IC7100 Antenna spacing...

[rjvalenta]

hello all, i currently have a comet UHV4 antenna feeding an old IC208h, which only does VHF/UHF while the antenna does 10m/6m/2m/70cm...

my plan is to get an IC7100, connect the UHV4 to the VHF/UHF antenna port and a my antennas 4010 EFHW to the HF antenna port.

BUT - I plan to put the balun feeding the EFHW just under the VHF/UHF antenna, attaching it to the tripod the VHF/UHF antenna is sitting on.

that will put 100w of HF 12 inches below the VHF/UHF antenna.... but it's attached to the radio transmitting the HF and thus not listening on VHF/UHF.

so - is this safe, or am I going to fry out my VHF/UHF receiving on the IC7100 when i transmit HF because this antenna can receive 10m or just because it's too close?

(i'm limited on space, going up on my roof involves a LOT of planning for safety and HOA reasons, and my general test isn't for a couple weeks, I'm trying to get ahead of things now).

thanks for any input,

Richard
N0TZC

 

[dkcorlfla]

I do not own the IC7100; however, being a mobile rig I would think it is designed to work with two antennas that are mounted close together. I'm thinking it switches off RX on both ports when transmitting on either VHF, UHF or HF but I could be wrong. Maybe somebody that owns one can chime in.

 

[prcguy]

Should be no problem, filters in the radio will take care of strong out of band signals at each antenna port. BTW I have three IC-7100s.

 

[rjvalenta]

Icom support just got back to me. A young ham asked around and confirmed what others saw in the IC7100 manual, it does not in any way shut down the VHF/UHF receiver, and they assume at least a 4 foot spacing between antennas or more... and even suggested that be a 4ft vertical spacing if the operation isn't mobile.

 

[rjvalenta]

Should be no problem, filters in the radio will take care of strong out of band signals at each antenna port. BTW I have three IC-7100s.

i would love to know your antenna setups - base or mobile? any EFHW? how much antenna spacing are you using?

thanks,

Richard
N0TZC

 

[prcguy]

i would love to know your antenna setups - base or mobile? any EFHW? how much antenna spacing are you using?

thanks,

Richard
N0TZC

All base and all remote controlled with RemoteRig boxes. One has a 133ft MyAntennas 80-10m EFHW and a Tram 1480 dual band, one has a home brew 40-10m EFHW and a Tram 1481 dual band and the third currently has a 133ft MyAntennas 80-10m OCFD and Comet GP-9 but that one will be moving to a mountain cabin soon with some kind of VHF/UHF dual band and end fed HF antenna.

They all have the VHF/UHF and HF antennas very close, between about 5ft and 20ft.

 

[rjvalenta]

All base and all remote controlled with RemoteRig boxes. One has a 133ft MyAntennas 80-10m EFHW and a Tram 1480 dual band, one has a home brew 40-10m EFHW and a Tram 1481 dual band and the third currently has a 133ft MyAntennas 80-10m OCFD and Comet GP-9 but that one will be moving to a mountain cabin soon with some kind of VHF/UHF dual band and end fed HF antenna.

VERY NICE! so... how much space is between each radio's HF and DualBand antenna? are they all horizontally the same?

 

[AK9R]

This is from the IC-7100 service manual. Note that an incoming signal on the HF/50MHz port will have to go through one of the band pass filters, L1 through L7. The highest BPF passes 33.0 to 74.8 MHz.

 

[vagrant]

@prcguy - I like your new cabin! Is it available to rent?

 

[prcguy]

VERY NICE! so... how much space is between each radio's HF and DualBand antenna? are they all horizontally the same?

All HF antennas are horizontal wire and the spacing to the VHF/UHF varies from about 5ft to 20ft from the HF antennas. Never had a problem.

 

[prcguy]

@prcguy - I like your new cabin! Is it available to rent?

View attachment 138734

Oh I wish. Unfortunately the USFS has some say on my new cabin ham station and I have to keep things reasonable. I can go a little crazy with a big temporary setup while I'm there but have to take it down when the cabin is not occupied.

