Using FT-857 or 897 with transverters

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Using FT-857 or 897 with transverters

Postby VK7HH » Thu Oct 04, 2018 12:25 pm

Hi All,
I'm after anyones experiences with using a FT-857 or 897 with transverters.


I've been led to believe that these rigs in particular have high RF power spikes on transmit, even when the power level is set to minimum, which, I'm afraid of blowing up my transverter I have coming.


Transverter will be a SG Labs 1296 one. From a few other posts I have read, nobody has reported any issues, but I wanted to double check with anyone on the forum who may have had issues?


857 is actually the rig I will be using in a remote configuration, so I will have a coax relay switching RF from the 2m output of the radio between a 2m amplifier and the IF input of the transverter with power being set on the radio to 5W maximum.


Regards
Hayden VK7HH
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Re: Using FT-857 or 897 with transverters

Postby VK4CZ » Thu Oct 04, 2018 1:46 pm

Correct Hayden - notorious for the spikes. You would need to be confident in being able to attenuate or manage the TX before using either as an IF... but whilst not impossible, the use of the FT-817 [as it can only deliver the max of 5 watts] is a more suitable/safer option.
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Re: Using FT-857 or 897 with transverters

Postby VK7HH » Thu Oct 04, 2018 2:10 pm

VK4CZ wrote:Correct Hayden - notorious for the spikes. You would need to be confident in being able to attenuate or manage the TX before using either as an IF... but whilst not impossible, the use of the FT-817 [as it can only deliver the max of 5 watts] is a more suitable/safer option.


Thanks for your reply ScottDo you have any practical suggestions on attenuating the signal from the IF? If I stick a 10dB pad inline from the IF to the transverter input, then that will mean that even with 50W (assuming this is the maximum spike in Watts), the power to the IF should never exceed 5W, and with 5W drive, should be getting 0.5W out the other end which is enough to drive the SG Labs transverter.

The downside I guess is that I'd need to make up 10dB on the receive side of things.

817 isn't really an option as it's a 857 controller via RemoteRig over IP.
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Re: Using FT-857 or 897 with transverters

Postby VK3ALB » Thu Oct 04, 2018 5:10 pm

Hi Hayden,

That's not such a big downside. Gain at 70cm is not that hard to develop - without checking I'm pretty sure MiniKits have suitable preamps.

While you're at it the VK3TU switch box will work with your rig allowing you to switch preamps for 2m / 70cm and well as controlling amplifiers transverters etc.

Also, have a look at the ALC input on the back of the rig. Applying the correct voltage there may help limit those big peaks.

<edit> Hmm, the link in my post is not working correctly for me. Scroll down a bit until you see my post about the switch box.
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Re: Using FT-857 or 897 with transverters

Postby ZL2WHO » Thu Oct 04, 2018 6:16 pm

Yep.. radio power out is unstable for the first few milisecs, not that great if your powering LDMOS if you protection is not upto scratch.
To get around this i dont use on AM or FM for testing. Needless to say an attenuator is mandatory.
This maybe of interest... http://ka4cid.blogspot.com/2008/11/rf-p ... -857d.html

73
Mark
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Re: Using FT-857 or 897 with transverters

Postby VK7HH » Thu Oct 04, 2018 6:26 pm

VK3ALB wrote:Hi Hayden,

That's not such a big downside. Gain at 70cm is not that hard to develop - without checking I'm pretty sure MiniKits have suitable preamps.

While you're at it the VK3TU switch box will work with your rig allowing you to switch preamps for 2m / 70cm and well as controlling amplifiers transverters etc.

Also, have a look at the ALC input on the back of the rig. Applying the correct voltage there may help limit those big peaks.

<edit> Hmm, the link in my post is not working correctly for me. Scroll down a bit until you see my post about the switch box.


Hi Lou,
Do you have doco on this? I can only find construction info. I assume boards are still available? The gain/attenuation issue would be on 2m as the 1296 transverter is driven with a 144MHz IF.

I’ll have a look at the ALC idea - must admit I’m a bit of a newbie with PA/transverter switching etc.

Thanks for that link Mark. I’m guessing my 10dB pad isn’t such a bad idea then?
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Re: Using FT-857 or 897 with transverters

Postby VK3ALB » Thu Oct 04, 2018 6:51 pm

Hi Hayden,

I'm sure Bert still has boards, drop him a line. vk3tu@hotmail.com

The article was published in AR May 2015 which I think you can download from the WIA website. Can't find a manual right now but he will have all the construction details.

