SARTS Repeaters

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Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

This links has some photos as to the correct shape of the tuned cavities for the TPRD-1556.

http://vk4zxi.blogspot.com/2018/03/2m-d ... e.html?m=1
Daniel Wee
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Re: SARTS Repeaters (Antennas)

Post by Daniel Wee »

We currently have several antennas for the repeater. At least two of them are a Diamond V2000A which is in use, and a Hy-Gain V42R which is not in use currently. Attached are relevant documents for these antennas.
Attachments
hyg-v42r_manual.pdf
(251.51 KiB) Downloaded 49 times
V2000A.pdf
(89.36 KiB) Downloaded 46 times
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

We now have the Sinclair Q2330E duplexer in place. Tuning procedure as follows:-



In this video, the cavities on the right side is the HIGH-PASS filter, which would be our TX cavity. This would have the notch/dip on the left of the peak with the lowest SWR on the right pass frequency. Conversely, the LOW-PASS filter on the left would be our RX cavity. This would have the insertion notch/dip to the right of the peak with the lowest SWR on the left pass frequency..

*Note to self: Switch to manual RBW, 30kHz or better helps.

In this video the top two screens of the R&S VNA indicates the return loss while the bottom larger screen shows the insertion loss of the DUT.
1. top left - return loss at the input port of the VNA
2. top right - return loss at the output port of the VNA
3. bottom - insertion loss of the DUT

Because we are using a T-connector, #1 and #2 are essentially the same. When using a reflection bridge, this should be the same as measuring the SWR into the DUT with a 50-ohm dummy load attached. In the video, this dummy load is actually presented by the VNA itself through the output port so no additional dummy load was required.

To raise the frequency of the cavity, you pull the tuning rod out. Conversely, pushing it in lowers the frequency.

For our convention and reference, the cavites nearest the RX and TX port are called R1 and T1 respectively, and the cavities nearest the antenna port R3 and T3 respectively. Our TX pass frequency (and RX reject) is 145.625MHz, while the TX reject frequency (and RX pass) is 145.025MHz.

The steps for each individual (disconnected) cavity are:-

0. Measure the insertion loss through the DUT and adjust the tuning capacitor so that the curve has the correct shape with the peak and notch on the correct sides. Then use the tuning rod to move the peak (lowest loss) to the pass frequency, and the tuning capacitor to notch the reject frequency. This gives us a coarse starting point but in the correct ball-park.

1. Adjust so that the minimum of the return loss (ie. lowest VSWR) is on the pass frequency ("desired frequency") with a 50-ohm dummy load attached to the DUT (through a T-connector). This is done by adjusting the tuning rod. Result loss and VSWR are not exactly the same but for our purposes, they both have the same resonant frequency so we can work with VSWR. In practice, minimizing the insertion loss at the pass frequency (highest peak in insertion loss curve) can be a little subjective and may not correspond to the lowest VSWR. We will follow the lowest VSWR/return loss method since it appears easier to find the minimum. This is performed with the SWR bridge attached, cable connected and OPEN CAL performed. After this, the cable is connected to the T-connector with a 50-ohm dummy load attached.

*using SWR bridge: lowest SWR (dip) on high side for high pass (TX), on the low side for low pass (RX).

https://www.electronics-notes.com/artic ... -table.php

2. Adjust so that the notch in the insertion loss falls on the reject frequency. This is done using the tuning capacitor. This adjustment might shift the minimum of the insertion loss (from step #1) by a tiny bit. This is performed in TG mode with the output set to 0dB, TG and RF input connector using a T-connector, and normalized before attaching to the DUT.

*lowest insertion loss (peak) on the high side for high pass (TX), on the low side for low pass (RX).
*maximum reject (notch) on the low side for high pass (TX), on the high side for low pass (RX).

3. Note that all the cavities have slightly different performance in that their insertion loss and reject levels are all a little different. The maximum reject can vary from around -26dB to about -30dB in our case. In the video, the single cavity reject appeared to be around -31dB or so.

4. This is done for all the cavities individually.

The steps for fine-tuning are:-

5. [INFO ONLY] In TG mode (insertion loss measurement), connect the TG to the TX port, and the RF input to the antenna port of the combiner/cavity harness. On the RX side, connect at 50-ohm dummy load. We will use this setup to tune the high pass (TX) filter first. Note that while the harness cabling itself is non-resonant, it introduces phasing effects that will move the tunings of the cavity. If you now, start connecting the TX filters individually, you will find that the reject notch on T1 and T3 has moved to ~145.169MHz while T2 has moved to ~145.209MHz from the 145.025MHz TX reject frequency. Also note that connecting the RX cavities, while affecting the overall curve shape, does not affect the TX side resonant frequencies. This means that only the TX cavity tunings affect the actual resonant frequency.

6. According to the video. The adjustment at this stage is to adjust for the minimum VSWR (or return loss) at the input port (TX or RX side). This means that we need a 50-ohm dummy load on the antenna port as well as another on the opposing input port. The adjustments now are made with the tuning rods. In theory no more adjustments need to be done to the tuning capacitors at this stage.

7. In this step of centering the low VSWR on the pass frequency, it is important to get it spot on, regardless of what the video might say about being approximate. The reason is that we will need to use this to set the pass-reject spacing with the tuning capacitor in the next step which will remain fixed thereafter.

