[AMPS] Power problems on 10/15 Meters HF2500

[2]

>
>Hi Rich,
>
>What happens if you put the exciter in transmit mode by closing the
>PTT line prior to applying RF? 

Depemds on how the radio is keyed.  If the keying is done by a mic, PTT, 
an FT-1000 transmits RF from the mechanical noise of the PTT switch 5mS 
after the PTT switch closes. 

>We had a similar problem using the
>FT-1000D driving an Ameritron AL-82 (slow buildup from a few
>hundred watts to full output) over at the local club station. When I
>would close PTT line prior to sending the leading dit with a keyer,
>there was no problem (in this case the amplifier T/R relay closes long
>before the RF arrives). I suspect the T/R relay on the Ameritron was
>hot switching due to the slow contact closure from the FT-1000D.

To see what's what, one needs a dual trace oscilloscope.

>During the hot switching, a large pulse of reflected power is seen by
>the protection circuits on the exciter, causing it to fold back (it thinks
>its looking into a high VSWR). 

Makes pretty good sense to me.  

>If this is your problem, then you may
>need some way to speed up the contact closure on the Commander's
>T/R relay. Its funny that it doesn't happen on 160-20, but this could be
>related to the length of the cable between the rig and the amp and how
>your exciter's protection circuits respond to different impedances.
>
Agreed.

>Try manually closing the amp T/R by using the PTT function on your
>rig, or a shorting plug on the amp's control line. If you still get
>foldback,
>then you may have another problem.

If an amplifier switches slower than c. 3mS, there is likely to be a 
problem with a 5mS radio like the FT-1000.  The fix is to update the 
amplifier with higher-speed switching.
>
cheers
>
>----- Original Message -----
>From: "Rich Hallman - N7TR" <N7TR@rnodx.org>
>To: <amps@contesting.com>
>Sent: Saturday, November 03, 2001 3:10 PM
>Subject: [AMPS] Power problems on 10/15 Meters HF2500
>
>
>>
>> I just noticed that on 10 and 15 meters there is a slow build from a few
>> hundred watts to the full 1500 watts when I begin to transmit. On CW the
>> first few characters are low in power then build.  15 meters seems to take
>a
>> second or so, and 10 meters seems to be a bit worse.
>>
>> 20-160 meters is full power out  with no problems.  I have also tried
>> another rig with the same results.
>>
>> Could this be an indication of bad 3cx800's?  This is a Commander HF-2500.
>>
>> Thanks...
>> Rich
>>
>> ******************************
>> Rich Hallman - N7TR
>> Reno, Nevada
>> http://www.n7tr.com
>>
>> N7TR DX-Cluster Access:
>> telnet://dxc.n7tr.com


-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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