
73s

DV Mega ,Raspberry Pi and mmdvmhost

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Ok it is time at last!!!well many other sites and fellow radio amateur operators have articles for this setup but allow me to provide my view as well. First of all i must say that DV-MEGA has nothing in common with other digital hotspot devices and at this point i am refering to DV4MINI. DV-MEGA is a realiable device with no glitches using either G4KLX's DSTAR Repeater software or MMDMHost software.

Athens HamFest 2017

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New look!!!

After many years with the same look at last the time has come to update it!!! 
Enjoy and thanks for your visit! 73s

1:1 Balun for HF Frequencies(λ/2 dipole)

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English instructions