Monday, 20 March 2023

SMC connectors

I nave been busy sending out SMC angle PCB mount connectors go builders of the F1CJN power meter. These are sent out for the postage cost. They are not being sold. Response from the build community has been good  and the connectors are now almost all gone.
I had previously built an 'analogue' power meter using one of the specified HP33330B diodes and a 100uA meter for a completely portable power meter that I could take out to the EME dish without worrying about mains power for the HP435 meters.
The battery-powered F1CJN meter is a step up from this, allowing for auto-ranging and offsets when using attenuator or couplers for range extension.on a nice colour LCD screen. Progress.....

Wednesday, 8 January 2020

Has it really been that long?

I had almost forgotten about my blog! I note that the last entry was back in August 2019.
An update on the IC9700 is required, together with my EME activities.

Having the IC9700 drift about on transmit and recovering on receive, especially when using digital modes on 23cm curtailed my EME activity.
I eventually bought one of the Leo Bodnar reference frequency injection boards as the VK1XX units were taking a bit too long to appear and the LB  boards were already  getting good reviews. Having to inject 49.152MHz rather than the 10MHz shack reference had previously put me off this approach. However, having a ‘spare’ dual output LB GPS source which would produce 49.152MHz, I decided to give it a go. Reliable reports had already shown that there was no impact on the transmitter composite noise over the existing, internal, reference TCXO. The new arrangement holds the IC9700 right on frequency, with no drift due to PA heating effects.

I am now back on 23cm EME and using JT65C with doppler tracking, I know where I am in frequency and can use the tracking to put my signal on top of the echoes from the other station, provided I know what frequency they are using for the transmit signal and their locator. I can easily see which stations are not using any form of frequency stabilisation, such as unmodified TS2000Xs and ‘stock’ IC9700 etc. by their drift characteristics.
This all makes EME operating so much more pleasant and reliable.

More anon

73 de Sam

Monday, 5 August 2019

IC9700 again

I have been busy remeasuring the reciprocal mixing dynamic range (RMDR) of the IC9700 receiver on 2m and 70cm.
Recent measurements have shown that the IC9700 has an RMDR of well over 90dB on both 2m and 70cm at close spacing (~10kHz) and even better further out.
This is a key measurement of a receiver’s dynamic range and is critically dependent on the local oscillator. Conventional superhet architecture receivers can be particularly bad. The fixed LO (clock) of an SDR receiver makes the design of ‘quiet’ local oscillators much easier than with an LOnthat must be tuneable as in VFO.
Older superhet receivers have typically given a RMDR in the 70dB range. More recent designs have improved this into the 90s and even as high as 115dB. However, this performance comes at a price. The SDR direct sampling  receiver can achieve high levels of RMDR at a much more acceptable price.
I will be presenting my measurements and those of a number of well-known experts at the RSGB Convention in October.


Sunday, 21 July 2019

4m noise

4m has always been  noisy here.
Using the arrangment in the previous blog, but on my IC7300, i was able to measure the noise level around my antenna.
In the worst direction (towards the house) the noise rose 18dB over the quietest direction. Not good!
I need to investigate what is producing that noise increase.
Now to repeat the measurement on the other  bands  covered.


Measuring noise using the IC9700

No, I didn’t get on the moon on 6cm for the Apollo EME commemorative event. Chesty cold knocked me for six. Just recovering. Courtesy of our  vistors from Australia........l

It did allow me time to consider how I could make continuum noise measurements using the IC9700 (on 23cm) when it doesn’t have an IF output in the usual sense. One thought was to try and use the 12kHz IQ IF output, but I failed to find any information on this or how it could be used with existing SDR software. I know it can be done.
I had played with using my SDR-IQ at audio (it goes down to 500Hz) to measure noise power in a defined bandwidth using Spectravue running on the SDR-IQ. This worked well, but I was not happy with the amount of amplitude ‘jitter’ on the trace.
I managed to find  a working HP3400 true RMS voltmeter at Friedrishshafen, to do the same measurement with a ‘proper voltmeter’!. Again flicker, because of the nature of noise and the restricted bandwidth, made this unsatisfactory.
Finally, I set up the IC9700 as a soundcard input to Spectravue (no SDR-IQ) and selected continuum mode. With a moderate amount of FFT and smoothing the trace is as stable as it was using the SDR-IQ on the K3 8.215MHz IF output. Not only, but the results agree very well with those previous  IF measurements.
Now I CAN use the IC9700 for EME noise measurements!


Thursday, 4 July 2019

Apollo commemoration - 6cm EME

Some of you may be aware Dean, VK6DSL, is working to get the 28 metre diameter dish at Gnangara, Western Australia, operational on 5.7 GHz EME to commemorate the Apollo 11 moon landings. Brian, G4NNS has been working to get Goonhilly GHY6 on air as GB6GHY as part of the celebration.
I thought it might be nice to try and get my 6cm EME system back on air to try and work them both. I haven’t used the 6cm system for about a year. As the local oscillator was not stabilised and the DB6NT MKU57 G2 transverter was located close to the dual (combined) power amplifier, if suffered badly from frequency drift due to heat. I never quite got round to modifying it for an external high stability LO source.

I viewed the new MKU57 G4 on the Kuhne Electronics stand at Friedrichshafen, last month, and decided I would buy one, especially as there was a small discount. 
To help things along I had been asked if I was prepared to sell my G2 and even my old G1. Of course!

The G4 has an external 10MHz reference input as well as a good internal TCXO. This should give me the frequency stability that I require. Doppler is bad enough to track without having to adjust for thermal drift as well.

