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eHam Forums => Elmers => Topic started by: AD7XN on March 04, 2013, 10:27:52 AM



Title: antenna switch
Post by: AD7XN on March 04, 2013, 10:27:52 AM
Is it OK to use an antenna switch in reverse i.e.-say a 5 position unit using the ant inputs for connections to transceiver's, and the output for a single antenna input ?
Thanks
Matt


Title: RE: antenna switch
Post by: G4IJE on March 04, 2013, 11:04:51 AM
Should be fine - I'm sure many people use them that way - although I wouldn't transmit whilst another receiver or transceiver was switched on. There may be enough isolation between ports but personally I wouldn't risk it.


Title: RE: antenna switch
Post by: KG4RUL on March 04, 2013, 11:11:09 AM
Make SURE that the switch does not ground the unused terminal(s)!


Title: RE: antenna switch
Post by: K2DC on March 04, 2013, 11:22:32 AM
Matt,

   That may not be good advice you're getting.  First of all, you absolutely DO want a switch that grounds the unused ports because it will offer higher isolation than a switch that does not.  Secondly, if you are using high power, it doesn't make any difference whether the other rigs are turned on or not, they could still be subject to damage.  At a TX power of a KW, each of the other rigs will see 1 mW of RF into their front ends.  I wouldn't call that a high risk of damage, but it's a risk that I wouldn't take unless I knew exactly what devices were in the front end of each of the other rigs, what their damage thresholds are, and what front end protection exists (likely none).  At 100W or less, you might be alright, but you'd better be careful,
and be absolutely sue you know which rig is selected before you transmit with any of them (which holds true whether the unused ports are shorted or not).

73,

Don, K2DC


Title: RE: antenna switch
Post by: KE6EE on March 04, 2013, 12:20:17 PM
I use two multipole antenna switches: the first at the input to my antenna tuner and the second between the tuner and multiple receivers and transceiver plus 400W linear. Between the second switch and each receiver I use a receiver front-end protection device (for example Array Solutions AS-RXFEP) to limit the rf voltage which can get to each receiver front end (the AS-RXFEP limits this to .3 mV).

Both antenna switches ground the unused ports, but I do not have confidence that this plus the other isolation characteristics of the switches is sufficient protection for my receivers' front ends.

I do not use the antenna switches built into my tuner for the same reason. The unused positions of the built-in switch are not grounded and the isolation between the positions is poorer than that of the antenna switches.

Last, I am using high-quality antenna switches.


Title: RE: antenna switch
Post by: WB6BYU on March 04, 2013, 12:59:41 PM
How do you make sense of conflicting recommendations?  One way is to
try to understand the situations that each respondent is envisioning and
see how well it matches what you are trying to do.

A good quality commercial switch may have 60dB of isolation, especially
if it shorts the unused ports to ground.  That means 1mW to the receiver
with 1kW from the transmitter, and virtually any receiver should tolerate
that.  (It may not matter whether the receiver is turned on or not.)  Most
receivers should handle 10mW, and many will take 100mW or more without
damage.  (That's not to say they will work properly at those levels, but that
the receiver won't be damaged.)  So if you are running a 100W transceiver
to a reasonably good switch on HF, you should be OK.

But not all switches are well built, especially those designed for CB or
HF operation at a low price point (or home built.)  A switch with 40dB of
isolation on 80m may drop to 30dB on 10m if the connecting wires inside
the box run parallel for some distance or common ground impedance among
the ports.

The switches designed for VHF/UHF use, or those with the connectors
in a circle out the back or sides, tend to be better (in the latter case because
they minimize the connecting lead length.)  Those in a large rectangular box
that require long connecting wires may be more problematic.


So at 100W on HF, you're probably OK in most situations.  If you are running
more power, or have a particularly sensitive receiver that needs protection,
it would be worthwhile choosing a good quality switch.


Title: RE: antenna switch
Post by: G4IJE on March 04, 2013, 02:16:57 PM
I was thinking 70dB was a typical isolation figure (http://www.radioworld.co.uk/catalog/cx-201n_global_2-way_coax_switch_n-type-p-4198.html?osCsid=5126f7572c4b3fd0a2b0113d55ea2f7d) and I hadn't considered an amplifier. Perhaps I should have said that a good quality switch and 100 watts should be fine.


Title: RE: antenna switch
Post by: K8AXW on March 04, 2013, 08:38:49 PM
I was recently confronted with the same question.  My coaxial switch grounds unused ports.  I rejected the plan because I was afraid that I might forget to switch in the correct radio and try to operate it into a dead short.  Since my gear is old it doesn't have the "foldback" feature.



