Around 40 people attended the TOG meeting (MPIfR Bonn, 2001). The following text tries to summarise the most important aspects covered during the meeting. Besides the on-going EVN FS development programme, the action items referred to in the text, set-out the TOG’s development programme for the next 6 months.
TOG meetings such as this represent a large investment in man-power and resources.
It is worth considering what we are trying to achieve. TOG meetings:
(i) facilitate knowledge sharing across the network and direct access to significant VLBI technical/operational expertise
(ii) provide an opportunity for people to volunteer their own expertise on behalf of network projects (the harvest is rich but the labourers are few!),
(iii) enforce self-assessment (both at the local and network level) i.e. just what has been achieved since the last meeting, what problems remain, how can they best be remedied etc,
(iv) generate a “plan of action” for technical and operational developments (including improved reliability) on both short (months) and long term (years) time scales.
Significant progress was recorded in several key areas:
1) the formatter upgrade is essentially complete (in terms of hardware) – components had been shipped (Freihold, Graham) and the hardware installed at all stations. A multi-mode fringe test had also been scheduled (Foley), producing fringes to all stations at JIVE. Graham had conducted some barrel rolling tests at Effelsberg and had also checked that various other features had been improved/removed (communication problems, apparent clock jumps with tape speed all fixed). First tests (Reynolds session 2/2001) of the remaining clock jump feature (clock jump vs BBC filter width) have been made and are expected to be correlated soon.
2) Garrett had obtained approval from the CBD to contract NVI to add features to the FS required for the EVN FS development programme (2 heads etc); Himwich had drawn up a FS development plan (together with several TOG people) and “costed”the man-power required to introduce these features; Garrett had arranged for a FS contract to be drawn up between the EVN and NVI – this contract is in force (1 April 2001) and runs for 1 year,
3) Graham had generated an IF switchbox design. A web page detailing the design is at: www.mpifr-bonn.mpg.de/EVN/ifsw.html
4) Two head hardware installed at all telescopes except Torun. Smythe had made available 2-head testing procedures via the Haystack ftp site. Local recording and playback tests made at the majority of stations. Reasonable results seen with 80 ips playback at Eb, Mc, Sh. Agreement reached w.r.t. Torun 2-head upgrade at JIVE – despatch of recorder is imminent. Van Langevelde (and Walker) had modified Sched to handle 2-head recording modes (512 Mbits/sec).
5) Starting from a Sched key file, Graham had exercised the full 2-head development path, culminating in a successful zero baseline fringe test (between the single head vlba recorder and the twin head MkIV connected to a common noise source) correlated at Bonn. The results are now online: www.mpifr.bonn.mpg.de/EVN/512.html
6) Since the last meeting (and the VIV upgrade) Shanghai had returned to robust and reliable operation.
7) 150 new this tapes had been re-reeled at JIVE (Buiter and Parsley) and dispatched to the stations (sessions 1 and 2, 2001). Shanghai, Urumqi, Medicina and Onsala had been switched over to thin tape only operations (in conjunction with other VLBI networks)
8) Improvements were made w.r.t. the automatic generation of ANTAB calibration data and their format (Reynolds). Further improvement relies on the EVN FS development.
9) Tuccari arranged for tenders to be placed w.r.t. the bulk procurement of MkIV decoders. The final order with Signatron was completed by the end of the year and processed rapidly - the first units arrived a few weeks ago. The decoders are now in routine operation at several EVN telescopes (but not all…).
10) Spare parts: Burgess has been active in several areas, a web page listing obsolete components (and possible alternative sources/components) has been created; Burgess and Tuccari have also placed a list of recommended local parts on the EVN operations page. Arno Freihold has agreed to be the EVN central spare parts Tzar. Garrett obtained approval from the CBD to provide a fund of 10 kEuro to be spent on obsolete parts/components.
11) EVN sensitivity: recent tests at 6cm (Garrett) had shown that the theoretical noise level (natural weighting) can be reached for relatively faint sources (and modest dynamic range limits < few thousand). The first test case reached 32 microJy/beam for a 261 minute on-source integration.
12) Logistics – a code of practice had been written (Porcas) informing non-EVN stations (and PIs) about operational practice required for co-EVN observing. The new test experiment naming convention had been introduced (not without problems).
