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Author Topic: Does an antenna switch create loss?  (Read 3598 times)
KC4YWW
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Posts: 11




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« on: March 29, 2013, 11:52:50 PM »

Hi all, While I'm waiting for my license (I passed the General last night after letting my license expire) I have a question.
Will an antenna switch create loss or interfierence?  I want to hook up my scanner using my 2m / 440 diamond whip.  It picks up beautifuly with this antenna at 40 feet in the air but I wouldn't want to have loses on my 2m rig.
Thanks
Pete
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PA1ZP
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Posts: 239




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« Reply #1 on: March 30, 2013, 01:16:49 AM »

Hi Pete

Yes an antenna switch creates loss, but not enough to mentione.
But you will have a much greater danger in blowing up your scanner with the 2 / 440 TX on the other end of the switch.

I trained a few hams for their licence andthat question you ask have been asked me many times before.
My advice is never do this to rigs on one switch.
The big trouble often is that you will blow up one reciever with the other transmitter.

For HF rigs my advice is even stronger.

Only one HF rig is hooked up to the antennas the others are is always connected to a dummy load.
I have seen to many blown up front ends because one rig was sending on antenna A and the other rig was recieving an antenna B.

Antenna B gave a complete overload of signal to the reciever and it blew up its front end.
We also blew up a few front ends in use with fielddays with multy ops on multy rigs.

There are solutions for that and that is use bandpass filters to prvent HF power from one rig to enter the other rigs.

A article about this just came up on Eham.
Read it here:
http://www.eham.net/articles/29774

73 Jos
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VE3QJ
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« Reply #2 on: March 30, 2013, 03:48:31 AM »

you mean that i could kill my new ft-857d at field day?
It's staying here, the club can ruin their own equipment!
Thank you very much for posting
Best 73
VE3QJ
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VE3FMC
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« Reply #3 on: March 30, 2013, 05:27:27 AM »

In the past I have had 4 HF rigs connected to a 4 position antenna switch and have not had any problems. Mind you the antenna switch is not a cheap piece of junk, and I NEVER have another radio turned on when transmitting with another radio.

So to answer the first poster. Yes you can hook the scanner up to the antenna switch, along with the 2 meter radio. Just make sure the scanner is turned off when you are transmitting with the 2 meter radio.

Also remember this. If it is a cheap coax switch it will have loses and you do not need that on 2 meters. So buy a quality switch and you will be fine.

73, Rick VE3FMC



   
   
RE: Does an antenna switch create loss?
« Reply #2 on: Today at 06:48:31 AM »
   
Reply with quoteQuote
you mean that i could kill my new ft-857d at field day?
It's staying here, the club can ruin their own equipment!
Thank you very much for posting
Best 73
VE3QJ

How do you think you are going to kill your radio at FD? I have operated during FD with 4 HF rigs operating and no one had problems with losing a front end on a radio. You are operating on different bands.

If you are worried about this happening then build some coaxial band pass filters.

 Pretty sure your club has no intentions of ruining their equipment.

 You must be a fairly new ham with a two letter call or you would have known that your radio would not get blown up during FD.



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AD4U
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Posts: 2167




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« Reply #4 on: March 30, 2013, 05:44:14 AM »

ANYTHING AND EVERYTHING you put between the transmitter or receiver and the antenna introduces loss.   The loss in each item (coax, connectors, "tuner", wattmeter, balun, SWR bridge, etc) is additive.  Whether or not the total loss in the system is acceptable or significant is what that really matters.

In your case even at UHF and with a decent antenna switch, I think the loss will be negligible.

Dick  AD4U 
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K1CJS
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Posts: 6034




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« Reply #5 on: March 30, 2013, 08:04:36 AM »

I wouldn't.  It's far easier to string up a short wire to connect to your scanner, even if it's only a five or ten foot piece outside the window, and it's safer for the scanner. 

To the question of 'blowing up' a receiver's front end, I've been told that a receiver does not have to be powered on for it to happen.  I haven't actually done experimentation since I have a better use for money than to repair a receiver that I've blown up that way!   Grin  73!
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VE3FMC
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« Reply #6 on: March 30, 2013, 09:47:15 AM »

I wouldn't.  It's far easier to string up a short wire to connect to your scanner, even if it's only a five or ten foot piece outside the window, and it's safer for the scanner. 

To the question of 'blowing up' a receiver's front end, I've been told that a receiver does not have to be powered on for it to happen.  I haven't actually done experimentation since I have a better use for money than to repair a receiver that I've blown up that way!   Grin  73!

Well I have never had a front end of a radio go out when it was shut off and I have operated 1000 watts through the antenna switch that had two rigs connected to it. Maybe it is different in Canada.  Grin
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PA1ZP
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« Reply #7 on: March 30, 2013, 09:53:30 AM »

Hi All

Yes in Canada everything is different.
They forgot the small m in front of the 1000 (m)W.
just kidding.
You were lucky we blew up 3 HF front-ends during fielddays.
We even blew up VHF 2 meter front end of Ft857D in use on HF, and connected to a 2 meter antenna.
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K1CJS
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Posts: 6034




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« Reply #8 on: March 30, 2013, 10:45:06 AM »

Well I have never had a front end of a radio go out when it was shut off and I have operated 1000 watts through the antenna switch that had two rigs connected to it. Maybe it is different in Canada.  Grin

The reason I answered as I did is this:  If someone who doesn't have the training and the knowledge were to get a cheap antenna switch and throw such a system together, he may well end up doing so.  Also, just because it hasn't happened to you (yet!) doesn't mean it can't happen to someone else. 

