Topics

QLG1 GPS Receiver for use with the Icom IC-7100 or ID-880H #gps #icom #qlg1

Curt M.
 

Hi guys, I was brainstorming last week on what I could do with a spare QLG1 board that I had sitting around.  I thought about ordering the parts to build another U3S or maybe even another clock kit.  I kind of forgot about it and moved onto something else and then I remembered that I can connect an external GPS to my Icom IC-7100's.  

I ordered a small enclosure and a DROK 2203 (buck booster) so that I could feed the GPS receiver with Powerpoles and drop the 13.8v down to 5 volts.  Being that I wanted to put the device in a rugged enclosure that meant that I would probably use an external active antenna so I ordered one of those along with some other miscellaneous parts.

After getting everything together and connecting it up, the radio did not see the GPS data.  This was the 5th QLG1 that I had built up so I was pretty sure that I had everything correct.  I double checked the baud rate on the radio and I had it set for 9600 which is the default baud rate for the QLG1.  Hmm???  I thought a GPS is a GPS and I had read where other people had purchased a few different models of external GPS units and their's seemed to be working fine.  After doing some more research I found that the IC-7100 is looking for an RS-232 signal and there are some GPS units that are TTL.  I couldn't find anything in the documentation for the QLG1 about what it's output is.  I sent an email off to Hans and he confirmed that the QLG1 has a TTL output.  Hans mentioned possibly using a MAX232 chip which I had also heard of before but neither one of us had used one.  After a little more research I ran across the MAX3232 from Sparkfun.  It's a $6 dual channel TTL to RS-232 converter that has all of the supporting components already on the board needed to run it and it just requires a 3v-5.5vdc.  It's also much smaller than some of the prebuilt MAX232 options that have a 9 pin port on them.

Last night I rewired everything and put the MAX3232 on the output of the QLG1 and connected it to my IC-7100 and it works GREAT!  You can buy an external Garmin GPS and there are a few people on eBay selling ones made from a USB stick for as low as $55 including shipping.  I suspect the QLG1 will be a more cost effective option as long as you don't mine building it yourself and you don't have to order a bunch of parts.  I would guess that many of the parts you may already have lying around but if you need to buy the parts or want to build something very special you may have to weigh the price difference between the QLG1 and an off the shelf model.  At east with the QLG1 you'll know how to fix it should something go wrong.

The guys building these out of a UPS dongle are powering them with one of the ports on the back of radio.  That may be an option with this setup but I've not tested this.  I haven't checked the current draw on the QLG1 with my choice of components and I also don't know how much current the Icom radio can source.  The disadvantage of using the USB stick is that you can't remotely locate the antenna very far like I'm doing here using the external active antenna.  Actually you can locate the active antenna on the outside of the vehicle if you have the right location to mount the receiver and the right gaps in one of your door panels.  

It's also pretty hard to beat the integral patch antenna so I suspect that would work better in vehicle than the USB dongle if you don't want to spring for the external active antenna.  I will post a circuit diagram below along with a few pictures.  I still need to put some heat shrink on the LEDs and neaten a few things up inside of the enclosure.  Also, I will post some links to some of the key components that I used.  You can definitely build this for less that what I did.  The metal enclosure wasn't really necessary but in my case I wanted something rugged.  

Remember....anytime you are interfacing with your radio you run the chance of damaging something inside of the radio.  Be sure to triple check my drawing for errors, your wiring for errors and the various diagrams provided with your radio.  My drawing does not provide for any type of fuse protection.  I highly recommend that you build yours with some sort of protection on the power circuit just in case.

Curt M

QLG1
http://shop.qrp-labs.com/qlg1

Enclosure
https://www.amazon.com/gp/product/B0107WU67M/ref=ppx_yo_dt_b_asin_title_o03__o00_s01?ie=UTF8&psc=1 

DROK Voltage Converter x2
https://www.amazon.com/Converter-DROK-Waterproof-Adjustable-Transformer/dp/B07F24WGBB/ref=sr_1_3_sspa?crid=2BYMXJIYA2KGM&keywords=drok+voltage+regulator&qid=1550160981&s=gateway&sprefix=drok%2Caps%2C125&sr=8-3-spons&psc=1 

