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Improving the audio response in the Zetron Model 30 Worldpatch By Stig Kristiansen OZ3XO HTML'd by Mike Morris WA6ILQ. |
Page maintainers note: This contribition is by Stig Kristiansen OZ3XO from Denmark.
In the process of HTMLing this I made a few changes in the spelling and sentence structure to improve the readability.If you've never seen a Zetron Model 30 it is designed to connect to any full duplex base station, connects to the receive audio, COR and optional PL decoder, transmit audio and PTT. It also connects to a regular telephone line. The Model 30 has an extensive feature set. All programming of the Model 30 is via a DTMF over the telephone line connection. In operation a DTMF sequence on the radio channel takes a telephone "off-hook", a telephone call can be made or answered, and another DTMF sequence puts the telephone "on-hook".
There is also a single Auxiliary Output with a pair of DTMF commands that pulls a connector pin to ground when switched On or floats it when Off.
Here is the most recent Model 30 manual: (2013 Version) Model 30 Worldpatch Instruction Manual (025-9140R)
Photo of the Model 30 circuit board. (off-site pointer, opens in a new browser tab)
We have been using an CSI autopatch repeater controller for some 35 years on the first VHF repeater in Greenland – OX3REP at Thule Air Base, and it was then also tied into the wired PA system, going all over the base, for any weather alerts, so we had instant alerts on the move, and autopatch has even been used by a Canadian C130, that lost all electrical power to their radios, on their approach, to get in contact with the ATC, and it was mounted in same building, as the ATC radar, so it did also have a diesel generator backup.
The CSI controller was further modified for a super fast squelch with virtually no squelch tail noise as the CPU was adding a great delay before the receive audio was muted. Also the transmit audio was modified so when connected to the telephone the receive audio will always have the same modulation level on the transmitter.
As I now do need to make myself another private repeater system, with an autopatch, (due to the instability here around east of Denmark, that I will have full control by myself), and the only hardware that was possible to obtain in today's world, was the Zetron Model 30 Worldpatch, so it was acquired from ebay, since a CSI controller was not to be located anywhere, and I do like it all in one box.
Once the acquired Worldpatch was operational and making test with one of my good HAM friends, I was able to get some very good modulation reports, and he reports it was a little "thin" as a lack of the low end in the voice.
So what I first did was to make my own complete manual of the 025-9140 R, where I did add the "missing" information needed, from the N, P and 025-9143 B, in order to have a complete "picture" of all the hardware.
After this, I did some measurements to confirm this, and after this I did make simulations of the audio path, in order to make changes, to obtain the same output, as was coming in, for a linear pass through (without having to stress the PCB with making all this testing).
So after the simulations, I started to replace the following components:
| Component | Original Value |
New Value |
Notes |
|---|---|---|---|
| R9 | 47 ohms | 0 | Just jumper it |
| R14 | 4.7k | 5.6k | |
| R45 | 3.3k | 2.2k | |
| C3 and C4 | 10nf | 100nf | ( 0.01uf to 0.1uf ) |
| C24 and C45 | 100nf | 220nf | ( 0.1uf to 0.22uf ) |
| C26 | 1nf | 330pf | ( 0.001uf to 330pf ) |
After these modifications, I am very pleased with the results, as for a more natural sound, and I has been very pleased, to find all the documentations used, on the repeater builders web site.
Contact Information:
The author, Stig Kristiansen OZ3XO can be contacted at ozx3xo //at// gmail //dot// com>.
Note that Stig added an extra letter in his email address to make it 6 characters (so that gmail would accept it).
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This page created 11-September-2025 by WA6ILQ.
This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.