Pipelining of EVN user data (calibrators only) was approved by the CBD. Users can veto the use of calibrators associated with their data set, and images can only go online with the PIs permission. Hopefully the ICN coordinator will begin pipelining EVN data later in the year – a much better idea of the networks performance will then be possible.
The CBD also approved funding of the EVN FS development contract. Funds for obsolete components were also made available.
The CBD decided that in the case of tape shipments and non-EVN stations the rule applied is that “sender pays”.
Changes to EVN membership included: Arecibo (assoc. member), DSN (affiliated member). The situation at HRAO is expected to become clear soon.
The CBD was reasonably satisified with the EVN’s performance and reliability over the last 12 months.
A release policy for the EVN correlator at JIVE had been agreed. This should release thin tapes back into the pool more quickly.
The CBD would like to move from 4 sessions per year to 3 sessions per year (each session would be slightly longer). The majority of stations have little problem with this change.
ACTION ITEM: VLBI friends who do not wish to move to 3 sessions per year must inform their local director. (A decision will be made at the next directors meeting – November 2001, JBO)
V. Altunin (JPL) had requested that the EVN supply a fully equipped 6cm receiver (amplifiers, feed etc) in order to ensure Robledo’s participation in more EVN experiments. The EVN is not in a position to supply a fully equipped receiver.
ACTION ITEM: Peter Poon (JPL) will discuss the issue of a JPL funded dual polarisation 6cm receiver with V. Altunin and report back to the TOG.
ACTION ITEM: Peter Poon (JPL) will discuss the issue of a dual polarisation
18 cm receiver at Robledo (the current system is only available in single polarisation – LCP)
The upgrade of Simeiz to MkIV was also discussed (see the Semeiz station report later in this report for the TOG’s initiatives in this area).
Performance of the EVN
Despite improvements in the quality of the recorded data there are still some problems. At the Bonn correlator PAH6 was being processed during the meeting – fringes to all stations. However, 3 stations (out of 9) have playback problems – JBO and WSRT (last reverse pass over-writing first forward pass). It turned out during Steve Parsley’s Recorder Test presentation (later in the day) that this had also showed up on the recorder tests.
ACTION ITEM: Stations are encouraged to continue to use the recorder tests as an independent assessment of their recordings
ACTION ITEM: Stations must inspect the recorder feedback data directly and carefully. Feedback from the EVN correlator should include a short written report, highlighting serious playback problems.
The question of ensuring a continuous reverse tape pass at the end of an experiment was discussed. This would require a 1 hour gap to be inserted between experiments (instead of the current 30 minutes). It was felt by many that this was an essential element of good operational practice.
ACTION ITEM: Garrett to request to the Scheduler that the gap between experiments be increased from 30 minutes to 1 hour (in order to permit a SFF and SRW of the tape to occur at the end of each experiment).
ACTION ITEM: Himwich to include an automatic SFF and SRW at the end of each experiment (in the event that the last pass was not complete and continuous).
ACTION ITEM: van Langevelde to change wording in Sched – discouraging recording at less than 40 ips.
ACTION ITEM: Himwich to check whether DRUDG inserts readback test every 2 hours even if operator replies (n)
Another hardware concern was the problems at Torun w.r.t. BBCs. At least 2 of these were no longer functioning and there were problems with several others.
ACTION ITEM: Borkowski, Tuccari and Burgess to ensure local tests are conducted in order to diagnose the problem. Further action might require the BBC to be shipped to JBO (Burgess will investigate whether this is an option). Alternatively the units could be repaired by Signatron (Metsahovi is in the process of obtaining quotes for new units in order to conduct geodetic observations).
TSYS data are now available for Cambridge (session 2/2001 onwards). There is still a problem at Robledo but this is expected to be resolved by the end of the year.
ACTION ITEM: Garcia-Miro and Poon to ensure TSYS data can be provided by Robledo before the end of the year.
Swapped polarisations continues to raise its ugly head (most recently Effelsberg with swapped VLBA terminal IF cables). The TOG was dramatically reminded that nothing less than “constant, never ceasing vigilance” was required in this matter (as with many others).
Operational/Observing efficiency was reasonable at most stations, but significant chunks
of WSRT time were being lost due to bugs in the continually developing Telescope Management System. Despite all best efforts, the continuing evolving nature of this software suggested that problems would continue for some time.
