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MFJ-998 Intellituner for remote--comments sought

Discussion in 'General Technical Questions and Answers' started by K8EA, Sep 16, 2018.

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  1. K8EA

    K8EA Premium Subscriber QRZ Page

    I posted earlier today about the LDG tuner so you may have seen that post. But I have been digging into this all day and it seems like the MFJ998 is the best in breed in the price class. I plan to use it with my RemoteHams server station and an ALS600 amp/7300 xcvr. When you've got a server station out there's not too much damage to be done with just the transceiver and the antennas. But I want to be able to offer power as well, thus the ALS600 and the tuner. My goal is to have a top drawer remote for use by those living in restricted communities, older or disabled hams, people deployed with their jobs like military people, etc. Check out and the K8EA station. It is coming along. But I need the tuner. I would really appreciate any thoughts or comments on this.
  2. WD4ED

    WD4ED XML Subscriber QRZ Page

    You must consider a few things that may not be obvious.

    1. Until the tuner has achieved an acceptable VSWR power must be kept below 100 watts. If that tuner attempts to tune under higher power it will probably be damaged.

    2. Controlling the remote power to the remote tuner. The MFJ-998RT often needs its power cycled to initiate or complete tuning. This must somehow be remoted.

  3. K8EA

    K8EA Premium Subscriber QRZ Page

    Thanks for the post WD4ED. I ordered the MFJ998. This one has an Icom cable. Also has amp bypass by way of interupting the relay cable to the amp. As I understand it it will take a 10W CW tone for tuning and will not engage the amp until it reaches an acceptable SWR. Owner sets the level, 1.5, 2.0, whatever. This is not the cheaper one. Check it out. It's coming UPS today and I am anxious to put it on line. Check this out
  4. KU3X

    KU3X Ham Member QRZ Page

    You made the best choice. At out club's station, we have both the LDG and the MFJ 998 tuner. Hands down the 998 is a much better tuner.
    It handles more power, it tunes faster, it can match a much broader range, it has a interupt line so the amp is not in line when the tuner goes through its tuning cycle, it can be adjusted to not stop tuning until it hits a perfect 1 to 1 match and it goes into bypass if the antenna is below a certain SWR value where the tuner is not needed.

    There is ONLY one downside to the 998 tuner, "it does not cover 6 meters. "

    Within the menu of the 998, you can tell it not to stop tuning until it sees a preset value. You can set that value to as low as 1 to 1 or maybe 1.7 to 1. If it can never tune down to 1 to 1, it will
    stop tuning at its best low value SWR.

    I have an MFJ 929, 200 watt tuner and it works pretty much the same as the 998. I liked mine so much I had two of them, one for the shack and one for portable.
    Good luck with your portable station.

    Barry, KU3X
    N4UP and K8EA like this.
  5. K8EA

    K8EA Premium Subscriber QRZ Page

    Many thanks Barry for this validation. It should arrive via UPS today and can't wait to put it in line so I can run my amp on my RemoteHams station.

    Funny, but I have been a ham for 52 years and have never made a QSO on 6 meters! It's the only band, 160-2 meters I have never been on. Maybe I should try it one day. In the meantime I don't allow any operation from my remote on six, so no problem with that missing functionality.
  6. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Oddly, my 998 has no problem tuning my antenna for 6m. It reports the correct frequency as well. Now my antenna is not really good for 6m (as it is for HF), but it does work for making contacts across the country when the band is open.

    Not sure why some people need to power cycle their 998 tuners. I never have. Make sure you have adequate power supply at the tuner (accounting for any remote wire drop as needed, ideally with separate sense wires back to the power supply.). I would use at least a 3A supply.

    Also filter your incoming power lines with a multi-turn ferrite torroid, and be sure you are using twisted pair for the power.
  7. N4UP

    N4UP Premium Subscriber QRZ Page

    I have LDG, 3 x MFJ-998, and Palstar HF-AUTO tuners. Didn't like the way the LDG works, so it sits on the shelf unused. I really like the way the MFJ-998 works.

    I have used the MFJ-998s for five years. For the first of those five years I had indoor antennas that required tuning on all bands.

    I have used the MFJ-998 with several different radios, so I have a stock of interface cables as each radio seems to require a different cable. I have multiple HF radios/amps/tuners.

    Now I have much better antennas, and only need and use the MFJ-998 on the high end of 80 and 40 meters, because my 8040 vertical antenna is cut for CW. It is easy to bypass the tuner.

    I only use the HF-AUTO on 6 meters.
    KU3X likes this.
  8. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    I have the 998rt in use with a random length 90ft wire. It tunes from 160 to 10 with the application of ~45 watt carrier. I like the unit because there are no controls or interface with the radio, I simply find a clear channel and key. The 998 hunts for about 10 seconds max and matches the wire between 1:1 and 1.5:1. There are occasions where if I have not used it in a while that I will need to cycle power with the bias "T". I have found that ~45 watts works best, higher seems to cause the tuner to sub-optimize the match. If >100watts is used the tuner does not tune. Since I repair radios I have used it with many different radios. The only issue I have found is that on some radios the SWR roll back keeps the tuner from working. The radio sees the initial hi SWR and rolls back power to 10 watts which appears to be too low for the tuning circuit.
  9. K8EA

    K8EA Premium Subscriber QRZ Page

    Help me understand why you need a 3.0 power amp supply. The specs call for 1.4 amps at 12vdc. I have a power brick from an old TiVo unit that provides 12vdc and 3.0 amps shouldn't that work fine?
  10. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Put a scope on the power rail and see if your supply is adequate. Many supplies, especially wall warts, are overrated. They say 1.5amps, but maybe can only deliver that for a few milliseconds (due to a large capacitor). Also, cheap wallwarts simply lie about their specs (especially if you bought it from ebay). Some supplies are unregulated (usually a linear supply without regulation) so their output could drop when you transmit because your radio and amplifier are bringing the line voltage down.

    A lot of circuits, especially those with micro controllers, do weird unpredictable things when their power rails are not steady. All those switching relays cause a lot of rapid, heavy changes in the power supply. Switching supplies in most Wall warts also tend to be more sensitive to RF. The cable for the supply goes right next to your legal limit coax. I put a bunch of ferrite on mine.

    The point is that good, clean, solid power rails are important, and it is best to make sure they are as good as they can be.

    I am speculating that this may be the cause of some people needing to power cycle their units. This is indeed just a guess on my part, and I do not have evidence to back it up. However, it is an easy and cheap thing to change. I don’t know what else would be different between people who have problems and myself, who does not. (I am sure lots would be different, but the power supply would definitely be different.)

    I would think a 3A supply from a TiVo is probably fine, though I would still put ferrite (multi turns mix 31) on the power cable.

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