What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
I'm using SSB Electronic preamps, and yes, they do RF sensing/switching.
I run separate DC power to mine because someday I might want to use a sequencer, but you can also power them up the coax.
73, Jim KQ6EA/0
On 1/18/2018 21:34, chilesp@verizon.net wrote:
What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
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I use the SSB, and yes they RF switch, are coax fed, will handle high power and have bandpass filters. Quality stuff. http://www.ssbusa.com/gaasfet.html
Michael Vivona Sent from my iPad
On Jan 18, 2018, at 4:34 PM, chilesp@verizon.net chilesp@verizon.net wrote:
What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
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I use SHF-Electronik Mini-2 for VHF. RF switched up to 150 watts SSB (50 watts FM). Powered either coaxial or externally. Will purchase the 70 cm model this Summer.
Joe KE9AJ
Sent from my iPad
On Jan 18, 2018, at 3:34 PM, chilesp@verizon.net chilesp@verizon.net wrote:
What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
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I'm going to throw something controversial into the mix here: RF sensing is NEVER a good idea!
I'm running a DG-8 for 2m and a Mutek SLNA for 70cm, both fed with DC up the coax (the Mutek has been modded to do internal biasing), and my rig switches the DC off before it transmits, which avoids the risk of the preamp being inline when you send DC the wrong way up it.
You'll find with most preamps that do RF sensing, their RF Sense max transmit power is significantly lower than their DC switched rating, and this is mostly because switching your relays 'hot' is a really bad idea. Much better to kill the DC, which switches the relays cold, before you send that RF up the coax and into the circuitry instead of the bypass line.
Depending on the rig you are using, some have built in DC sending up the coax. Any rig that works like that will 'sequence' its transmit stage; it will switch off the DC output feed before switching in the RF power amplifier. If you're using external bias tees to send DC up the coax, I can thoroughly recommend the PTT-switched kits designed by M1GEO, which will have a similar effect - the PTT line from your rig will switch out the bias tee via its PTT input before it actually starts transmitting. Again, this is sequenced inside most rigs in order to prevent hot-switching of the relays.
As an aside, if you're planning to leave them at the top of the mast permanently, and not power them from your rig, then I would strongly recommend a solution that kills the DC when you're out of the shack. We had a remote station set up that someone left the bias tee connected permanently for, leaving the preamp constantly in-line for RX only purposes. It got hit by lightning during a big lightning storm that hit every tower and building in the area, and because there was power to the system, rather than the lightning just running down the bypass line, it fried a few components in the preamp. It's a miracle that's all that it fried!
73, John (XLX)
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of chilesp@verizon.net Sent: 18 January 2018 21:34 To: amsat-bb@amsat.org Subject: [amsat-bb] Mast mounted low noise amps
What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
_______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Good point, John. Especially given that I use my preamps mainly for satellites, I usually use one antenna for Rx and one for Tx with an SPDT, center-off switch to power one , the other, or neither depending on the satellite. So the RF switch is there more in case I screw up than for anything else.
For the local repeater (all on the same band, of course), I can turn the preamp off entirely.
73, Burns WB1FJ
On Fri, Jan 19, 2018 at 4:53 AM, John john@amber.org.uk wrote:
I'm going to throw something controversial into the mix here: RF sensing is NEVER a good idea!
I'm running a DG-8 for 2m and a Mutek SLNA for 70cm, both fed with DC up the coax (the Mutek has been modded to do internal biasing), and my rig switches the DC off before it transmits, which avoids the risk of the preamp being inline when you send DC the wrong way up it.
You'll find with most preamps that do RF sensing, their RF Sense max transmit power is significantly lower than their DC switched rating, and this is mostly because switching your relays 'hot' is a really bad idea. Much better to kill the DC, which switches the relays cold, before you send that RF up the coax and into the circuitry instead of the bypass line.
