w8cbc
05-31-2006, 12:14 AM
I've run this thing long enough now that I feel I can make a fair assessment, with this disclaimer: it needed quite a bit of work when I got it. Some problems noted below may not be the fault of the design.
Anyhow.
50000.0-53999.9 kc
10-80 watts CW/SSB/FM, 5-40 watts "AM" (USB with the carrier thrown back in)
Receiving:
Sensitivity - adequate. I can hear ambient noise above the receive section's floor.
Selectivity - good - it separates signals well, but see below.
PBT - in this case, it messes things up - the unit's filtering is very peaky.
Dynamic range - I haven't heard it overload at all so I'd say it's good.
Noise blanker - I haven't really been able to check it as there's very little pulse noise to be heard in 6 metres.
Audio - bloody awful. In SSB, it's a squawkbox. That has in part to do with the peaky PBT filtering - but it's rather tinny in FM as well. This is with a good external speaker.
Stability - it seems to stay put on whatever frequency it's tuned to.
Tuning accuracy - variable. The VXO (100-cycle step, 10 kc range) isn't linear. It can read up to half a kc off in some parts of each 10 kc range.. This may be due to component drift. I've tried to line it up better and haven't yet succeeded.
Image rejection - poor. There's a local dispatch service at 33900 kc FM. The 551D hears it fairly well.
Squelch - excellent. I can set it to the noise threshold and leave it monitor for an Es opening. Anything above the noise will open it up.
Transmit:
Audio - I've been told it's a bit bassy in SSB. That's with the PBT set for the most tolerable RX audio. The TX IF goes through the PBT unit as well. In this case, I think it's poor design. I'm told it sounds clean in FM.
CW operation - semi break-in, comfortable once I adjusted it to my sending rate.
Metering - relative RF output only, uncalibrated (I did as the svc manual said and set it to read 80% at 80W - but I think it reads voltage so you have to do squares when reading it).
Power consumption - a little higher than full-output spec (15A) but not too bad.
General operation:
Switching VFOs is awkward - one has to make sure of the step and mode settings before doing so. I generally use the one VFO and leave memories and so on alone.
I prefer the thing's mode switch over shifted buttons.
Tuning steps are awkward for FM - you get a choice of 1 kc or 10 kc. 5 kc would be much better for the "coarse" step.
Memories and VFO settings are lost without DC input. You need an external voltage source to keep them.
Conclusions:
It's okay - I've been able to work some of the stronger Es on a dipole with it - but there's a lot of room for improvement.
I plan to figure out what the memory backup voltage is supposed to be (none of my documentation hints as to it) and put in an appropriate battery.
I plan to tap the reflected-power sense circuit and run it to a meter switch so I can get rid of the SWR meter I have in-line.
The PBT unit was an option for the earlier, 10-watt IC-551. If I can bypass it, I will. It cannot be disabled as it sits and I've done my best to align the thing per the service manual.
I suspect maladjustment of the front-end bandpass filter. I was lazy and didn't try to align it. Checking into it is the next priority.
Final biasing was one of the initial problems. It may still be a bit hot, thus the current draw. That'll get looked at again.
---edit---
An intermittent in the VXO showed up again tonight. I pulled the PLL unit, found lots of iffy-looking solder joints and redid them. The problem however turned out to be one that looked good.
The biasing problem in the finals was another bad solder joint.
This thing has evidently been through some temperature cycling.
---edit---
Well, the thing held up well through the VHF QSO party. I ran it pretty hard and there were no "surprises". So I think I've hunted down all the intermittents. With the band so nicely opened up on Saturday there was no shortage of signals. It certainly isn't deaf. It apparently gets out just fine as well. I got a few more comments about the bassy audio in SSB. I still haven't fixed or bypassed the PBT.
Anyhow.
50000.0-53999.9 kc
10-80 watts CW/SSB/FM, 5-40 watts "AM" (USB with the carrier thrown back in)
Receiving:
Sensitivity - adequate. I can hear ambient noise above the receive section's floor.
Selectivity - good - it separates signals well, but see below.
PBT - in this case, it messes things up - the unit's filtering is very peaky.
Dynamic range - I haven't heard it overload at all so I'd say it's good.
Noise blanker - I haven't really been able to check it as there's very little pulse noise to be heard in 6 metres.
Audio - bloody awful. In SSB, it's a squawkbox. That has in part to do with the peaky PBT filtering - but it's rather tinny in FM as well. This is with a good external speaker.
Stability - it seems to stay put on whatever frequency it's tuned to.
Tuning accuracy - variable. The VXO (100-cycle step, 10 kc range) isn't linear. It can read up to half a kc off in some parts of each 10 kc range.. This may be due to component drift. I've tried to line it up better and haven't yet succeeded.
Image rejection - poor. There's a local dispatch service at 33900 kc FM. The 551D hears it fairly well.
Squelch - excellent. I can set it to the noise threshold and leave it monitor for an Es opening. Anything above the noise will open it up.
Transmit:
Audio - I've been told it's a bit bassy in SSB. That's with the PBT set for the most tolerable RX audio. The TX IF goes through the PBT unit as well. In this case, I think it's poor design. I'm told it sounds clean in FM.
CW operation - semi break-in, comfortable once I adjusted it to my sending rate.
Metering - relative RF output only, uncalibrated (I did as the svc manual said and set it to read 80% at 80W - but I think it reads voltage so you have to do squares when reading it).
Power consumption - a little higher than full-output spec (15A) but not too bad.
General operation:
Switching VFOs is awkward - one has to make sure of the step and mode settings before doing so. I generally use the one VFO and leave memories and so on alone.
I prefer the thing's mode switch over shifted buttons.
Tuning steps are awkward for FM - you get a choice of 1 kc or 10 kc. 5 kc would be much better for the "coarse" step.
Memories and VFO settings are lost without DC input. You need an external voltage source to keep them.
Conclusions:
It's okay - I've been able to work some of the stronger Es on a dipole with it - but there's a lot of room for improvement.
I plan to figure out what the memory backup voltage is supposed to be (none of my documentation hints as to it) and put in an appropriate battery.
I plan to tap the reflected-power sense circuit and run it to a meter switch so I can get rid of the SWR meter I have in-line.
The PBT unit was an option for the earlier, 10-watt IC-551. If I can bypass it, I will. It cannot be disabled as it sits and I've done my best to align the thing per the service manual.
I suspect maladjustment of the front-end bandpass filter. I was lazy and didn't try to align it. Checking into it is the next priority.
Final biasing was one of the initial problems. It may still be a bit hot, thus the current draw. That'll get looked at again.
---edit---
An intermittent in the VXO showed up again tonight. I pulled the PLL unit, found lots of iffy-looking solder joints and redid them. The problem however turned out to be one that looked good.
The biasing problem in the finals was another bad solder joint.
This thing has evidently been through some temperature cycling.
---edit---
Well, the thing held up well through the VHF QSO party. I ran it pretty hard and there were no "surprises". So I think I've hunted down all the intermittents. With the band so nicely opened up on Saturday there was no shortage of signals. It certainly isn't deaf. It apparently gets out just fine as well. I got a few more comments about the bassy audio in SSB. I still haven't fixed or bypassed the PBT.