The EVN is reaching the rms noise level at 6cm (NME session 2/2001). Runing at 128 Mbits/sec with an on-source integration time of 261 minutes the EVN reached 32 microJy/beam (see www.jive.nl/~mag/nme_6cm_map.gif). The result probably relies on external amplitude calibration from a nearby phase-reference source. This will be more fully investigated once the NME is re-correlated in its entirety. By simple extrapolation an 8 hour (on-source) run would correspond to 23 microJy/beam (by comparison the VLBA reaches 48 microJy/beam). With 2-head recording at a sustained rate of 512 Mbits/sec over 24 hours should be possible resulting in image rms noise levels of better than 7 microJy/beam (better than either MERLIN, WSRT or the VLA at this wavelength).
We need to repeat this experiment at 18cm, and see if we get the same result.
ACTION ITEM: Garrett to request via the EVN PC chair a repeat of NME performance test during the next L-band session.
Van Langevelde and Sjouwerman highlighted the problem that PIs were not scheduling enough fringe finders in experiments. Garrett noted that all EVN PIs could call upon the support of JIVE support scientists w.r.t. scheduling and the new users were assigned support automatically. It was difficult to extend this service due to man-power problems and the nature of EVN sessions. In particular, having the same fixed deadline for all experiments in a given session made schedule checking difficult without delaying the deposition of schedules on VLBEER further (there was a general feeling from stations that time-scales were already much too tight, so another delay in the deposition of schedules is not favoured and pushing back the schedule deadline is simply not an option). In addition, many experienced PIs objected to being assigned a support scientist.
There was a general feeling that the nature of the EVN (in particular no facility for central scheduling) required that observing appropriate fringe-finders must (at least for the moment) remain the primary responsibility of the PI. The best way to proceed was via the direct education of users.
ACTION ITEM: van Langevelde and Garrett to ensure that Support Scientists attached to projects being correlated at JIVE inform PIs when the schedule is non-optimal.
ACTION ITEM: Garrett to check with Tiziana Venturi what is now checked w.r.t. schedules.
Romney reported that even without direct support (Sjouwerman, Reynolds) the VLBA correlator could handle the current level of EVN correlation at Socorro. The “backlog” was shrinking but tape supply is still marginal. The VLBA requires 120 thin tapes per week.
For globals NRAO was concerned about the inefficient use of thin tapes (multiple projects on a single tape were only possible for VLBA only observations currently).
Romney urged the EVN correlator to modify their software so that multiple projects per tape could be handled (at least for VLBA telescopes). There was some discussion about this – clearly there are some trade-offs between network efficiency and new correlator capabilities. Given the desire to move to thin-tape only operations in the EVN, the TOG concensus was that multiple projects per tape should be given higher priority. Extending this to tapes associated with EVN stations was some way off because it required central scheduling. In addition, the TOG felt that the block schedule should be created in such a way that all experiments on a given tape should go to only one correlator (otherwise there is a significant risk of tapes being released or erased prematurely).
ACTION ITEM: van Langevelde to raise the priority of multiple-project per tape processing at the EVN correlator.
ACTION ITEM: Garrett to contact the EVN PC chair and check that observing time was quantised in terms of thin-tape record duration (this is already believed to be the case).
Romney reported that the way in which the VLBA correlator provides feedback to antennas will change shortly. Diagnostic plots will replace the “Dear PI” letters (its hoped this will be an improvement for stations). Stations may inspect these and ask questions about the plots but should not expect a detailed analysis or follow-up investigations to take place. Observations scrutinisation will soon be abandoned for the most straight-forward cases. A weekly fringe/system test will be introduced at the VLBA.
Van Langevelde presented some results regarding (2-bit, 4-level) EVN station sampler statistics. It appears that errors in sampler thresholds are larger than expected, resulting in a loss of sensitivity at those telescopes worst affected and amplitude scaling errors in the cross and auto-correlation data. In these cases of non-optimal sampler statitiscs a correction to the amplitude scale of the signal is required. So far no correction has been made at the EVN correlator and the first investigations show that some telescopes have much larger errors than others.
One interesting effect could be seen at Onsala where the effects of the AGC can be clearly seen at source changes. MkIV BBCs have analogue AGC while VLBA BBCs are digital. The analogue system reacts more quickly to changes in the input level according to Graham.
