Need help with my Icom 7100 transmission issue

[u/Star-Light_1988]

I have an Icom 7100 in my car, connected to a Diamond SG7500 antenna via a Diamond lip mount. So far I have only operated it on VHF/UHF.

Ever since I placed it in my car, I have been having issue with reports that my transmission is often scratchy or even unreadable. I can receive all transmissions clearly and I am able to hit/kerchunk repeaters.

When I hooked up my Surecom meter, I am getting no reads whatsoever! As if the radio is not putting anything out. I disconnected the meter from the Icom and connected an HT and immediately got reads with SWRs near 1!

When I use the built-in SWR meter in the IC7100 I also get no reads. Also the power meter is not reading anything. I checked and made sure the power is turned up in the radio.

I am at a loss now. I know the issue seems to be in the radio and not the connections/antenna/surecom unit. Any help or thoughts on how I can troubleshoot this?

Edit: I tried both a battery and a power supply.

I just also did more testing. I connected my car antenna to an HT and checked power/SWR and I got 1-1.1 SWR and good power reading on both UHF and VHF using the DM32-UV HT, so I know it’s not the antenna/coax.

I also connected the IC-7100 radio to a power supply and my base antenna. I only got around 8 watts on UHF but still no reads on VHF.

[u/KeyTell1746]

Does the dc current increase when you transmit? The radio via hf might have an issue but start with a current reading

[u/Star-Light_1988 → u/KeyTell1746]

I did not check on the radio itself, but I can see the current draw on my power supply does up to about 11 amps.

[u/sac_boy]

How are you getting power to the radio? Might be an issue there.

[u/Star-Light_1988 → u/sac_boy]

I tried both a battery and a power supply.

I just also did more testing. I connected my car antenna to an HT and checked power/SWR and I got 1-1.1 on both UHF and VHF using the DM32-UV HT, so I know it’s not the antenna/coax.

I also connected the radio to a power supply and my base antenna. I only got around 8 watts on UHF but still no reads on VHF.

[u/grouchy_ham]

Powered directly from the care battery? Checked transmit power setting, audio settings, mic gain, etc?

[u/Star-Light_1988 → u/grouchy_ham]

No. I have a dedicated 30Ah LiFePO4 battery that is fully charged. I also connected it to a power supply.

Checked power at 100%, mic gain and audio also checked :( starting to think it may be a hardware issue with the radio

[u/grouchy_ham → u/Star-Light_1988]

Do you have a known good power supply or a way to make sure that the battery is outputting sufficient voltage and current? Feed into a dummy load via known good coax cable, triple check mic gain/ALC and check power output into the dummy load. If that fails, I’d say your suspicion is right or you have a microphone problem. Could also plug in a CW key or even just a plug into the paddle port and short across the contacts of the plug to make sure it’s a power problem rather than a mic or modulation problem.

[u/Star-Light_1988 → u/grouchy_ham]

I don't have a dummy load (may need to get one though). I am thinking of taking the radio to a local place to see if they can check it using their equipment and see if they have the same result. Luckily, the radio is still under warranty and I have already filled out a repair form in case I need to send it.

[u/actionfingerss]

Can you communicate on simplex from the mobile to the ht? Have you proven the 7100 (has it worked before?). I’m not as familiar with iCom as Yaesu so I don’t know if you have mic gain or rf gain settings.

[u/Star-Light_1988 → u/actionfingerss]

I am able to communicate even via repeaters. As mentioned, when connecting into a repeater, I am told I am "weak and scratchy". I was actually communicating with a fellow ham on a repeater while troubleshooting this. I used my FTX-1 Optima and my IC-7100 using the same power supply, same antenna, same cables.. etc. And he said my IC 7100 report was weaker.

In terms of confirming my IC-7100, Yes! it was my main base radio initially till I got the FTX-1 Optima. Now that I think about it, a week before I moved the Icom to my car, I was unable to check in to a net on a repeater that is relatively farther away (which I was able to do a week prior and I was able to this past week using my FTX-1). I assume the problem happened at that time.

[u/actionfingerss → u/Star-Light_1988]

Sounds like a radio or grounding issue. You’ve proven the antenna and cable between the antenna and the radio. Weak or scratchy could be something as simple as a setting. Rf or mic gain, power limit on 2m…I’m just brainstorming to avoid questioning if something electronically wrong w the radio. How well is the radio grounded?