Re: LF: A/G FREQS

["mal hamilton" <g3kevmal@talktalk.net>]

To enlighten those that do not know. Not so many moons ago 2m es 70 cms was mainly CW and AM then SSB as well and FM was used only by repeaters when it first arrived. Then for some reason the FM spread to the rest of 2m es 70 cms but there was still a segment at the bottom of each band for cw es ssb, mainly used for DX contacts.

Like you say in the old days it was tuning Hight to Low or vice versa nearly everyone was xtal controlled. The Liner 2 es Liner 430 black boxes came along with vfo es cw es ssb, then simplex became the norm. 4 metres was also AM on 70.26 calling channel.

For local chats FM is fine but looking further afield then AM, SSB and CW have more punch and better.

The LF/MF operator will also find this info useful.

g3kev

 

 

----- Original Message -----

From: M0FMT

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, June 26, 2012 4:42 PM

Subject: Re: LF: A/G FREQS

Well Graham when I were a Jate we only had one xtal and a QQV02-6 on 432.00 amplitude modulated on the plate in the good old days. After all its just the product of mixing two frequencies 432 with audio in a nonlinear device like a Class C amp works from almost DC to light!. Nowerdays I guess you would PWM the carrier on the PA gate/ base producing the same effect and using considerably less power over all. Class E an all.

73 es GL Pete M0FMT IO91UX

From: Graham <g8fzk@g8fzk.fsnet.co.uk>
To: rsgb_lf_group@blacksheep.org
Sent: Tuesday, 26 June 2012, 17:09
Subject: Re: LF: A/G FREQS

Steady on Mal !   this  is getting  technical  !"

 

Your  right  , FM has a  cut off  point  , where  demodulation fails  and  also  a  capture  effect , where the  stronger of  2 signals  will  acquire  and  hold the  demodulator ..always   fun  on 2  mtrs   when a  mobile  suddenly  takes  the  channel

 

Am  has no  cut off  point , but  gradual  degradation  until the  recovered  audio  is no  longer usable  ......eg,  mcw  would  readable  much  lower  than  AM speech

 

I think  much over  250/300 MHz   its  actually  not  possible to  produce  AM  , could be  wrong  , but  there is a  limit  , may   be  by  high  level  modulation falls over , dont  see  why  could  not  be  via  transverting  .......

 

G..

From: mal hamilton

Sent: Tuesday, June 26, 2012 8:36 AM

To: rsgb

Subject: LF: A/G FREQS

As stated Air/Ground vhf/uhf is AM and simplex working.  I have also noticed a well modulated AM transmitter is more potent than a FM transmitter when working at max range. On AM the RX bandwidth can be opened up to receive several stations simultaneously then select the one of interest by closing down the selectivity, the same applies on CW.  On FM if you tried this the transmission would fall into a black hole, in other words the FM rx has to be tailored to the exact bandwidth of the transmission (same deviation value)

g3kev