A correction for biased sampling will soon be made at the EVN correlator but this cannot correct for the loss of sensitivity. It is extremely important that stations pay attention to this area. One of the worst cases seen so far is Noto where (according to Sergei Pogrobenko) some of the BBCs are so badly affected that the telescope’s sensitivity may be reduced by up to a factor of 2). In addition, the recently purchased (upper) set of BBCs at Effelsberg (BBCs 5-8) may show much poorer characteristics than the original BBCs.
According to Smythe there is a FS procedure (chk2bit.sna & chk2bit.prc) that allows one to see significant differences between sampler thresholds in each BBC channel. The procedure is available at ftp://dopey.haystack.mit.edu/pub/mark4/DAS/
It was also noted that it might be useful to seek more clues by reviewing the station logs, in particular attenuation levels reported for each BBC.
ACTION ITEM: Tuccari will investigate sampler levels at Noto and report back to EVNtech.
ACTION ITEM: Stations to use chk2bit.prc and report back via EVNtech.
Stations were advised that they could obtain more information directly from Campbell (email@example.com) on their sampler stats.
ACTION ITEM: van Langevelde and other correlator staff at JIVE to evaluate the effect of sampler bias on EVN data and report back to the TOG via EVNtech.
ACTION ITEM: Stations to read and implement Himwich’s memo on setting MkIV VC levels (see http://ivscc.gsfc.nasa.gov/nc/vclevels.txt)
ACTION ITEM: Garrett to organise a test (session 3/2001) of new formatter capabilities (barrel rolling/modulation – individually and together). The thin tapes (2 VLBA and 2 MkIV) will be available to all correlators (EVN, Bonn and VLBA).
ACTION ITEM: Garrett to ensure that results from the recent formatter test (using different filter combinations) are fedback to the correlators and TOG (via EVNtech).
Graham has produced a web page detailing the results from the tests conducted last year at Effelsberg (see www.mpifr-bonn.mpg.de/EVN/fup.html). It is hoped that once the deterministic apparent clock jumps with filter width have been measured and accounted for, the EVN telescope clock-offsets will be much better than a microsecond (the current level of stability).
ACTION ITEM: All stations were reminded by van Langevelde not to correct for formatter clock jumps during experiments but to make the correction between experiments.
The continuing FS default is for barrel rolling and modulation options to remain switched OFF by default.
There was some discussion about the effect of modulation on data quality. According to Graham only highly over-sampled data (by a factor of 8) showed any significant improvement. Barrell-rolling would help alleviate the problems of bad-tracks however.
There was some confusion about whether MPIfR had sent out invoices to the stations for the new firmware components.
ACTION ITEM: Graham/Freihold to ensure that stations have been invoiced for costs associated with upgraded firmware.
FS version 9.5 will be released shortly. This version paves the way for the implementation of the EVN FS development programme. The list of associated priorities
was discussed later in the meeting. Substantial progress was expected by the time of the next meeting. There was a suggestion (after the meeting) that the next workshop might focus on the FS and the new features available.
ACTION ITEM: Stations to provide Himwich with direct feedback w.r.t. FS bugs/features etc.
ACTION ITEM: Himwich, Orfei, Tuccari and Garrett to consider whether a short 1 day workshop before the next TOG is possible/appropriate.
2-head Recording Development Programme
With the hardware installed at the vast majority of stations a development programme emerged which is embodied in the following actions:
ACTION ITEM: All stations to complete LOCAL 2-head 160 ips recording (80 ips playback) tests before 31 July 2001. Stations to report their status via EVNtech.
ACTION ITEM: Smythe, Parsley, Burgess to agree on the format of a 2-head Recorder Test(s) and Smythe to produce procedures for these also by 31 July 2001.
ACTION ITEM: All 2-head stations to run the new 2-head Recoder Test procedures and send tapes (and logs!) to the EVN correlator at JIVE. Deadline for the receipt of tapes tapes is 20 August 2001.
ACTION ITEM: Parsley to ensure feedback to the stations w.r.t. Recording Tests by
August 31 2001.
There was some discussion about what had to be fixed (features uncovered by Graham –see www.mpifr-bonn.mpg.de/EVN/512.html) before a fringe test could be conducted:
ACTION ITEM: van Langevelde and Himwich to test Sched/DRUDG interaction for 2-head schedules.
