FT 991A Antenna Tuner FAQ

FT-991A Antenna Tuner FAQ

1. What is this Tuner for?

Your FT-991A expects to transmit to a nominal 50 Ohm Antenna - however, this is not always possible. The FT-991A internal antenna tuner tries to match the best combination in its electronic components (capacitors and inductors) to try to bring your radiant system between 16-150 Ohm (max. SWR 3:1) to the nominal expected 50 Ohm to your transceiver.

2. What are the limitations of the built-in antenna tuner?

• The built-in tuner is only capable to match up to 3:1 of SWR mismatch. Some antennas has an intrinsic high impedance (like G5RV or long wires, end-fed, etc.) which is outside the internal tuner capability, and thus the internal tuner might not be able unable to tune it.
• The internal tuner works only in HF 1.8-30 MHz and 6m (50 MHz) bands.
• 144 and 430 MHz bands are not covered by internal ATU.

3. How do I check my SWR?

• Disengage the Tuner (no TUNER indicator in the panel). Use the SWR setting in your Meter during your (brief) transmission to check your SWR. Ensure to use an low power setting (no more than 10W) and continuous carrier, like CW, RTTY, AM, FM or C4FM modes. Do not use USB or LSB.
• If the HI SWR indication pops up in the screen, stop immediately - and the ATU won't be able to tune it.
• Remember: the SWR is only metered during the transmission mode. During the receive mode, your meter will measure the received signal strength (S-unit, the higher scale of the bargraph).

4. What is the "TUNE" button for?

1. Long press, lots of relay clacking: It engage the "Discovery" mode where the radio tries the best Inductor + Capacitor combination to bring the best SWR to your transceiver. After the relay clicking you should be presented the TUNE indication in your screen.
2. Long press, a single "Click" and no TUNE indication in the screen: Dude, sorry and caution: SWR is too high and the internal tuner is not able to match it. You will probably need an external tuner - or something is very wrong with your 'tenna.
3. Quick press, showing TUNE in Screen: The Tuner is engaged and enabled. Does not exempt you to monitor your SWR - Keep an eye on it. If SWR is bad, try 4.1 again.
4. Quick press, no TUNE indication in Screen: You have disengaged the antenna tuner and it is not active.

5. Do I need to reduce the power in order to tune using the internal ATU?

No. The radio reduces to a special power level when doing the tune operation, you do not need to change the power settings.

6. Do I need an external tuner?

If it falls in item 4.2, yep.

7. Is it good to have the Tuner engaged all the time?

Usually, only if your SWR with the Tuner disengaged is higher than 1.5. Otherwise, not really a great idea, because there's a inherent signal loss when the it traverses the ATU - you are unnecessarily wasting some Watts.

8. When I transmit, my TUNER indication goes away / my ATU disengages!

You are probably using WSJT-X. There's a TX setting in WSJT-X that will cause your radio to transmit in split mode. While you have engaged the Tuner in VFO A, the VFO B (used to TX in split mode) probably has the Tuner disengaged. Stop transmitting, press the A/B button and enable the Tuner.

9. Any other gotchas?

1. Yes - develop the habit to check your SWR at the start of your transmission to ensure that you are driving your 991A within its safe operating envelope.
2. The Antenna Tuning setting for a given frequency is memorized, meaning, once you tune it (item 4.1), this setting is saved.
3. If you change your antenna, at very least you will want to check the SWR level with the new antenna. If it presents a mismatch even with TUNE mode engaged, you will have to to re-tune, since the impedance might have (probably have!!!) varied! The tuner does not guess that you have a new antenna; it is working with the previous known/discovered setting (item 4.1)
4. The tuning "memory" is pretty narrow - It is only 10 kHz wide! Meaning, you tuned for 7.075, the tune setting is only good between 7.070 - 7.080. If you want to transmit outside this frequency, say, 7.093, do another tune discovery (hold tune) over there. But remember!!! Have you changed your antenna? All tune settings might be void and you will want to check the SWR with the Tuner enabled: if it is high, re-tune!
5. Good thing is - the radio memorizes the settings. Once you ran the initial discovery, the radio will memorize and recall that setting again, without the need to rescan.
6. Read your manual pages 63 and 64.

10. My ATU discovered the best SWR setting, I have the TUNE indication, but I'm presented HI SWR!

1. Redo 4.1
2. If after redoing 4.1 the issue persist, your culprit is a grounding issue in the Tuner board. Check this article

11. My FT-450 has a button where I push and it outputs a low-power constant-power carrier to use with my external ATU! Does the 991 provides such functionality?

No, there's no such button function in the 991/A even buried into the menus.

12. Does my RX signal traverses the Antenna Tuner?

No. The signal only passes through the ATU during Transmission and if the ATU is enabled. During RX, the signal is diverted right after the antenna connector to the Main Unit, where it is processed.