Wednesday, 26 September 2012

My new 2m Power Amplifier

Now that I am using my Wouxun handheld unit in my car, I feel that its 5 watt output is a little on the weak side. Recently I spotted a 2m amplifier on eBay and decided to try a few bids. The device was described as untested but the seller said the lights came on and there was a circuit diagram available on the Internet. I kept my fingers crossed as the minutes ticked away but I eventually won the amplified for just over £30. It soon arrived so I set about making up some new patch leads so I could test it.

This amplifier produces around 30 watts of output from 5 watts in. It also has an adjustable RX amplifier. The unit is made by "Tokyo Hy-Power" and the model number is HL-37Vsx. I first decided to power it up and ensure it didn't do anything strange such as smoke or draw too much current. In its idle state all seemed well. I then connected it to my rig and antenna so I could test the RX amplifier. I found a suitable signal which was a conversation on the local Cambridge repeater. As you will see from the short video below, moving the sliding potentiometer adjusted the signal strength. This RX amplifier can be left at a suitable level or turned off altogether. As I tend to use the Cambridge repeater when mobile, I will probably set this to a reasonable level as it'll be hidden away and not accessible whilst driving.

Next on the "todo" list was to check the SWR whilst transmitting 5 watts into a dummy load. I did this with the amplifier switch off and then switched on. With the unit off the SWR was about 1.3:1 and with it on it was just about 1:1.

The final test was to see if the amplifier was living up to its name and actually amplifying. My transmitter was configured to output 5 watts. With the amplifier turned off and my power meter set to 20 watt fsd, the meter showed an output of just over 3 watts of FM.

I then changed my meter to display 200 watts fsd and switched on the amplifier. The meter showed an output of 40 watts of FM.

The manufacture's specification says I can expect an output of around 20 to 35 watts with a maximum input of 5 watts. With my meter showing an output of 40 watts I am happy that this is probably about right, give or take a few watts. At this point my dummy load was getting rather warm so I completed my basic testing. The next test will be to try some on-air contacts to see that the audio isn't being distorted etc. I will then need to buy some additional coax to enable me to set this up in my car. So far this amplifier seems like a good purchase.

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