ACTION ITEM: Garrett, Tuccari, Graham, van Langevelde, Himwich to ensure that a 2-head Fringe test is conducted in September 2001 (date to be fixed after station constraints and results via Recording Tests are known).
ACTION ITEM: Himwich to ensure that 2-head capability is given sufficiently high priority in EVN FS development programme.
ACTION ITEM: Smythe and Himwich to ensure that in FS 9.6 there are clear instructions w.r.t. any hardware changes required (switching head cables etc).
Romney noted that for the VLBA, data generated via multiple passes requires that the AIPS task MATCH be used in conjunction with VBGLU.
ACTION ITEM: EVN correlator to ensure that 2-head data is exported in a valid FITS format (assuming 2 heads are not yet installed and multiple-passes are required).
ACTION ITEM: Garrett to investigate whether the (multiple pass) 2-head fringe test data can be processed cleanly in AIPS.
On these time scales 2-head recording might be advertised to EVN users in session 2/2002.
Misc. Points: Recorder Test tapes and fringe test tapes (logs) will also be made available to Bonn and Socorro correlators.
The speed at which the units had been delivered was impressive. Foley highlighted a number of items that might form the basis of a “decoder wish list”.
ACTION ITEM: Tuccari will act as a central focus for the generation of a “decoder wish list” and will make contact with Haystack (Capello) on this issue.
ACTION ITEM: Tony Foley to find out what is involved in contributing to the decoder software.
Vincente raised the issue of how to connect the new decoder to VLBA terminals (rather than MkIV).
ACTION ITEM: Smythe, Tuccari and Mujunen to inform VLBA stations (e.g. Yebes)
w.r.t. connection of MkIV decoder to VLBA terminals
ACTION ITEM: Garrett to encourage (via the CBD) those stations that have not purchased a decoder to do so asap.
Graham presented his IF switchbox solution. For various reasons it seems to be difficult to get a prototype built (no volunteers).
After a minute silence no further progress was made on this issue.
Tuccari noted that the IF switchbox situation was a good example of how ineffective the EVN TOG can be in such circumstances (another case of the harvest being rich but the labourers being few, coupled together with the TOG’s exercise of influence rather than any real power).
Graham and Alef felt that there might be a “cheaper” solution - restricting users to a few special modes in Sched that would not require patching. Van Langevelde is not convinced.
ACTION ITEM: Graham, Alef, van Langevelde and Garrett to look further into a possible Sched based solution.
ACTION ITEM: Garcio-Miro to supply to Alef information regarding the company that constructed the DSN IF switching system. (Perhaps there is a new, cheaper, off the shelf option ?).
The TOG encouraged Burgess to continue his efforts in the area of obsolete components (see web server: http://newton.jb.man.ac.uk)
ACTION ITEM: Burgess and Tuccari to acquire obsolete components via 10 kEuro CBD authorised budget.
ACTION ITEM: ALL to inform Burgess of sources of obsolete components.
Attention was also brought to Burgess’ list of Local Spare Parts as listed on the EVN Operations Group Page (see www.ira.noto.cnr.it/evn/partlist.html)
ACTION ITEM: All stations to review the Local Spare Parts list, and to procure any recommended parts they do not have in stock.
Arno Freihold (firstname.lastname@example.org) has agreed to be the contact person w.r.t. major spare parts held centrally at MPIfR (e.g. capstan motors etc).
ACTION ITEM: Tuccari and Garrett to contact Freihold and establish what is available
within this central pool and whether any important items are missing. All three to discuss how this pool should operate and what if any additional resources are required.
ACTION ITEM: Garrett and Tuccari to inform the TOG how this central pool will operate via EVNtech.
Further progress in this awaited the implementation of the EVN FS development programme.
ACTION ITEM: Garrett to check that Conway would continue to be one of the main points of contact within the EVN w.r.t. the FS developments.
A short report was presented by van Langevelde. Sched is now able to produce 2-head (512 Mbit/sec) schedules. Reynolds was now responsible for updating the station frequency catalogue file (freq.dat)
ACTION ITEM: All stations to report changes in their receiver set-ups (freq.dat) to email@example.com
The naming convention for test experiments was discussed. In order to reduce the possibility of clashes with the geodetic community it was decided to replace “C”(correlator test) with “D”.
