ad: AbAuRe-1

FT-1000MP output power control problems

Discussion in 'Amateur Radio Amplifiers' started by TF3T, Mar 24, 2011.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: Left-3
ad: l-BCInc
ad: Subscribe
ad: Left-2
ad: abrind-2
ad: l-gcopper
  1. TF3T

    TF3T Ham Member QRZ Page

    Hi - I have been having issues with a FT-1000MP driving a RF-110 Amplifier/military unit.

    Not to dive to deep into the RF-110 amp, it must not be driven to hard, we are using a 30dB attenuator as it must not be driven over 100mW.

    The power (drive?) pot works as expected on CW - seamless power control from 1-100w.
    On SSB it behaves very strange, from 0-1/8 of a turn the power reading is 1-20w, but when we exceed the 1/8 (approx) it gets very touchy and we end up with peak power going from 1/8th to 2/8th. Then the rest of the pot circle seems to have no/little effect.

    If we limit the power output to 50w from the menu, we observe similar behavior but on the scale 1-50w.

    This is not my transceiver, but I have become custom to digital controls, if you set the power output to 20w - even if you put mic gain and proc to max it will not go over the set 20w.

    Is this somewhat different in the FT-1000MP - or is this possibly a bug

    we are looking into getting ALC into the amplifier - but we must somehow be 100% sure we don't overdrive, and the strange non-lineariy/control of the SSB output power on the transceiver is pussling us.
     
  2. KM6MB

    KM6MB Ham Member QRZ Page

    No idea, never checked mine, but as you have a maximum power input limit of 100mWs, then it might be a good idea to use a "50 ohm swamping resistor" across the input of the amp of suitable power rating???
    I do have an old grid driven amp that has an inbuilt 50 ohm swamping resistor on the input to prevent the grids being overdriven.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    He said he's using a 30 dB pad on the input, that's a lot more than a swamping resistor.

    I don't remember seeing this issue with the FT1000MP, but then it's been a few years since I used one. The symptoms sound like the ALC doing something weird, and that may be typical of the MP but I don't recall.

    Have you tried the Yaesu reflector to see if others have noticed this?
     
  4. W8JI

    W8JI Ham Member QRZ Page

    The first question, before anyone can answer or give help, should be HOW are you measuring power?

    As for the FT1000MP, it generally has a fairly smooth power control but not near the low end. At low power it is touchy. It also has overshoot in the ALC, like most radios have. I would NEVER run one at less than 50 watts because of the overshoot problems. The only radio's I run at low power are my K3 (which is perfect power control) and the FT1000D (which has a drive gain control).

    How do you measure power?
     
  5. TF3T

    TF3T Ham Member QRZ Page

    To answer the question how I'm measuring power, Using a LP-100 power meter.

    We made some measurements on the setup few days ago, using a SDR receiver to analyse the output signal. The FT1000MP is clean. on CW with 43W drive - the output is clean (800w out). 47W the output is clean but the signal is getting "fat" - but still -70dB under the main. at 49W everything goes wild, We get strong carriers up and down from the carrier.

    I'm now going to get another power meter to look better at the drive power, but with the 30dB pad we should not be able to overdrive the amp - 10*log10(p1/p2) means that we should be able to fully drive with 100W to get 100mW out.

    There are few unknowns still - but I think the drive control of the MP is strange.

    Thanks.
    - Benni, TF3CY
     
  6. W8JI

    W8JI Ham Member QRZ Page

    You are not overdriving the SDR receiver are you?
     
  7. TF3T

    TF3T Ham Member QRZ Page

    About overdriving the SDR, I don't think so

    The difference in output power was not much, going from around 800W to 850W RF out.

    We also had another SDR monitoring from a distance, when we go from 43W to 49W our remote SDR clearly notices the cw far off the center frequency. Sad to say, but we got a comment on cluster from a very well known DXer that we had the uncleanest signal on band.
     
  8. W8JI

    W8JI Ham Member QRZ Page

    100 mW drive amplifiers can be problems. We noticed a USA contestor using one in the 160 meter contest and he had a horrible signal on CW. He had spurious signals everywhere.

    Unless the FT1000MP has a problem, it should be good by itself. Every FT1000MP sold has ALC issues, but they are not severe near the 100 watt level. It sounds to me like you have a stability problem.

    External attenuators of any type, especially of very high values, are not the most desirable thing for amplifiers. Ideally the swamping or dissipating network should be placed inside the amplifier stage as close to the active device as possible. Perhaps you can modify the amplifier.

    I'm sorry you are having that problem. Is the FT1000MP clean all by itself? Some have been known to have instabilitly in the power amplfier modules, but it is rare.

    73 Tom
     
  9. TF3T

    TF3T Ham Member QRZ Page

    here are pictures of the SDR - this is not very scientific:

    http://www.tf3cy.is/tests-of-ft-1000mp-and-rf-110

    We plan to do this test better, the methodology was not very scientific, we did not have a proper power meter between the FT-1000MP and the amplifier - so the drive levels are not very accurate. But we are pretty sure what the product of the overdrive is, but now we just need to find out why this is happening.
     
Thread Status:
Not open for further replies.

Share This Page