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Author Topic: RF return issue  (Read 590 times)

Matt285

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RF return issue
« on: April 27, 2021, 1133 UTC »
I recently bought a Yaesu FT-950 and I'm quite happy with it so far, however I seem to be having what I suspect is RF return. The power on the rig seems to be folding back even thought the radio is tuning for a good SWR. A couple of people I worked on HF SSB said they thought I had RF issues due to the way the radio sounded. I lowered the mic gain a bit and carried on. After these Qso's I worked a station and he helped me adjust my mic gain and compression and said it sounded great. The problem seems to come and go, but it was quite active yesterday. So far I removed the RG8 coax (Choke balun 9 turns 10'' diameter) going to the OCF fed dipole at 25'. I'm going to replace it with a brand new run of RG-213 I have on hand, ground the power supply (Samlex) and try to install toroids on varies cables. Also going to shorten the 6 1/2' power cable that goes to the rig. Any other suggestions or advice? Thanks

Offline Stretchyman

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Re: RF return issue
« Reply #1 on: April 27, 2021, 1204 UTC »
Check your mic lead/use a different mic.

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Online RobRich

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Re: RF return issue
« Reply #2 on: April 27, 2021, 1418 UTC »
What type of balun at the OCFD feedpoint? I suspect a 4:1, but is it a voltage or current balun? Ideally you want a current balun on an OCFD, though many ship with a voltage balun due to cost, wanting additional vertical radiation like a windom, or whatever the builder hoped to achieve.

You could try adding a current balun below the feedpoint if the antenna already has a voltage balun, or just outright replace a voltage balun with a current balun.

Adding the popular airwound coaxial balun might work, too, but note those often have very small working ranges and can even make issues worse depending upon feed characteristics. A current balun with a wide working frequency range for RF resistance is typically the better approach.
« Last Edit: April 27, 2021, 1926 UTC by RobRich »
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Matt285

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Re: RF return issue
« Reply #3 on: April 27, 2021, 1621 UTC »
Yes I suspect its a voltage balun.

Online RobRich

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Re: RF return issue
« Reply #4 on: April 27, 2021, 1741 UTC »
Try winding coax on a toroid below it. Several turns on a mix 43 torrid is a popular choice. You can weatherproof the toroid with clear coat or similar if just putting it inline with the feedline.

You can compare various types of chokes here:

http://www.karinya.net/g3txq/chokes/

Note the charts show an air-core coax choke can work, so you might try one of the listed designs if it covers your band or two of primary interest, but otherwise the resistive ranges are rather limited compared to many common toroid chokes when looking for a better multi-band solution.
« Last Edit: April 27, 2021, 1758 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals | 2x PA0NHC MiniWhips

Offline Looking-Glass

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Re: RF return issue
« Reply #5 on: May 12, 2021, 1048 UTC »
Make sure the radio is properly earthed too, decent copper strap/wire from rear of set on earth lug to a copper pipe at least three feet long driven into the ground. Copper lead run to earth rod should be as short as possible.  Older Yaesu's need to be earthed properly, otherwise RF issues.
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Matt285

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Re: RF return issue
« Reply #6 on: May 12, 2021, 1142 UTC »
I actually replaced my RG8X with some RG213 I had on hand, re did my choke balun, made sure everything was grounded securely and added some random clip on toroids  to various cables. So far so good. Haven't had any issues so far, knock on wood!

Offline CoolAM Radio

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Re: RF return issue
« Reply #7 on: May 12, 2021, 1248 UTC »
YAESU FT-950 SERVICE MANUAL

https://www.mediafire.com/file/1d5k471nr88vlxu/Yaesu_-_FT-950_-_Service_Manual.pdf/file

Maybe there is some setting in Hidden Menu?

Push [on/off]+[1.8][3.5][7.0] together to open this hidden service menu,
turn VFO-A to "walking" thru this menu. Ending=just power-off the rig

André
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« Last Edit: May 12, 2021, 1252 UTC by CoolAM Radio »
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Matt285

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Re: RF return issue
« Reply #8 on: May 12, 2021, 1739 UTC »
Thanks. I'll check it out. I haven't had the radio for very long. I just set up my CW speed and adjusted the Mic gain a bit so far. I need to look into compression also. Audio reports have been good so far though.

Offline syfr

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Re: RF return issue
« Reply #9 on: May 18, 2021, 1324 UTC »
Have you tried transmitting into a dummy load just to isolate the potential cause? 
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