SWR bridge 160 meter

I need a SWR meter for the 160 meter transmitter. So I build one in an old 27 Mhz CB SWR meter enclosure. It is a ressitortype  bridge.It looks like this one:

I use 2 100Ohm resitors in parallel to make the 50 Ohm . Those resistors can handle 1 Watt so I can use the bridge for 5 watt QRP transmitters.

A bridge like this limits the mismatch for the TX. That is ideal for testing homebrew transmitters on air. 

It is no ready yet I need to add a switch to bypass the bridge when tuning has finished.  The bridge consumes 75% of the power.  So a bypass switch is needed.

PLL for AM transmitter

I Build a synthesizer for the AM transmitter. The diagram was found at.
Nederlands forum over oude radio's It is pretty straight forward. A refrence oscillator, a 4046 PLL including VCO and a progrogrammable divider.

I have build a similar PLL in the past. using a seperate VCO and 74192 dividers. It was not hard to build but the vco did not work. I had to use a  15K resistor form pin 12 to earth. This also limits the VCO range to 800 KHz to 2 MHz. That should improve the quality of the signal as well. I am pleased with the result. I listened to the signal in cw mode. It sounds clean.

I have used a different xtal. Now my stepsize is 7 KHz instead of 9 KHz. That is Ok for 160 meter.

The box that contains my 1.8 Khz AM transmitter has no more room so I have mounted it on the back. It is in a metallic enclosure so it should be fine.

ic-255

I bought a IC-255E on Ebay for sentimental reasons. I used to own an IC-260E. That was my first transceiver. I worked during the summer holliday to finance it. 

The radio did not come with the  mic so I had to find one myself. Fortunately I have quite a lot of microphones for CB radio's. The Icom however needs an amplified mic. So I had to build a amplifier in the mic. Icom was kind enough to provide the schematic diagram. I did no have the transistor so I used a bc547 instead. It worked. Modulation sounds great.

The Icom was deaf when it arrived. No output was available either. It turned out that the tracks on the output filter PCB were damaged. Most of them were loose. That could be fixed easily.

Another problem was the receiver. It was 5 KHz off frequency.  Fortunately the manual provides some pictures of the internal controls. So I could fix that problem too.

The only remaining problem is the duplex switch. The control need to be cleaned internally as it cracks. The set switches back and forth between duplex and simplex. I have to find a some kind of spray.

160 meter AM using tuner.

I started to build a simple 160 meter AM transmitter using a old tuner. Target output is 1 Watt.

The plan was to build the complete transmitter in the tuner. Unfortunately It did not fit in my tuner. So I put it in a old printer switch box.

The design is straight forward. The signal out of the tuner is amplified by a few bc547 amplifiers. then that signal is used to drive a 4427 mosfet driver. This driver drives a IRF510. It works in Class D. The output is filtered by a 7 element Lowpass filter. Modulation is done by a darlington transistor. That works as a modulatable power supply.

At this stage it is functional but there is room for improvement. Modulation depth is 75 procent maximum. Harmonic suppression can be improved. Especially between 15 MHz and 25 MHz. The signals are 40 db below carrier. That is probably good enough but I think it can be improved easily.

500 KHz on hold

I shelved my 500 KHZ project. It seems we are not going to get 500 KHz access after all.
So I will focus on other projects.