Ferri-inductor 10 uH

Discussion in 'Wireless & RF Design' started by KF5J, May 11, 2014.

  1. KF5J

    Thread Starter New Member

    May 10, 2014
    4
    0
    I have a question about a ferri-inductor in my Kenwood TS130se transeiver. I tried to post the question yesterday but it did not show up as a new thread. If this message is posted then I will follow up with my question

    John KF5J
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
  3. KF5J

    Thread Starter New Member

    May 10, 2014
    4
    0
    Hello Everyone,
    I have a Kenwood TS130se that has a transmitter problem. As I switch from band to band starting with 80 meters (3.5 mc) up to 10 meters (28.5 mc), the maximum output power drops with every band change as the frequency increases. On 80 meters the power output is normal for this transceiver 125 watts, but by the time I get to 10 meters the maximum output has dropped to 5 watts.

    The final board consists of a single predriver Q1 followed by two driver transistors in push pull, followed by the two final transistors which are also push pull. I have been told that the problem may be a 10 uH ferri-inductor that is attached to the base of Q1. The other side of the inductor is attached to an 820 ohm resistor that is connected to the bias supply. At the junction of the inductor and the 820 ohm resistor are two caps 0.001 and 0.047 uf, a 330 ohm resistor, and a diode all in parallel to ground. All of the voltages both in transmit and receive are very close to what is shown on the schematic diagram.
    Here are my questions:
    1. What is the purpose of the 10 uH inductor? a filter? a choke?
    2. If the 10 uH inductor is shorted even if only a few turns will this cause the effect I am seeing in the transmitter output as the frequency is increased?
    3. I have a monitor scope which I can use as an oscilloscope. I have checked the RF level at the base of Q1 and on the other side of the inductor and the level appears to be the same. Does this indicate that the inductor is shorted? I have checked other RF chokes on the final board and they also show no difference in level. I have also checked this inductor in circuit with a RCL bridge and it reads 10 uH. I have not taken the inductor out of the circuit yet because removing the final board is a major task I will do if I can confirm the problem.

    The schematic of this TS130 is on line. When I get the site I'll post it.

    Thanks for your help in advance.

    John KF5J
     
  4. KF5J

    Thread Starter New Member

    May 10, 2014
    4
    0
    Hello Everyone,

    Here is the link to get to the service manual for the TS130se:

    http://www.radiomanual.info/schemi/TS130_serv.pdf

    Look on page 50 there is schematic of the Final Board. I tried to attach the manual but was told it was too large.

    John KF5J
     
  5. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Ugh!

    It's one of those horrible circuits drawn on a PCB layout!

    It looks as if the 10uH is part of the decoupling for Q1's base bias.
    it will look like about 220 Ω Reactance at 3.5 MHz,& 1760 Ω at 28MHz,so it will normally do a better job of decoupling at higher frequencies.

    If there is the same level of RF on both sides,it draws the condition of C3 & C4 into doubt.

    I'm a bit more suspicious of the previous stages,though
    Unfortunately,I'm not really familiar with the TS130SE,although I did have a TS120V at one time.

    My Yaesu FT301 has the 100w PA as a separate module,so you can use it as the 10watt version,by just removing the PA coax & power connections,re-routing the 10w amp through the filters & driving the antenna directly from that stage.

    I'm not sure if Kenwood does the same------if so,you could check the output of the previous stage into a Test load.
    Even if the connections are small board to board coaxes,they are probably at 50Ω impedance,so you could maybe still do the same thing--a bit messier,perhaps:D.

    Finally,this is a site devoted to Electronics in general--there are some Hams here,but most are not.

    The very clever non-Hams here will probably be able to sort the problem out from "first principles" but you may be better served by trying QRZ.com,which as its name implies,is a dedicated Amateur Radio site.
     
    Last edited: May 11, 2014
  6. KF5J

    Thread Starter New Member

    May 10, 2014
    4
    0
    Hello Everyone and vk6zgo,
    Thank you vk6zgo for your post. When you say that the 10 uH inductor is part of the "decoupling" of the base does this mean the inductor prevents RF from getting back into the bias supply, or does it prevent the amp from going into oscillation?

    A little more history on this rig: When I started trying to fix this transceiver the output on all of the bands was about 1-3 watts. I have replaced Q1 the preamp, Q2 and Q3 the drivers, on the Final Board, and the three transistors on the RF board which are the input to Q1. These transistor replacements plus some adjustments on the Filter Unit have got me to where I am today.

    Unfortunately this rig's final board is not set up like your Yaesu. There is a 50 ohm output on the RF Board going to the Final Board and an 50 ohm output going to the Filter Board. The inter stage connections are all direct. I have tried bypassing the filter board but the power loss was the same.

    I know about the QRZ Forum. When I got to a point where I did not know what to try next I posted my problem. I have got a lot of good suggestions and help there especially from Cliff who works on Kenwood gear. Cliff is the person who told me that my problem may be this 10 uH inductor L1. If you would like to read a more complete history of my trouble shooting activities go to the QRZ Technical Forums, Radio Circuits Repair and Performance, and look for "Kenwood TS130se - Low Transmitter Output". You will see my call sign KF5J there so you will know you at the right place. I first posted on March 9th so I have been at this for a while and will not give up.

    While doing some research on the purpose of the 10 uH inductor I came across this site and thought that the Radio Communications Forum might be able to help.

    Thanks again for the help and hope to hear from you on the questions posted above.

    John KF5J
     
Loading...