[ARC5] BC659 dummy load

[Richard Knoppow]

     Since I am not familiar with the equipment this may be obvious to 
those that are.  What exactly was this transmitter meant to drive?  If 
an antenna is it meant to drive it directly or through a tuning unit of 
some sort, if its meant to drive some other equipment, like an amplifier 
what sort of input impedance does it have?
     300 ohms is a reasonable impedance for a balanced antenna of the 
folded dipole type. The drive point impedance can be anything over a 
rather large range depending on the relative diameter of the elements 
and their spacing but 300 ohms is pretty common. Vertical antenna 
impedance depends on the type. The often used quarter wave antenna 
working against a ground plane is half the impedance of a free-air 
dipole or about 35 ohms.  If its a half wave center fed wire its 
impedance will be similar to a horizontal dipole in free space or about 
73 ohms.  All this can be found in many text books.

On 6/17/2016 7:59 AM, J Mcvey wrote:
> I see that passage about the 300 ohms.I guess I'll cobble an RF ammeter
> together and give it a try.
> However, as far as I know, end fed half wave antennas are much higher
> impedance than 300 ohms, on the order of a few thousand ohms.
> Why the discrepancy?
> At first I though it may have been a typo, meaning 3000 ohms, but the
> the math for the power works out according to the 1.3 watt spec.
> I get 1.27 watts for 65ma into 300 ohms, which the text  says it should
> be at least that.
> It must be correct? Antenna theory does not apply to the DOD? Hmmmm...
>
>
>
> On Friday, June 17, 2016 3:47 AM, Richard Knoppow
> <1oldlens1 at ix.netcom.com> wrote:
>
>
>     I realize that I misplaced a decimal when calculating the power. I
> got too much power.  57ma in 300 ohms is slightly less than a watt.
>
> On 6/17/2016 12:42 AM, Dave Jackson wrote:
>> All:
>>
>> TM11-615 for the SCR-609A/B and SCR-610A/B calls for a 1/2 wave antenna- a
>> fairly high impedance depending on the configuration.  There is an
> internal
>> matching network to make it look like 1/2 wavelength at the system center
>> frequency (app. 32.5 MHz)
>>
>> Page 91, paragraph 127: Minimum Test Requirements calls for a minimum of 1
>> watt to the antenna also using a 300 ohm resistor in series with an r.f.
>> milliameter on the 0-100 scale.  Figures out to be about 57 ma for
> just the
>> 300 ohm resistor.
>>
>> Hope this helps,
>>
>> Dave, WA4OBJ
>>
>> -----Original Message-----
>> From: ARC5 [mailto:arc5-bounces at mailman.qth.net
> <mailto:arc5-bounces at mailman.qth.net>] On Behalf Of Richard
>> Knoppow
>> Sent: Thursday, June 16, 2016 11:34 PM
>> To: arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>
>> Subject: Re: [ARC5] BC659 dummy load
>>
>>    I am not familiar with this transmitter. If 30 ohms the power would be
>> on the order of 13 Watts, does that sound right for it?  300 ohms would be
>> close to 130 Watts.
>>
>>>>    On 6/16/2016 8:26 PM, WA5CAB--- via ARC5 wrote:
>>>>    >The only place in any of the literature where I find the use of a
>> dummy
>>>>    >load mentioned is in TM 11-4023, page 26, paragraph 28.  It says
>> that to
>>>>    >check the transmitter output power, use a 300 ohm resistor in series
>>>>    >with a 0-100 RF milliammeter.  Minimum reading on both channels
>>>>    should
>>>>    >be 65 mA.
>>>>    >
>>>>    >Robert Downs - Houston
>>>>    >wa5cab dot com (Web Store)
>>>>    >MVPA 9480
>>>>    >
>>>>    >In a message dated 06/16/2016 17:12:51 PM Central Daylight Time,
>>>>    >arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>
> <mailto:arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>> writes:
>>>>    >>Don't need the military one , but just what the resistance is
>> supposed
>>>>    >>to be. Anybody know?
>>>>    >>
>>>>    >>
>>>>    >>Jim
>>>>    >>Ac2EU
>>>
>>>
>>>    Robert & Susan Downs - Houston
>>>    wa5cab dot com (Web Store)
>>>    MVPA 9480
>>
>>
>>
>
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com <mailto:1oldlens1 at ix.netcom.com>
> WB6KBL
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL