[Moon-net] IC746 transient output spikes

[Russ K2TXB]

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
> 
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