DV4Mini desensing MD-380 DMR

[popnokick]

I've only tested this with the DMR mode of the DV4Mini, but I think I am experiencing receiver desense when my TYT MD-380 is close to my DV4Mini. The DV4Mini Tx output is only 12mw max... didn't expect it would be strong enough to desense the front end of the MD-380... but I think that is what is happening. Whenever I was within 7-10 feet or less of the DV4 with the HT I was seeing transmissions (red light on DV4) but hearing nothing. So I reduced the Tx output of the DV4 to about 5.5mw using the output power slider bar... and sure enough... I was receiving audio again on the HT even when close to the DV4 antenna (within about 3-5 feet anyway). It may even need further reduction. Just wanted to post this in case anyone is experiencing "no audio" with their MD-380 and the DV4. You may want to reduce the Tx output on the DV4 Control software. Haven't tried this yet with DStar because my DStar rig is an IC-7100 and is several hundred feet away on the other side of my property. But would be interested if anyone notices a difference with DStar.

 

[jonwienke]

Desense isn't caused by transmitter power, it's caused by signal hitting the receiver. It doesn't matter if TX power is only a few milliwatts if the TX antenna is right next to the RX antenna.

 

[popnokick]

There is a direct relationship between the level of "signal hitting the receiver" and transmitter output power. Other factors (antenna gain, distance, receiver shielding, for example) all enter into the total "link budget" in dB between the receiver and the transmitter. But decreasing Tx power will reduce the power getting to the receiver, whether via the antenna or directly into the front end components of the HT.

 

[N4KVE]

A few of the locals were discussing this exact subject. Since these "budget" radios do not have a front end, this is the result, & I'm not surprised. When one of the guys tried to duplicate this using a XPR6550, there was no desense at all.

 

[popnokick]

As far as the XPR6550 goes, do they EVER experience desense? I thought they were totally immune to desense and there is nothing on record of an XPR ever experiencing desense.

 

[N4KVE]

As far as the XPR6550 goes, do they EVER experience desense? I thought they were totally immune to desense and there is nothing on record of an XPR ever experiencing desense.

My point exactly. By substituting the TYT radio for the XPR radio, the point was made.

 

[RFI-EMI-GUY]

As far as the XPR6550 goes, do they EVER experience desense? I thought they were totally immune to desense and there is nothing on record of an XPR ever experiencing desense.

There is virtually no receiver that is immune from desense. It has to do with the dynamic range of the receiver. In my experience, most of the cost of a radio is in making a decent receiver. You pay little you get little. Why are portables so bad? 1) Battery drain is impacted more readily by the amount of time in standby or receiving. Having a decent RF preamp requires heavy DC biasing (= heavy current drain) 2) Having front end selectivity takes a large bandpass filter, you can't make a tiny radio and have decent filtering. 3) Wading through all the engineering tweaks to make a decent receiver requires many hours of design, bread-boarding a pilot run and revisions to the design. At least in the old days, Motorola invested that effort. These cheap radios are probably designed on a computer model and thrown together with no thought to a pilot run and extensive testing. If it works, it ships, Specs? Well has anyone complained? Well now, but good luck getting satisfaction.