Tuesday, 28 June 2016

Yet more IC7300

I have taken delivery of an Alpha Delta 4 way coax switch to direct the output from the 7300 to the 4/6m antenna, HF antenna, dummy load or to the Anglian 2m transverter.
I have opted for the simple approach go interfacing to the Anglian and Gemini 2 PA.
I use just a 20dB power attenuator after the switch into the Anglian. I have the 7300 28MHz band power set to 8W. The reasoning is that if I was to accidently forget to turn the 28MHz power down (it is set per band) then the max that would hit the Anglian would be 1W and transverters tend to be more tolerant of overlod due to the usual input attenuator before the mixer. The 20dB attenuator is a25W unit which will stand a degree of overload before burn out.
My tests using the spectrum analyser on max hold etc indicated no significant spiking of output power when set to low power. I have seen some reports of ALC overshoot on SSB and CW. I have not seen this.

I had an interesting problem when set up. The Gemini 2 would fail to SWR when driving bove 100W output. This was eventually traced to the bulkhead lightning arrester on the antenna feed starting to trigger at this

level. The arrester has been replaced by an N bulkhead adapter. All is well now.

This evening saw several new locators added to my 6m total in the NAC contest. Now to try and leave  the system as it is now instead of yet another rearrangement.........


Saturday, 18 June 2016

More IC7300 tests

Since I want to try my 2m system with the IC7300 I was interested to know how well the power control on the new Icom works. In particular, does it spike on switching between receive and transmit?
I set the rig to 28.2MHz and (carefully) connected it through a 150W/40dB attenuator to my HP8592 spectrum analyser. The analyser was set to 20mS sweep and 5MHz span. With the IC7300 set for full output, the reference level was set to 0dB on screen. The mode was SSB. The analyser was then set to Max Hold in order to capture any spikes. The IC7300 mike gain was set to zero.
Keying the IC7300 transmitter on and off produced a small spike, caught by the Max Hold on the analyser. The level of the spike was around -55dBc
The IC7300 was keyed in different modes with similar results.
Winding the power down to '0%' resulted in the spike amplitude being similarly reduced.
Power output at 0% was 22dB down on maximum output, or about 700mW. This is below the  2W claimed.

It would appear that the IC7300 does not power spike to any significant level.

Connecting the IC7300 to my 2m Anglian transverter with DG8 mast head preamp, though the 40dB attenuator, produced a barely audible increase in noise.  No surprise there!
Reducing the in-line attenuator value to 20dB result in a greatly increased noise output and lots of beacons appearing on the 7300 spectrm display.
16dB is about optimum for my system and so it was with an MCL 15dB 2W attenuator that the system seems to work well and achieve about as good a dynamic range as I could expect with this set up.

Using a 15/20dB power attenuator is required to further reduce the power into my Anglian. I don't like to dissipate more 28MHz power in the transverter than absolutely necessary.

Although the IC7300 does not appear to spike, this is still not proof against forgetting to turn the power down.............

A 20dB, several watt, IF attenuator will give some protection and then fuse if severely overdriven. Hopefully you will have noticed a problem by then and there could even be time for an overdrive protection circuit to operate. I do not advocate this approach in order to drive an LDMOS SSPA as it would probably fail a whole lot faster than any protection circuit unless carefully designed to prevent any drive reaching the PA before checking its level.