[TowerTalk] Remote Antenna Switches

[Steve Katz]

> Steve,
> 
> This switch will work very well at VHF and UHF frequencies.  See:
> <http://www.eham.net/classifieds/detail/75982>
> 
> Big photo at: <http://www.w2fla.com/switch.jpg>
> 
> Regards,
> 
> Sherm
> W2FLA
> 
	[Steve Katz]  Hi Sherm, I looked at the photos and I don't see why
this design would work at VHF or UHF -- lots of series inductance shown
there (buss wiring between rotary switch and SO-239 connectors), lots of
stray capacitance in such a design, too.  I'd wager to guess that on a
network analyzer, this switch looks bad above about 50 MHz, but if you'd
like me to measure it, I surely can, in about five minutes.  The Transco
switches I referred to aren't anything like this, they are built as a
rotating 50 Ohm coaxial line section activated by a motor, kind of like a
motorized Bird Electronics coaxial switch (the kind you have to push,
rotate, then pull, to move from one port to another).  That's the kind of
design that has <0.2 dB loss at 1 GHz and >60 dB port to port isolation.
-WB2WIK/6











> At 11:01 AM 02/04/2003 -0800, you wrote:
> 
> 
> 	Homebrew switches using relays do not fare well at VHF, and less so
> at UHF.
> 	Relay and wiring reactance takes over pretty quickly.  Even using
> small form
> 	factor relays interconnected by a good circuit board layout such as
> 	Ameritron does, performance drops off pretty quickly above 144 MHz
> for the
> 	"control line" version, and the "biased through the coax" version is
> worse.
> 	
> 	For VHF-UHF remote antenna switching, I'd go with surplus Transco
> motorized
> 	coaxial switches.  Pretty much what everybody uses at VHF and above,
> most of
> 	the Transcos are good to at least 2 GHz, some higher.
> 	
> 	-WB2WIK/6
> 	
> 	"Success is the ability to go from failure to failure with no loss
> of
> 	enthusiasm." -Winston Churchill
> 	
> 	> -----Original Message-----
> 	> From: KG4QDZ [SMTP:kg4qdz at arrl.net]
> 	> Sent: Tuesday, February 04, 2003 9:46 AM
> 	> To:   towertalk at contesting.com
> 	> Subject:      Re: [TowerTalk] Remote Antenna Switches
> 	> 
> 	> I am trying to design something similar.
> 	> Have you measured loss? How do you think these would do at VHF/
> low UHF
> 	> freqs? Has anyone tried these at higher freqs?
> 	> 
> 	> 73 Skip (KG4QDZ)
> 	> 
> 	> 
> 	> ----- Original Message ----- >
> 	> > I made my own switch box.  I used 10 amp Radio Shack relays.  I
> have had
> 	> one
> 	> > relay burn up on me when I was having trouble with one of my
> mono
> 	> banders,
> 	> > and I burned the insulator on an SO-239 when the PL-259 barrell
> 	> loosened.
> 	> I
> 	> > run 1500 watts cw & ssb, 160, 80, 40, 30, 20, 15 & 10, and the
> box has
> 	> been
> 	> > in service for 9 years.  1500 watts into 50 ohms will have about
> 5 1/2
> 	> amps
> 	> > of current.
> 	> >
> 	> > And the relays are very similar to the ones in an Ameritron
> relay box
> 	> that
> 	> > was given to me.
> 	> >
> 	> > As long as the spring contacts have sufficient power rating, a
> little
> 	> follow
> 	> > (wiping action) when the contact makes or breaks, and mounted so
> the
> 	> relay
> 	> > springs are vertical (so any dust will fall out), You should be
> able to
> 	> use
> 	> > just about anybodies box.
> 	> >
> 	> > de Paul, W8AEF
> 	> 
> 	> 
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