Wednesday, November 1, 2017

Valve Audio Amplifier

Magnetic Loop Antenna For Transmitting

After the success of my receiving magnetic loop, i wanted to give a try on transmitting loop. It has both good and bad results.

One fine evening my friend OM Prem VU2RPC and myself started fabricating the magnetic loop to transmit on 40meter.

Used 3/4" copper tube used for air conditioner with a length of 9 feet.
Wide spaced variable capacitor 30-300pF salvaged from old valve transmitter
2.5SQm wire for inner loop.
Construction is as simple as possible. Just used 3/4" PVC pipes.
Just maintained the outer loop dia as 3feet, and inner loop 0.5feet.

We had about 10 contacts within 15 mins, it was sunday. The tough part is to keep the SWR.
The loop is very narrow bandwidth, even 10KHz change is frequency will affect the SWR to 3:1. Really bad, so maintain power level not more than 50 watts.
The RF from the antenna was also very severe, we can feel the radiation.

Result :
The overall result is,
It is definitely compromised antenna for receiving. There is no doubt, we had no noise pick up, and very good gain also.

For transmitting it not a good antenna. Unless we want to use just for only one frequency, like beacon. Because the bandwidth is too narrow. We have to adjust the variable capacitor for every change on frequency.

Magnetic Loop for Shortwave Receiving

DRM AIR +6100 KHz Shortwave receiving Magnetic loop antenna for 80m to 20m band

This is my trial during year 2015 to receive All India Radio DRM signal from Delhi, India. I'm located south India which is 3600Km far. The actual DRM on 6100KHz is transmit to cover 80Km surrounding Delhi. I made a simple Magnetic loop to get signal from that far. It was a huge seccess. Since i'm using magnetic loop the noise level was very low, and i can null alomost to zero. Below you can find the pictures of my AIR DRM 6100KHz.

I used old Oats container filled with sand on it as a post support. 3/4" PVC pipe, inside is a house electric wiring wire (3-20swg wire). Its about 3feet diameter. The outer loop is connected with a 365pF broadcast set variable capacitor. Inner loop is 1/2 feet dia. I used the same wire.

The radio Redsun (Kaito) RP-2100 comes with a IF out. I made a small converter to convert the RF to AF. Its inside the small black color box.

Saturday, January 7, 2017

VU3XVR Software Defined Radio SDR Using Si5351 DDS VFO and ATMega8 Microcontroller

This is a demonstration on Software Defined Radio Using Si5351 DDS VFO. Original designer is Burkard Kainka, Author of Elektor  SDR-2007. I Just modified VFO by using my own Si5351 based VFO, For more details please chek my blog vu3xvr dot blogspot dot in

Specification :

Frequency Range : 3 to 30 MHz
Mode  : AM - SSB - CW - DRM
Hardware Used :
Software Used : SDRadio by I2PHD available from this website

Thursday, January 5, 2017

VU3XVR Si5351 DDS VFO to Use BITX40

Click here for the video demo of sending CW using BITX (real carrier !!! not modified tone)