Home |
Search |
Today's Posts |
|
Electronic Schematics (alt.binaries.schematics.electronic) A place to show and share your electronics schematic drawings. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
RF switching
Heya folks!
Because of my location & topography, I'm forced to run several preamps on my different radios just to hear anything. So, I need a circuit to switch out my UHF receiver preamps whenever I use my ELH730 to boost the output of my VX7. A carrier-driven relay circuit would do the trick but I can't seem to locate one. Thanx in Advance! =KC7PSX= |
#2
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
RF switching
Meepus wrote:
Heya folks! Because of my location & topography, I'm forced to run several preamps on my different radios just to hear anything. So, I need a circuit to switch out my UHF receiver preamps whenever I use my ELH730 to boost the output of my VX7. A carrier-driven relay circuit would do the trick but I can't seem to locate one. Thanx in Advance! I've seen a lot of grief with carrier-driven relays. Either they wore down fast or the RF amp complained about a glitch one day with an expensive KABLOUIE. I built all amps myself and usually you must feed it some DC via the coax. Take the DC away - Pass-thru. http://www.ssb.de/amateur/englisch/amsat/mvvfsp_e.shtml -- Regards, Joerg http://www.analogconsultants.com/ |
#3
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
RF switching
On Tue, 26 Feb 2008 18:23:14 GMT, Joerg
wrote: http://www.ssb.de/amateur/englisch/amsat/mvvfsp_e.shtml Wow, cool link, that preamp controller would be just the ticket. I know the Alinco amp has a connection which inhibits the amplifier, my main question then becomes: What cicuit would "see" the presence of a low- wattage (.5w) 440 carrier & bypass the receiving preamps Does cutting off the DC to a outboard preamp adequately protect the preamps' FETs or is it necessary to =bypass= the receiving preamp? Thanx! =Meepus= |
#4
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
RF switching
Meepus wrote:
On Tue, 26 Feb 2008 18:23:14 GMT, Joerg wrote: http://www.ssb.de/amateur/englisch/amsat/mvvfsp_e.shtml Wow, cool link, that preamp controller would be just the ticket. I know the Alinco amp has a connection which inhibits the amplifier, my main question then becomes: What cicuit would "see" the presence of a low- wattage (.5w) 440 carrier & bypass the receiving preamps If you can't get a reasonable DC response via a diode you can amplify, then detect. A nice stiff MMIC or something, they are cheap. But you'd have to use one that won't croak at a few hundred mV of output level. As I said I never did that myself since I don't trust RF-autoswitch relays. Seen too much grief there. Does cutting off the DC to a outboard preamp adequately protect the preamps' FETs or is it necessary to =bypass= the receiving preamp? On a well designed preamp with T/R relays, yes. Else you should provide fast input protection diodes. I always pre-bias them a few hundred mV so that they don't cause intermodulation during receive, when strong signals are around. Take a look at the voltage levels at the worst case SWR and see if that exceeds the transistor's datasheet limits. Hotrod RF transistors often cannot take more than 3V, some even less. The ARRL Handbook used to explain passive diode T/R switching for VHF/UHF preamps. But I never really trusted that in terms of intermodulation. Then again I didn't do much above 30MHz anyhow. -- Regards, Joerg http://www.analogconsultants.com/ |
#5
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
RF switching
On Thu, 28 Feb 2008 08:34:23 -0800, Joerg
wrote: I was hoping for something quick & dirty.Something like using the Alinco ELH-260 power/preamp schematic as a reference, hack up an RF-driven relay to bypass/de-energize my Anzac preamp whilst my ELH-730 is hot. I've noticed this NG deteriorated into some kind of agitprop troll hangout - surprised I got any on-topic response at all . Appreciate your input Joerg, I need to slog through my old ARRL Handbooks & see what I can dig up. Thanx again! =KC7PSX= If you can't get a reasonable DC response via a diode you can amplify, then detect. A nice stiff MMIC or something, they are cheap. But you'd have to use one that won't croak at a few hundred mV of output level. As I said I never did that myself since I don't trust RF-autoswitch relays. Seen too much grief there. Does cutting off the DC to a outboard preamp adequately protect the preamps' FETs or is it necessary to =bypass= the receiving preamp? On a well designed preamp with T/R relays, yes. Else you should provide fast input protection diodes. I always pre-bias them a few hundred mV so that they don't cause intermodulation during receive, when strong signals are around. Take a look at the voltage levels at the worst case SWR and see if that exceeds the transistor's datasheet limits. Hotrod RF transistors often cannot take more than 3V, some even less. The ARRL Handbook used to explain passive diode T/R switching for VHF/UHF preamps. But I never really trusted that in terms of intermodulation. Then again I didn't do much above 30MHz anyhow. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Steamer keeps switching off | UK diy | |||
Ariston switching on | UK diy | |||
switching | Electronics Repair | |||
it keeps switching off!! | UK diy | |||
Hitachi TV keeps switching itself off | Electronics Repair |