How to connect this Active Antenna Loop and 100MHz version upconverter?

[Harold Chan]

I have bought an Active Antenna Loop for receiving MF/HF signal. I found that there is signal from the antenna (tested by using another radio), but I can detect no signal when connecting to upconverter. I think I have connected them wrongly. May you advice the way of connection? 

[Opendous Incorporated]

First, please check that the Upconverter is functional. Plug in USB
for power, set the switch to Upconvert, then connect it to your RTL
dongle and see if you see a signal peak around 100MHz when tuned to
100.01MHz (this is the LO bleed).

To connect the 3.5mm connector to the SMA plug it would help to know
the pinout. The sleeve is likely to be GND so connect it to the SMA
bulk (you can wrap wire around both connectors). The tip is likely to
be the signal so wrap some solid single-strand wire over the 3.5mm
connector tip and stick it into the SMA connector. It should work but
can easily damage the SMA connector. Other option is soldering to the
SMA connector pads on the PCB.
http://en.wikipedia.org/wiki/Phone_connector_(audio)#References

You could use three adaptors: 3.5mm Stereo Female to RCA Male, RCA
Female to BNC Male, then BNC Female to SMA Male. I could not find a
3.5mm to SMA adaptor. Note shipping is several weeks for these
listings.
http://www.ebay.com/itm/2pcs-3-5mm-1-8-Stereo-female-jack-two-dual-RCA-male-Y-Splitter-Audio-adapter-/330899088073
http://www.ebay.com/itm/BNC-male-plug-RCA-female-jack-center-TV-RF-adapter-connector-/220952676989
http://www.ebay.com/itm/BNC-female-jack-SMA-male-plug-RF-coaxial-adapter-connector-/220952674347

[Opendous Incorporated]

After coming across your Ultra-Cheap-SDR group post I realized
connecting the antenna directly to the Upconverter will be a bit more
complicated.

The Degen31MS's Tuning Box provides DC Power/Bias to the amplifier
which you would have to recreate with a Bias Tee.
http://en.wikipedia.org/wiki/Bias_tee

Not too difficult but would require soldering.
http://www.digikey.com/product-detail/en/BC2AAW/BC2AAW-ND
http://www.digikey.com/product-detail/en/4622-RC/4622-RC-ND
http://www.digikey.com/product-detail/en/FK24X5R1C106K/445-8497-ND

The Upconverter has a BAV99 Diode for protection so the RF_Only side
would connect to the Upconverter RF and the RF+DC side of the Bias Tee
would connect to the antenna. However, I could not find the pinout of
the antenna's stereo jack.

The easiest way to connect the active antenna to the Upconverter is
to use the Tuner Box and clip the Black Ground clip to the SMA
connector bulk and clip the White Antenna Clip to a short piece of
wire and stick it into the SMA connector.

[Opendous Incorporated]

This is the correct picture of the Upconverter RF input.

[Harold Chan]

Hi, 

Thanks for your help. I can now get some signal peak at shortwave range. But it is only 20dB higher than noise, I cannot hear the voice by those AM stations (But it is ok by using radio). The attached photos show my connection to SDR (SMA - BNC - PAL), would it be also the problem of mismatch impedance? Or other reasons? Please advice.

Regards,
Harold

[opendous]

  The connection looks correct.  You can check for continuity with a multimeter but the adaptors look new.

  Please post a pic of the spectrum when tuned to 100.01MHz with the Upconverter on.  There should be some LO bleed, otherwise the oscillator or LO circuit may have problems.

  It could be as simple as reseating the oscillator in its socket.  Remove it, wipe the leads with Isopropyl Alcohol, let it dry, then stick the oscillator back in.