[Moon-net] IC746 transient output spikes

Sat Mar 8 13:21:14 CST 2008

Lance and all:

This was my challenge when I started setting up my FT-847 for eme 
use.  I had heard of the Tx power transients but never actually 
experienced a problem with any (dumb luck).  The very best thing I 
did to protect my preamps was modifiying the FT-847 for separate Rx 
antennna connection.   I never had another preamp failure due to 
RF.  But  I have only been running 125w at the tower top (QRO will be +10 dB).

I have wired my station using the 4-stage DEMI sequencer and have an 
input selector switch for mic/computer/manual control of the 
sequencer.  The routing of the mic thru the sequencer produced an AC 
hum-noise problem and I abandoned that for the present (use manual 
T/R switch).  For CW, a manual switch on the sequencer gives very 
positive control, and for computer (CW-KEY5) or WSJT the computer 
interface controls the sequencer.   Very similar to the description 
given by W5UN.

One thing left to try is controlling the Tx inhibit line on the 
FT-847 with the Mic PTT for easy PTT transceive SSB operations on 
VHF/UHF QRO operations.

Anticipating QRO (soon) has me revisiting the T/R relay isolation 
issue (CN-600N 48-dB) and I plan to add enable/disable control of my 
Rx pol relay in the sequence where the antenna relays switch (or not 
switch power on the preamp and use that step).  The sma H/V relay 
defaults to internal 50-ohm loads on all the terminals when the relay 
is unpowered (no +28v supply).  I plan the switch the 28v as an 
additional bit of protection from RF to my preamp in QRO operations.

In fact, eventually I have an ambitious plan to build a master 
station control panel that includes relay controls, sequencing, 
computer I/F with possible computer control for two radio 
operations.  Mostly with VHF/UHF/mw contesting in mind.  Quite a bit 
down the list at this time ;-)

Well, sun's up...burning daylight...painting day for the 8877 front panels.

73 Ed - KL7UW

At 08:43 AM 3/8/2008, LANCE COLLISTER wrote:

>Russ K2TXB wrote:
> > Lance, Dave W5UN has the absolute best solution.  But in order to have the
> > transceiver tx out be last you have to do one of several things 
> that are not
> > always easy.  The best solution is to have or build a TX inhibit line into
> > the transceiver, so that when you key the radio PTT with mike or CW paddle
> > (or computer program), the PTT out to the sequencer works normally, but the
> > radio makes no RF until you enable the inhibit line via the 
> sequencer (which
> > is driven from the radio PTT).
> >
> > Another way is to operate the sequencer directly from the Mic or paddle or
> > computer, and have the sequencer key up the radio last.  That requires some
> > specialized circuitry to be built. (And if you should forget and key the
> > radio directly form a MOX switch or otherwise, your sequencing fails!)
> >
> > On 10 GHz, I only needed milliwatts to drive the transverter.  So 
> I placed a
> > BNC relay between the RF out and the transverter, after the attenuator.  I
> > sequenced the relay last so even though the radio was sending it's RF
> > through the attenuator, it did not reach the transverter until the relay
> > switched.  WHAT? Hot switching an antenna relay?  That is against 
> the rules.
> > But when you are only handling milliwatts the relay can handle it just FB.
> >
> > 73, Russ K2TXB
> >
> >> -----Original Message-----
> >> From: moon-net-bounces at list-serv.davidv.net
> >> [mailto:moon-net-bounces at list-serv.davidv.net] On Behalf Of
> >> LANCE COLLISTER
> >> Sent: Saturday, March 08, 2008 10:21 AM
> >> To: moon-net at list-serv.davidv.net
> >> Subject: Re: [Moon-net] IC746 transient output spikes
> >>
> >>
> >> Many thanks to the many fine folks who replied with
> >> assistance to my inquiry.  It seems that the Icom rigs are
> >> notorious for these transients.  I know when I chatted with
> >> the TE Systems people yesterday, they said they had tested an
> >> IC746 recently and found very strong spikes on it.  Their
> >> recommendation was to drive their solid state amps at half
> >> power rating.
> >>
> >> Most of the replies I received suggested running the IC746 at
> >> full output and using attenuators to reduce the power to the
> >> desired level of drive for the solid state amplifier.  This
> >> is what I have been doing in the past, and I probably will go
> >> back to this.  I have purchased some nice high power
> >> non-inductive resistors (amazing what is available these
> >> days!) and plan to build a new attenuator for the exciter.
> >> My primary application with the solid state amplifier is for
> >> the 6m band, so it is not quite so simple as conrolling the
> >> power on 2m, where RG-58U coax is very convenient for that purpose ;-)
> >>
> >> On 2m, I already use the rig on highest ouput power, and use
> >> a long length RG-58 coax over to my 8877 (which is quite
> >> forgiving of such power spikes anyway).  I already use a
> >> sequencer with my rig, but in order to protect my relays and
> >> preamps, the IC746 is the LAST thing to turn on, so the
> >> spikes often get through the system :-(
> >>
> >> Thanks also for the clarification regarding the ALC pin on
> >> the accessory jack on the rear panel of the rig.  I recall
> >> this was discussed years ago as a way to lower the power down
> >> below what is the normal minimum for the front panel RF
> >> control.  I think this is a very interesting approach, and I
> >> hope to be able to have time tomorrow afternoon to experiment
> >> with that.
> >>
> >> I am investigating the Elecraft K3 for possible purchase, and
> >> this is a good question to ask about that rig.  Hopefully, as
> >> Leif suggested, a rig like that which is so highly controlled
> >> by a built in computer processor will have such spikes well
> >> suppressed.
> >>
> >> Thanks again to everyone for your guidance!  It always seems
> >> there are SO MANY projects to do, and just not enough time to
> >> get all of them done!
> >>
> >> Good DXing and VY 73, Lance
> >>
> >>
> >> --
> >> Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN,
> >> WA1JXN/C6A, ZF2OC/ZF8) P.O. Box 73 Frenchtown, MT  59834  USA
> >> QTH: DN27UB
> >> TEL: (406) 626-5728
> >> URL: http://www.bigskyspaces.com/w7gj
> >> 2m DXCC #11/6m DXCC #815
> >>
> >> _______________________________________________
> >> Moon-Net posting and subscription instructions are at
> >> http://www.nlsa.com/nets/moon-net-help.html
> >>
> >>
> >>
> >
> >
> >
> >
>Hi Russ,
>
>Yes, I can imagine that it would really be neat to connect the ALC 
>negative control
>voltage on the back of the rig all the time except during XMIT, and 
>have that control
>voltage be the last thing to turn off.  I think I would need another 
>sequencer ;-)  I
>hope to play around with it more tomorrow - difficult to do when you are busy
>operating EME ;-)  TNX again and VY 73, Lance
>
>--
>Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
>P.O. Box 73
>Frenchtown, MT  59834  USA
>QTH: DN27UB
>TEL: (406) 626-5728
>URL: http://www.bigskyspaces.com/w7gj
>2m DXCC #11/6m DXCC #815
>
>_______________________________________________
>Moon-Net posting and subscription instructions are at 
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