ACTION ITEM: Garrett to update the naming convention and distribute it via EVNtech and directly to the scheduler and PC chair.
Problems of shipping tapes to and from stations/correlator were discussed. Van Langevelde also noted that there had been some problems in tape shipments from the VLBA antennas to JIVE but these did not affect operations so far.
ACTION ITEM: All stations to ensure that their CORRECT shipping address appears on the EVN Home Page (under “contact information”). Corrections should be sent by e-mail to firstname.lastname@example.org
ACTION ITEM: All stations were reminded to use TRACK at all times.
3 sessions vs 4 session was discussed and stations were encouraged to express their view.
Porcas suggested that one might conclude that the sessions might not be any larger than they are now (even after the move from 4 to 3 sessions) since VSOP observing would no longer be included.
ACTION ITEMS: Stations with problems with the move to 3 sessions should inform their directors asap, and in case before the next CBD meeting (November 2001).
Garrett requested that stations ensure that the NME tapes are shipped in a timely fashion. In particular, tapes from Medicina and Urumqi are often very late (> 7 days) and the full correlation and pipelining of the NME must be repeated until these tapes arrive.
ACTION ITEM: All stations to ensure that NMEs and Fringe test tapes arrive at the correlator as quickly as possible.
The report by Garrett and Alef had highlighted good practice w.r.t. thin tape logistics viz.
(i) stations should not stockpile thin-tapes locally as this effectively removes them from the system,
(ii) there should be no concept of “geo-only”or “astro-only” tape pools operating locally at stations,
(iii) correlators should keep to a minimum the number of test tapes required to debug/verify the system,
(iv) stations must use TRACK in order for the tape pool to be effectively monitored
(v) The EVN, together with the VLBA will try to monitor tape activity on a monthly basis.
ACTION ITEM: Garrett to identify someone in the EVN to monitor the tape pool via TRACK.
Parsley reported on the EVN’s contribution to the thin tape pool. 685 tapes had now been invested in the pool. A further 150 were on order. These would be re-reeled at JIVE and
begin to enter into the system from before session 3 onwards.
ACTION ITEM: Parsley and Buiter to ensure that as many as possible of the newly ordered tapes are quickly re-reeled and ready to be shipped to the stations well in advance of session 3/2001 (start date: 1 November 2001).
This latest round of thin tape procurement would bring the EVN’s contribution to 835 tapes (ignoring those that have been retired, damaged, lost etc). There was a general feeling, that given that the number of thin tapes currently required to run a typical EVN session was about 220 thin tapes (even without multiple projects being assigned to the same tape) and taking into account the current effieciency of the EVN correlator, the EVN should aim to conduct all future sessions with thin tape only.
ACTION ITEM: Alef to communicate this EVN “thin tape only” declaration to the (geodetic) community at large.
A presentation was made by Spoelstra. CRAF has tried to establish a database of RFI which can be queeried by frequency and time. Potentially this database could be of great interest to the EVN. Unfortunately, due to a lack of feedback from the European observatories (most of whom are EVN members) the database is severely incomplete.
ACTION ITEM: Participants of the TOG meeting to go back to their institutes and encourage the RFI station feedback situation to be improved.
The TOG found Gabuzda’s report a good and useful summary of the EVN’s current capabilities in this area.
There were a couple of comments:
(i) 70 second switching was too fast – particularly for WSRT where a complete re-configuration of the local correlator was required resulting in the loss of a large fraction of the data,
(ii) the TOG supported further tests of EVN frequency agility but felt that good progress was being made via user driven experiments (such as those led by Gabuzda).
Nevertheless, there was some discussion about what things needed to be tackled before this frequenct agility mode could be offered to all users. In particular, how best to implement automatic frequency switching via the FS. There were many solutions but it was felt that a consistent approach was required.
ACTION ITEM: Himwich and Burgess to discuss the best way to implement frequency switching under the FS and DRUDG.
ACTION ITEM: Stations to understand that this frequency switching mode could become quite common and that switching automatically via the FS would be required.
ACTION ITEM: Stations to remember to update their frequency flexibility status in the EVN status table (email@example.com)
A development programme that will facilitate rapid frequency switching is expected to begin at the end of this year.
