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MDT 40mtr extreme low power SSB kit

Discussion in 'Survival Communications' started by WastedDaze, Sep 26, 2015.

  1. WastedDaze

    WastedDaze Monkey

    I recently built an MDT transceiver kit. This is an extreme low power 40 mtr radio to communicate with Sigle SideBand radios. It is very small & light weight too.
    The receiver only draws 50 Ma on receive and the transmitter consume 250 Ma with 2 watts RF out. It's fairly easy to build and adjust. I'd say beginner to intermediate skill level.

    But it doesn't transmit SSB.... MDT stands for Minimalist Double sideband Transceiver. Yes, DSB has some limitations but also makes for an easy to build and inexpensive radio for talking to SSB radios. It transmits both upper sideband and lower sideband at the same time. Combined with a well designed Direct Conversion receiver makes a great low cost / low power combination for backpacking or emergency use or whatever. An NVIS antenna is ideal for this little rig.

    First, the kit is complete with case and knobs and everything. Leon Williams, VK2DOB is the designer and sells the kit out of Australia. I was surprised that even with shipping the total was just over $80 US.

    Second, I built the kit in less than a day. Spent a couple hours the next day adjusting it. and had it on the air that afternoon.

    Third, the real test was using it in the field on battery power not in the shack with the base antenna and power supply.
    I strung up a light weight 40mtr dipole I made a couple years ago... Fed with 20' of RG-58 coax with no balun at the feed point. The antenna was only 10' off the ground. I made contacts out to 400 miles... The first to answer my CQ was N3APA out of NoCal. Also made contacts into Montana and Nevada. Even QRP to QRP contacts. One guy was using an Elecraft KX-3 bicycle mobile! I check into the west coast Noon Time Net about every other day wen I think about it.
    For field use I power the MDT with 3 old cell phone batteries in series. They last a couple days before I have to recharge.
    I also made a little antenna tuner to compensate for the detuning of the antenna when low to the ground and different ground conductivity. It has a built in SWR bridge with LED indicator.

    I think the MDT is a terrific kit radio for the beginner or seasoned ham. Not hard on the budget, easy to build and good daytime NVIS performance. Something fun to take camping or hiking to give your emergency comm experience a little exercise.

    Here are some photos of my set up.
    Last edited: Sep 26, 2015
    Radioman, KAS, 3M-TA3 and 6 others like this.
  2. JohnSteven

    JohnSteven CHUNKY MUNKY

    Very Nice- glad you posted it.
  3. stg58

    stg58 Monkey+++ Site Supporter+ Founding Member

    Ganado likes this.
  4. whynot

    whynot Monkey++

    Any specific tools needed for the setup/ adjustment phase?
  5. KAS

    KAS Monkey++

    please excuse my lack of knowledge .. .. this is a radio {vhf ? uhf type ?} that u built yourself from a kit ??
    interesting ... what will it be used for??
    cool hobby
  6. JohnSteven

    JohnSteven CHUNKY MUNKY

    can you send me the contact info to reach the seller of this kit?
    Not sure if I will absolutely order it, but you sure can't beat the price.
  7. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    ozQRP.com QRP Radio Kits
    JohnSteven likes this.
  8. Altoidfishfins

    Altoidfishfins Monkey++

    Yes. It is a low power, double-sideband, 40 meter (7.000 - 7.300 MHz depending on modulation type) HF radio. It operates at a much lower frequency than VHF. Ham VHF bands are from 50-54 MHz (6 Meter) and from 144-148 MHz (2 Meter).

    The fact that it operates at a lower frequency means that, under favorable conditions, the signal has the tendency to "carry" much farther than with signals from radios that operate at higher frequencies, as it bounces off of the atmospheric layers and the ground. That's why, even though its power output is only two watts, Wasted Daze was able to contact people out to 400 miles away.

    Hope that explains a little.

    Actually, it looks like a pretty cool project.
    Last edited: Sep 28, 2015
    KAS, JohnSteven, BTPost and 1 other person like this.
  9. KAS

    KAS Monkey++

    thanks !!
  10. Altoidfishfins

    Altoidfishfins Monkey++

    No problem. Don't hesitate to ask.
    Someone here will have an answer, or point you in the direction to get one.
  11. WastedDaze

    WastedDaze Monkey

    Sorry, haven't checked in for a few days...

    Yes, this transceiver is for the 40 meter Amateur Radio Band. This is in the shortwave or HF (high frequency 3-30 mhz) spectrum.
    The AM Broadcast band is below HF in the MF band (medium frequency 0.3-3 mhz) and FM Broadcast band in in the VHF (very high frequency; 30-300 mhz.)

    The best antenna to use with this radio is a half wave dipole 10'-20' above the ground and parallel to it.
    Here is a good primer on dipole antennas http://www.arrl.org/files/file/Technology/tis/info/pdf/9106023.pdf

    Most antenna articles recommend you put your dipole as high in the air as possible. This is for long range communications. The radio signal is low angle, that is it's going tword the horizon and getting the most distance before it skips off the ionosphere back to earth. Skip can range 1000-3000 miles.

    To better utilize our low power transceiver and talk more local we want a high angle signal going as straight up as possible. When our signal going up bounces off the ionosphere it makes very short skips at 200-400 miles and it can go right over a mountain just a few miles away so you an talk to another station in the next valley over. This type of operation is called NVIS (Near Vertical Incidence Skywave). Placing our dipole antenna low to the ground and parallel to it causes most of our signal to go nearly straight up! Cool huh?!
    Here are a couple presentations on NVIS NVIS

    NVIS is not theory but proven science and has been used since the 1930's. It really adds to your emergency preparedness and can add an element of entertainment and enjoyment too.

    Maybe it's time to study up for a Amateur Radio License (Ham)....?

    And for those who are licensed and know about HF propagation... Carry on!
    Last edited: Oct 3, 2015
    kellory and Tobit like this.
  12. WastedDaze

    WastedDaze Monkey

    Having an HF or shortwave radio with a digital dial and a 50 ohm dummy load is all your really need.

    An old analog 100 ma meter movement helps when nulling the carrier but it's not necessary. I put one in the power lead to the MDT. It should be indicating ~50 ma. Adjust the balance controls TC1 & VR2 for minimum current draw. This should null the carrier. But if you have an oscilloscope or spectrum analyzer then use those.
    Last edited: Oct 3, 2015
    kellory and Tobit like this.
  13. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    I like learning new things, carry on.
  14. WastedDaze

    WastedDaze Monkey

    And a word about modifications...

    I did two mods. The two toggle switches....

    There is a jumper on the board to change the tuning range. The toggle switch on the left is wired to where the jumper would go so the ranges can be selected without opening the case. Between the two ranges my MDT will cover just over 80 khz, from 7.217 to 7.300 mhz.

    The toggle switch on the right is to mute a little cell phone speaker I added. The speaker is mounted behind the holes in the upper right of the front panel. The audio feed to the headphone jack goes through a limiting resistor. The speaker audio bypasses the limiting resistor to get the full output of the LM386 audio amp to the speaker.

    Thanks for the kind comments. It's a hoot to use on the air especially when you tell the other station how little power you're transmitting.
    Last edited: Oct 3, 2015
    whynot likes this.
  15. shootanyangle

    shootanyangle Monkey

    hitchcock4 and Yard Dart like this.
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