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Author Topic: Antenna for split operation  (Read 529 times)
KG6IBW
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Posts: 13




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« on: March 19, 2002, 11:47:43 AM »

I am lucky enough to have a transceiver with a linear and another receiver (IC-R71A).  So I would like to listen to Ducie on the R71a and get into the station on the linear.  How do I do this with a single antenna?  Do I leave the linear permanently connected and use another pole in the send relay to disconnect the rx while transmitting?  Is there chance of bad timing or RF feedthru to the front end of the R71A destroying it?  Or?Huh  Plenty of folks run split, so there must be a way.  Many thanks for your wisdom and help.
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WB2WIK
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Posts: 20611




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« Reply #1 on: March 19, 2002, 11:54:27 AM »

What is your transceiver?  All the modern ones (last 10-15 years or so) have "split" operation as a standard feature, using firmware to allow the frequency synthesizer to switch instantly between two frequencies, one for RX and one for TX.  

If you're using an older analog rig that doesn't have this feature, you can surely use the second receiver instead.  Antenna switching should be done via a coaxial relay that has substantial isolation, however.  Your "linear" (amplifier) could indeed cause considerable damage to the R71A if it's not very well isolated.  Using another contact on the amp's T-R relay is very likely not sufficient, although measurements could be made to determine if it will work.

A simpler idea, especially for "strong" stations like VP6DI and XR0X, which are pounding in S9+++ into the U.S. (they have great locations and aren't very far away), is to simply use a random wire or loop antenna on the R71A, and don't connect the R71A in any way to your transceiver or amplifier.  If the wire or loop antenna is spaced 30-40-50' away from your transmitting antenna, there should be enough isolation to prevent damage to its delicate circuitry.

Last night I worked VP6DI on 12m CW about 0130Z, it wasn't difficult.  I could have easily used a short random wire antenna to hear him -- I know that for sure, since when I first turned on my rig, I heard VP6DI on 24.902.5 almost immediately, and I had not yet switched my antenna switch to my 12m antenna!  It was sitting in the "ground" position, connected to no antenna at all.  Pretty strong signal...

WB2WIK/6
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KG6IBW
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Posts: 13




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« Reply #2 on: March 19, 2002, 11:57:12 AM »

Thanks, WB2WIK, I have an Icom 718 with VFO A and B.  Is that what they are for?   Is there a good book to learn to use one of these things?   The manual is less than helpful unless you already know the jargon.  
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WB2WIK
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Posts: 20611




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« Reply #3 on: March 19, 2002, 12:40:29 PM »

With the IC718 you already have a "split" function and there's no need to use a second receiver.  VFO A is set to one frequency (for example, RECEIVE), VFO B is set to the other (for example, TRANSMIT), and you engage the SPLIT mode.

I don't have an IC718 manual, nor do I own an IC718, so I can't tell you offhand how to engage SPLIT operation.  On the "big" radios, it's almost always a button (front panel control) labeled SPLIT.  In some of the smaller radios, it may be a "menu" feature.

Although I don't have an IC718, I have lots of other Icom stuff and their manuals are excellent, I think.  Look up "split operation," it should certainly explain how to access this feature.

WB2WIK/6
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KD6ELB
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Posts: 48




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« Reply #4 on: March 19, 2002, 12:42:02 PM »

I have an IC-718.  The way you work split is to tune one of the VFOs to the receive frequency (the one you can hear the DX station on) and then hit the A/B button in the top right to switch to the other VFO.  Tune that one to wherever the DX is listening - often it is "up 10" meaning 10KHz higher - often it is a spread of 5-10 or 10-20 KHz up.  You'll here all the other DXers frantically signing.  Now you hit A/B again so that you can hear the DX station.  Finally hit the button marked "SPL" and you'll see a box with "SPL" in it appear on the display.  Now when you transmit you'll see the display change to the other VFO and as soon as you unkey it will switch back.  It's a bit like using a repeater on VHF/UHF except that you always select the Tx frequency manually.

Now you are ready to play the tricks of trying to figure out where the DX is actually listening at any moment in time.  A common trick is to wait until he acknowledges a call and then hit A/B and tune around until you hear the other station.  If the DX stays on that frequency for a little bit you might try keeping that as your tx frequency in the hope of making it in.  You can try to look for patterns that the DX station is following.  Can't say I've had much success with any of that.  

Good luck

Richard
KD6ELB
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KG6IBW
Member

Posts: 13




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« Reply #5 on: March 19, 2002, 12:57:29 PM »

Thanks, WB2WIK, I have an Icom 718 with VFO A and B.  Is that what they are for?   Is there a good book to learn to use one of these things?   The manual is less than helpful unless you already know the jargon.  
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RobertKoernerExAE7G
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Posts: 1435




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« Reply #6 on: March 19, 2002, 09:46:07 PM »

But the best way to hunt DX is using dual receive.  One receiver on the DX transmitting, and on your tranceiver you tune untill you find the station the DX is working.  When you can hear both side of the Q, you can tail-end, or xmit right after the station stops xmitting.  With dual receive, it is also easier to track how the DX is working the pile up.  If the DX is working the East Coast, and you are in AZ, you can xmit where you think the DX will go, rather than trying to get into the East Coast pile by being ontop of where the DX was listening.

If you are new to running split VFOs, ALWAYS have the A VFO your receive and your B VFO the transmit, and always use your full call.  If you don't use your full call, and you get on the wrong VFO, when the traffic cops tell you you are xmitting ontop of the DX, you won't recognize who they are yelling at (you).

Have FUN
Bob
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