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Re: AFSK for JUMA TX500

Completely awesome. Being able to quickly shift the frequency makes a number of modes possible. It should even be possible to send PSK31, or JT65. I'll look into this more.

Dave
by VE3GSO
04 May 2014 19:51
 
Forum: Juma Discussion
Topic: AFSK for JUMA TX500
Replies: 1
Views: 1825

Re: Harmonic Content of Juma LF

If you are worried about suppressing a third harmonic further, add another five pole low pass filter between the transmitter and the antenna. Two toroids and three capacitors, identical to what is already in the rig. That may also help reduce any signals from nearby broadcast transmitters getting in...
by VE3GSO
04 May 2014 19:43
 
Forum: Juma Discussion
Topic: Harmonic Content of Juma LF
Replies: 1
Views: 1603

Re: JUMA TRX500 half alive, no tx output

I've built and got working two TX500 Juma Kits. On the second unit there was an error in the IC shipped. Instead of the 74LS04, which is a buffer inverter, the chip was a 74S14, which is a Schmidt trigger. The chip oscillated at about 80kHz and took out the fuse. Replacing the chip with the correct ...
by VE3GSO
25 Apr 2013 01:12
 
Forum: Juma Discussion
Topic: JUMA TRX500 half alive, no tx output
Replies: 1
Views: 1907

Re: PSK on TRX1

The FET outputs are very efficient, and so is PSK31. If you are running more than QRP levels on PSK31 you are QRO! And that is frowned upon as you close down everyone's receive AGC and make it difficult to work other weak stations. So go ahead and use your rig at low power, put out a clean low disto...
by VE3GSO
25 Apr 2013 00:59
 
Forum: Juma Discussion
Topic: PSK on TRX1
Replies: 5
Views: 4167

Re: Juma TX500

An over current can only occur on transmit, because the current is monitored by R41 to the final transistors. Use a strong magnifying glass and check the traces and pads around Q8 and the two finals for solder shorts. The solder resist should prevent this but anything is possible. Also check the Tan...
by VE3GSO
14 Jan 2013 01:37
 
Forum: Juma Discussion
Topic: Juma TX500
Replies: 6
Views: 5996

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