Use of lower frequencies (was: [Milsurplus] Freq. Coverage of Navy xmtrs)

[D C Macdonald]

The old expression "Calling All Cars" came from the days
when the HQ station was a one-way deal in the 1600-
1700 (or so) kHz region.  The police cars used regular
auto broadcast receivers that had been modified to
receive those frequencies.  They had no way in which
to answer the HQ station other than to simply follow
the "broadcast" instructions.

I worked for Elmo Black, W5JCB, between 1985 and
1993 in his 2-way radio shop.  He had helped to set up
the original system of this type here in Oklahoma City.
Elmo had also been a high-speed CW operator for the
Highway Patrol before teletype service was put into
use for communication between various H.P. stations.

Elmo told of the problem that the Oklahoma City P.D.
had with patrolmen not responding to the "all" calls.
It seemed that many of them would put their radio
receivers on a local high power AM station instead of
maintaining watch on the police frequency!!  KOMA
at 1520 kHz ran 50 kW and could be heard at the
Grand Canyon at night!!

Yes, the ARRL Mobile Handbook mentioned that the
ground wave coverage at 1.8 MHz was sufficiently
better than that at 3.8 MHz so that the greater loss
in antenna efficiency was more than just made up.

Mac, K2GKK/5



----Original Message Follows----
From: Bob Camp <ham at cq.nu>
To: Hue Miller <kargo_cult at msn.com>,Milsurplus <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] Freq. Coverage of Navy Transmitters
Date: Wed, 03 Nov 2004 19:38:04 -0500

Hi

A lot of the early mobile communications was done at frequencies we now  
consider "too low". The original police communication nets were just  above 
the AM broadcast band.  The system was a one way (base to mobile)  setup. 
First trials were in the 1920's with Detroit being the pilot  location.

By the early 1930's two way communication was an issue and they went to  
VHF. A picture of high tech 1933 style is at:

http://www.ieee.org/organizations/history_center/milestones_photos/ 
two_way.html

Ham communication on 160 meters was common early on. The advantage  being 
that an AM radio could be "bumped up" to the 160 meter band. I  can't find a 
quick reference.

One dead giveaway of the low frequency mobile setups is the antenna.  The 
whip mounted on the rear bumper with the tip of the antenna tied  off to the 
front bumper shows up in a lot of old pictures.

I suspect that the police systems in the 1920's had at least some  impact on 
the Navy's planning for their communications setups.

	Take Care!

		Bob Camp
		KB8TQ



On Nov 3, 2004, at 2:37 AM, Hue Miller wrote:

>
>----- Original Message -----
>From: "howard holden" <holden7471 at msn.com>
>
>>The puzzle to me is why did the TBW have the LF unit? Any antenna  they 
>>could
>>set up on the beach would be a pretty inefficient radiator in the LF  
>>range.
>
>Well, not on the beach, but this wasn't only a beach radio.
>Yes, the shoreside antenna would be pretty inefficient. But the  
>inefficiency
>didn't persuade the German and Italian military planners from making  use
>of LF/ MF, even in armored scout cars.  I think this was for ground  wave
>coverage in rolling country, even tho i don't think i have yet  explicity 
>seen
>this idea in print elsewhere. It just popped into my head just now, i  
>recall
>reading something in an ARRL mobile book, i think it was, that stated  that
>for mobile with same power and antenna, 160 actually gave somewhat more
>coverage. This just as an example that lower is not automatically  "worse".
>Sorry, wish i had that reference handy to cite.
>
>>The upper MF and HF would be far more useful and practical for  shore-ship
>>comms. Perhaps it was to be able to communicate with merchants  involved 
>>in
>>landings, who might have had only MF/LF rigs. That could explain the  MCW
>>capability on many Navy transmitters.
>
>Landing missions and shoreside portable stations wouldn't be  communicating
>with cargo type vessels no matter the owner. The comms would be  funneled
>thru other appointed communication ships. Pretty sure i can back this  up, 
>with
>some trouble and digging, but that's absolutely the lesson from the  actual
>landing invasion radio traffic quoted in the book, "Navy Retread".
>
>>The other puzzle is why the Navy used suppressor-grid modulation  instead 
>>of
>>plate  mod on some transmitters? Typical power output with suppressor  mod 
>>is
>>about 1/4 of the CW output. Granted, the weight and space savings  over 
>>plate
>>mod on the TBW might mean something to the guys who had to muscle it  
>>ashore,
>>but with a hulk like a TBL, at 700 lbs (not including the MG set),  what
>>would another 150 lbs mean, instead of the 75 lbs for the suppressor
>>modulator.
>>
>>Howie WB2AWQ
>
>Actually, 150 lbs.  more can be a big deal for aircraft or for  portable 
>equipment that
>has to be moved around by man power. But here's another great big  reason, 
>i
>think:  AM was considered to be the secondary mode for the  transmitter, 
>maybe
>not the main show with cw as a fallback.
>-Hue Miller
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