Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Recomend dual band VHF / UHF antenna for two radios
On 3/15/2015 11:54 AM, Brian Reay wrote:
Well, I several of us often run full duplex 2m/70cm or even triplex 4m/2m/70cm nets locally and use a common 2m/70cm antenna without problems- hence my comment that I've never experienced any issues. (Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband duplex while mobile with a common antenna and with dual antennas on the roof of a SUV. True, I've not used the harmonic of the 2m frequency but the desense was never an issue. While mobile and using the single antenna, I relied on the internal duplexer of the radio. When using two antennas, there was no filter or duplexer added. If you think about it from a practical stand point, dual band radio with the ability to operate full duplex cross band would be pretty useless if it was an issue. I'm simply relating my experiences of actually using 2m and 70cm on a common antenna with a duplexer. If your experiences differ, fine. Brian, Have you actually measured desense with good test equipment? If not, you really don't know, do you? I've run 2m/70cm crossband mobile also. However, I also haven't measured the desense when trying to receive on the third harmonic. Have you? Additionally, when running crossband mobile, I've always gone from a nearby handheld on 70cm to a 2m repeater. Never tried it the other way around, and since the handheld is always (relatively) nearby, it always has a strong signal into the mobile. So even if there were desense I wouldn't see it. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#2
|
|||
|
|||
Recomend dual band VHF / UHF antenna for two radios
On 15/03/15 16:40, Jerry Stuckle wrote:
On 3/15/2015 11:54 AM, Brian Reay wrote: Well, I several of us often run full duplex 2m/70cm or even triplex 4m/2m/70cm nets locally and use a common 2m/70cm antenna without problems- hence my comment that I've never experienced any issues. (Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband duplex while mobile with a common antenna and with dual antennas on the roof of a SUV. True, I've not used the harmonic of the 2m frequency but the desense was never an issue. While mobile and using the single antenna, I relied on the internal duplexer of the radio. When using two antennas, there was no filter or duplexer added. If you think about it from a practical stand point, dual band radio with the ability to operate full duplex cross band would be pretty useless if it was an issue. I'm simply relating my experiences of actually using 2m and 70cm on a common antenna with a duplexer. If your experiences differ, fine. Brian, Have you actually measured desense with good test equipment? If not, you really don't know, do you? I've run 2m/70cm crossband mobile also. However, I also haven't measured the desense when trying to receive on the third harmonic. Have you? Additionally, when running crossband mobile, I've always gone from a nearby handheld on 70cm to a 2m repeater. Never tried it the other way around, and since the handheld is always (relatively) nearby, it always has a strong signal into the mobile. So even if there were desense I wouldn't see it. I haven't measured the desense, I was relating practical experience as I said. In the circumstances, they are probably more relevant in my opinion*. Tom is free to take which ever advice he decides is relevant. * The desense would have a number of variables, including the tx power (which may vary), tx and rx frequency (also variable). Plus the impact of the dense on the receive performance is almost impossible to predict in terms of who/what you could receive- by which I mean you could generate a raft of numbers for loss of system sensitivity but how do you translate that into practical link budgets, other than for known stations? It would be virtually useless for a random contact. 73 Brian |
#3
|
|||
|
|||
Recomend dual band VHF / UHF antenna for two radios
On 3/15/2015 4:47 PM, Brian Reay wrote:
On 15/03/15 16:40, Jerry Stuckle wrote: On 3/15/2015 11:54 AM, Brian Reay wrote: Well, I several of us often run full duplex 2m/70cm or even triplex 4m/2m/70cm nets locally and use a common 2m/70cm antenna without problems- hence my comment that I've never experienced any issues. (Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband duplex while mobile with a common antenna and with dual antennas on the roof of a SUV. True, I've not used the harmonic of the 2m frequency but the desense was never an issue. While mobile and using the single antenna, I relied on the internal duplexer of the radio. When using two antennas, there was no filter or duplexer added. If you think about it from a practical stand point, dual band radio with the ability to operate full duplex cross band would be pretty useless if it was an issue. I'm simply relating my experiences of actually using 2m and 70cm on a common antenna with a duplexer. If your experiences differ, fine. Brian, Have you actually measured desense with good test equipment? If not, you really don't know, do you? I've run 2m/70cm crossband mobile also. However, I also haven't measured the desense when trying to receive on the third harmonic. Have you? Additionally, when running crossband mobile, I've always gone from a nearby handheld on 70cm to a 2m repeater. Never tried it the other way around, and since the handheld is always (relatively) nearby, it always has a strong signal into the mobile. So even if there were desense I wouldn't see it. I haven't measured the desense, I was relating practical experience as I said. In the circumstances, they are probably more relevant in my opinion*. Tom is free to take which ever advice he decides is relevant. So you really don't know if you have any desense or not. You just haven't noticed any. That does not mean it's not there. * The desense would have a number of variables, including the tx power (which may vary), tx and rx frequency (also variable). Plus the impact of the dense on the receive performance is almost impossible to predict in terms of who/what you could receive- by which I mean you could generate a raft of numbers for loss of system sensitivity but how do you translate that into practical link budgets, other than for known stations? It would be virtually useless for a random contact. 73 Brian Actually, knowing the characteristics of the transmitter and receiver, as well as the characteristics of whatever filters are used, it's possible to quite accurately determine desense. That allows you to predict with pretty good accuracy how much signal it would take to attain a certain signal level (i.e. 12db SINAD) in the receiver. But that's the important part of ANY system. And it's impossible to predict the results of ANY random contact without knowing the details of the other station. But then that's true on any frequency with any mode. Something I did a fair amount of back in the mid 70's when I worked for a worked for a 2-way shop and planned UHF repeater systems. I doubt it's changed any today. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Recomend Size of Aux Antenna for use with MFJ-1025/6 or ANC-4 | Antenna | |||
Flower Pot Antenna a Dual-Band (20m and 10m) 'portable' Antenna | Shortwave | |||
Inquiry: dual band hand held radios | Swap | |||
dual band radios that transmit frs channels | General | |||
dual band radios that transmit frs channels | Policy |