[Milsurplus] [ARC5] Smart People: Antenna Matching Mystery
Michael Hanz
aaf-radio-1 at aafradio.org
Mon Aug 7 16:16:00 EDT 2017
There is a general treatment of the problem at
http://aafradio.org/docs/Aircraft_Antenna_Design.html - along with
nomographs for doing approximations.
On 8/7/2017 3:35 PM, MICHAEL ST ANGELO wrote:
>
> I recall a document detailing the load impedance of antenna on various
> planes. Does anyone have a copy of that document for the Command
> antenna for those planes?
>
>
> Once we have a range of impedances the set is supposed to match we can
> design an L network to go from that impedance R + jX to our antenna load.
>
>
> Mike N2MS
>
>
>> On August 7, 2017 at 2:43 PM Michael Hanz <aaf-radio-1 at aafradio.org>
>> wrote:
>>
>> Peter is correct. But what he didn't say was how easy the
>> explanation will be, or how long it would take to teach you, or even
>> if you would feel any satisfaction at the end. RF design, and
>> transmission line and antenna design in particular, is sort of a
>> specialty area in EE because so many other factors start showing up
>> at different rates with frequency. The differential equations start
>> going nuts. They mess up the nice, well behaved lumped component
>> view and math that you get in Physics 101. You either love the
>> complexity of the specialty, or you don't.
>>
>> RF engineers have a different frame of mind - a sort of other-worldly
>> look in their eyes, peering into the depths of space as if they can
>> see something several light years away. Okay, I made that last
>> sentence up in fun, but from a specialty choice standpoint, it does
>> take a slightly different talent than, say, circuit design or power
>> distribution. You can get a whiff of the problem by reading all the
>> antenna theory battles that go on endlessly on the web.
>>
>> 73,
>> Mike KC4TOS
>>
>> On 8/7/2017 1:46 PM, Ray Fantini wrote:
>>>
>>> A statement like that almost makes me want to say, Ok so explain it
>>> to people like me who don’t know! Being of relatively small mind and
>>> limited capabilities myself am left to looking at what’s been out
>>> there in the printed world. Looking at the basic output tank it’s a
>>> straight forward parallel resonate circuit with T54 also serving to
>>> match the high impedance of the plate tank to the low impedance of
>>> the antenna. The kind of thing a transformer works best at. L 52
>>> adds inductance to the output to compensate for the short electrical
>>> length of the antenna and that’s about all there is to it. No
>>> suppression of unwanted harmonics or anything else just a great
>>> example of fast and expedient engineering.
>>>
>>> Like I said I am not that smart so if I got it wrong feel free to
>>> correct, most of my knowledge of the inner workings of the ARC-5
>>> family beyond my limited experience was gleamed from the CQ Surplus
>>> conversion Manual or better yet the $1.50 Command Set compendium
>>> published back in 57. Some of the later articles in the book outline
>>> how to modify the set for TVI proof operation but almost all of the
>>> modifications for Ham use first involved removal of L52 the roller
>>> inductor and directly connecting to the secondary of T54
>>>
>>> I know conversion is a dirty word around these parts but much can be
>>> learned from that book. This is a web link to it:
>>>
>>> http://hilltoparmyradios.com/command_sets.pdf
>>>
>>> Would be real advantageous for one of the smart people to run a
>>> software model and see just what type of voltage is developed across
>>> that capacitor and better yet what RF current. Assume an output load
>>> 50 Ohms and L52 set to 0, minimum inductance. Think it may be
>>> surprising!
>>>
>>> Ray F/KA3EKH
>>>
>>> *From:*milsurplus-bounces at mailman.qth.net
>>> <mailto:milsurplus-bounces at mailman.qth.net>
>>> [mailto:milsurplus-bounces at mailman.qth.net] *On Behalf Of *Peter
>>> Gottlieb
>>> *Sent:* Monday, August 07, 2017 12:54 PM
>>> *To:* arc5 at ix.netcom.com <mailto:arc5 at ix.netcom.com>
>>> *Cc:* ac2eu at yahoo.com <mailto:ac2eu at yahoo.com>; arc5 at mailman.qth.net
>>> <mailto:arc5 at mailman.qth.net>; milsurplus at mailman.qth.net
>>> <mailto:milsurplus at mailman.qth.net>
>>> *Subject:* Re: [Milsurplus] [ARC5] Smart People: Antenna Matching
>>> Mystery
>>>
>>> It's not voodoo, just electrical engineering, and pretty well
>>> understood.
>>>
>>> Peter
>>>
>>>
>>> On Aug 7, 2017, at 11:50 AM, arc5 at ix.netcom.com
>>> <mailto:arc5 at ix.netcom.com> <arc5 at ix.netcom.com
>>> <mailto:arc5 at ix.netcom.com>> wrote:
>>>
>>> Sent from my Ain't Smart Phone.
>>>
>>> ------ Original message------
>>>
>>> *From: *J Mcvey
>>>
>>> Antenna Matching Mystery
>>>
>>> ...The 50 ohm coax at the terminal causes a host of reactance
>>> and reflection issues by itself.
>>>
>>> Bet if you added coax length, the situation would change to
>>> something else, maybe better, maybe worse!
>>>
>>> RF is spooky stuff!!
>>>
>>> ----
>>>
>>> You are so right. I switched the coax jumper to a long one,
>>> coiled into a big spool "shield RF choke." It completely
>>> changed the tuning. RF is Electronic VooDoo.
>>>
>>> 73 Dave S.
>>>
>>> On Monday, August 7, 2017 10:13 AM, Ian Wilson
>>> <ianmwilson73 at gmail.com< a="">> wrote:</ianmwilson73 at gmail.com<>
>>> <mailto:%3cianmwilson73 at gmail.com>
>>>
>>> I have noticed that the roller coil has distributed capacitance,
>>> so it
>>>
>>> does not always behave as a simple inductance even at lowly RF.
>>>
>>> To a reasonable approximation, it could probably be modelled as
>>>
>>> "a few" L-C sections. 4 would be a good starting point.
>>>
>>> 73, ian K3IMW
>>>
>>> On Mon, Aug 7, 2017 at 6:57 AM, David Stinson
>>> <arc5 at ix.netcom.com <mailto:arc5 at ix.netcom.com>> wrote:
>>>
>>> OK y’all- here’s a mystery (at least to me),
>>>
>>> Series circuit, designed to match a normally 5-12 Ohm
>>>
>>> Aircraft radio output to resistive 50 Ohms.
>>>
>>> Follow me here:
>>>
>>> Series circuit:
>>>
>>> PA Tank coupling link – Roller coil –
>>>
>>> 120pFd ceramic cap mounted at antenna post –
>>>
>>> 50 Ohm Load = 25 W out.
>>>
>>> PA Tank coupling coil – 120pFd ceramic cap mounted
>>>
>>> at the input of the Roller Coil – Roller Coil –
>>>
>>> 50 Ohm Load = 15W out.
>>>
>>> The ceramic cap is near chassis ground both ways,
>>>
>>> so it’s not circulation currents.
>>>
>>> The PA tuning cap setting does not change,
>>>
>>> so it’s not de-tuning the PA tank.
>>>
>>> Why the difference between these two series circuits?
>>>
>>> 73 Dave AB5S
>>>
>>>
>>>
>>>
>>>
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>
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