The head block from Urumqi is now in the hands of Wunderlich and Blaschke. The recent poor recordings may be due to a tilted head or the build up of deposits at the headblock edges. Hopefully the re-conditioning of this head block will improve recording at Urumqi.
ACTION ITEM: Urumqi to send a Recorder Test tape to JIVE once the head has been re-installed.
During the meeting Volvatch gave a presentation on the Simeiz telescope. Geodetic MkIII observations are still being made but astronomical observations have effectively ceased after the EVN upgrade to MkIV. The current situation regarding
the upgrade of the stations is: (i) the MkIII terminal is owned by NASA, they are prepared to allow the terminal to be upgraded by other parties (alternative sites for the terminal are not favoured), (ii) around half of the necessary funding for the upgrade is already available via the Ukraine government. There are a couple of areas that need to be investigated w.r.t. the EVN's “contribution” to these efforts:
ACTION ITEM: Tuccari to contact Freihold and establish the whereabouts of the EVN MkIV spare formatter and consider whether a spare was justified in terms of EVN reliable operations.
ACTION ITEM: Volvatch (with help from Tuccari) to contact the former EVN VLBA stations (Noto, Yebes, Cambridge, Torun, Metsahovi) in order to see whether an old VLBA formatter might be made available between these stations.
Lovell upgrade and eMERLIN
Lovell upgrade progressing well, eMERLIN also looking good.
Might be able to participate in one of the NME sessions (session 3/2001)
ACTION ITEM: Ghosh to contact Garrett asap if Arecibo is able to participate in the NME (before September 30, 2001).
A large effort was underway to replace most of the existing receivers with improved replacements. This would occur over the next year or so.
3mm observation with 8 stations expected by January 2002. BR and SC only antennas
without 3mm capability. 512 Mbit/sec capability now available at VLBA (being implemented at GBT now). VLBA actively supporting Arecibo start-up operations with VLBA4. Both VLBA maser spares broken – replacement expected in the next few months.
ICN Reliability Programme
Several of the stations reported on activities related to the ICN. In most cases a positive impact was recorded at many EVN stations. In other cases the funds had not yet been allocated.
Real Time Correlation
The report from Verkouter was discussed. With the MkIV decoders now in place, a new version of DBGET would need to be written.
ACTION ITEM: van Langevelde to contact Verkouter and see if this is feasible and report back to the TOG via EVNtech.
The MkV project had been discussed at the Effelsberg mini-workshop the day before.
Discussion at the workshop was more focussed than at the TOG: the general view was that the sooner we could replace the recorders with disk based systems the better! Savings in manpower (recorder maintenance) would be substantial - data quality (and eventually data rates/capacity) would also improve. The recent progress made at Haystack was applauded by all.
During the course of the workshop/TOG meeting the discussion focussed on areas of the Mk5 that were considered less than optimal. In particular, the use of the Boulder Instruments disk interface card was viewed uneasily by many. Mujunen suggested that the next VLBI system should aim for a pure COTS solution, that could take advantage of OTS PC systems that would become available over the next few years. For example, a system based on multiple PC systems running in parallel would eliminate the need for a specially designed disk interface card. A single PC system could probably handle data rates of up to 128 Mbits/sec even now. A pure COTS solution at this stage would provide many benefits downstream - directly taking advantage of the rapid evolution in OTS PC computer/disk technology that could be expected to emerge over the next few years. For some people a Mk5 development effort that could not be a pure COTS based system was premature. Some expressed the opinion that there was a danger of moving from one obsolete medium to another.
Despite critical comment, the overall view of the TOG was that the Mk5 development should be encouraged, and for many a more active role for the EVN within this development programme was desired.
The fibre project had not obtained funding via the EC IST programme. Nevertheless, a scaled down project involving fewer stations was still thought to be a realistic option.
Parsley felt that the Mk5 was not obviously optimal for use as an platform for e-EVN tests. A solution involving multiple PCs is safer and considerably more cost effective. If Mk5 is developed for general deployment the EVN should confirm that the interface design takes adequate account of the real-time VLBI application.
Tuccari, Alef and other lecturers (Himwich, Smythe and Kraus) were thanked for their efforts. Feedback on the workshop and ideas for future workshop meetings should be directed to Tuccari.
To be hosted by Bologna/Medicina, at a convenient time (still to be decided) - probably between session 1 and 2/2002 (i.e. March/April/May 2002 ?).