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Close-spaced rover antennas

Scott K5TA
 


I have a brand-new IC-9700 that I’m itching to try out in the ARRL contest next weekend.  That rig has 3 separate antenna connections, one for each of its bands (144-432-1296).  I have all the antennas ready to go, and am planning a “rover simulator” operation on my own property — i.e. a mast with the yagis, planted in the ground, and a vehicle pulled up next to it with the radio(s).

I have looked at numerous pictures of rover setups, and it seems that most, if not all, have short masts with antennas spaced 1-3 feet apart.  I plan to emulate that design, but since the '9700 has 3 separate antenna ports, and only one transmits at a time, I started to be concerned about frying the front-ends of the non-TX bands.  I posted a question about this on the IC-9700 io group, and received loads of responses, ranging from “no problem except for KW power levels” to “you absolutely need all sorts of relays, sequencers, triplexers, filters, or whatever.”  As has happened many times before, my experience with these fora has been less than satisfying.

I know there are extremely experienced rovers and contesters on this list, and I wonder what your ideas are.

-Scott K5TA

Keith Morehouse
 

I don't know the exact answer, but one thing you can do to protect yourself if you're using any kind of amplifier on the three ports is to T/R all the amps together, even though you're only using one band at a time.

Assuming all the amps are stable into whatever load the 9700 port appears to be while in RX mode, this gives you lots of isolation.

-W9RM

Keith Morehouse
via MotoG


On Sat, Jun 1, 2019, 9:38 PM Scott K5TA <k5ta@...> wrote:

I have a brand-new IC-9700 that I’m itching to try out in the ARRL contest next weekend.  That rig has 3 separate antenna connections, one for each of its bands (144-432-1296).  I have all the antennas ready to go, and am planning a “rover simulator” operation on my own property — i.e. a mast with the yagis, planted in the ground, and a vehicle pulled up next to it with the radio(s).

I have looked at numerous pictures of rover setups, and it seems that most, if not all, have short masts with antennas spaced 1-3 feet apart.  I plan to emulate that design, but since the '9700 has 3 separate antenna ports, and only one transmits at a time, I started to be concerned about frying the front-ends of the non-TX bands.  I posted a question about this on the IC-9700 io group, and received loads of responses, ranging from “no problem except for KW power levels” to “you absolutely need all sorts of relays, sequencers, triplexers, filters, or whatever.”  As has happened many times before, my experience with these fora has been less than satisfying.

I know there are extremely experienced rovers and contesters on this list, and I wonder what your ideas are.

-Scott K5TA

Scott K5TA
 

That’s a good idea (amps) but I’m going to be totally barefoot. I’m thinking I’ll just keep it down to 10 watts or so, and play it by ear. 

-TA


On Jun 1, 2019, at 9:57 PM, Keith Morehouse <w9rm@...> wrote:

I don't know the exact answer, but one thing you can do to protect yourself if you're using any kind of amplifier on the three ports is to T/R all the amps together, even though you're only using one band at a time.

Assuming all the amps are stable into whatever load the 9700 port appears to be while in RX mode, this gives you lots of isolation.

-W9RM

Keith Morehouse
via MotoG

On Sat, Jun 1, 2019, 9:38 PM Scott K5TA <k5ta@...> wrote:

I have a brand-new IC-9700 that I’m itching to try out in the ARRL contest next weekend.  That rig has 3 separate antenna connections, one for each of its bands (144-432-1296).  I have all the antennas ready to go, and am planning a “rover simulator” operation on my own property — i.e. a mast with the yagis, planted in the ground, and a vehicle pulled up next to it with the radio(s).

I have looked at numerous pictures of rover setups, and it seems that most, if not all, have short masts with antennas spaced 1-3 feet apart.  I plan to emulate that design, but since the '9700 has 3 separate antenna ports, and only one transmits at a time, I started to be concerned about frying the front-ends of the non-TX bands.  I posted a question about this on the IC-9700 io group, and received loads of responses, ranging from “no problem except for KW power levels” to “you absolutely need all sorts of relays, sequencers, triplexers, filters, or whatever.”  As has happened many times before, my experience with these fora has been less than satisfying.

I know there are extremely experienced rovers and contesters on this list, and I wonder what your ideas are.

-Scott K5TA

John Klem
 

I have wondered the same thing.  On my antenna stack, which is not even that closely spaced, I have played it safe and disconnected the coax on the non-transmitting antennas.  So far.  I had a bad experience (actually, two bad experiences) with satellite antennas and an expensive GaAs FET preamp years ago to guide me.
If you have a sensitive RF power meter, it would be interesting to connect it to one of the non-transmitting antennas and see if you can measure any power coming down the coax when you transmit into the adjacent antenna.  I may try that next weekend.
John, AA5PR

Bill
 

Scott,

I didn’t have “RF fratracide” problems until I started using the 400 watt TE Systems amplifiers. My stack allowed about 18” between Yagis. I toasted the front end of an Elecraft 222 transverter, which I later found to be particularly sensitive to 144 energy.

I tried some duplex cavities for 144, 222, 432 and 902. They worked, but they had noticable loss on receive. They took up a lot of volume inside the rover. 

