[usa2003ardf] Transmitters

[Gerald Boyd]

>What battery are you going to use for 2 transmitters and
>a controller for 6-10 hours? If you use it for a homing beacon too
>that's an altogether different problem (100% duty cycle).

Sam,

See attached graph, which supports the following comments.

Battery is a 5 Ah see attached photo.

Notes:

1. FM operation mode for VHF for worst case calculation. Keyed carrier AM
will have a reduced duty cycle.

2. 80m CW 100% keyed carrier for worst case calculation. In real use the
duty cycle will be less because of CW keying.

3. Transmitter power output 1 watt at antenna connector.

4. Both VHF and HF transmitters operating at same time for practice session
mode, worst case calculation. Only one will be on for a national ARDF event.

5. Transmitters are in "MO" mode.

6. This is a transmitter assembly, No receiver to add current draw during
off time.

7, Controller current is less then 5ma.

Case 1. Assuming each transmitter generates 1 watt of RF and it takes two
watts of DC input (poor efficiency) that will require 4 watts DC power. 4/12
or (.33a) on a 5 amp hour battery (see graph) will provide approximately
14.5 hours of operation (both transmitters in MO mode).

Case 2. For a single transmitter, let's use VHF FM in MO mode for worst
case. Operating time 2/12 (.16a) will be around 34 Hours.

For transmitters operating in the standard ARDF cycle run time is even
longer.

The 5 AH battery weighs 3.8 pounds and is 3.5 X 2.8 X 4 inches compared to
the 8AH 6 pound 6 X 2.6 X 3.7 inch battery we are currently using.

A design goal would be to make the transmitter PCB fit on the side of the
battery. Also there are things that can be done in the controller design for
normal (MOE-MO5) operation to reduce power during off time, which would
extend operating time by a small amount.

>And battery failure at a big important event with lots of people depending
on you is
>bad news.


We replaced all batteries with new ones for our event. Using proper care
they last a long time. For something important don't take a chance with old
batteries. We where able to get a local electronics distributor to donate
them. Also you should test discharge them every so often to verify capacity.
Keep a logbook for each battery so you can keep track of its performance. If
one is showing reduced capacity, junk it.

Jerry

----- Original Message -----
From: "Sam Smith" <sam.smith at ece.gatech.edu>
To: <usa2003ardf at kkn.net>
Sent: Friday, August 08, 2003 6:13 AM
Subject: Re: [usa2003ardf] Transmitters


Gerald Boyd wrote:
>
> However the problem we are having is that the ammo case based transmitters
> are just to heavy.
>

I think most of the weight is in the battery. Big heavy battery means
big heavy box. What battery are you going to use for 2 transmitters and
a controller for 6-10 hours? If you use it for a homing beacon too
that's an altogether different problem (100% duty cycle). And battery
failure at a big important event with lots of people depending on you is
bad news.

It's the same old problem - you can optimize for a few of the desired
parameters, but to get them all is difficult. If you are taking wishes,
here are mine:

1) lighweight.
2) dependable (and foolproof).
3) run for 2 days (2 transmitter sessions of 6-10 hours on 2 consecutive
days) without recharging.
4) remote control, with each receiver on a different control frequency.
5) cheap.

Sam N4MAP


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