Basically, it takes the 4 bit band data from the back of the rig and decodes it using a 4 to 16 TTL chip - no micro in sight. As a bonus you get a TTL output for each band which means you can do some clever relay switching if you want to run other bands.
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Re: Using FT-857 or 897 with transverters

Postby VK4VU » Thu Oct 04, 2018 10:09 pm

Hi Hayden,

I've just realised that you have a parallel thread going on ahrdf.net, so I thought it sensible to post the same information here in case anyone else is interested. Nothing like reaching a wider audience :)

Coincidentally this exact topic has very recently been discussed on the WA1MBA Microwave Reflector.

I've copied this response from Gerry K0CQ, which refers to a paper he has written detailing a setup procedure that reduces the incidence of power spikes in your application.


Message: 1
Date: Mon, 01 Oct 2018 21:25:46 -0500
From: "Dr. Gerald N. Johnson" <geraldj@netins.net>
To: microwave@mailmanlists.us
Subject: Re: [Mw] FT-817/818 Questions
Message-ID: <5BB2D72A.2030308@netins.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I have run an 817 on 10 or 24 GHz a few times. For my own 10 GHz rig I prefer my FT857D. The DSP is good at reducing the audio noise bandwidth on SSB. There is audio noise beyond the SSB filter because the filter is in front of several IF gain stages in nearly all radios. The DSP CW filter is narrower than I care for. The 500 Hz mechanical IF filter definitely improves the S/N of weak signals, the DSP doesn't as far as I can tell.

One option of the 857D that is not available in the 817 is running CW in SSB mode. All it takes when enabled is to close the key to transmit CW while listening in SSb mode. I have that disabled in my 10 GHz rig because it gets RF to the antenna relay while its moving and that hot switching is hard on tiny microwave relay contacts. I do use that automatic CW option with the home station 857Ds for HF, VHF, and UHF operations. For transverter service I require squeezing the microphone PTT button to get any RF out on CW or the internal CW beacon. That manual sequencing protects the microwave antenna TR relay.

I went into the main alignment menu and reduced the 2m TX gain to reduce the output down to 2 watts rather than depending on the front panel setting. The front panel setting uses ALC and often spikes at the beginning of each transmission which is not good for the transmit side of the transverter that needs only a couple watts or less. Actually the transmit mixer probably needs only a few milliwatts. Lowering the transmitter gain prevents those ALC spikes in all modes including FM. I checked it with my Tek 475 200 MHz bandwidth scope and I am sure there are no spikes. I wrote an article for CSVHF in 2010. I have a version on line at:
http://www.geraldj.networkiowa.com/papers/CSVHF2010/xvtr857align.pdf

I haven't tried a fixed DC bias into the external ALC jack on the back of the radio.

The 857d does draw a couple amps on receive, twice that of the 817 but it has more front panel controls than the 817 and I think some more options. I don't use RIT. The 857D isn't enormously larger than the 817.

73, Jerry, K0CQ



For the record, I don't own either an FT-817 or an FT-857 so can't verify whether this approach works - but I do know that Jerry K0CQ is always spot on with any technical topics.

Hope this helps.

73

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Re: Using FT-857 or 897 with transverters

Postby VK7HH » Thu Oct 04, 2018 10:13 pm

Thanks Rod!

Appreciate you sharing that post. I might try to get in contact with Jerry to see how he progressed with it. This sounds like the best approach then I can continue using my 2m PA for higher powered application on 2m whilst leaving the 857 at 5W or less by turning it down in the alignment menu.

Thanks
Hayden VK7HH
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Re: Using FT-857 or 897 with transverters

Postby VK7HH » Mon Oct 08, 2018 8:09 am

VK3ALB wrote:Hi Hayden,

I'm sure Bert still has boards, drop him a line. vk3tu@hotmail.com

The article was published in AR May 2015 which I think you can download from the WIA website. Can't find a manual right now but he will have all the construction details.

Basically, it takes the 4 bit band data from the back of the rig and decodes it using a 4 to 16 TTL chip - no micro in sight. As a bonus you get a TTL output for each band which means you can do some clever relay switching if you want to run other bands.



Hi Lou,
I emailed Bert but haven't had a reply as of yet. I wonder if you talk to him regularly?

I've found the AR magazine, I'll have a bit more a of a in depth look shortly. Thanks for your help.

Regards
Hayden
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Re: Using FT-857 or 897 with transverters

Postby VK3ALB » Tue Oct 09, 2018 5:47 pm

Hi Hayden,

I believe you now have mail from Bert. He's a busy man.

Sent from my SM-T350 using Tapatalk
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Re: Using FT-857 or 897 with transverters

Postby VK7HH » Tue Oct 09, 2018 6:27 pm

VK3ALB wrote:Hi Hayden,

I believe you now have mail from Bert. He's a busy man.

Sent from my SM-T350 using Tapatalk


Yes thanks Lou, I did.

Regards
Hayden
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