[Yaesu] Yaesu FT-980 Driving a linear

[Dr. Gerald N. Johnson]

Sounds like the Dentron is switching slowly present and open to the 
FT-980 and its high SWR protection is kicking hard on the ALC which is 
recovering slowly. As if like with a microwave transverter, some 
sequencing is needed to allow PTT or VOX to key the amp but the exciter 
power output be held off for a bit longer than the relay switching time. 
There is a TXINH line on my FT-857 that works great for that, I don't 
know about the 980. Tentec rigs and PAs use a TX enable line that the 
controls in the PA enable when the PA is ready for drive. You could use 
something like that if the 980 has a suitable input with much faster 
rise than the slow decay of ALC.

If the 980 has plenty power, you could add a resistive attenuator to 
absorb some of that drive and also limit the SWR it sees while the PA 
relays are switching.

73, Jerry, K0CQ

On 7/28/2011 11:49 PM, David Thompson wrote:
> I have had a total of 4 different FT-980's since my original 980 in 1983.  I
> remember having this problem driving a linear but as I recall adding the
> FRB-1 relay box cured this problem and the QSK
> problem.
>
> I am driving a Dentron 2000L with an 8877 in the final.  The problem is that
> you key the amp the current builds up slowly.  You have to key the rig or
> talk into the mic to get full power.  I looked in my notes and saw I had
> written that  Bill Means then at Yaesu (late 1983) told me about negative
> going ALC. The note was the FRB-1 relay box cured this problem and allows
> the FT-980 to key an amp.
>
> I have always driven the Dentron or a LK-500NTC.  I just picked up this
> FT-980 in a trade
> late last year.  I have a second 980 that I use to drive an old Henry 2K.  I
> am modifying the Henry 2K so it is not available right now.
>
> I would like to keep this 980 on the Dentron but have got to solve this
> delay problem.  I have checked and there is no FRO feed back.
>
> I looked through all the old Fox Tango notes from 1983-5 and other than the
> relay Box I don't see anything.
>
> Ideas please
> Thanks in advance
> 73 Dave K4JRB
>