Will it cause front end damage?

[ClemsonSCJ]

Background:
I moved my Icom 2730 into the house after thinking I was “upgrading” to a Yaesu FTM-300. Aside from the native APRS, I like the Icom WAAAYYY better. So, I have acquired a Yaesu FT-2600M 2m radio that I have no use for at the moment. The FTM-300 would suit my needs for a shack radio and the 2730 would work much better back in my vehicle, however I would like the ability to continue running APRS in my vehicle WITH the equipment that I ALREADY have (not looking for suggestions on what all products are out there…I’ve looked into them and may be future projects but this is for right now).

So on to the question:
I had planned to have the 2 antennas mounted on the roof of my Grand Cherokee and would likely be about 2ft apart. With my 2730 transmitting at 50 watts for however long during conversations, and the FT-2600 transmitting at 60 watts for 1-2 seconds at a time every couple minutes (can be lowered to 25, 10, or 5 watts, but I prefer to leave it at high power if possible), is there a risk of damaging the front end of either radio?

To be clear, I understand there will be desense on either radio when the other is transmitting, I’m not concerned with that. I am only concerned with damage.

 

[mmckenna]

So on to the question:
I had planned to have the 2 antennas mounted on the roof of my Grand Cherokee and would likely be about 2ft apart. With my 2730 transmitting at 50 watts for however long during conversations, and the FT-2600 transmitting at 60 watts for 1-2 seconds at a time every couple minutes (can be lowered to 25, 10, or 5 watts, but I prefer to leave it at high power if possible), is there a risk of damaging the front end of either radio?

It's entirely possible. It's not something I'd gamble with.
I've had 35 watt UHF commercial radios wipe out the front of a dual band hammy radio with antennas spaced that close together.

But, as always, there are variables, coupling between antennas, feed line loss, design of the radios.

One thing you can try is hooking up a good wattmeter to one antenna, terminate into a 50Ω load, and then transmit on the other. I think I've read that anything over 250mw probably isn't a good idea in most applications.
Your milage may vary.

 

[ClemsonSCJ]

It's entirely possible. It's not something I'd gamble with.
I've had 35 watt UHF commercial radios wipe out the front of a dual band hammy radio with antennas spaced that close together.

But, as always, there are variables, coupling between antennas, feed line loss, design of the radios.

One thing you can try is hooking up a good wattmeter to one antenna, terminate into a 50Ω load, and then transmit on the other. I think I've read that anything over 250mw probably isn't a good idea in most applications.
Your milage may vary.

I will give that a try and see what kind of numbers I see. Another option that I would prefer not to do but would be willing to try over scrapping the project all-together is using a Diamond K400 lip mount for the APRS antenna and mount it on the hood. This would give about 5-6ft more horizontal separation and about 1.5ft of vertical separation with some sheet metal partially between the 2 antennas.

 

[ClemsonSCJ]

It's entirely possible. It's not something I'd gamble with.
I've had 35 watt UHF commercial radios wipe out the front of a dual band hammy radio with antennas spaced that close together.

But, as always, there are variables, coupling between antennas, feed line loss, design of the radios.

One thing you can try is hooking up a good wattmeter to one antenna, terminate into a 50Ω load, and then transmit on the other. I think I've read that anything over 250mw probably isn't a good idea in most applications.
Your milage may vary.

Ok so I just tested it out and transmitting 50W from my Yaesu FTM-300 I was picking up 1 watt through the antenna 2ft away. So I moved the antenna to the K400 lip mount that I have my CB antenna on the hood and tested it again and the watt meter picked up nothing. I then flipped it so that I was transmitting on the hood mounted antenna and measured from the roof mounted antenna and again nothing. So I believe I’m gonna be safe going with that option.

Curiosity’s got me though…when measuring SWR, I see higher than 1 watt going back into the radio a lot of times so is that not the same thing or is that just not going through the front end and rather returning into the radio only through the finals?

 

[prcguy]

Reflected power when measuring SWR goes back down the coax to the transmitter incurring whatever feedline loss you have then usually some or most of that reflects back towards the antenna minus feedline loss again and some gets radiated and some gets reflected back towards the transmitter endlessly all the time you are transmitting.

Curiosity’s got me though…when measuring SWR, I see higher than 1 watt going back into the radio a lot of times so is that not the same thing or is that just not going through the front end and rather returning into the radio only through the finals?

 

[jaspence]

!/4 wavelength is the minimum, with other searches saying 1/2 to a full wavelength. Do a google and check it out.

 

[mmckenna]

The internal Transmit/receive switching diodes isolate the receiver from the antenna when transmitting.

 

[prcguy]

Minimum for what? For front end damage or antenna pattern skewing or ??? Fraction of a wavelength spacing for front end protection is meaningless, you can have a 1 watt transmitter and snuggle another antenna up against it an inch away and it wont hurt anything. If you have a 100 watt transmitter then 1/2 wavelength or a full wavelength won't do you any good, its all dependent on the power levels and types of antennas.

For antenna pattern skewing a higher frequency antenna 1/4 or 1/2 wavelength away from a larger lower frequency antenna will destroy the omni antenna pattern, you have to get several full wavelengths away to start calming that down and at VHF that can be 6ft or more.

!/4 wavelength is the minimum, with other searches saying 1/2 to a full wavelength. Do a google and check it out.

 

[BMDaug]

Can damage occur even when one of the radios is powered off? I have a manpack running at 25-30 watts with a Hascall-Denke manpack dipole and I usually keep an HT in the pack as a backup. The HT is almost directly below the dipole, which is vertically polarized. It’s probably 18” from the bottom of the dipole so about 28” from the feedpoint. Should I remove the antenna from the HT when not in use?

Thanks,
Brian

 

[prcguy]

Depends on the radio. An HT probably won't hurt anything. I had a PRC-70 manpack and blew out the first mixer twice by having its whip antenna on and within 25ft of another 100w HF station with a dipole. Lots of other radios would have no problem under the same conditions.

Can damage occur even when one of the radios is powered off? I have a manpack running at 25-30 watts with a Hascall-Denke manpack dipole and I usually keep an HT in the pack as a backup. The HT is almost directly below the dipole, which is vertically polarized. It’s probably 18” from the bottom of the dipole so about 28” from the feedpoint. Should I remove the antenna from the HT when not in use?

Thanks,
Brian

 

[BMDaug]

Depends on the radio. An HT probably won't hurt anything. I had a PRC-70 manpack and blew out the first mixer twice by having its whip antenna on and within 25ft of another 100w HF station with a dipole. Lots of other radios would have no problem under the same conditions.

Hey thanks! Just to clarify, I don’t want to damage the HT while operating the manpack… so I’m outputting 30 watts with the manpack and don’t want to damage the HT. The HT is 5W so I’m not really worried about damaging the manpack… should I be? Sometimes I’ll test programming between the manpack and HT with both set at 5W in the same room. Is that really bad?

 

[prcguy]

What frequency is the HT and manpack on? If they are on the same band and with 30w I would move them apart some, if they are different bands its probably nothing to worry about.

Hey thanks! Just to clarify, I don’t want to damage the HT while operating the manpack… so I’m outputting 30 watts with the manpack and don’t want to damage the HT. The HT is 5W so I’m not really worried about damaging the manpack… should I be? Sometimes I’ll test programming between the manpack and HT with both set at 5W in the same room. Is that really bad?

 

[BMDaug]

Both are 136-174, 380-520, 762-870… so all the same bands. I really need to get an rf meter…

Removing the antenna should protect the HT when not in use though.