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[F6GYF]

Hello dear OM,
I need your skills.
Sorry for my bad English 

I own an ICOM 7300 and a Yaesu FL2500 amplifier.
I control the input of the Yaesu with the SEND and 13.8V output pins of the 7300.
The output pins ALC from 7300 and amplifier are not used.
On transmission, I have a very strong TOS for a second, visible on the 7300 
I thought the latency of my miniature relay that drives the amplifier relay was too high.
I replaced it with an optocoupler followed by a transistor, but the problem is the same...

I use a Signalink USB in FT8 which drives the 7300.
I solve this problem, but no practical, as follows:
On the Signalink, I set the TX potentiometer (ALC) to zero, then switch to TX on the 7300.
A second later I put the TX potentiometer (ALC) back to normal value.
No more TOS problem 
It's the ALC at the start of TX that's the problem.

How to inhibit the ALC for 1 second when switching to TX ?
Or another idea 

Thank you very much for all your much appreciated help.
Cordially. 73 Gilles - F6GYF 

[G4AON]

Gilles do you really need ALC? I use an IC-7300 with an Elecraft KPA500 without ALC and it works fine.

Using an ALC connection between a transceiver and an amplifier dates from the 1960s and is not needed with modern transceivers. In fact some amplifiers, such as the Acom 1000, don’t even have an ALC socket.

73 Dave

[F6GYF]

Hello Dave,
Thank you for your help 
The output pins ALC from ICOM 7300 and amplifier are not used.
With my 7300, I have no output power if the ALC is zero.
Best 73. Gilles F6GYF

[G4AON]

I forgot to ask, why use Signal Link? The IC-7300 has built-in USB sound, it works perfectly without any additional accessories on data.

73 Dave

[F6GYF]

Ok Dave,
But I make also RTTY, PSK, CW with interface PC, Multipsk software.
I have also the TOS problem on SSB !
73 

[KC8HXO]

What is TOS?

[ZS5WC]

You simply need to supply ground/ ov to key linear normally.
Never heard of Yeasu fl2500..
Could be IC7300 is seeing high swr into linear, cutting back drive.
Make sure linear is keyed properly and input swr is ok.
William, ZS4L

[F6GYF]

Hello William,
Thank you for your answer  and your help.
I checked your instructions, everything is correct 
Best regards. 73 Gilles F6GYF

TOS is SWR.
Yaesu FL2500 idem Sommerkamp FL2500.

[VE7RF]

If you are  seeing momentary high swr between the 7300..and the input of the amplifier, you are hot switching the amplifier's relays.... which probably has a 3PDT slow mech relay (typ 15-17 msecs to operate). 

You need to introduce a  17-25 msec delay in the 7300, before RF flows from the 7300.   IE: the relays in the amp need a 17-25 msec..'head start'   BEFORE RF flows from the 7300.

If there is an adjustable delay for tx RF on the 7300, use it.   I have a 0-30 msec delay on my yaesu MK-V.... but only for CW.   On SSB, I have to use a 5 msec delay...(5 msec delay, then the TX inhibit lead is grnded)...to give the vac relays in the amp a head start.

[KA4DPO]

What is TOS?

Transmit OverShoot.

[F6GYF]

Hello dear OMs.
Thank you to everyone who took the time to read me

Thank you very much VE7RF for your help and your very useful answer which corresponds well to my SWR problem (TOS in French)
Concerning the ICOM 7300 and the transmission delay, I can validate a maximum of 30 ms which is too short 
I need about 0.5s which is the closing time of the amplifier relay contacts.

I'm thinking of adding an electronic delay (Integrated circuit NE555) on the modulation output of my Signalink. .
If other OMs have other ideas, i'm taken 


 Sincerely. 73 Gilles F6GYF 

[G4AON]

Concerning the ICOM 7300 and the transmission delay, I can validate a maximum of 30 ms which is too short 
I need about 0.5s which is the closing time of the amplifier relay contacts.

I have never heard of a linear that needs a key up delay of 500 mS, that is ridiculous.

You mentioned TOS as being SWR, another reply suggested transmission overshoot. Are you able to obtain an oscilloscope and check your IC-7300 to ensure that it really puts out only 10, 20, 30 Watts when set to that power level?

There have been suggestions that the IC-7300 puts out high power “spikes” at the start of a transmission, mine doesn’t, except on 4m.

It appears that the FL-2500 has a maximum power input of 100 Watts, which is the maximum output of the IC-7300.

From the above, I am guessing that you have a faulty replay in your amplifier. It is only a guess though.

The FL-2500 looks like an awful amplifier, can you not replace it with a more up to date one?

73 Dave

[KD6VXI]

Concerning the ICOM 7300 and the transmission delay, I can validate a maximum of 30 ms which is too short 
I need about 0.5s which is the closing time of the amplifier relay contacts.

I have never heard of a linear that needs a key up delay of 500 mS, that is ridiculous.

You mentioned TOS as being SWR, another reply suggested transmission overshoot. Are you able to obtain an oscilloscope and check your IC-7300 to ensure that it really puts out only 10, 20, 30 Watts when set to that power level?

There have been suggestions that the IC-7300 puts out high power “spikes” at the start of a transmission, mine doesn’t, except on 4m.

It appears that the FL-2500 has a maximum power input of 100 Watts, which is the maximum output of the IC-7300.

From the above, I am guessing that you have a faulty replay in your amplifier. It is only a guess though.

The FL-2500 looks like an awful amplifier, can you not replace it with a more up to date one?

73 Dave

Obviously you've not worked on 1960s / early 70s cheap Yeasu open framed relay sweep tube amps.

A half second is a bit much, but.

That amplifier has no tuned input. It's not designed nor was built for a solid state radio to drive it.

Use the built in antenna tuner.

Keep output to appx 300 watts.  Otherwise you will have an IMD generator.

--Shane
WP2ASS / ex KD6VXI

[F6GYF]

Hello everyone 
Thank you very much DAVE for your sensible comments.
Sorry I don't have an oscilloscope !
My 7300 does pull out 10 watts for the primary setting.
Then I go up several times up to 100 watts.
Indeed it's an old gentleman (less than me 1957/05), but which allows me to contact weak DX stations with pleasure 
Thank you also Shane for your help and your good understanding of the problem 
Reminder : TOS (taux ondes stationnaires in French) means SWR.
Sincerely. Best 73 Gilles F6GYF