SARTS Repeaters

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Daniel Wee
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SARTS Repeaters

Post by Daniel Wee »

We have two repeaters:-

ICOM IC-FR5000 VHF (in use)
ICOM IC-FR6000 UHF
Attachments
icfr6100.pdf
(8.97 MiB) Downloaded 55 times
icfr5000.pdf
(7.8 MiB) Downloaded 47 times
FR5000_configuration.pdf
(414.04 KiB) Downloaded 49 times
Landmobile_IC-FR5000_FR6000_InstructionManual.pdf
(612.91 KiB) Downloaded 50 times
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Programming software for the repeaters:-
https://quality2wayradios.com/store/ind ... 20software
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Photos of the station at 9V1AI's place:-
20201229_162051.jpg
20201229_162051.jpg (2.38 MiB) Viewed 3851 times
20201229_152701.jpg
20201229_152701.jpg (2.25 MiB) Viewed 3851 times
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

The old UHF repeater appears to be the Tait T-800 unit.
T800ii.jpg
T800ii.jpg (77.74 KiB) Viewed 3834 times
Attachments
M800RACK-00-100.pdf
(691.16 KiB) Downloaded 56 times
TA703_Change_Over_Module_SM_M703-01-0004.pdf
(2.25 MiB) Downloaded 56 times
Tait_T800_SeriesII_Brochure.pdf
(3.48 MiB) Downloaded 48 times
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Telewave VHF Duplexer - similar to TPRD-1484/1584 (500kHz minimum frequency separation, 80dB rejection at 500kHz offset)
TPRD-1484.jpg
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Duplexer-specs.jpg
Duplexer-specs.jpg (113.06 KiB) Viewed 3816 times
The cavity tuning guide is also attached below.
Attachments
duplexer (1).pdf
More interesting information
(1.88 MiB) Downloaded 14 times
duplexer.pdf
Tuning and theory
(342.88 KiB) Downloaded 42 times
Telewave-Cavity-Tuning-July_2017.pdf
(586.02 KiB) Downloaded 46 times
TWDS-6039.pdf
(55.37 KiB) Downloaded 52 times
TWDS-6040.pdf
(55.57 KiB) Downloaded 49 times
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Measurements of the repeater cavity shows that it is very likely detuned and will require re-tuning of at least one of the receive notches and one of the transmit notches. Of the four, only two are correctly tuned at the moment.
S11loss-9V1cavity-6Jan.png
S11loss-9V1cavity-6Jan.png (7.05 KiB) Viewed 3756 times
VSWR-9V1-6Jan.png
VSWR-9V1-6Jan.png (10.09 KiB) Viewed 3756 times
The markers are as follows:-
Red 144.9MHz
Green 145.41MHz
Blue 145.62MHz


The little ledge to the right of the red marker is 145.02MHz. I didn't place a marker here because the software can only place three markers.

The cavity consists of two notch filters for 145.625MHz (on the TX side) and two notch filters on 145.025MHz (on the RX side). The two filters are stacked should line up to give a deeper notch. From the plot, we can see that only one filter on each side of the TX and RX are correctly tuned. The other two are off tune (145.41MHz and 144.9MHz). This is resulting in an insufficient rejection of the TX frequency, hence leading to the desensing of the receiver. This detuning also returns in less than optimal SWR and the output would see more loss than necessary, meaning that we're probably not putting out the power we think we are.

The resolution of this problem should minimally involve the retuning of those two notches that are off. In a properly tuned repeater, the two notches on the right (green and blue) should line up giving a deeper notch at 145.625MHz, and the two on the left (red and the "ledge") on 145.025MHz. The fact that we can see 3-4 notches is a sign things are not aligned.
Daniel Wee
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Posts: 2328
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Re: SARTS Repeaters

Post by Daniel Wee »

Baseline parameters of the repeater

Input voltage currently 12.88V being supplied by a Diamond GSV1200 that is rated for 12A continuous and 15A intermittent.

