IC-910 mod as transverter driver

23cm, 2.4/3.4/5.7/10/24/47 GHz and above - antennas, propagation, operating, etc. Includes Optical communications, with light,
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IC-910 mod as transverter driver

Postby VK4GHZ » Wed Dec 22, 2010 1:09 pm

Hi all

Been mulling over how to drive my transverter.
From what has been posted about the FT-817, it sounds like a great I.F. rig, but the extra expense is out of the question at this stage.
(Will probably get an 817, if I build more transverters in the future.)

The VK3XDK transverters need 7dBm (5mW) of drive.

I already have an Icom IC-910. Specified at 75W o/p @ 70cm.

Before I go any further, driving the transverter needs to be idiot proof!
I can't rely on myself remembering to turn the power down.

The original plan was to design everything so that the IC910 always ran full power o/p. (Nothing to turn down!)
However, this seems like a waste of power, and would require a higher powered (read as: bigger, more expensive) relay that would split off the TX and RX paths inside the transverter.

How's this for an untested concept;

I don't plan on having an external 70cm preamp, so why not use that "feature" (on/off in SET mode) to activate an relay that kills the 13V feed to the UHF PA transistors Q151 and Q512.
See attached diagram.

ic-910 uhf pa mod.gif

I wonder how much "leakage" of the TX signal would end up at the antenna connector?
We only need 5mW here don't forget, and the RX path in the IC-910 remains unaffected.
Only one 10A 12V relay + 1N4001 diode required.

I would also use that 12V preamp power appearing on the UHF antenna connector to activate the transverter.
ie; DC sense inside the transverter, which would be the master 12V switch to the rest of the transverter.
No power switch on xverter required... a bit like having it in a STDBY state.

So, the [SET mode] PRE-440 setting would;
1) Reduce the 910 UHF power output to bugger all, by killing the 13V to the PA stage
2) Activate the transverter

This idea totally relies on having enough RF drive pass through the Q151/152 base-collector junctions.
A bit like, bugger all output, when you've blown your finals. :wink:

How dumb is this idea?
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Re: IC-910 mod as transverter driver

Postby VK3ALB » Wed Dec 22, 2010 1:58 pm

Hi Adam,

I'm not sure what the significance of [SET mode] is in the 910 but if you're planning to use the 910 for normal UHF operation as well as a transverter driver I reckon the time might come where you forget to set the radio to the right mode before you TX.

Would it work besides that? I'm not sure if matching becomes a consideration but it seems easy enough to try by pulling W153 and measuring the output.

I think a better alternative might be to borrow a low power UHF all mode rig. Also, take note of other posts on this subject regarding the use of high power radio running at low power. They all seem to put out a large spike when first keyed.
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Re: IC-910 mod as transverter driver

Postby VK4GHZ » Wed Dec 22, 2010 2:40 pm

Hi Lou & Justin

Bearing in mind the PWR o/p control will remain on 'maximum', do you expect the 910's driver stage to spike at all?
I can understand a spike might occur if the PWR control is set lower than maximum.

The 13cm transverter I will be building will have a Spectrian 2.4GHz 30W PA module.
These things draw about 13A, not efficient compared to other offerings, but they are a good plug n play solution requiring only 10mW drive from the xverter.
It has already been bought, so not changing that aspect.

By running the IC-910 at flea power, I could then run the 910 and transverter off a single 20A PSU.
If the 910 were running at full output (wasting the power by whatever scheme), that would immediately require one PSU for the 910, and another PSU for transverter.

Borrowing a UHF multi-mode rig is not an option either.
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Re: IC-910 mod as transverter driver

Postby VK3ALB » Wed Dec 22, 2010 4:08 pm

Hi Adam,

I don't think there would be a problem with spikes if the PA was disabled and your idea is an interesting approach. I like Justin's idea of the coupler which but I can't see how you could implement it without affecting the receiver unless you split the TX/RX path. I think your first step will be to pull that link and see what you get from the radio on TX.
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