Tony’s Cafe

I’ve been putting together plans to get G-NET2 working — a wireless data link between my house and my friend’s house 6-7 miles away. I tried a few different antenna designs to work with WaveLAN cards and no luck yet! Each antenna design was a learning experience — after making each antenna, I’d review what I did wrong and try to make a better antenna. Now I think I’ve come up with a good antenna design but to test it, I decided to use a phone (voice) mode instead of data. If I test the antenna with two 900MHz radios, I can at least hear Doug on the other end and see if he’s coming in strong… or not at all.

I did some research on (of course) cheap 900MHz radios. Now that I’ve had my ham license for a year, I’ve learned lots of good stuff about radios and antennas. I learned that a cheap way to get on 900MHz phone is to convert a commercial 900MHz radio. Most commercial 900MHz radios transmit over 1 Watt, the unlicensed limit. Since I have my ham license, that is not a problem! I settled on the E.F. Johnson 86xx series mobile radio. Here’s what I did…

Getting the Radios

The E.F. Johnson (EFJ) 86xx series radio comes in a few different varieties and each model is explained at K0KN’s EFJ Radios Page. The EFJ radios are meant for talking with a repeater (they transmit on one frequency and receive on another) and trunking (radios can communicate on different channels (groups) on the same frequency). I decided on getting a 8655 and a 8640. Both can be configured for conventional (non-trunking) use. The 8655 can be reprogrammed for simplex use (transmit on 927MHz and receive on 927MHz). The 8640 can only receive in the 927MHz range, which is ok — I just want to be able to transmit from one radio and receive on the other. (If I ever want to build a 900MHz repeater, I can by connecting a 8655 and 8640 together with something like the ID-O-Matic.) Oh, why did I choose the 8640 instead of two 8655 radios? Well, because the 8640 is usually cheaper! I bought both radios on eBay.

Reprogramming the Radios

To reprogram the radios, I had to do six things:

1. Order the replacement Ham-Only CPUs for the 8640 and 8655
2. Build a programming interface (a RS-232 to TTL converter)
3. Install the Ham-Only CPUs and replacement capacitors that came with the CPUs
4. Reprogram the radios
5. Check the voltages on receive and transmit
6. Check to see if the 8655 can transmit to the 8640 on the same frequency

Replacement Ham-Only CPUs

I ordered these from Pete, N2MCI. Email him at n2mci //at// hvc //dot// rr //dot// com and let Pete know what radio models you’re programming. He’ll send you the appropriate CPUs and capacitors.

Build a Programming Interface

I built a programming interface following K0KN’s recommendations. I had made a TTL to RS-232 converter using a MAX233 chip to build a RS-232 interface for my Commodore 64. Using the MAX chip is a bit expensive, so I was glad to see K0KN’s “Two Transistor Level Converter”. It was cheap, simple to build, and did the same thing as that MAX233 chip! I modified K0KN’s schematic to pull power from the EFJ jack. Click on the schematic thumbnail on the left to see the modified schematics. After building the interface, I had to shave off around 2mm from either side of the RJ-45 plug so it would fit into the EFJ’s front microphone jack.

Install the Ham-Only CPUs and Capacitors

The CPUs are a drop in replacement. See K0KN’s EFJ Page for instructions on how to do this. The capacitors were a little tricky, as they’re surface mount and very small. Check the voltages on receive and transmit following K0KN’s directions. On two of the three 8655 units I have, I needed to replace C917 to fix the receive voltage. (Yep — one of them I didn’t need to do a thing!) To give you an idea of what the actual voltages were like after the receive capacitor modification, I had 7.25VDC on receive and 1.48VDC on transmit. Receive needs to be >= 2VDC and transmit needs to be <8VDC on TP801 on a 8655.

On the 8640 I had to replace C720 to fix the receive voltage. I did not need to do any transmit modifications as all transmit voltages were in spec. You must download the model’s service manual to see where each capacitor is. For C917 on the 8655, it’s in grid B5 on the bottom of the main board, shown on manual page 9-7. You’ll have to remove the bottom cover, then remove RF sheild (15 Torx screws!) For C720 on the 8640, it’s on the top of the main board, in the VCO module (see service manual, p. 9-8). The VCO module is under the RF shield panel, held down with 4 Torx screws.