I have decided fo locate the G4 away from the PA and LNA. That probably means at the back of the dish. That has several advantages.removing the transverter from that heat source and reducing the weight of the feedpoint equipment because I can also remove the control box and sequencer from the feedpoint.

Two low loss coaxial cables will connect the feedpoint PA/LNA/feedhorn. Both the high gain of the PA and the reasonable gain of the LNA  (a DB6NT LNA  - I don’t make one for 6cm) will enable me to run this arrangement with negligible receive system sensitivity loss and no transmit power loss.
One of the shortcomings of my previous arrangement was that the SSPA relied on simple conduction cooling to the aluminium frame at the feedpoint. Whilst this never led to any failures of the PA, a better cooling arrangement was a definite requirement.
With the transverter removed from the RF feedpoint frame I am now able to fit a 12V fan to blow air between the two PA modules that comprise the dual balanced amplifier. I found in test that I could increase airflow by cascading two identical 12v fans, one blowing into the other. In this arrangement the two fans tend to synchronise and definitely increase airflow. Whether it is twice a single fan is still unknown.....but it’s more than a single fan.


Thursday, 13 June 2019

IC9700 v1.11 firmware upgrade. Updated from previous blog

First a bit of advertising.
My review of the IC9700 is in the current issue of Practical Wireless, out today, for those of us without a subscription.

Having now upgraded to V1.11 firmware, in order to improve the reference stability, here are my observations.

By now the IC9700 reference oscillator stability is a well-known problem. In fact, for most users of CW, SSB and FM, the stability is a non-issue. It is only with the narrow digital modes that the stability problem shows. It seems to be associated with poor thermal control around the 49.xMHz reference TCXO.

The cooling fan comes on on transmit only. It does not run continuously. Not only that, but it only comes on when required on transmit. When it does come on it causes a small, but noticeable drift in frequency. Without the fan coming on, drift is much less noticeable.
On 2m it is hardly noticeable, even on FT8. It is more noticeable on 70cm and definitely noticeable on 23cm, although not really a big problem using JT65C on 23cm, compared to many other rigs.

Several ‘fixes’ have been proposed, including causing the fan to run continously, albeit at half speed; full reference locking using an add-on board and the possibility of a firmware upgrade to implement a locking system in the internal FPGA.

As designed, the external reference 10MHz input is little better than a modern version of a crystal calibrator. A facility is provided to automate the calibration of the internal reference against the external reference input. Once calibrated in this way, the internal reference is once again free to ‘drift’,  controlled only by the TCXO function.

Version 1.06 firmware improved on the correction algorithm and did make a big difference. The IC9700 is able to achieve a frequency accuracy only dreamed of in rigs like the TS2000x without frequency locking mods.

With firmware v1.10 and now V1.11the reference is periodically corrected, once invoked, and now works much like the system used in, e.g. the K3.
However, the period is possibly a little long as there is still a noticeable shortbterm drift under some conditions. I can see some further work, to refine the process, may yet be forthcoming from ICOM.

So, how well does V1.11 work to stabilise the reference oscillator?
On 2m FT8 I could see no change in frequency between transmit and receive, fan operating or not. Well, maybe a Hz!
FT8 on 70cm barely showed showed any change. Certainly not enough to cause any problems.
As FT8 is not recommended on 23cm, I didn’t bother to check for change with these short, 15 second, transmit/receive periods. However, JT65 uses a 47second transmit period followed by a 1minute, 13 second receive period. This puts a much bigger strain on the thermal characteristics of the reference oscillator and drift, even with the wider spaced tones of JT65C, was previous noticed with drift exceeding 20Hz when coming back to receive after the 47 second transmit period. This is important as any difference in the tone frequency from the expected frequency leads to a small but definite degradation in sensitivity. Keeping the tones where they should be gives the highest sensitivity.

So does V1.11 improve the situation at 23cm.
Basically, yes. 
To test the drift I set up one of my signal generators to produce a very weak reference carrier signal about 2.4kHz above the dial frequency I had chosen for my JT65C tests (into a summy load). This carrier produced a nice, straight, line on Spectran. The span on Spectran was set to show just a few hundred Hz either side of the tone. A drift of 10Hz was quite noticeable at this setting.
WSJT-X was then set to give repeated CQ calls of 47 secs on followed by the receive 1minute 13 second od receive, during which the 2.4kHz tone could be seen and measured. This was done at maximum 23cm output power (100% or 10W). 
As the signal generator was GPS displine-locked the frequency of the test carrier was very stable.
On test the tone frequency was always within a few Hz of 2.4KHz when returning to receive. It would then wander up to a peak of about 10Hz HF (2.410kHz) over the first few seconds, returning close to 2.40kHz reasonably quickly. Sometimes overshooting to a few Hz below 2.40kHz.
This happened each tx/rx cycle (over) although the peak excursion didn’t always reach 10Hz and averaged about 5-8Hz.

Although not yet perfect, this is a big improvement over the v1.05, v1.06 and v1.10 firmware.

I would expect a further improvement with a refined version of the firmware.

I am quite happy with this result. It would be interesting to do this level of testing with a few of the other transceivers covering 2,70 and 23cm!

I know from experience that the TS2000x drifted about 50Hz between transmit and receive on 23cm JT65C, before doing the fan-always-on mod.
This suggests that it might be worth still doing this mod to the IC9700 to keep the fan turning all the time, as when run at low power on 23cm (1.5W) the fan rarely comes on and drift was noticeably less in these tests.

More testing to do!