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Author Topic: FT-817 rear ant socket  (Read 2450 times)
M5AEO
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Posts: 259




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« on: August 02, 2012, 08:48:14 AM »

Calling all FT817 users.  I have been trying out a new antenna and kept getting terrible SWR readings when trying to tune it for 432Mhz.  I was using the rear antenna socket on the rig for these adjustments.  I was about to give up when I tried the front (BNC) antenna socket.  Hey presto!  Suddenly the antenna worked!  I am assuming that the rear output just doesn't work because the socket is a dreaded SO239 which is just not up to scratch on UHF (in spite of being known as a 'UHF plug'), whereas the BNC socket is much better at UHF frequencies?
Any advice/wisdom would be appreciated.

Jonathan, M5AEO, London (home of the bloody Olympics!).
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VA7CPC
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Posts: 2357




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« Reply #1 on: August 02, 2012, 09:09:49 AM »

The FT-817 menu lets you change the "active antenna socket" from "front" to "rear".  [I think it's the "ANT" item, but I'm not sure.]

This setting is 'per band' -- you can set the HF bands to use the SO-239 socket, and the VHF bands to use the front (BNC) socket.  Or vice versa.

It's one of the common "gotchas" for the FT-817.

If it's set to use the rear (SO-239) socket, on whatever band you're set to,  a small "R" appears on the display.

             Charles
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KA4POL
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Posts: 1910




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« Reply #2 on: August 02, 2012, 10:24:10 AM »

Manual page 17: In its default setting this jack (the M-type SO239) does not function on 50/144/430 MHz bands. If you want to enable this jack on 50/144/430 MHz bands, recall and change the settings of Menu #07.
The same applies for HF operation regarding the front BNC jack.
And you are right about the SO239 and 70cm. This is not the best combination. The impedance drops to 30 to 40 Ohm in the central portion for frequencies above 300 MHz.
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M5AEO
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Posts: 259




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« Reply #3 on: August 02, 2012, 12:30:55 PM »

Thanks both.  I was aware of the menu setting and did set it appropriately.  It just seems that the SO239 can't really handle UHF.  It worked perfectly well on 144Mhz, but on UHF the SWR shot up to 3:1.  I wonder why The SO239/PL259 is called a "UHF plug"??!!

M5AEO



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AD4U
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Posts: 2153




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« Reply #4 on: August 02, 2012, 02:29:58 PM »

From my personal experience with my FT-817 and with other 440 rigs (FT-100D and FT-8900 are two examples) that use a SO-239 connector, the SO-239 will "handle" 440 MHz RF quite well.  I think you have another issue.

Dick  AD4U
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KE3WD
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Posts: 5694




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« Reply #5 on: August 02, 2012, 04:59:24 PM »

From my personal experience with my FT-817 and with other 440 rigs (FT-100D and FT-8900 are two examples) that use a SO-239 connector, the SO-239 will "handle" 440 MHz RF quite well.  I think you have another issue.

Dick  AD4U

Undoubtedly, he said, staring over at his 440 repeater with the SO-239 on it...

Your '817 may not be switching at the moment, or may be suffering from a dirty or damaged relay, or might just need the processor to be reset. 

73
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G8YMW
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Posts: 191




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« Reply #6 on: August 02, 2012, 05:07:59 PM »

Dick
The FT8900 has an N socket, well my XYL's 8900 has. I dont know if they are different on your side of the pond?
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KA4POL
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Posts: 1910




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« Reply #7 on: August 02, 2012, 10:00:07 PM »

I wonder why The SO239/PL259 is called a "UHF plug"??!!
You got to see this from a historical point of view. The SO239 is a WWII design. At that time the frequencies above 30 MHz were considered as UHF.

Your connector may be the problem. To find this out you could try connecting a dummy load. If the SWR still behaves like observed with the new antenna than its time to think about exchanging the connector. Take a look at the internal connection may be a bad solder joint leads to the effect.
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STAYVERTICAL
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Posts: 854




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« Reply #8 on: August 03, 2012, 02:08:13 AM »

A 3:1 SWR is poor but it does indicate that your antenna is being matched to some extent, otherwise the SWR would be much worse.

OK, I did some tests with my FT817ND:

The test setup:
FT817ND, adjustable whip with a BNC connector, and a right angle PL259 adaptor and a PL259 to BNC adaptor, band 438Mhz.

With the adjustable whip on the BNC(front) connector I was able to get 1:1 with ease at a particular length of whip extension.
After transferring the output to the rear connector, I connected the whip to the PL259 to BNC connector on the rear.
The SWR was about 3:1 as you obtained.

By shortening the adjustable whip about 2 inches I was able to get a 1:1 SWR on the rear connector and it worked as well as the front.

It appears that the combination of my adaptors (PL259->SO239[Right angle] -> PL259->BNC) added some effective inductance.
This meant I needed to shorten the antenna to compensate.

On both connectors I keyed a local repeater at about the same strength, so I would say both connectors work well in the 70cm band.
But due to extra length added some antenna tweaking is required.

This is the beauty of the FT817ND - its so easy to just grab it and try out some tests.

Hope this helps.

73 - Rob

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AD4U
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Posts: 2153




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« Reply #9 on: August 03, 2012, 06:27:28 AM »

Dick
The FT8900 has an N socket, well my XYL's 8900 has. I dont know if they are different on your side of the pond?

I just checked and my FT-8900 (USA version) definitely has a single SO-239 connector on the rear panel.  All transmit RF coming out of the rig (28 MHz - 450 MHz) exits through this single SO-239.

Dick  AD4U
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M5AEO
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Posts: 259




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« Reply #10 on: August 03, 2012, 08:51:48 AM »

Many thanks to everyone who responded.  Last night I tried the two sockets into a dummy load and found no difference on 144Mhz and lower, but on 430Mhz the SO239 on the rear showed an elevated SWR reading of about 2:1, but when using the BNC socket on the front this came down to 1:1.  So I guess the answer is not to use the rear socket on UHF.  I think I can live with that!

Jonathan, M5AEO, London.
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KA4POL
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Posts: 1910




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« Reply #11 on: August 03, 2012, 10:25:53 AM »

So definitely the connector is bad. Probably the internal isolation material. I'd exchange it either for a new one or even a fitting N-type.
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W8JX
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« Reply #12 on: August 03, 2012, 10:45:47 AM »

So definitely the connector is bad. Probably the internal isolation material. I'd exchange it either for a new one or even a fitting N-type.

I would not jump the gun here as the problem could be internal due to cabling or switching and in which case changing the connector will do nothing.
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KA4POL
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Posts: 1910




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« Reply #13 on: August 03, 2012, 12:48:57 PM »

There s a relay for connecting to one of the outputs. Nothing else in between. And checking the connections internally is what I had recommended before. Assuming this has been done nothing else remains. On assembly the connector might have been overheated.
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KQ6Q
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Posts: 965




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« Reply #14 on: August 03, 2012, 02:00:01 PM »

The difference in internal cable lengths from the relay to the two coax connectors may be enough of a fraction of a wavelength at 440mhz to be providing some impedance transformation, which could account for the difference in SWR to the same attached load.
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