Topband: Receive ant question

[Eddy Swynar]

On 2011-10-26, at 5:32 PM, Rik van Riel wrote:

> 
> With the RX antenna a reasonable distance (>100ft) away
> from the TX antenna, would an RF limiter (like the one
> ICE makes) be an acceptable substitute for a front end
> protector with relays?
> 

Hi Rik,

I can only share my own personal experience here with you, for what it's worth...

First-off, I use TWO old transceivers for 160-meters, i.e. a Yaesu FT-980, & an Icom 751A. I use them (separately, of course!) to drive a pair of 813s, for 1 kilowatt input. I also use SEPARATE receiving antennas on the band, to cut-down on noise.

All was well with the Yaesu, utilizing the separate receive antenna jack at the back of the transceiver...however, on those occasions when I used the Icom, my observed signal on the scope looked absolutely HORRIBLE. Obviously RF was getting back into the rig when I used QRO, this despite the fact that the 751A has a separate receive antenna jack at the back, as well. 

A look at the schematic of each rig told the tale: the receive antenna jack in the Yaesu is AUTOMATICALLY GROUNDED when the transceiver transmits---in the Icom, however, there is no such safety feature: the jack "floats" at all times, inviting RF to get into the transceiver, playing havoc with it.

The ultimate "fix" was an outboard, separate grounding relay that is activated whenever the Icom transmits---it grounds the separate antenna jack, and I have had no further problems along this line. Check the schematic of your transceiver: if the auxilliary antenna jack grounds in transmit, you should be OK.

~73~ de Eddy VE3CUI - VE3XZ