Active Antenna
https://www.amazon.com/gp/product/B00LXRQY9A/ref=oh_aui_search_asin_title?ie=UTF8&psc=1 

Right Angle SMA Cable
https://www.amazon.com/gp/product/B00COJWKGC/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1 

SMA Connector
https://www.amazon.com/QMseller-Launch-Straight-Connector-Adapter/dp/B07GXSN7VS/ref=sr_1_1_sspa?crid=18EO0RUT5QDUP&keywords=sma+connector+pcb&qid=1550161776&s=electronics&sprefix=SMA+connector%2Celectronics%2C123&sr=1-1-spons&psc=1 

2.5mm Cable (I cut mine in half to make two of these)
https://www.amazon.com/gp/product/B0742NQKT5/ref=ppx_yo_dt_b_asin_title_o03__o00_s02?ie=UTF8&psc=1 

Inductor for Active Antenna (you'll also need a misc 10 ohm resistor)
https://www.mouser.com/ProductDetail/api-delevan/1026r-02j/?qs=xY1IUdBv1vSWscnP2uRHTw%3d%3d&countrycode=US&currencycode=USD 

MAX3232
https://www.digikey.com/product-detail/en/sparkfun-electronics/BOB-11189/1568-1193-ND/5673779

Misc toggle switch and 10 ohm resistor and grommets also needed also with some hookup wire and powerpoles.

Alan G4ZFQ
 

Curt

After getting everything together and connecting it up, the radio did not see the GPS data.  This was the 5th QLG1 that I had built up so I was pretty sure that I had everything correct.  I double checked the baud rate on the radio and I had it set for 9600 which is the default baud rate for the QLG1.  Hmm???  I thought a GPS is a GPS
I do not know about the IC-7100 but all computer RS232 COM ports are compatible with TTL.
The difference is polarity. The TTL output of most GPS modules requires inverting for a computer port to read the data. I guess the MAX232 effectively does this, or a simple inverter could be used.
Of course a RS232 TX signal must not be connected to a GPS RX input without a resistor/zener to convert to TTL.

73 Alan G4ZFQ

Jerry Gaffke
 

I've seen it work, a well behaved RS232 device can be wired directly to TTL logic.
Can work bidirectionally (if the RS232 receiver has a threshold above 0v).
Sometimes.

Problem is, RS232 can be anywhere between +/- 3v and  +/-25v, and able to deliver 50ma or more.
If on the high end, an RS232 driver will have no trouble blowing out a TTL receiver.
If you have long cables, there can be ringing on top of that +/- 25v.

I'd always use a proper RS232 inteface chip, such as the MAX232. 
They're cheap enough.

Jerry


On Thu, Feb 14, 2019 at 01:47 PM, Alan G4ZFQ wrote:
I do not know about the IC-7100 but all computer RS232 COM ports are compatible with TTL.

z_ kevino
 

This post may help me with my problem. I have a IC-9700 and tried to hook up the QLG1 to it, and just like the original poster's description, the Icom did not see it. I will check out one of the MAX3232 and see if that fixes my probelm.
Just one question:
When the advanced radio manual  says to connect the 2.5mm cable like this:
Tip = TxD
Ring = RxD
Sleeve = GND
Is the TxD as referenced by the QLG1 ? in other words, did you connect the 3rd pin or 4th pin of the 6 pin header to the Tip of the 2.5mm?
thanks,
Kevin 

Alan G4ZFQ
 

did you connect the 3rd pin or 4th pin of the 6 pin header to the Tip of the 2.5mm?
Kevin,

I've no idea what you are doing, what is this IC9700?
But COM ports connect RXD to TXD and TXD to RXD. Crossover.

73 Alan G4ZFQ

Alan G4ZFQ
 

Kevin,

But COM ports connect RXD to TXD and TXD to RXD. Crossover.
And if you connect the IC9700 TXD you must be sure it sends TTL. If not some sort of conversion is required. A resistor/zener is the simplest way.

73 Alan G4ZFQ

Per - LA9XKA
 

Hi Kevin

You can't connect a QLG1 directly to the IC-9700 as the QLG1 is 5V TTL level and the radio is RS-232. You need to implement an level converter as the MAX232 or even easier pick up an ready made converter on ebay, just search 'RS232 to TTL converter'.

Per