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Re: SARTS Repeaters

Posted: Mon 01 Feb 01 2021 7:11 pm
by Daniel Wee
Initial reports suggest that the repeater is now usable:-

1. No significant receiver desensitizing being reported so far. 9V1KG is able to trigger and hold the repeater. There is some "crackling" noises in the audio but it is unclear where this is coming from. This is apparent even from the audio at the repeater itself.

2. TX is managing the increased output power quite well - no sign of significant overheating so far, and decent reception by those who have tested (so far). More testing is required to get a better picture of this. *UPDATE* There was overheating after long usage - this was at the high power setting. It turns out that the IC-FR5000 was not specced to operate at 50W on 100% duty-cycle. See next post for more information about this.

Repeater overheating

Posted: Mon 01 Feb 01 2021 10:21 pm
by Daniel Wee
It would appear that the IC-FR5000 is only rated for 100% duty-cycle when operated at 25W. At 50W, it is only rated for 50% duty-cycle - which makes this power setting (50W) unsuitable for rag-chewing and long conversations. This means that the over-heating may not be indicative of a fault, but of operating outside of design specifications. Actual output is about 45.5W but this may be because the PSU being used is unable to deliver the 15A required for 50W.

For reference, see attached brochure.

Re: SARTS Repeaters

Posted: Mon 08 Feb 08 2021 2:25 pm
by Daniel Wee
Last night's usage test showed the repeater heating up from ambient and took about 25-30 mins to reach the point where the TX LED started to blink and about five more minutes before there was noticeable power output drop.

Work done today:-

1. Checking actual voltage at the radio. When receiving, it was at 12.86V and 12.26V when transmitting. The nominal current draw according to the meter on the PSU was about 7A. Cable resistance checked out so no issues here.
20210208_130858[1].jpg (2.35 MiB) Viewed 1098 times

2. Checked out the ventilation - while there was some dust build up, it was not significant. Nevertheless, this was cleaned up and some WD-40 applied to the rusting just beneath the vent holes in the outer casing. The fan was tested and was working normally.
20210208_112830[1].jpg (3.07 MiB) Viewed 1098 times

3. While checking all of the connections - it was discovered that the flange for the TX N-connector was actually loose and the connector itself was rattling. This might have been the result of heating and cooling over time as this part of the chassis got considerably hot. This was tightened and all other connections double checked. The RX N-connector was not loose.
20210208_123557[1].jpg (2.09 MiB) Viewed 1098 times

4. A TX test at 25W for 45-minutes into the dummy load. At 15-minutes everything was still moderately warm. By 25-minutes the chassis was hot but the heat had not moved into the TX N-connector. By 35-minutes, the chassis was hot to the touch and while tolerable, was uncomfortable. The connector itself was also getting hot (from the chassis). By 45-minutes the situation seems to have stabilized and was not getting any hotter. The TX LED did not blink throughout this test (100% duty-cycle).

5. Tentatively, it looks like the crackling and popping sound that was present before is now gone in repeated signals. This may have been due to the loose connector.

Re: SARTS Repeaters

Posted: Mon 08 Feb 08 2021 8:37 pm
by Daniel Wee
Further testing reveals that the repeater will still overheat at 25W output after about 35-minutes of continuous usage. We do not know if this overheating condition has always been happening (for years). All we know is that we have just noticed it - possibly as a result of higher repeater usage and more attention paid to the repeater. That said, the IC-FR5000 is rated for 100% duty-cycle at 25W which we are not seeing.

The course of action now would be to:-

1. Check all the cables and connectors

2. Run the repeater at 13.8V instead of 12.8V. This will hopefully lower the current draw which may, in turn, lower the heat dissipation. The TX current was 7A@12.8V and is now 6A@13.8V. This may not sound like much difference but we are looking at potentially 26% less heat dissipation. Oddly, this higher voltage is resulting is a slightly lower output power, which could be a good thing. The rate at which the temperature of the repeater rises has also fallen.

3. Try to further optimize the TX cavities to eke out a bit more performance and lower SWR. Hopefully the overheating condition is marginal and slight improvements here may be enough to prevent overheating.

4. The discone itself exhibits a SWR of 1.7:1 and this may not be good enough in our configuration. Not much can be done about this at the moment.

The good news is that the crackling and popping seems to have disappeared and we are getting very good audio from the repeater.

Re: SARTS Repeaters

Posted: Mon 08 Feb 08 2021 9:49 pm
by Daniel Wee
Even with the voltage increased to 13.8V (actual was 13.7V) and the lowered TX current, we still managed to reach thermal foldback in about 35-minutes of operation. This was shorter than the 45-minute 100% duty-cycle dummy load test, suggesting that maybe SWR is more critical than we had assumed. A second session managed to go 40-minutes before showing any signs of overheating. It may be possible that we're just on the margin of operability.

At this point we really have to consider that:-

1. This situation is "normal" for this particular repeater/antenna configuration and that it has always been doing this in times past without our notice.

2. It might be a sign that the repeater has deteriorated and no longer in spec. This could be a real possibility given what we are seeing. It might be time to start exploring options for a new repeater, perhaps with more modern features.

3. There is something in the connections or cavity that could be tweaked to make things better. Although this possibility exists - given that the discone antenna exhibits a 1.7:1 SWR to begin with, I'm not sure how far we will get with this.