Title: RE: antenna switch
Post by: G7MRV on March 05, 2013, 05:02:07 AM
I was recently confronted with the same question.  My coaxial switch grounds unused ports.  I rejected the plan because I was afraid that I might forget to switch in the correct radio and try to operate it into a dead short.  Since my gear is old it doesn't have the "foldback" feature.



The watchword here is 'listen'. If a grounding switch is used, even more so than a non-grounding one, if the transceiver is not switched to the antenna then you will likely hear NOTHING, no signals, no noise, nothing. Always listen prior to transmitting, no matter what your setup (mine is rig direct to antenna for one particular rig), not only is it polite as it prevents jumping on someones QSO, it can also prevent such damage. For the radios i have that are switched, I have a routing to exercise the switches prior to transmitting, listening on each setting of the switch. If im on the wrong port, it will become aparent when the correct one is selected and the noise/signals increase.

This is something that is drilled into me by my line of work - In what I do, if I select a transmitter to the wrong port i can cause massive damage and huge economic loss, not to mention lose my job. So everything is double checked before a control is sent.

Of course, if your selecting a transmitter only (seperate boat-anchors) then you cant listen! Excellent, high quality and accurate labelling, and a sensible check routine are all thats needed.


Title: RE: antenna switch
Post by: K8AXW on March 05, 2013, 07:25:50 AM
MRV:  Of course your are absolutely correct in all respects!  While I was working I had the same situation..... it was necessary to monitor closely every motion and adjustment I made on my panel boards. 

However, with my radio setup and age, there is the excellent possibility of screwing the pooch.  I maintain two separate diagrams under my desk glass showing what switches need to be in what position to operate.  More importantly, since I have to swap cables on occasion I use these diagrams to keep track of what I'm doing.

Then there are times when I don't use the gear at all and have to refresh my failing memory before operating.  At other times I use one particular setup and ignore the other and lose track of what is hooked to what.

To have an additional coaxial switch in line to deal with became too much.  I'm now seriously considering a checklist like we used on our boilers.

If this sounds like a tottering old man with more than he can deal with, you're right!


Title: RE: antenna switch
Post by: NR4C on March 05, 2013, 10:00:08 AM
Well, you now have lots of good information.

But, how many radios are you going to hook up to this one antenna?

If the answer is two (2), look at MFJ.  They have a switch that connects radio A or B to antenna 1 or 2.  you could use the antenna and a dummy load on the antenna side, and two radios on the radio side.  Now if radio A is connected to antenna 1, radio B is connected to the antenna 2 (Dummy load). 

If you have more than 2 radios, look back at the other answers.

Good luck  -73-

...bc  nr4c


Title: RE: antenna switch
Post by: AD7XN on March 06, 2013, 04:38:11 PM
Thanks guy's for the info, and it sounds like -all rigs off--ant switch to rig--turn rig on---turn rig off---ant switch to next rig--turn that rig on etc.   RULE- All rigs off before switching ant switch !


Title: RE: antenna switch
Post by: WB6BYU on March 07, 2013, 08:41:05 AM
Quote from: K8AXW

I was recently confronted with the same question.  My coaxial switch grounds unused ports.  I rejected the plan because I was afraid that I might forget to switch in the correct radio and try to operate it into a dead short.  Since my gear is old it doesn't have the "foldback" feature.




I'm not sure that a dead short is any different than a dead open in this
respect.  The actual impedance seen by the rig will depend on the
length of coax between the rig and the switch in any case.  I haven't
used a ham rig yet that would fail due to a momentary test into a short
or open, long enough to see that the rig is properly connected.  On voice
you can just blow into the mic to get about 10% output power and see
that the power meter deflects.  Similarly with a single dit on CW.

If you're worried about that, then you can get a switch with an extra
set of contacts and wire them to light a lamp over the rig that is
connected to the antenna, or get more fancy and wire PTT switch
through them so you can't transmit on a radio that is not selected.


Title: RE: antenna switch
Post by: M5AEO on March 07, 2013, 12:03:52 PM
I asked the same question on this forum some time ago.  I have been using a 3-way coax switch by Diamond for several years in this situation: one antenna feeding 2 transceivers and a receiver.  It has worked fine with no problems.  The Diamond switch is specified to 60dB isolation on each port.  Just check and double-check that you have the right rig switched BEFORE you transmit!

Jonathan M5AEO, London.


Title: RE: antenna switch
Post by: G3TXQ on March 07, 2013, 01:32:30 PM
I also have a 3-way Diamond switch that I use to feed the outputs from 3 radios through to a single amp/tuner/antenna. On 10m, if I transmit on one radio at 100W and tune one of the unused radios to the exact same frequency, I see an S meter reading of S9+60dB. That's a little more than 60dB isolation.

Steve G3TXQ