Later I replaced the 144 and 432 cans with bandpass filters from DCI Digital Communications and that reduced the volume and receive losses. They’re expensive.

I still have all those filters if you want to experiment.

With that protection concept I liked the fact that everything was passive and didnt require a bunch of rf switching.

I never protected my 1296 receive equipment until I adopted the simultaneous keying concept. Never had a problem. Maybe I was lucky but the 1296 antenna was located further away fron the high powered 50, 144 and 222 antennas.

The best approach is to key all bands simultaneously but drive only the one you want to use. I found that idle current for most amps is low until they are driven. That practice isolates sensitive receive front ends especially if there’s a sequencer on the transmit band, that adds a delay to transmit energy.

I don’t know how you’ll implement that with your new IC-9700. If you have an amp on each of your outputs it’s easy.

GL es 73 Bill W7QQ 


On Jun 1, 2019, at 9:38 PM, Scott K5TA <k5ta@...> wrote:


I have a brand-new IC-9700 that I’m itching to try out in the ARRL contest next weekend.  That rig has 3 separate antenna connections, one for each of its bands (144-432-1296).  I have all the antennas ready to go, and am planning a “rover simulator” operation on my own property — i.e. a mast with the yagis, planted in the ground, and a vehicle pulled up next to it with the radio(s).

I have looked at numerous pictures of rover setups, and it seems that most, if not all, have short masts with antennas spaced 1-3 feet apart.  I plan to emulate that design, but since the '9700 has 3 separate antenna ports, and only one transmits at a time, I started to be concerned about frying the front-ends of the non-TX bands.  I posted a question about this on the IC-9700 io group, and received loads of responses, ranging from “no problem except for KW power levels” to “you absolutely need all sorts of relays, sequencers, triplexers, filters, or whatever.”  As has happened many times before, my experience with these fora has been less than satisfying.

I know there are extremely experienced rovers and contesters on this list, and I wonder what your ideas are.

-Scott K5TA

James Duffey
 

Scott - I think you will be fine with no extra protection. Remember that the 9700 operates full duplex in the satellite mode, that is transmitting on one band while simultaneously listening on another. That requires good front end protection. Also, satellite antennas are usually pretty close spaced.

My TS2000X, and I suspect other mult-mode multi-band VHF rigs, including the 9700, terminate the inactive bands when operating simplex. I wouldn’t worry until you start running power. 

I’m sending this from our campsite at 7200 feet in the Black Hills of South Dakota, so I hope it goes through. My e-mail coverage has been poor this whole trip. 

I probably won’t be back in SD until Friday, so I will probably do a hastily thrown together limited rover. Let us know your planned route so I can avoid being in the same place as you at the same time. 

Good luck in the contest!

James Duffey KK6MC
Cedar Crest NM

On Jun 2, 2019, at 07:17, Bill <bill4070@...> wrote:

Scott,

I didn’t have “RF fratracide” problems until I started using the 400 watt TE Systems amplifiers. My stack allowed about 18” between Yagis. I toasted the front end of an Elecraft 222 transverter, which I later found to be particularly sensitive to 144 energy.

I tried some duplex cavities for 144, 222, 432 and 902. They worked, but they had noticable loss on receive. They took up a lot of volume inside the rover. 

Later I replaced the 144 and 432 cans with bandpass filters from DCI Digital Communications and that reduced the volume and receive losses. They’re expensive.

I still have all those filters if you want to experiment.

With that protection concept I liked the fact that everything was passive and didnt require a bunch of rf switching.

I never protected my 1296 receive equipment until I adopted the simultaneous keying concept. Never had a problem. Maybe I was lucky but the 1296 antenna was located further away fron the high powered 50, 144 and 222 antennas.

The best approach is to key all bands simultaneously but drive only the one you want to use. I found that idle current for most amps is low until they are driven. That practice isolates sensitive receive front ends especially if there’s a sequencer on the transmit band, that adds a delay to transmit energy.

I don’t know how you’ll implement that with your new IC-9700. If you have an amp on each of your outputs it’s easy.

GL es 73 Bill W7QQ 


On Jun 1, 2019, at 9:38 PM, Scott K5TA <k5ta@...> wrote:


I have a brand-new IC-9700 that I’m itching to try out in the ARRL contest next weekend.  That rig has 3 separate antenna connections, one for each of its bands (144-432-1296).  I have all the antennas ready to go, and am planning a “rover simulator” operation on my own property — i.e. a mast with the yagis, planted in the ground, and a vehicle pulled up next to it with the radio(s).

I have looked at numerous pictures of rover setups, and it seems that most, if not all, have short masts with antennas spaced 1-3 feet apart.  I plan to emulate that design, but since the '9700 has 3 separate antenna ports, and only one transmits at a time, I started to be concerned about frying the front-ends of the non-TX bands.  I posted a question about this on the IC-9700 io group, and received loads of responses, ranging from “no problem except for KW power levels” to “you absolutely need all sorts of relays, sequencers, triplexers, filters, or whatever.”  As has happened many times before, my experience with these fora has been less than satisfying.

I know there are extremely experienced rovers and contesters on this list, and I wonder what your ideas are.

-Scott K5TA