 

[rjvalenta]

This is from the IC-7100 service manual. Note that an incoming signal on the HF/50MHz port will have to go through one of the band pass filters, L1 through L7. The highest BPF passes 33.0 to 74.8 MHz.
View attachment 138726

ok so the HF portion is protected, but are VHF and UHF protected from the significantly stronger HF transmissions with a high pass filter?

rjv

 

[prcguy]

ok so the HF portion is protected, but are VHF and UHF protected from the significantly stronger HF transmissions with a high pass filter?

rjv

The pickup of HF on a VHF/UHF antenna is low so its really nothing to worry about. I put out 1,200 watts on HF all the time with my HF wire antenna very close to my VHF/UHF antennas and its a non issue. I also used to do 500w HF mobile with the HF whip about 4ft from my VHF/UHF whip, also never a problem.

 

[dkcorlfla]

Icom support just got back to me. A young ham asked around and confirmed what others saw in the IC7100 manual, it does not in any way shut down the VHF/UHF receiver, and they assume at least a 4 foot spacing between antennas or more... and even suggested that be a 4ft vertical spacing if the operation isn't mobile.

Good thing you double checked. Perhaps a A/B switch on the VHF/UHF with A to the antenna and B to a dummy load will keep the rig safe.

 

[prcguy]

Good thing you double checked. Perhaps a A/B switch on the VHF/UHF with A to the antenna and B to a dummy load will keep the rig safe.

Not needed, there are band pass filters for VHF and UHF that protects them from out of band energy, you won't hurt the radio with 100w on any HF band close to the 2m/440 antenna.

 

[dkcorlfla]

Not needed, there are band pass filters for VHF and UHF that protects them from out of band energy, you won't hurt the radio with 100w on any HF band close to the 2m/440 antenna.

Roger that, I missed your reply before I posted. Looks like you have the hands on info the OP needed.

 

[KC3DYW]

These are very good suggestions, with the IC-7100 you could check the specs to see what the maximum rejection is, also if your in doubt you can use a very good quality RF Relay, so when you actively key up or transmitt, you will automatically shunt or ground the input of the radio you are concerned with, thus further protecting it, this method is not new!
I have done major radio work for various government agencies with antennas of different frequencies mounted close within 18” of each other.
This method was not only used to protect sensitive equipment that already had robust bp/br filtering but we sometimes used methods of grounding like this to correct the reflected wave or swr problems occurring on the transmitting equipment.

Again just a suggestion👍

 

[popnokick]

I have... as do several of our club members... IC7100 radios. Whenever we do a single-site event involving multiple radios / antennas in close proximity (e.g. Field Day, Winter Field Day, VHF Contest, etc) we often put EFHW or OCFD balun and antenna very close to VHF / UHF antennas. Often the antennas are mounted on the same mast / tower / or other support structure within 5 - 10 feet of each other... or closer. The interaction between the HF and VHF / UHF antennas is practically non-existent, and not noticeable at all on the 7100. We routinely run full (100W) power on HF. And all of our 7100s after six or more years now are in fine operating condition. Your concern with the 7100 is simply a non-issue. I am not asserting that there is not some RF getting into the radio from HF... I'm stating that with the 7100 it is not a concern.

 

[KC3DYW]

Understood👍
What I was referring to is antennas that I have personally worked on, trimmed and tuned on various applications which I can’t disseminate , these antennas are of various frequencies and very close together 12” apart in some cases, transmitting a few hundred watts, the other antennas that are not transmitting are automatically grounded via a hi quality rf switch thus protecting the equipment and reducing or eliminating swr interference with antennas being in close proximity.
Because the unused antennas are grounded they actually become part of the ground plane, it’s interesting to play with if you have time and at least a good bird meter, you can study what happens with the reflected wave as you bring another antenna close to a transmitting antenna, grounded and ungrounded you can see a marked difference, this difference is different at different frequencies.

For very sensitive applications or critical applications i have built and installed/ tuned
A 3 stage BR (low) BP (center frequency) BR (high)
With a good bridge and service monitor these can be tuned soo tight i can actually clip speech but allow digital voice or info to pass through while maintaining good throughput and swr with minimal db loss to provide rejection to other hi output rf sources.

It is interesting and theory comes into play with mostly all that we do with communication be it Ham or commercial comms, learning never ends.

I’m still learning 😂👍👍

73’s