HF/VHF Mobile Operation

Well it seems that the VHF/UHF repeaters I have been complaining about having a lack of activity may actually have been more active than I had thought! Turns out my old Yaesu FT-857D radio had developed a fault with 2 out of 3 of its ceramic filters rendering my receiver virtually deaf except to very strong local signals. This is apparently a very common hardware design failure for this model of radio that has since been rectified with newer ones sold having different filters not subject to this problem.

Had my FT-857D repaired very quickly and cost effectively by the staff of Martin Lynch & Sons and it is like having a new radio in my vehicle once again, I also took the opportunity to have the radio modified to transmit on 5 MHz for portable operation too (mobile 5 MHz operation not being permitted here in the UK).

This has enthused me to be more active when mobile (or Portable) and using either a dedicated 144/432 MHz colinear or a Yaesu ATAS-120A for the 7-50 MHz bands or a dedicated single band 5 MHz aerial left me with the question did I have anything to use on the 3.5 MHz band?

A quick search in the garage resulted in me dusting off my old 0.9m long Australian Terlin Outbacker Stealth Plus antenna to see if it would tune around 3.760 MHz without an ATU so that I could potentially participate on the Worked All Britain (WAB) net. Many years ago before 1998 I used to be very active on the WAB net from my car on 14 MHz and drive all over remote mountain areas to activate the grid squares for WAB awards collectors.

stealth-plus

Initially the SWR was found to be far too high and seemed high even at its lowest frequency around 3.5 MHz  I had added a 3/8″ to PL259 adaptor to the antenna which was part of my problem, the other was I had lost the original 36″ wander lead and had only a slightly longer lead available to me for shorting out the coils for the bands I want to operate on. Basically the aerial was electrically too long to resonate in the part of the band I needed.

I looked again at the Outbacker Stealth Plus and wondered if instead of using the 80M socket would the SWR be any better using the 75M socket nearer to 4 MHz? As luck would have it this worked with the tuning stub lowered to minimum and 1:1 SWR without an ATU seems to be around 3.740 MHz and still low enough at my desired 3.760 MHz.

Now I know people will say how can a 90 cm long antenna be efficient on 3.760 MHz? Well it can’t, however when I used this antenna before from home as a base antenna I had fantastic results with it, so I’m going to give it a go on the vehicle and see what happens!

 

 

 

 

 

Advertisements
This entry was posted in Amateur Radio and tagged , , , , , , . Bookmark the permalink.