PA8W Amateur Radio              

Back
What receiver to use with my Radio Direction Finder?





 
Conventional receivers:

I've been using several conventional receivers with my RDF's and almost all worked fine.
In fact, all "normal" conventional receivers I know work fine in conjunction with a peudo doppler RDF.
For example I've got great feedback from radio hunters using an Icom R30,
but even a cheap radio like the Uniden Bearcat UBS 125XLT should do an excellent job.
The only radio that I found was useles was the Baofeng UV3 as explained below.

Generally, we use the audio (earphone) output of a receiver to feed into the RDF41 or RDF42.
But quite often a discriminator output works fine as well for RDF work.



My radios:

For mobile use I have a Stabo XR2000 handheld scanner, which is compact and very versatile.
It has NBFM as well as AM so it can be used with pseudo dopplers arrays as well as amplitude arrays.

For fixed applications on UHF and SHF I use the AOR2000, the predecessor of the AOR3000 in the picture.
It also has NBFM and AM mode.
I added a discriminator output to this radio and that output is equally useful for RDF work.
This second output may even come in very handy when you're hunting AM signakls such as Airplane communications. If I switch the radio to AM to hear the pilots speak the discrimination output will still give out FM output so my pseudo doppler will have a fine signal to work with.

For fixed applications on VHF I use the Icom IC-746pro, which has a DSP last IF stage.
An excellent transceiver but beware not to hit the transmit button if you don't want to blow the electronics in the array, as it may output about 100 watts in the 2 meter band!












No RLT-Stick receivers:

I've tried to make RTL-SDR receivers work with the RDF42 direction finder, instead of using a standard radio scanner or communications receiver.

Basic setup: RTL dongle RTL2832U from RTL-SDR.com, connected to a laptop running SDRsharp.
The RTL dongle is connected to the coax output of a standard pseudo doppler array.
The RDF42 controls the array and gets audio from the laptop.

Result: it works, sort of....
Issue: using an older Acer laptop I noticed a slow but serious drift in the bearing showed on the RDF42.
That means the latency (time-lag) in the laptop is not constant enough.

A brand new Lenovo laptop showed similar issues but with additional sudden jumps.
Maybe at points where the laptop decides to turn its processor speed up or down.

So, a standard RTL stick receiver setup is simply NOT an alternative for a classic receiver.
However, I didn't yet test a Raspberry Pie with RTL dongle, so maybe that could work.





Other No-no's:

Beware of radio's with a "smart" squelch: A squelch that doesn't simply open or close but uses a few stages of audio filtering depending on signal strength.
The idea is that the weaker the station, the more receiver noise needs to be suppressed, and so the more agressive the audio high cut filter must be.
Since audio filtering introduces phase shift, it will immediately result in an serious error in the calculated bearing of the RDF.
Phase shift is fine if it is constant, so you can calibrate it out, but when it adapts itself during signal fluctuations you're cooked...
The Baofeng UV3 is one of these ugly creations.

73, Wil 

Back

/>