HF radio only transmitting clearly with high VSWR

[MPir]

Hi all, ive ran into an interesting issue with my Xiegu G90 HF transceiver, the quick run down is at any point where VSWR is high through any antenna, the radio will transmit clear audio, but when VSWR is low or perfect even, the audio comes out like a cyclic buzzing sound, the Receiver used is the BELKA all mode receiver, I am just looking to see if anyone has seen this before or know what the issue could be.

Here are the tests conducted thus far;
Note: I have tried multiple modes (LSB, USB, AM, NFM)

20W output through 50 Ohm dummy load - VSWR 1.05~ - Receiver 1M distance = Perfect audio (The Load is the only exception that works at low VSWR)

1W output through Mono-pole (ANT 1) usable at 20 - 22 MHZ - VSWR 1.15~ - Receiver 1M distance = Buzzing

1W output through (ANT 1) - VSWR 1.15~ - Reciever 100M distance = Buzzing

1W output through (ANT 1) with 30db atten - VSWR 1.1~ - Reciever 5M distance = Buzzing

20W output through (ANT 1) - VSWR 1.15~ - Reciever 100M distance = Buzzing

1W output NO ANTENNA only RF cable - VSWR 70 - Reciever 1M distance = Perfect audio

1W output through Dipole (ANT 2) Usable at 27 - 28 - VSWR 1.1~ - Receiver 1M distance = Buzzing

1W output through (ANT 2) - VSWR 1.1~ - Receiver 100M distance = Buzzing

15W output through (ANT 2) - VSWR 1.15~ - Receiver 100M distance = Buzzing

1W output through (ANT 1) at (ANT 2) Freq range - VSWR 6~ - Receiver 1M distance = Bad Audio

1W output through UHF Antenna - VSWR 15~ - Receiver 1M distance = Perfect Audio

1W output through 50 Ohm dummy load - VSWR 1.05~ - Receiver 1M distance = Perfect audio

Some general conclusions:
The antennas are good, its only when they too are generating high VSWR that they operate with understandable audio
The receiver is good
The Cables are good, Ive used multiple cables during these tests and yield the same results
Grounding yields no change, changed grounds three times through the test
Change in Frequency Yields no change, except if changed to generate high vswr
Change in Power output (Radio settings) Yields no change
Antenna Orientation Yields no change, moved antenna multiple times during testing

 

[dlwtrunked]

I am not totally convinced that this is not a receiver overload problem even after looking at your data. IF not, likely about your antennas. I would only consider the G90 as the 3rd contender for the source of the problem - if it works fine in a dummy load, I really do not think expect it is the G90. How do you know the antennas and receiver "are good"? I do not consider the Belka a receiver that I would trust to tell me that with confidence.

 

[K6GBW]

It sounds like you are getting RF into your transmit audio. You need to use a longer coax to get it further away. Also put a choke under the antenna to prevent the coax from radiating. I have used many QRP rigs and this is a common problem.

 

[dlwtrunked]

It sounds like you are getting RF into your transmit audio. You need to use a longer coax to get it further away. Also put a choke under the antenna to prevent the coax from radiating. I have used many QRP rigs and this is a common problem.

Sounds more plausible than my response.

 

[merlin]

Definately receiver overload. Keep your radios separated a good 50 yards and use a 20 to 30 Db attenuator at the receiver.
That should give you good audio 10 watts or lower. Talking a foot of antenna wire on the receiver here.
That bad SWR has your EIRP below that which is overloading the receiver, hence good receive audio.
Bad SWR with poor grounding can cause RF bleeding back into mics or other peripherals and not good.
A number of years back, I had a Q-Mac field pack with a 30 foot long wire. I tried monitoring rception to my truck with a Barrett HF rig.
It was awful across HF until I disconnected the antenna to the Barrett.
My bet is all your equipment is good, your method of testing is all wrong.
Like back in CB days, perfect mobile setup, then drive into another CBers driveway running 100 watts and audio was uninteligable both ways.

 

[dlwtrunked]

Sounds more plausible than my response.

But I still do not exclude the receiver as the problem. I would try to get someone to remotey (miles away) monitor your signal while you test.

 

[FKimble]

What SWR meter are you using? Is it made for the frequency you are transmitting on?

Frank

 

[prcguy]

I also think it’s receiver overload. The BELKA is a toy receiver at best and I wouldn’t trust it for anything.