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Author Topic: ICOM IC-740 real operational performance question  (Read 943 times)
KG6DFT
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Posts: 3




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« on: April 27, 2008, 09:29:43 PM »

Hi.

I'm trying to help check out an ICOM IC-740 of a friend.

I am wondering the following about how much maximum power these units typically put out in the real world.

Select RTTY mode on a frequency in the 40 meter band when transmitting into a well matched load (e.g. 50 ohm test termination).

Raise the RF PWR knob to its maximum possible power level.

Set the METER switch to monitor 'RF'.

Connect an external watt-meter inline with the transmitter output.

Start with the apparatus warmed up but 'cold' without having transmitted significantly for many minutes; i.e. PA cooling is not overheated.

Key down with your mic. key or whatever to begin transmission, and look at the RF watt meter indication.

What is the actual power typically seen / generated by one of these units in these conditions?  Does it vary significantly from unit to unit?

I thought that they were nominally capable of around 100W+ output from my recollection of some marketing specification, though it is always possible that various internal losses may reduce the actual figure somewhat below that.  

I'm wondering what the threshold is for saying a given unit is operating reasonably and at what point one might start questioning either one's power meter calibration or the transmitter's capability / matching.

Marketing watts don't always even approximately equal real watts, so hence I'm wondering what others' experience has been with these units.
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VE3GNU
Member

Posts: 83




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« Reply #1 on: April 28, 2008, 08:38:10 AM »

Hello---

As per my unit:  serial #180 02681---original owner---

Power supply:  IC-PS20---switching unit---and your requirements---
Dummy load:  Heath Cantenna
Ant:  G5RV
External power meter: Viewstar VS300A (on ant. tuner)
Freq:  7.050
RF Power out:  full
Power on IC-740 meter---just short of 80 watts
Power on External meter-70 watts

My IC-740 is in the original condition, and has never had any modifications or repairs done.
Please be aware that there is an internal switch that
permits you to choose between 50 watts out or 100 watts out.  It is S1 on the right-side board once you remove the top cover.
I hope this is of some help.

73---Ernie


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KG6DFT
Member

Posts: 3




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« Reply #2 on: April 28, 2008, 10:03:30 PM »

Thank you very much, Ernie, that was exactly what I was needing to know.  Your results are reassuringly similar to the unit we've been looking at, so I am reassured that nothing is necessarily amiss about not getting closer to 100W out of the unit.

I wasn't aware of the power switch, that's good to know, though I think it must be in the 100W position now and is just delivering output in the 60-70W (+/- measurement accuracy) range as seems to be approximately normal relative to the results you've shared.

Thanks again & 73.
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VE3GNU
Member

Posts: 83




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« Reply #3 on: April 29, 2008, 12:00:34 PM »

Hello KG6DFT---You're very welcome.  In addition, I neglected to mention that the input power, as stated in the original brochure is 200W for A1 and F1, as well as 200W for A3J (SSB)---As well, "A good
measure,if the radio is open, is to replace the electrolytics in the REG Unit, it is fairly easy to do, and generally higher voltage-rated replacements will fit in the existing space".  This was the advice from another operator several years ago, and who had the same rig.
There are a number of sources for advice, namely the Yahoo Group: icomclassic, and Scott Malcom's MT Website----

The only thing that has 'gone bad' in my rig is the COMP switch (a generally well-known issue), so I don't use it!
The meter light went out a few months ago, but that is not much of an issue.

73---Ernie
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