SDR Pan Adapter

Ham radio operators have a long history of using pan adapters to visualize an entire range of the radio spectrum. Traditionally, an adapter was essentially a spectrum analyzer that shows a trace where the X-axis is the frequency, and the Y-axis shows the signal strength at any particular frequency. You can quickly find either busy frequencies or empty frequencies at a glance.

Although the pan adapter has been around since the 1930’s, they aren’t as common as you’d think with regular analog radios. However, if you’ve used an SDR (Software Defined Radio), a spectrum display is par for the course. [Mehdi Asgari] did what a lot of hams have been doing lately: he married an SDR and his traditional receiver to provide a great pan adapter with very little effort.

To understand this hack, you have to remember how a superheterodyne receiver works. A mixer adds (or subtracts) a variable frequency with the frequency of interest. This shifts the received frequency to a fixed frequency where the radio can easily amplify and filter the signal. [Mehdi’s] radio, an Icom R72, uses a fixed frequency of 70.45 MHz. This is known as the intermediate frequency or IF.

[Mehdi] used a PlaySDR, although even the inexpensive RTL-SDR dongle will work at that frequency. The trick is finding a place to tap the IF from the receiver without hampering the radio’s operation. He found a likely place to tap the IF and used a small resistor to ensure the SDR input didn’t load the radio’s IF stages. Then it is a simple matter of setting some SDR software to the IF frequency, and you have a pan adapter. You could even use GNU Radio to do something custom if you wanted.

This isn’t an original hack. However, every radio needs a little different method for tapping the IF. The video below, for example, shows a similar hack with an RTL-SDR dongle and a Kenwood TS-570.

 

 

10 thoughts on “SDR Pan Adapter

  1. Looks as if I need to dig out the service manual of myKenwood TS 140S to see if the a similar point inside it…. Sheet I route have touted the cable before I solder on the plug is a rite og passage, one of us experience often. I had to think a hardware store cable clamp would have been an more elegant strain relief solution.. They are cheap enough yo have several sizes in ones hardware inventory. Stick my dongle into pin? No thank you that sounds like an odd mating.

  2. Silly me. I thought a panadapter used two (or more) radios, and varied the phase delay between channels to effectively “beam steer” the radio coverage.
    Someone I know was tuning into a faint station using this technique, and showed the results on a waterfall display. I got the Panadapter term mixed up with the beam steering.

  3. Read up on how the original Hallicrafters Panadapter enabled the rescue of downed airmen and helped win WW2.
    Like Enigma (a civilian commercial product (not German)) it went to war.
    The rest is history.

  4. I use an RTL-SDR with my TS-480HX but have a buffer amp between the IF and the RTL input (see here: http://www.cliftonlaboratories.com/z10000_buffer_amp.htm) This isolates the receiver from signal coming back from the RTL and also provides a bit of gain. Then the RTL is feeding HDSDR. This allows me to tune either on screen using a cursor or via the TS-480. Obviously, one needs the CAT rig control setup via serial (USB-serial adapter) to control the transceiver.

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