Question about building my own antenna switch

[smokeyjones666]

I have a question I hope some of you can answer for me. I have two antennas mounted to the trunk of my car: a Larsen 150/450/800 that I use to monitor my local 800MHz trunked system with my PSR-500, and a larger Maldol that I use for monitoring VHF with the same PSR-500 as well as some occasional tx on 2m and 70cm Ham with my Yaesu HT. I would like to build an antenna switch to make this setup more convenient for myself (as well as to hide the large hoops of coaxial cable that seem to be dominating the passenger compartment of my car .)

I was thinking of a shielded box with antenna connectors and some form of a DPDT switch, where when the switch is thrown the scanner is connected to either the Larsen or the Maldol, while at the same time the Yaesu is connected either to the Maldol or to a small 50 ohm dummy load (in case I do something stupid, like transmit.)

My question is what kind of switch do I use? Can I assume that going to RS and getting a toggle out of the drawer is a BAD IDEA that would leave me victim to all sorts of signals crossing over inside the switch body, potentially destroying the front end of my scanner as I blather on and on with my Yaesu? Are there internally shielded toggle switches available for just this purpose? Do I need to do some crazy crap with relays or physically-separated toggle switches? Does somebody already manufacture an 'antenna swapper', where I could realize all of this in a product that's already available on the market?

 

[Lowa2]

you can get coaxial relays. Use an off the shelf switch to activate the relay.

like this: http://www.rfparts.com/coaxial/cx1054a.html

61$

 

[rfradioconsult]

You want something along the lines of an MFJ-1703; unfortunally it's only rated to 30MHz, however it may be worth trying, who knows.

 

[Mike_G_D]

you can get coaxial relays. Use an off the shelf switch to activate the relay.

like this: http://www.rfparts.com/coaxial/cx1054a.html

61$

If you're willing to pay that then you might try looking at these ready built options from the same supplier: http://www.rfparts.com/coax_accessories.html#switches.

Scroll down toward the bottom; the model CX210N looks good and is $74 - saves the build effort.

If you need TX and 800MHz usage it's probably better that you get a pre-built well spec'ed switch though if you really want to build one then I would go for something like the relay and switch approach that Lowa2 mentioned.

-Mike

 

[kb2vxa]

What you need is a VHF/UHF coaxial switch, Daiwa, MFJ and a few others are available at Amateur Radio supply houses. Coax switches are different beasts altogether, made for HF they simply aren't suitable for a host of technical reasons I hope you learn by furthering your studies on RF theory. Now Ryan crack the books, acing a simple multiple choice quiz didn't prepare you to be a ham. Oh not sarcasm but a simple truth since testing was dumbed down to the point most foreign countries refuse to recognize US licenses for reciprocal operation.

Please note I used two different terms, a coax switch is not a coaxial switch.

 

[smokeyjones666]

What you need is a VHF/UHF coaxial switch, Daiwa, MFJ and a few others are available at Amateur Radio supply houses. Coax switches are different beasts altogether, made for HF they simply aren't suitable for a host of technical reasons I hope you learn by furthering your studies on RF theory. Now Ryan crack the books, acing a simple multiple choice quiz didn't prepare you to be a ham. Oh not sarcasm but a simple truth since testing was dumbed down to the point most foreign countries refuse to recognize US licenses for reciprocal operation.

Please note I used two different terms, a coax switch is not a coaxial switch.

Crack the books? I'm too busy spewing RF everywhere with my crackerjack ham license!

Seriously, I think I may have to look into rigging up a couple of coaxial switches in a cascading series to get something close to what I wanted to have and remember to keep the PTT locked when I'm not ready to transmit (isn't this kind of like having the safety on?)

 

[kb2vxa]

LOL! Now crack the books so you can get that RF to go where you want it rather than wasting power by spewing all over the place... durn CBer. (;->)

Yup, seriously you can connect multiple switches to route RF where you want it to go. Placing them back to back you can switch multiple rigs to multiple antennas but don't forget to label the ports. I would think that's a bit of common sense only nobody told the guys at HRO about it so it was like a blind man looking for a black cat in a coal mine at midnight trying to work their demos.

One last thought, the PTT lock on a base mic works opposite the safety on a gun, you can lock it on but if you want to lock it off turn the rig off. Cummon now, at least read the manual so you know that the lock only disables the remote control buttons on the hand mic, not the PTT. That reminds me of something (I don't remember which rig has it) I call the potato mic. This monstrosity is the size of a yam and has buttons all over it. I have no idea how anyone can work that thing or even if the rig would stay put when holding the potato or in some cases eating it.

Now start cracking those books, meanwhile you can temporarily change your screen name to Cracker Jack. (;->) When you have the basics down pat wear your callsign like a badge of honor and take the ferry over to the Island of Misfit Hams. You'll enjoy your stay at our luxurious Alpha Hotel with a courteous staff all dressed up in their foxtrot uniforms. http://www.hamisland.net/forums/

 

[smokeyjones666]

...One last thought, the PTT lock on a base mic works opposite the safety on a gun, you can lock it on but if you want to lock it off turn the rig off...

My Yaesu's just a little 5w HT without the external mic, good for hitting local repeaters in my metro area. It has a keypad lockout feature, which you can configure to apply to certain buttons only - one of them is to lock out only the PTT button (which I usually keep locked out.)

I was poking around on google, trying different variations on the words 'antenna', 'switch', 'rf' and whatever else - I came up with a bunch of items like this one: http://cgi.ebay.com/Dow-Key-SPDT-SM...73170QQcmdZViewItemQQ_trksidZp1742.m153.l1262

I'm not quite sure what to make of them, the specs on these things (when available) usually speak of isolation around 80dB in the range from DC to 1GHz. There seems to be a lot of them on the used market, I'm not sure what they're from but I get the impression they might have an application in some sort of cellular switching apparatus. It almost looks like I could take three of these things and a toggle and make some short jumpers for it - trouble is, the 12v variety seems to be rather rare, with 24v and above being the most common that I see.

If I can find three of the 12v variety for a reasonable price, they might be perfect. I'm already using SMA connectors for all of the stuff in my car, so the SMA connectors that come on the unit might be a bonus for me.

 

[kb2vxa]

I've been familiar with Dow Key products for decades, their coaxial relays go back as far as those old boat anchor Amateur transmitter-receiver combos and were used for antenna switching between them. I still have one from the 60s kicking around somewhere and highly recommend them. If it's remote switching you want the latching types are ideal, a push button console is easy enough to make and the relays hidden away somewhere out of sight out of mind.

Hey, are we having a private conversation here? (;->)