4. Unorthodox solutions to work around the problem include running the repeater at the lowest power setting and using an external power amplifier between the TX output and the cavity input. We could also explore better cooling solutions for the repeater (bigger fan, heat pipes, etc.)

Re: SARTS Repeaters

Posted: Mon 15 Mar 15 2021 7:29 pm
by Daniel Wee
Cavity Inspection and Tuning

0. Duplexer model is Telewave TPRD-1554
Screenshot 2021-03-15 215846.jpg
Screenshot 2021-03-15 215846.jpg (33.86 KiB) Viewed 345 times
spec-18.jpg (237.32 KiB) Viewed 343 times
desc-16.jpg (99.7 KiB) Viewed 343 times ... 4-174-mhz/


1. Cavity #2 (TX) coupling loop and capacitor appears to be undamaged. Good!

2. By peaking the pass on 145.625MHz and the notch on 145.025, you end up with the lowest SWR somewhere in between the two frequencies - which makes sense. So, how do we tune those peaks and notches, and still end up with a low SWR on the pass frequency (145.625MHz?)

Re: SARTS Repeaters

Posted: Fri 19 Mar 19 2021 6:07 pm
by Daniel Wee
Retuning the Cavity (again)

1. It looks like all cavities affect the final tuning. The TX cavity can be perfectly tuned but the moment the RX cavities are connected - everything goes off.
S21 from TX port to antenna without RX-side
S21 from TX port to antenna without RX-side
S21 TX-Ant without RX.png (9.85 KiB) Viewed 317 times
S21 from TX port to antenna with RX-side connected
S21 from TX port to antenna with RX-side connected
S21 TX-Ant with RX.png (10.71 KiB) Viewed 317 times

Re: SARTS Repeaters

Posted: Fri 19 Mar 19 2021 7:18 pm
by Daniel Wee
Tuning procedure
1. With all cabling harness in place - connect VNA port 1 to TX port and port 2 to the Antenna port.
2. Disconnect the RX-side and the connection to cavity 1 (TX)
3. This leaves only cavity 2 (TX) connected

On cavity 2 (TX)
1. Adjust the flange rotation to get exactly 600kHz separation between the peak and the notch
2. Use plunger to move notch to 145.025MHz
3. Adjust flange rotation so that the left slope of peak crosses 0dB at 145.625MHz
4. With the red mark lined up, anti-clockwise widens split separation, clockwise narrows it
5. Adjust capacitor for maximum dB differential between insertion loss at 145.025MHz and 145.625MHz
6. Once you get the optimal settings, lock the flange and check that separation has not shifted
7. Cavity 2 has sunk in so the washers don't lock well. They are bent in order to provide more bite. Red dot inwards.
8. Lock plunger and confirm frequency has not shifted.

On cavity 1 (TX)
1. Connect port 1 of VNA directly to cavity 1
2. Adjust flange rotation to get exactly 600kHz separation between peak and notch
3. The flange adjustment for this cavity is very finicky and you may have to find a different quadrant where it sits better for the separation of 600kHz
4. Adjust capacitor for maximum dB differential
5. Lock flange and check separation again. This is a very tedious finicky step because locking it moves the flange
6. Lock plunger and confirm frequency has not shifted.
7. Remove VNA from cavity 1 and reconnect cavity 1 to the cabling harness
8. At this point, with cavity 1 and 2 connected but RX side disconnected, everything should line up on S21 TX-Ant

Re: SARTS Repeaters

Posted: Tue 23 Mar 23 2021 4:26 pm
by Daniel Wee
VHF Duplexers

Telewave TPRD-1444C
Min. separation: 600kHz
Insertion loss: 1.5dB
Rejection: 70dB
Weight: 8.7kg
USD2267.33 ... xer-517711 ... TPRD-1544C

Telewave TPRD-1554
Min. separation: 600kHz
Rejection: 77dB
Weight: 8.6kg
USD1964.00 ... LTPRD-1554

Comprod 66-13-44 (4)
Min. separation: 500kHz
Insertion loss: 1.5dB
Rejection: 70dB ... -66-13-44/

Comprod 66-13-74
Min. separation: 500kHz
Insertion loss: 1.5dB
Rejection: 85dB
Weight: 20kg
USD2628.00 ... xer-290473 ... -66-13-74/

Comprod 66-13-44-RE
Min. separation: 500kHz
Insertion loss: 1.5dB
Rejection: 70dB
USD1645.00 ... vhf-236034 ... uplexer-2/

Sinclair Q2220E
Min. separation: 500kHz
Insertion loss: 1.5dB
Rejection: 70dB
Weight: 12.71kg
USD1655.00 ... exer-63068 ... =SINQ2220E

Sinclair Q2330E
Min. separation: 500kHz
Insertion loss: 1.4dB
Rejection: 85dB
Weight: 20.43kg
USD2370.00 ... exer-11461

Xinlun XL-PRD-1506-4
Min. separation: 600kHz
Insertion loss: 2dB
Rejection: 80dB
Weight: 27kg ... 98180.html

Re: SARTS Repeaters

Posted: Wed 24 Mar 24 2021 7:29 pm
by Daniel Wee