[aprssig] Receiver overload issues with Kenwood TH-D72

Max Harper kg4pid at yahoo.com
Fri Feb 8 12:01:48 EST 2013

If the radios are only a few feet apart I would put dummy loads on both radios, even that may overload. I've noticed that when two radios are close together that you will hear all kinds of strange noises generated. As a test, take a radio and put it into transmit with no mic connected. Then listen on a second radio and lightly tap on the case of the transmitting radio. Most of the time you will hear the tapping sound even though there is no mic connected. This goes away when you get some distance between radios.

From: Andrew P. <andrewemt at hotmail.com>
To: "aprssig at tapr.org " <aprssig at tapr.org> 
Sent: Friday, February 8, 2013 10:05 AM
Subject: [aprssig] Receiver overload issues with Kenwood TH-D72

Greetings, all.

I was conducting some software tests that required passing data between two stations to ensure the data would be transmitted and received correctly. So, I had my transmitting station (Alinco DR-135T mobile and Byonics TinyTrak 4) and receiving station (Kenwood TH-D72 HT) sitting on the bench, both tuned to the same idle simplex frequency (I picked a quiet frequency not used for anything in my area), with the Kenwood HT about 1 meter from the Alinco's antenna. When I transmitted packets from the Alinco to the Kenwood, I could see the transmit indicator on both the TinyTrak and the DR-135T, but the TH-D72 would only occasionally squawk and acknowledge receipt of the packet (about 15% success rate). Transmitting in the reverse direction had an even lower success rate (zero packet detections at the receiver).

Could it be I was overloading the radios' front ends by being too close to the other radio's antenna? I made sure to use the factory "rubber duck" antenna on the Kenwood to minimize gain, and even turned the HT on its side to ruin polarization, but that didn't help.

Any suggestions (other than getting help because my arms aren't long enough to reach both rigs further apart)? I'm considering replacing the Alinco's antenna with a dummy load and depending on leakage to conduct the test, but I'm not sure if that will help.

Andrew Pavlin, KA2DDO
Sent from my Verizon Wireless BlackBerry
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