MAR-6 based VHF Masthead Amplifier


I used the manufacturers suggested circuit (simple !).
However for the power supply I used 2 series'd 9V batteries
with a variable resistance to increase current as terminal voltage of cells falls away with time.
The ammeter allows me to adjust for the optimum 16 - 20 mA range. (see graph below)
When this is not achievable - replace batteries!

Reference 1# RF/IF designers Guide book: DG96/97 Mini-Circuits
Reference 2# Ready to use RF amplifiers. Ian Hickman: Wireless World Feb 1994



Another alternative to the MAR-6 device is the SGA-3486
(good spec'/cheap/available in small quantities.)



Want to construct you own Mar-6 type amplifier from discrete components ?
João Kolar De Marco, PY2WM (SK) shows you how!

Link to: VHF UHF TV Antenna Aerial Booster Preamplifier using SGA3486 chip

During August-Dec' 2011; I have been receiving S S T V pictures from the ARISSAT-1 satellite if and when it passes overhead.
Downlink is 145.95 MHz FM.
Although I am using a 7 element Yagi (DJ7ZB design) optomized for 146 MHz with claimed 10.7 dBd gain, F/B >30dB the addition of the masthead amplifier detailed above, has resulted in better SSTV pictures (less "grainy") as per examples, shown below.
This is technically an "untuned" RF amplifier, but you could consider the Yagi as being the input tuned cct and the front/end of the receiver as the O/P tuned cct ?



7 Element YAGI - constructed from re-cycled commercial TV antenna parts.


FOOTNOTE 1:
As the Arissat-1 battery has failed which means no satellite downlink transmission "after dark" and as all good passes over the Australian continent seem to be between dusk and dawn (local), no pictures are being received at my station!
Also if you do get a pass just after dawn (satellite moving west to east, coming out of eclipse) there seems to be quite a delay after leaving eclipse before the satellite electronics "boots-up" - such that you only get a short amount of downlink just before LOS.

Also: from http://www.ariss-sstv.blogspot.com//
Thursday, September 29, 2011
Southern Hemisphere
Seems with the current orbital timing that folks in the Northern hemisphere are at a disadvantage due to the early morning passes being silent because the delay timer is not activating the transmitter until about 15 minutes after the satellite comes out of eclipse.
For folks in the Southern hemisphere there are some excellent day and evening passes occurring for the next couple of weeks.
Hope to see a few more images from Australia, South America, Africa and some of the equatorial regions during this time frame.

FOOTNOTE 2:
SUCCESS, one of my 'downlinks' has been included in the ARISSAT SSTV Gallery !

FOOTNOTE 3:
Previously I had tried (without much success) a dual JFET based masthead amplifier, the design and function which looked appealing. Here is a link for those who may be interested ?

The Amateur Radio satellite ARISSat-1 deployed from the ISS on August 3, 2011 fell silent on Wednesday, January 4, 2012 when it re-entered the Earth's atmosphere.
In my time tracking ARISSat-1, I was able to receive about 110 - 120 SSTV images of various quality.
The graphic below shows the last telemetry frame and SSTV images received before descent and "burning-up" on re-entry!
Its predicted impact point was in an open area of the South Atlantic west of Angola.
An ignominious end for the little satellite!