[Milsurplus] Freq. Coverage of Navy Transmitters

[Bob Camp]

Hi

A lot of the early mobile communications was done at frequencies we now  
consider "to 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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