TX Power settings currently:
Lo1 = 5W
Lo2 = 25W
High = 45W (rated 50W, actual measured 45.5W but PSU was rated for 12A so that might be the problem)
FR5000-Specs.jpg
FR5000-Specs.jpg (146.74 KiB) Viewed 2748 times
The discone antenna itself is exhibiting an SWR of around 1.6:1 at the input frequency of 145.025MHz.
Discone-SWR142-148.png
Discone-SWR142-148.png (8.58 KiB) Viewed 2764 times
Before adjustment, the SWR from the TX port of the repeater is 6.226:1 while the SWR of the receive port was a more reasonable 1.75:1

The TPRD-1484 cavity consists of two pass-reject cavity in series on the RX, and two more in series on the TX side.
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

The cavity tuning was originally optimized for rejection. The S11 from the antenna port into the cavity is as follows:-
Dup-S11-144-147.png
Dup-S11-144-147.png (6.86 KiB) Viewed 2764 times

Work done

1. The cable connecting the TX port of the repeater to the cavity was mis-assembled, leading to the cable coming apart. This was rectified by re-assembling it with the washers and gaskets in the right order - providing a now secure connection on both ends of the cable. Both sides had to be re-assembled. This was further sealed to provide some water resistance on the external side.

2. Only the TX cavity closest to the repeater side was adjusted. The idea was to make as few adjustments as possible so as not to change the already good receive performance. That said, all the cavities affect each other in some ways so some change on the receive side is inevitable. The tuning was done per the Telewave recommended procedures outlined in the manual.

3. Primarily, it was found that the pass-reject spacing had to be adjusted via the capacitor because it was less than 600kHz. This was done with the single cavity isolated from the rest - and for maximum rejection at 145.025MHz (input frequency) and for the minimum loss at 145.625MHz (output frequency). The insertion loss was not adjusted in keeping with the aim of making minimal changes. The following plot shows that the rejection peaks and pass peaks had not been adjusted for 600kHz so when RX is optimized, TX would suffer, and vice versa.
TX1-SWR144-147.png
TX1-SWR144-147.png (10.77 KiB) Viewed 2763 times
This plot after tuning shows that receive loss had deteriorated by about 1dB but transmit side had improved by nearly 10dB.
Final-S11-144-147.png
Final-S11-144-147.png (7 KiB) Viewed 2764 times
Looking from the TX port of the repeater - the SWR is now 1.4:1 at 145.625MHz after the adjustment.
After-SWR144-147.png
After-SWR144-147.png (10.29 KiB) Viewed 2764 times
Summary

1. This was by no means an exhaustive tuning. The work was limited to the TX cavity that was deemed most out of tune, with the mind of bringing the SWR down sufficiently to enable higher TX power without causing the repeater to overheat. This seemed to have been achieved with weaker stations such as 9V1KG being able to trigger and hold the repeater, and get a good readability from it.

2. That said, the other TX cavity may also be suffering from a pass-reject spacing that needs to be adjusted with the tuning capacitor for optimal performance. This might also be true of the RX cavities but those were not thoroughly measured due tp the lack of time.

3. From the measurements taken - it appears that we can further optimize the tuning and gain about 5dB improvement or more from the TX path. The RX path can also be tuned to gain back the lost 1dB.

4. Further usage is needed to see if the RX side rejection of the TX signal is still as good as before.

5. I would say that the current tunings are not optimal but should be good enough to keep everyone happy until we can do a more thorough tuning. It looks like better performance can still be achieved with more careful tweaking.

Work to be done

1. Cables need to be labelled. There are some unconnected cables around that can lead to some confusion.

2. Use compressed air to clear out ventilation holes and check if fan is clear and running.

3. Check current draw and voltage sag during QRO transmission. If the voltage is sagging too much, this will result in higher operating current.
Daniel Wee
Site Admin
Posts: 2328
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: SARTS Repeaters

Post by Daniel Wee »

Some additional photos:

1. Power supply measured at 12.88V
20210201_123105.jpg
20210201_123105.jpg (2.64 MiB) Viewed 2752 times
2. Cable problem - mis-assembly. Fixed.
20210201_130607.jpg
20210201_130607.jpg (2.15 MiB) Viewed 2752 times
3. Cavity on the service balcony with protective cover removed.
20210201_135734.jpg
20210201_135734.jpg (3.32 MiB) Viewed 2752 times
4. Water proofing has come off. Replaced.
20210201_135743.jpg
20210201_135743.jpg (2.71 MiB) Viewed 2752 times
5. Adapters used to adapt to the N-connectors, sees some corrosion. Probably need proper cables made for the purpose.
20210201_135855.jpg
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6. Connection configuration
20210201_140124.jpg
20210201_140124.jpg (2.94 MiB) Viewed 2752 times
7. Finally back in place
20210201_155552.jpg
20210201_155552.jpg (3.54 MiB) Viewed 2752 times
8. SWR as seen by the transmitter
20210201_160436.jpg
20210201_160436.jpg (1.65 MiB) Viewed 2752 times
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