I am nervous as well, Tom...hi Hi I'm really thinking of employing a separate relay that I control with a simple switch, vice depending on the rig to switch "correctly" using a simple switch is antiquated and slow but....for certain I can control the switch over mo betta AND prevent damage to the low noise amplifier...
> From: [email protected] > To: [email protected]; [email protected] > Date: Mon, 13 Jan 2014 11:37:50 -0500 > Subject: Re: Topband: Single antenna port xcvr but want to employ > separatereceive antenna > > > Anyone have an RTR-1 or 1A that is excess to their needs and willing to > > sell OR have another idea of how I can employ a separate receive antenna > > when I have one antenna port? > > Thank you, in advance, for any replies....off line replies work for me. > > 72/73, Jim Rodenkirch K9JWV > > > > Be REAL careful how you do this, Jim!!!! What works for one radio or system > will not always work for another. This is highly radio (and even amplifier) > dependent. I can say that based on some very good field experience in how > things interface. (I'm actually looking at newer radios today to check their > control systems.) > > > Many radios only have a few milliseconds between the low signal and the RF > output, some don't have any time between the TX signal and the RF output. > You have to get any relay completely transferred and all of the bounce gone > before RF appears. Normally the "back to receive" end of the sequence is > not a worry. > > Many radios do not have the best timing for the external amplifier relay > control ports. Some amplifiers do not like other stuff hanging on the TX > control line. > > If you pull a relay low to go TX and you ever lose power to the relay, lose > the relay, or lose the relay path, the system defaults with the transmitter > running into the receiver antenna. You have to decide if that can damage RX > antenna stuff. This requires a fast relay pull in time, and a slow release > time.. > > The solution seems to be to release a relay to go from RX antenna to the TX > antenna, but this system requires a very fast release time and sometimes a > slower actuation time. This means we cannot use a backpulse diode because it > will slow the relay too much, and it will go into TX mode after the RF > appears. > > In all cases the relay has to be pretty fast compared to the radio's window > between pulling the TX line low and outputting RF. If the relay is ever > mid-way in transfer, still bouncing, or in the wrong position when RF > appears, the least that happens is broadband transfer clicks. The most is > usually damage to the RX antenna. > > If there is a reasonable way to do it, it is better to add a RX port in the > radio and avoid all this. :) > > 73 Tom > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