Depending on the rig you are using, some have built in DC sending up the coax. Any rig that works like that will 'sequence' its transmit stage; it will switch off the DC output feed before switching in the RF power amplifier. If you're using external bias tees to send DC up the coax, I can thoroughly recommend the PTT-switched kits designed by M1GEO, which will have a similar effect - the PTT line from your rig will switch out the bias tee via its PTT input before it actually starts transmitting. Again, this is sequenced inside most rigs in order to prevent hot-switching of the relays.
As an aside, if you're planning to leave them at the top of the mast permanently, and not power them from your rig, then I would strongly recommend a solution that kills the DC when you're out of the shack. We had a remote station set up that someone left the bias tee connected permanently for, leaving the preamp constantly in-line for RX only purposes. It got hit by lightning during a big lightning storm that hit every tower and building in the area, and because there was power to the system, rather than the lightning just running down the bypass line, it fried a few components in the preamp. It's a miracle that's all that it fried!
73, John (XLX)
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of chilesp@verizon.net Sent: 18 January 2018 21:34 To: amsat-bb@amsat.org Subject: [amsat-bb] Mast mounted low noise amps
What brand of mast mounted pre-amps are you using and do they sense RF for switching out of the feed line?
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
If you really wanted to do it right, you could always make your own with WA5VJB's MMIC boards. I've used a Qorvo SPF5043Z on them successfully several times, so the BOM for one is around $5. You'd still have to figure out sequencers, sensing, switching and what not if you wanted to. -Jordan KF5COQ
On Fri, Jan 19, 2018, 6:49 AM Burns Fisher burns@fisher.cc wrote:
Good point, John. Especially given that I use my preamps mainly for satellites, I usually use one antenna for Rx and one for Tx with an SPDT, center-off switch to power one , the other, or neither depending on the satellite. So the RF switch is there more in case I screw up than for anything else.
For the local repeater (all on the same band, of course), I can turn the preamp off entirely.
73, Burns WB1FJ
On Fri, Jan 19, 2018 at 4:53 AM, John john@amber.org.uk wrote:
I'm going to throw something controversial into the mix here: RF sensing
is
NEVER a good idea!
I'm running a DG-8 for 2m and a Mutek SLNA for 70cm, both fed with DC up the coax (the Mutek has been modded to do internal biasing), and my rig switches the DC off before it transmits, which avoids the risk of the preamp being inline when you send DC the wrong way up it.
You'll find with most preamps that do RF sensing, their RF Sense max transmit power is significantly lower than their DC switched rating, and this is mostly because switching your relays 'hot' is a really bad idea. Much better to kill the DC, which switches the relays cold, before you
send
that RF up the coax and into the circuitry instead of the bypass line.
Depending on the rig you are using, some have built in DC sending up the coax. Any rig that works like that will 'sequence' its transmit stage; it will switch off the DC output feed before switching in the RF power amplifier. If you're using external bias tees to send DC up the coax, I
can
thoroughly recommend the PTT-switched kits designed by M1GEO, which will have a similar effect - the PTT line from your rig will switch out the
bias
tee via its PTT input before it actually starts transmitting. Again, this is sequenced inside most rigs in order to prevent hot-switching of the
relays.
As an aside, if you're planning to leave them at the top of the mast permanently, and not power them from your rig, then I would strongly recommend a solution that kills the DC when you're out of the shack. We
had
a remote station set up that someone left the bias tee connected permanently for, leaving the preamp constantly in-line for RX only purposes. It got
hit
by lightning during a big lightning storm that hit every tower and
building
in the area, and because there was power to the system, rather than the lightning just running down the bypass line, it fried a few components in the preamp. It's a miracle that's all that it fried!
73, John (XLX)
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of chilesp@verizon.net Sent: 18 January 2018 21:34 To: amsat-bb@amsat.org Subject: [amsat-bb] Mast mounted low noise amps
What brand of mast mounted pre-amps are you using and do they sense RF
for
switching out of the feed line?
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions
expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
participants (7)
-
Burns Fisher -
chilesp＠verizon.net -
Jim Jerzycke -
Joe Werth -
John -
Jordan Trewitt -
Mvivona