Re: Topband: Post contest season: TX antenna vs RXantenna cros-stalk. What do you do?
Good point. On 160 there was also a relatively nearby 829KHz AM BC station. The RDX PI4YLC Field-Day-style station used an OM-Power 6 BPF in its TX path. But no additional BPF or AM BCB HP filter in the RX path. A mistake I should have recognized. Thanks for the test procedure. Will use that additionally for sure at home and at any FD QTH in the future. 73 Mark, PA5MW -Original Message- From: JC Sent: Thursday, March 24, 2016 1:14 PM To: 'Mark van Wijk, PA5MW' ; 'william radice' ; topband@contesting.com Subject: Re: Topband: Post contest season: TX antenna vs RXantenna cros-stalk. What do you do? I was wondering what people do besides the obvious 'kill the TX antenna input during RX mode' ?<< There are several reasons why it is necessary to detune the TX antenna during RX, however disconnecting the center of the TX coax during RX on 160m is a MUST. If you don't understand the problem you never implement the solution. Some broadcast signal can reach -10 dbm or even 0 dbm. Most radios have very poor isolation and pin 1 problem on both the RX input and TX input. In order to open the center pin at the antenna feed point you need a fast vacuum relay to avoid hot switch. For an inverted L it will improve all RX antennas removing re-radiation noise from the TX antenna. Open the circuit between the transverter and the amplifier is a good idea. You need a fast relay but it can be small. Filters must be strong enough to hold at least 200w with low insertion loss. The test to know if you have this problem is simple, disconnect the RX antenna and use a 50ohms, shielded load to terminate the RX input. Tune on the AM band and if you hear strong BC signals coming from you TX antenna during RX with the RX port terminated with 50 ohms you have some homework to do. No carriers at all indicate that you have shield, grounding and choking in good shape, if you hear strong AM signals means that you have isolation and common node noise problems. If the BC signal can come in all QRN and other noise sources also can come in and raise the noise floor of the receiver. My station is quiet, I cannot detect any trace or light carrier doing the test above. Regards JC N4IS _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Post contest season: TX antenna vs RXantenna cros-stalk. What do you do?
Hi Terry, I have no access to the K3's as they belong to someone else. But I learned there is no such thing as total isolation. Not even with the Frond end savers, unless they incorporate several relays in series. But I did check my TT ORION using the Elecraft XG3 generator; isolation is abt 65dB You do the math when you have 9+40 signals on a large antenna like a fullsize TX deltaloop on 40 & 80m 73 Mark, PA5MW -Original Message- From: Terry Posey Sent: Thursday, March 24, 2016 12:04 PM To: 'Mark van Wijk, PA5MW' ; 'william radice' ; topband@contesting.com ; Eric Swartz -WA6HHQ, Elecraft Subject: Re: Topband: Post contest season: TX antenna vs RXantenna cros-stalk. What do you do? Hi Mark - I have not experienced K3 TX/RX antenna isolation problems with my station configuration. I expect that if there is an isolation problem with your rig's TX and external RX antenna routing/switching, that problem would be nearly impossible to quantify using your station's TX and RX antennas. The rig's TX/RX isolation would need to be measured on the bench, using good laboratory grade equipment. Perhaps, Elecraft can provide a list of expected isolation values that were measured for each of the TX and external RX antenna routing/switching configurations possible with the K3 and K3S. Those measurements would surely have been done during the rigs' design performance verification tests. GL 73, Terry K4RX ++ Hi Bill, I think this is not what I meant here; I also do use BPF's and the Front End Savers. The problem is that while listening to your receiving antennas, there is also some signal from the transmit antenna getting through thanks to the internal cross-talk of your rig's TX/RX relay. I was wondering what people do besides the obvious 'kill the TX antenna input during RX mode' ? 73 Mark, PA5MW _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
