FT 990 IF output

General discussions
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Joined: Sun Dec 09, 2018 4:38 pm

Re: FT 990 IF output

Post by sdrom33 » Fri May 10, 2019 6:56 pm

In some Yaesu units the IF rides on 9 V d.c. better check. If this is the case you can isolate with an in between capacitor. Your RSP measures the power level it receives very accurately in dBm, so you can immediately judge if you are safe or not. You approach the safety limit with 0 dbm and you CANNOT exceed + 10 dbm, which level you can apply for very short periods only!

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D.C. Alden
Posts: 10
Joined: Wed Mar 20, 2019 2:38 am

Does fT-990 antenna out provide sufficient isolation?

Post by D.C. Alden » Wed May 15, 2019 5:10 pm

Well I figured out that when the “Recieve Antenna” button is engaged a relay switches the main antenna (SO-239) to the “Antenna Out” rca jack on the radio. This allows the connection of an external receiver to the main antenna.

At the same time, the “Antenna In” rca jack is activated which allows for the connection of a second receive only antenna.

So connecting a 2 way cable TV splitter input to the Antenna Out rca jack allows you to connect the splitter outputs to both the RSP and the Antenna In jack on the FT-990. In effect this allows both the 990 and the RSP to use the main antenna with only a 3.5 db loss, about 1/2 S unit. Acceptable loss on HF.

This would allow me to mute the RSP, view the spectrum on the SDRuno, click on the signal, tune the 990 via cat control, and listen to the station through the 990.

When PTT is pressed the relay in the 990 returns the main antenna to the transmitter and disconects the external receiver (RSP) from the antenna.

Apparently Yaesu thought this system provided enough isolation that an external recever could remain connected to the Antenna Output rca jack wihout the external receiver being damaged during even 100 watt transmit.

My question is, assuming all connections are made with sheilded cables, DO YOU GUYS think this is sufficient to protect the RSP?

Your opinion would be appreciated.
Last edited by D.C. Alden on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Posts: 14
Joined: Fri Dec 16, 2016 8:06 am

Re: FT 990 IF output

Post by g4jnw » Thu May 16, 2019 12:07 am

Its probably ok but i use a diamond splitter on mine which has served me well and never had issues with the RSP

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