If you need to turn off the squelch or adjust it, this can be done by turning the potentiometer located at R13. This is on the CPU board.

Reprogram the Radios

You’ll need the E.F. Johnson programming software to program the radios. It is DOS based, very old, and you’ll have to search the Internet to find it. Once you have it, unzip its contents and do the following. In the examples below, the radios are programmed for 927.0125MHz.

Run: TRUNKING.EXE
Press any key to continue

To Program a 8655 Radio
Choose: Select – Mobile – 8605/10/15/20/55
Use the arrow keys to select “Setup”. The down arrow will display the
Setup menu and you can make sure the right COM port is selected.
Select “Edit” and press the down arrow to see the Edit menu.
Select: Clear Worksheet
Press Y
Select: Edit Current Worksheet
Use the arrow keys to move between fields. After changing a field, press
the Enter key to accept. Change the following field:
Frequency Band of Radio: 900
Press any key when the frequency change warning appears.
Arrow down to “1 – Unused”, select the “Unused” next to the “1″ and press Enter
For the mode selection, choose “Conventional Radio” and press Enter
Type a “Note” (e.g. Test)
For each group number, program a channel. For example, we’ll program 927.0125MHz (channel 401 — for other channels see the frequency chart) into Group 1 in talkaround (simplex) mode.

Use the arrow keys to go to “CHN NUM” next to “GR No 1″ and type 401
Change the “N” under “Talk-around” to Y.
Do not change any other values.

Press CTRL-Enter to accept changes.
Press CTRL-Enter again to accept changes.
Press Enter to continue if prompted.

Program the radio
Select “Radio Interface” from the main menu.
From the Radio Interface menu, select: “Prompted – Write Configuration to
Radio/Unit”
Press Y to execute
Press any key to begin
After “Data was transferred – Hit any key!” is displayed, press any key!

Power off and power on the radio.
Channel 401 in talkaround mode is now programmed into System 1, Group 1.

To program a 8640 Radio
Choose: Select – Mobile – 8600/01/04/40/44
Use the arrow keys to select “Setup”. The down arrow will display the Setup menu and you can make sure the right COM port is selected.
Select “Edit” and press the down arrow to see the Edit menu.
Select: Clear Worksheet
Press Y
Select: Edit Current Worksheet
Use the arrow keys to move between fields. After changing a field, press the Enter key to accept. Change the following field:
Frequency Band of Radio: 900
Press any key when the frequency change warning appears.

Arrow down to “1 – Unused”, select the “Unused” next to the “1″ and press Enter
For the mode selection, choose “Conventional Radio” and press Enter
Type a “Note” (e.g. Test)
For example, we’ll program 927.0125MHz (channel 01 — for other channels see the frequency chart) for RX

Use the arrow keys to go to “CHN NUM” and type 01
Do not change any other values.

Press CTRL-Enter to accept changes.
Press CTRL-Enter again to accept changes.
Press Enter to continue if prompted.

Program the radio
Select “Radio Interface” from the main menu.
From the Radio Interface menu, select: “Prompted – Write Configuration to Radio/Unit”
Press Y to execute
Press any key to begin
After “Data was transferred – Hit any key!” is displayed, press any key!

Power off and power on the radio.
Channel 401 in talkaround mode is now programmed into System 1, Group 1.

Check the Voltages

See K0KN’s EFJ Page [pdf] and read about checking the receive and transmit voltages on TP801.

Check the Radios

Now that the 8640 and 8655 were programmed, I hooked an antenna up to each one (a random wire antenna) and talked into the 8655 and listened on the 8640. It worked! Many thanks to Pete’s (N2MCI) hard work to develop a replacement ham CPU and many thanks to Kyle’s (K0KN) efforts to put together all the EFJ 86xx information onto one web site.

This entry was posted on Sunday, April 12th, 2009 at 9:27 pm and is filed under Amateur Radio, G-NET, Wireless. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.