COAX and ALTIMETER questions

WiseGuy · #1 08-15-2007, 03:38 PM

Two questions:
1. Apparently Garmin 430W needs special coax for GPS antenna? Can I use RG400 or RG142? If so, which is better?
2. Does anyone know where I can purchase a reasonably priced 2.25 in. altimeter with 2 needles?
Thanks in advance.

w1curtis · #2 08-15-2007, 04:21 PM

Quote:

Originally Posted by WiseGuy

Two questions:
1. Apparently Garmin 430W needs special coax for GPS antenna? Can I use RG400 or RG142? If so, which is better?

RG-400, *MINIMUM* 14 feet to meet the db loss spec.

WiseGuy · #3 08-15-2007, 05:17 PM

Thanks William,
RG400 it will be then. Length will be less than 14 feet!

BuckWynd · #4 08-15-2007, 07:03 PM

Quote:

Originally Posted by WiseGuy

Thanks William,
RG400 it will be then. Length will be less than 14 feet!

WiseGuy:

I just wanted to make sure that you read W1curtis's post correctly. You need to install NO LESS than 14 feet of RG400 coax. This is because the 430W requires between 3dB and 7dB of attenuation. 3dB occurs at about 13 feet of cable length.

Regarding your other question about altimeters -- Here are a couple of links to 2-1/4" units with three needles:
Falcon Altimeter
Winter Altimeter

The Winter units have been used in the sailplane community for a long time -- they're good quality, and therefore relatively expensive. I don't have any experiences, good or bad, with the 2-1/4" Falcon unit.

Good luck!

az_gila · #5 08-15-2007, 07:29 PM

Quote:

Originally Posted by WiseGuy

Thanks William,
RG400 it will be then. Length will be less than 14 feet!

Apparently, you also need a TNC connector, which are usually not easy to get locally...

gil A

WiseGuy · #6 08-15-2007, 10:37 PM

Thanks to everyone for responding. Sure glad I asked. I was going down the wrong direction. I was going for short coax with BNC connector. Also for the info on the altimeters. I will check them out tomorrow. Sure shows the value of this group. Any additional info welcomed and appreciated.
Thanks again,
Guy
RV7A forever finishing it seems

craigvince · #7 08-15-2007, 11:41 PM

Quote:

Regarding your other question about altimeters -- Here are a couple of links to 2-1/4" units with three needles:
Falcon Altimeter
Winter Altimeter

The Winter units have been used in the sailplane community for a long time -- they're good quality, and therefore relatively expensive. I don't have any experiences, good or bad, with the 2-1/4" Falcon unit.

Good luck!

Be very cautious if considering the Falcon Guage instruments. I have no personal experience with them, but there have been many, many comments here on VAF recently about them. Do a search and your homework.

johnp · #8 08-16-2007, 08:12 AM

Quote:

You need to install NO LESS than 14 feet of RG400 coax. This is because the 430W requires between 3dB and 7dB of attenuation. 3dB occurs at about 13 feet of cable length.

kind of begs the question -- if the loss is the determining factor, why can't i use a 3-4 foot section of rg-58? i don't know what the comparative losses are at 1.2G, but at 120MHz, the 58 is about 2db/100 foot lossier than 400.

(i have about 1000 feet of 58 lyin' around, sure would like to use it. i probably will use it for everything except the gps.)

az_gila · #9 08-16-2007, 08:45 AM

Quote:

Originally Posted by johnp

kind of begs the question -- if the loss is the determining factor, why can't i use a 3-4 foot section of rg-58? i don't know what the comparative losses are at 1.2G, but at 120MHz, the 58 is about 2db/100 foot lossier than 400.

(i have about 1000 feet of 58 lyin' around, sure would like to use it. i probably will use it for everything except the gps.)

There is a shielding issue - some cable loss is needed, and less "pick-up" through the co-ax shielding.

RG-400 has much better shielding than the RG-58, and the TNC connector ensures the shielding is continued through the connector more efficiently...

gil in Tucson

johnp · #10 08-16-2007, 11:15 AM

Quote:

Originally Posted by az_gila

There is a shielding issue - some cable loss is needed, and less "pick-up" through the co-ax shielding.

RG-400 has much better shielding than the RG-58, and the TNC connector ensures the shielding is continued through the connector more efficiently...

gil in Tucson

i suspected as much (notice i said i was going to use the 58 for everything except the gps). just looked at my 430W, and the rear connection is bnc -- the tnc is only at the antenna end.