8. Switch to measuring insertion loss (TG). Connect up all the harness. Connect the TG output to the RX port and the RF input to the ANT port. Connect a 50-ohm dummy load to the TX port. This will now allow us to fine-tune the LOW-PASS FILTER (RX) side. I tend to start with the center cavity, adjusting only the tuning rod to minimize insertion loss and maximize reject. Work your way to the first and last cavity. You'll have to play with this a bit to get it just right and it will NOT look as sharp as the training video suggests unless your span is very wide. I found a 2MHz span to be useful here.
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

Some more useful info about duplexers.
Attachments
Antenna_duplexers(15-26).pdf
(141.62 KiB) Downloaded 23 times
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

19 Aug 2021 - Repeater situation update

1. Arrived at Harish's place to rectify yagi orientation (nose up) and discovered that repeater is not responding. Upon inspection, the current draw was constantly at 5A and the radio was very hot. It was not responding to buttons and LCD was blinking ("Bcn, Txn"). No RF output was detected on a monitoring HT on 145.625MHz. No audio from the repeater indicating it was receiving transmissions. At this point, it was decided to power cycle the repeater.

2. Upon restarting, everything was responding as expected. RX was receiving. Menus and buttons were responding and functioning normally. Current draw was around 1A or less which is normal. The repeater was set to Low1 (5W) output power. A brief press of the PTT on the attached microphone (<0.5s) saw current go up to about 7A and then go back to 5A, beep, and went back to 1A for normal operation. No RF was received though on the HT but this needs to be verified. A longer press of the PTT (1s) saw the current go up to 7A and then back to 5A, no beep, and the current now stays at 5A. The repeater is now locked up. The buttons are not responsive, there is no receive audio. Nothing works. Pressing the PTT in this state does nothing either.

3. Upon inspection, the cable from the TX port was connected to the cavity side marked "Low Pass" with the "Rx" label nearby.
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

Sinclair 2330E retuning

1. Step 1 is to individually bring all the cavities, T1-3 on the TX side (high-pass), and R1-3 on the RX side (low-pass) into the ball park. This is done in two steps per cavity:-
a. find the point of lowest insertion loss (be it a high/low pass point). This is done using an SWR reflection bridge to get the pass frequency to coincide with the lowest SWR. This is done using the tuning rod.
b. measuring the S21 insertion loss for each of the cavity, and adjust so that the notch is at the reject frequency. This is done using the tuning capacitor.
T1 insertion loss
T1 insertion loss
T1.png (16.01 KiB) Viewed 340 times
T2 insertion loss
T2 insertion loss
T2.png (16.1 KiB) Viewed 340 times
T3 insertion loss
T3 insertion loss
T3.png (15.96 KiB) Viewed 340 times
R1 insertion loss
R1 insertion loss
R1.png (15.94 KiB) Viewed 340 times
R2 insertion loss
R2 insertion loss
R2.png (15.96 KiB) Viewed 340 times
R3 insertion loss
R3 insertion loss
R3.png (15.88 KiB) Viewed 340 times
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

2. The next step is to re-attach the harness completely, on both the TX and RX sides and tune up per above state procedure.
TX-ANT insertion loss
TX-ANT insertion loss
TX~ANT.png (15.36 KiB) Viewed 339 times
RX-ANT insertion loss
RX-ANT insertion loss
RX~ANT.png (15.65 KiB) Viewed 339 times
TX-RX isolation (insertion loss)
TX-RX isolation (insertion loss)
TX~RX.png (15.99 KiB) Viewed 339 times
SWR looking into TX port
SWR looking into TX port
TXSWR.png (15.83 KiB) Viewed 339 times
SWR looking into RX port
SWR looking into RX port
RXSWR.png (15.76 KiB) Viewed 339 times
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

Final tuning results

1. TX-to-RX isolation @145.625MHz = -82.79dB (advertised -85dB)
2. TX VSWR @145.625MHz = 1.08
3. TX-ANT insertion loss @145.625MHz = -1.34dB (advertised -1.4dB)
4. RX-ANT insertion loss @145.025MHz = -2.22dB

Notes: The RX side could probably be done up even better than this by narrowing down the notch-reject gap. As it stands, the procedure used resulted in potentially a larger gap than allows for the RX reject notch to align better. If this were to be done, I would try using the insertion-loss setup to determine the gap rather than using a combination of the VSWR-IL/notch procedure. The goal is to have a slightly smaller gap.
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

Schematics of TX-RF amplifier stage:-
IC-FR5000 finals.png
IC-FR5000 finals.png (556.78 KiB) Viewed 333 times
Source for RA60H1317M:-

https://www.rfparts.com/catalogsearch/r ... ra60h1317m
https://www.radioparts.com/icom-1150002073
RA60H1317M pinout.png
RA60H1317M pinout.png (61.51 KiB) Viewed 330 times
Attachments
ra60h1317m.pdf
(239.49 KiB) Downloaded 15 times
Daniel Wee
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Re: SARTS Repeaters

Post by Daniel Wee »

Testing preliminaries:-

1. Check quiescent RX current before lockup
2. Check current during TX lockup
3. Check if there is RF output during brief PTT with beep
4. Check if there is RF output during TX lockup

5. Assuming T8V is present, check Q38 collector voltage to ensure that driver stage is still functional
6. Test for RF at IC22 pin-1 (RA60H1317M)

Q: What is causing the unit to go into lockup state upon TX?
- could it be that the radio is detecting a fault and then going into an error state, thus blinking the LCD?
- none of the documentation explains this locked up state. It consistently produces this result which is unlikely to be an MCU error
- my guess is that the MCU has detected an error condition but it does not explain the 5A current draw
- that could be due to the RA60H1617M fault
Attachments
InkedInked20210208_121100_LI.jpg
InkedInked20210208_121100_LI.jpg (3.59 MiB) Viewed 329 times
ICFR5000 PTT.png
ICFR5000 PTT.png (42.52 KiB) Viewed 332 times
T8V regulator.png
T8V regulator.png (1.31 MiB) Viewed 332 times
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