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Author Topic: Update on changeover problem  (Read 2017 times)

Posts: 3235

« on: April 17, 2004, 09:59:04 AM »

Several weeks ago, I reported on my "intermittent changeover problem," and got lots of useful replies.  Recapping, I had problems in changeover from Tx to Rx with my TS-850S and AL-80B setup.

Just wanted to report on how I fixed the problem.  I purchased an "AmpKeyer" interface from Sunlight Energy Sytems.  It is a fine little piece of electronics that provides a measure of isolation by using an opto-isolator to drive either an intermediate relay or a MosFet to key the amplifier relay.  (I chose to use the MosFet output). This interface reduced the current passing through the TS-850S relay from 100 mA to 5 mA.  Using the interface alone, however, did not completely eliminate the problem, although it seemed to occur less frequently.  Since I was still using the Ts-850 relay, I was still "hot switching" the transceiver, as pointed out by Joe, K0BX.

So I ended up designing an NPN switch to use the 12V on transmit line from the transceiver (pin 7 of the ACC jack) to key the AmpKeyer input (which requires a ground on transmit).  Now I have the TS-850 relay turned off and the amplifier switches on faster with less noise, and no more changeover problem.  I'm using a 2N4400 NPN with 3.3K from pin 7 to the base, and 390 ohms from base to ground.  The collector goes to the AmpKeyer "radio" input.  You can use a beefier transistor to key the amp relay directly as Joe, K0BX, does.  (See his web-site at QSL.Net). I chose to use the AmpKeyer to minimize the current draw from pin 7 (rated at 10 mA, maximum) and to provide additional isolation between the transceiver and amplifier.

I should also point out that I got by with keying a different AL-80B directly from the rig with no interface for about 7 years with no problems.

Finally, Ameritron also sells an rig/amplifier interface (ARB-704), which is a little more expensive than the AmpKeyer.  I down-loaded the Ameritron manual in which they speak of the changeover problem I experienced, which they attribute to a sticking T/R relay in the exciter.

Thanks to all who helped out with suggestions for my problem, especially K0BX, and WB2WIK who pointed to a problem in my transceiver.

73 de Chuck  NI0C

Posts: 1109

« Reply #1 on: April 19, 2004, 06:09:13 AM »

I have used the K0BX transistor switching unit with my 850 and Alpha 89 and it works great.  Your absolutely right about leaving the relay off, the swiching is dead silent...and fast!  It also worked well with a FT-1000d that I had on long term loan.  That was really a boon as the on/off swich for the amp relay was located INSIDE the damn radio!  You had to take the bottom off to access the switch.  I liked the circuit so well that I built about 4 of 'em.  They don't work with high voltage keying lines like found on the SB-220 (120v) but will switch an L4B at around 20v.
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