Oh, BTW, I HAVE had the front end of a scanner go out because of proximity to strong RF, and the scanner wasn't hooked up to a power source--it just had its collapsible antenna attached--and that wasn't even extended!  73!
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NH7O
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« Reply #9 on: March 30, 2013, 10:54:32 AM »

To the OP: Some antenna switches have much more isolation between connectors than others. The best are those which short the unused connections to ground. Some are rated for power levels, and the loss will be least for the highest power level switches; but it will be too small to measure easily in any case.

In FD situations, it is best to use the radios with attenuators turned on. Again, there is a wide range of differences in how front ends are protected, and some are pretty immune to damage.
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KM3F
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Posts: 506




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« Reply #10 on: March 30, 2013, 11:50:29 AM »

Pete, for the use your going to use a switch for all but the cheapest ones won't be an issue.
For instance, a device you may never use but hear about is the diplexer.
A signal splitter/combiner to enable radios to feed and receive from two antennas on widely different vhf/uhf bands off one coax cable.
They also have some loss, some small reflected power and good isolation between their ports.
I have used one in a mobile installation and fixed antenna install and can't tell a difference from loss or any other parameter on signals above the noise level involving repeaters at a distance.
For uses like this, no problem but I would not do it for weak signal long distance work where everything counts.
Just another perspective for you.
Good luck.
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VE3QJ
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« Reply #11 on: March 30, 2013, 03:05:54 PM »

 You must be a fairly new ham with a two letter call or you would have known that your radio would not get blown up during FD.

i have been a ham since 2001 and have had plenty of experience on the bands. i am a recent past president of out local radio club, started and ran a local net.

i was reading a post which read "You were lucky we blew up 3 HF front-ends during field days."
It kind of got my attention. I guess i am just being careful.
to say "you must be a fairly new ham with a two letter call" can be taken as an insult.
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KC4YWW
Member

Posts: 11




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« Reply #12 on: March 30, 2013, 09:27:06 PM »

Thanks to all who answered.  Since I was getting such a good signal from the Diamond, I thought that using the switch would cancel one unit totally while the other was in use.  Apparently this is not always the case .  I have decided to buy a cheap external antenna for the scanner and place it high on the tower.  After all, most of my use will be on the transceiver anyway.
Thanks again
73's
Pete
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WB6BYU
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Posts: 13288




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« Reply #13 on: March 30, 2013, 10:15:50 PM »

That might actually be worse than using a switch, because when you transmit
the scanner antenna is still connected.  Depending on the distance between them,
the scanner antenna can pick up a lot of RF from the transmitting antenna.
Whether or not that is enough to damage the scanner depends on the design of
the radio.

Personally I'd use a 2-pole switch rated for UHF operation, of type that shorts
out the unselected port. Or, if you find some coaxial relays, connect them to the
transmitter power supply and use two:  one to switch the antenna and a second
to ground the scanner antenna right at the antenna port.  That way whenever
you turn on the power to the transmitter the antenna automatically disconnects
from the scanner and connects to the transmitter.  When you turn off the power
supply the antenna automatically reverts to the scanner.  Keeps you from
accidentally transmitting without the antenna connected.
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VE3FMC
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« Reply #14 on: March 31, 2013, 05:37:44 AM »

OK so tell me something that apparently after being a ham for 21 years that I don't know.

You own 6 HF rigs. All of them are out of the box and sitting on your operating desk.

You are transmitting on one of those rigs and also using a 1000 watt PEP output amplifier.

None of the other 5 rigs are connected to the current system you are using by any means, not through a coax switch, none of the 5 rigs are turned on. None of the rigs have any antennas connected to them.

According to some opinions those 5 rigs are all at risk of losing the front ends due to excessive RF exposure.

Ok, fine, now tell me how do you protect those rigs? Box them up and put them in a lead encased vault when not in use?

Seriously, how do you protect those rigs? How do you protect your 2 meter rig when transmitting high power on HF (yes someone stated they lost the 2 meter front end in a FT-857 while transmitting HF on FD)

I have had numerous HF rigs connected to an Alpha Delta 4 position coax switch over the past few years. All of those rigs were capable of being transmitted on using one antenna system.

I have never had a front end get damaged. I shut the rigs off when not in use. I know of many other hams who do the same thing and have never had any issues. I know a local ham who has a radio set up for just about every HF band. When not in use they are shut off. He runs power, he has never lost a front end of another rig in his shack.

How about the amateur dealers who have 15 HF rigs on display, all connected to antennas so you can test them out, receive and transmit. How do they protect those other 14 HF rigs while a customer tries out one rig?

What is the secret?
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