The Icom IC-9700 external pre-amp DC supply is a bit odd too ...

This is more on the oddities of the IC-9700 unexpectedly continued from four days ago in the last posting which is here and then even more here. The last one has a link which expalins it fairly well.

I have to confess that I made a mistake (wot, another one after Wrong-band-gate?).

Yes, when I wrote my initial review of the Icom IC-9700 (you can find that here) I was mystified by the lack of any proper explanation of how the external power supply to power a mast head external pre-amp worked. I described it as "an issue I am not so sure is really an issue".

Well, the mistake I made was to think I had the masthead preamp supply turned on when it was turned off. The reason why I made that mistake was the same as the issue I described, the manual does not explain this well enough. Actually, it does not explain it at all.

The procedure I followed at the time to get the masthead preamp supply turned on was in fact that procedure for the IC-9100. Thanks to Andrew, G0JCC, for clearing that one up for me. I was happily turning on and off the internal preamp and assuming it was the external supply.

It soon dawned on me that something was wrong. Not that it mattered much as I was using an outboard sequencer and bias-tee system so I did not need to rely on the internal 9700 supply. Nevertheless I did check and found no voltage on the 144MHz socket and I came to the conclusion that something had stopped working. Then soon after I discovered the 23cm socket was the same. The issue went into the "to do later"pile along with various clocks computers and linears that need fixing.

It did irritate me though. An issue that doesn't matter usually bugs me for ages.

Then this weekend I got an email from John G3WZT. He had found exactly the same thing, though fortunately he took it a bit more seriously that I did. After 24 hours of mind-wrangling it finally dawned on me what was wrong. The supply was indeed turned off, not faulty. In my long experience of these things I find they never work well if they are turned off.

And ... I did not know how to turn it on.

You have in fact to turn it on in two places for each band, in other words six times for all of them, and if you press the P.AMP button you get the internal one instead which will throw you right off course. And I had been thinking that the button applied to both pre-amps (because it says so in the manual - silly me). The idea that the button turned on the external preamp power came from the way the IC-9100 works, helped by the misleading manual for the IC-9700.

There is a lot of resistance put in your way If you want to turn this supply on.

The first line of resistance is page 1-1 of the manual which says the button on the front panel controls two preamps.

The second line of resistance you need to cross is the External pre-amp control in "Connectors". You should only need to do this once.

IC-9700 Selecting External P.Amp in "Connectors"

The third line of resistance you need to cross is on "Function page 2".

IC-9700 Selecting Function page 2 after External P.Amp has been enabled for that band.

Right, so here goes.

This, I think, is the way to turn on the IC-9700 DC supply for external preamps.

1) Select "SET"
2) Select "CONNECTORS"
3) On Screen 1 of Connectors select "External P.AMP
4) Turn the DC power supply on for the bands you want to use.
5) Return to main screen
6) Select FUNCTION
7) In Function select page 2
8) Turn on EXT P.AMP.

If you do not do steps 1 - 5 then the EXT P.AMP button on Function page 2 is greyed out.

Having done this the EXT P.AMP button on Function page 2 becomes your toggle switch for the external preamp and the button on the front does that job for the internal preamp. There is no indication on the display that you have the external supply turned on, you need to rely on the button on the Function screen for each band in turn.

Now there is very little in the manual to explain what is going on here. No wonder various people are confused. The manual misses the following piece of information:-
1) that the radio has DC over the rx coax at all, because how the DC gets out of the rig is never explained
2) the voltage
3) the polarity
4) the maximum current available
5) whether it is sequenced
6) if so how much it is delayed
7) whether the delay time can be varied and, crucially, -
8) HOW TO TURN IT ON AND OFF, EXPLAINED IN A LOGICAL WAY.

Briefly, these are the answers I can cover based on my observations (1) DC bias is available on rx once you find out how to turn it on (2) about 13.8V falls to 11.7V at 330mA, (3) +ve to coax centre meaning commercial preamps like SSB and SHF products work natively (4) not sure but it runs two of my 200mA preamps on two bands (5) apparently so, but don't count on it because we are not told (6) no idea (7) apparently not (8) I have done my best above.

It is not really my job to re-write the Icom instruction manual. Without much information I can only surmise these things so please do not take them as definite.

What information they do give is pretty cryptic, as here on Page 4-1 of the main manual:-

Part of Icom IC-9700 main manual page 4-1

This makes sense to me now, but only after I know what is happening. Just a bit of info - like what this is and how it works - would have helped me enormously. And the key bit of info missing for me is that it does not say that you have to come back out of Connectors to go to Function page 2 and turn it on for each band in turn.

I think what threw me right off the track is the comment on  page 1-1 "PREAMP/ATTENUATOR KEY Turns ON or OFF and selects one of two receive RF preamplifiers ..." What? The button acts on two preamplifiers? One of two? Which? One at a time, and how does it select them? I took that to mean the button worked on both internal and external preamps depending on how you set Connectors. This was not an unreasonable assumption as on the IC-9100 the equivalent button controls its external preamp. If that was not so, where are the two preamplifiers? This reference to two preamplifiers seems to be wrong.

'Onest Gov, it wasn't a mistake, I was misled good an' proper.

Anyway I am not one to be bitter, as you all know. Oh no. Icom, also, this type of thing would have been a lot easier if you had got page 1-3 correct in the original digital manual, then updated the manual available at the Icom UK site to correct that mistake, and not left me to resort to a paper copy where you have stuck a corrected page 1-3 into a sheaf of loose papers.

It is working now. I have been able to take out my cobbled-together sequencer and bias arrangements, freeing my rats nest behind the bench of 0.32% of its clutter. I also have 47mm of freed-up shelf space. [One of those two statistics is made up, the other is true]. I can do this now because my 2m and 70cm linears both pass the DC supply through to the preamps on receive. My 70cm one does not have a DC path through it, but then I do not use the IC-9700 for 70cms.

EDIT - I discovered that my 2m DCI cavity bandpass filter does not pass DC. I know this now because the IC-9700 must check for a short circuit on the coax. When it found the short it automatically turned off the DC supply (the button on the Function page 2 screen turned to "off") and posted a message on the display warning me of what had happened. I can find no mention of that in the manuals either but at least it works. 

I have checked the sequencing and there appears to be no SWR spike on going to transmit. At that level anyway everything checks out with the sequencing. We shall see however. I hope nothing gets blown up due to faulty timing. I would have more confidence if I had some information in the manual to support the evidence that it works. So, for now, all I can say is that it seems to be OK.

I now expect emails from sad individuals saying that I am carping and that I should have worked this out at the start. OK, the Icom IC-9700 is a very good radio. This DC supply is now working perfectly well. What I am going on about is that several of us have been left confused. I thought there was something wrong with the radio, not because I am totally dense but because it is very hard to understand the way it has been documented.

There are 96 pages in the basic 9700 manual. The basic manual is just a quick start guide as there are 173 pages in the advanced manual. I would have thought that any radio that claims to be a VHF/UHF DX-capable device would make things like this able to be understood, even by me. Surely a page could have been found to give us the details?

Much help was received in solving this from Andrew, G0JCC, and John, G3WZT. Thanks both of you for setting me thinking.

73

Jim GM4FVM