Help with Sampler Specifications

Discussion in 'Radio Circuits, Repair & Performance' started by KD9IQO, Jul 29, 2018.

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  1. KD9IQO

    KD9IQO Ham Member QRZ Page

    I purchased this RF sampler on an eBay auction. It was identified as a Motorola SLN6321B. I can find no specifications. Does anyone recognize this device and perhaps have specifications?

  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    It is an "iso-T". Depending on the coupling between the BNC and the direct connection between the UHF (PL-259 / SO-239) connectors, the isolation should be between 20 dB and 40 dB.

    There are several ways to measure the isolation. The easiest way is with a receiver that has an "S" meter and a signal generator with a well calibrated attenuator. With the signal generator connected to one of the UHF connectors and the receiver connected to the other, set the signal generator at a certain reading on the "S" meter (at S-9 would be a good value. Read the signal level on the attenuator and write it down. Then, disconnect the signal generator from the UHF connector and then connect it to the BNC.

    Increase the signal level until the receiver "S" meter reads the same value as before. Write down this level.

    If the attenuator has dB calibration, then you can read the attenuation value directly. Otherwise, you are going to have to calculate the attenuation using the following formula:

    dB = 20(log base10(V1 / V2))

    This method will get you a pretty good value of the isolation between the BNC connector and the other 2-connectors. There are ways that will give you a more precise measurement. However, the method outlined will give you the value within a dB, or so.

    Iso-T units are used when tuning duplexers (without needing a lot of test equipment) and for things like coupling an oscilloscope to a transmitter, and so forth.

    Glen, K9STH
  3. KD9IQO

    KD9IQO Ham Member QRZ Page


    I'm sure you have accurately described this device. I say this because I tested it at 10 meters and calculated a 52 dB attenuation in the HF region. So, even though it was not intended for use in the HF bands, I am able to get a reasonable transmission sample-signal into my oscilloscope using this device. Any thoughts on maximum power capability?
  4. N6GRG

    N6GRG Ham Member QRZ Page

    This device is a little more simple than the power divider you speak of. Mine has what might be an additional feature in that you can change the isolation amount in decibels. I feel its more accurate to call it a sniffer. Just how flat it is , do not know. At one time I needed to work with a bunch of VHF radios. This device would allow me to connect the bnc output to a spectrum analyzer and run power though the device into a dummy load. It also would allow rf to go through the opposite direction, with the amount of isolation I needed, basically attenuation, which I calibrated. Saved equipment in those days, which did not have internal dummy loads like the HPs I work with now. Yours doesn't look like it has the two set screws and rotatable gadget witch allows you to change the amount of coupling into the BNC. Mine would handle 100 watts easily, but I do not know how flat it was. It is not s resistive sampler and is not flat I'm sure. I may be able to test mine now and get some details. Not made for HF. Mine has a S inside of a half round circle, flat on the bottom, very small symbol. 24932 26as101 is also on it.
  5. N6GRG

    N6GRG Ham Member QRZ Page

  6. N6GRG

    N6GRG Ham Member QRZ Page

    MIne was "air" coupled, yours may not be but looks to be the same device. I received mine in the 70s and who knows how old it was at that time !
  7. N7MOT

    N7MOT Premium Subscriber QRZ Page

    Loosen the nut under the BNC connector, which will then allow you to slide the BNC to adjust the coupling. This per the Motorola Communications Parts and Data Handbook, Page 183, 1980 Second Printing.
  8. N6GRG

    N6GRG Ham Member QRZ Page

    I used to work for a Motorola communications shop, and one of these was in a bucket of stuff. I love it, it will help you by , for instance, making it possible to protect your favorite signal generator, although you must calibrate it to use it that way. You can add an additional 10 to 20 db at the sampling point if you would like.

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