EMRFD Message Archive 11894

Message Date From Subject
11894 2015-11-17 02:46:43 petervk3ye 6.11 A portable DSB/CW 50 MHz station

Refer p6.90 EMRFD

This is a 50 MHz DSB station comprising a DSB transmitter (using a 14.318 MHz xtal) and a receiving converter. 

In connection with the latter it is suggested that a better choice would be a 43 MHz crystal as it would allow a 7 MHz transceiver to be used.

As it happens 14.318 x 3 is very close to 43 MHz.  50.110 translates to 7.156 MHz which may be covered by a 7 MHz DSB rig.  It may be possible (I haven't tried it) to tap off some 14.318 MHz energy and feed to a tripler which is only used on rx.  So you wouldn't necessarily need any extra crystal for the receive converter. 

The main problem I see is if using a direct conversion receiver on 7 MHz as an IF.  Its local oscillator x 7 will be in the 6m band - very close to 50.110 MHz.  So you might get a birdie in an annoying place. It may be possible to switch in an inductor in series with Y1 (along with having two in parallel) on receive so that the frequency conversion is a little different and the birdie is moved. 

There may be other complications and birdies.  All this came about when trying to look up something on ladder crystal filters for another project. 


11895 2015-11-17 08:16:23 kb1gmx Re: 6.11 A portable DSB/CW 50 MHz station
Several things.

50.110 is the DX calling frequency, Even for USA to Canada and the islands...  thats 
the nominal usage we see.  Rulse down older may allow other.

The frequency you want to hit is 50.125 (7.16007 * 7).  

Also a 7mhz IF may be not so good for the reason noted if you are down converting
from 6M to 40M.  The design in EMRFD used a 8mhz RX with its own LO.  It can work but
a quick run with the calc says you will have a birdie that follows you around.
The problem is you can pull 14.318 to maybe 14.321 on the high side but it 
usually can be pulled down easily 20-25khz to say 14.293, here in the USA below
50.100 is CW only (no data).

The alternate is use the same LO as the TX and use that as LO for the DC RX.

For one radio (rock bound with VXO I used an if of 9.6mhz and 13.515 (13.515*3=40.545)
and with the 9.6 If that got me to 50.145 on paper and the VXO used would pull up 10khz 
and down over 30khz to give wa working range of 50-163 to 50.120.  That was a 
satisfactory range for common usage in this area.  A second crystal at 13.56mhz 
allowed 50.250 to 50.280.

I'd warn you that when 6M opens typically from 50.125 to about 50.200 
turns into bedlam (think 20M during a major contest) and selectivity is everything
in an RX.  I tried Eskip season with a simple RX using 4 crystals in the filter
and it was not very satisfactory,  I would later upgrade the filter to 6 poles
and that was tolerable.  Same thing can happen during mountaintop ops
where LOS range is enough to bring in a lot of activity.

Just some ideas from the opposing side of the globe.