(119) MARC January 2023 meeting - YouTube

Here is my rookie YouTube PowerPoint on the mode “VARA”.

This was given to the MidAtlantic Amateur Radio Club Jan 2023.

The talk followed a Zoom talk to the MIdAtlantic ARC by Jeremy N2ZLQ on FT8 and an earlier Zoom talk last spring to MidAtlantic ARC by Steven K3FZT on Winlink. So, I kind of used their talks to transition to VARA.

The YouTube begins with a Business meeting of the MidAtlantic ARC.

 So, if you wish, jump ahead 15 minutes or so to the start of the VARA presentation.

Thank you to NY3J, Ron, in Bensalem (Bucks County) PA for being the other half of the VARA FM link we used to demonstrate sending an American Red Cross “Daily Shelter Report template” on 2m FM with Winlink Express software. Since Ron and I are 40 miles apart, we could not do this link on SIMPLEX, so we used an analog (voice) 2m FM repeater to enable our radios to hear one another - for our RF link (with permission of the owner of the repeater). We could also have used a dedicated VARA FM digipeater if one were available then (and now there are a few digipeaters in the area).

What is VARA?

VARA is an exchange MODE where two stations form an ARQ “link” (like a dance).

Once the link is established (called handshaking) we then continue to exchange data or emails until our message is delivered. Then we discontinue our link, and the frequency is available for the next VARA link.  VARA will not share a frequency (like PACKET). That is one big difference between VARA and PACKET.

VARA (and PACTOR) are unlink other modes that have a fixed speed (Thor, Olivia, MFSK, PSK).  Vara can be sent on HF on two SSB modes: 500 Hz and 2300 Hz bandwidths (user option). VARA FM (2m/70cm) can be sent on a “narrow” (3 kHz bandwidth) which fits into the passband of a repeater.  VARA FM NARROW worked well in our trial on the demo passing audio through a voice repeater.  But VARA can also be sent in VARA FM “WIDE” mode (6 kHz) which needs special FM radios and sound cards on cable of sending at the equivalent of what is called 9600 baud, even though VARA is nothing like 9600 baud legacy PACKET. I did not want to get too deep into the weeds of 1200 baud vs. 9600 baud VARA FM although that is an interesting topic.

I tried to hit the highlights of VARA as a modulation structure, showing AM, FM and PM modulation on HF SSB and FM. I made one technical error (maybe you caught it) about bandwidth.

When you modulate a single-pitch TONE (say 1500 Hz) on an AM radio you get one RF spectrum: a carrier and an upper sideband and a lower sideband => double sideband.

When you send the same single TONE on SSB you get a very different RF spectrum, missing the CARRIER and the unwanted sideband.

So, what happens when you send a one-pitch TONE on an FM transmitter?

I try to briefly show the FM spectrum of multiple sidebands on a 2m radio (weird)

It’s even stranger when you send a mode like THOR 22 via an FM radio on 2m.

To explain the RF spectrum involves some very fancy mathematics (Bessel functions).

So, for ham radio ops, bandwidth is important to convey information, and AM, SSB, and FM work very differently.

Every time I give a talk on some technical topic (antennas, Nano VNA, Sound Cards) I learn from my own mistakes, or from the questions that come flying at me. If you watch this to the very end, you will see and hear an exchange about QAM (amplitude and phase changes) and a question about COM ports (what they are are when you need them) and especially at the end was a question about why CW is a digital mode. What are the 0’s and 1’s in CW anyway? This is interesting for me as an instructor in high school and college. Sometimes we miss the forest while looking at one tree.

Have fun. I always enjoy trying to teach someone something that I (think) I understand.

But in terms of VARA and Winlink, I am learning as I go - we call these ROOKIE errors.

The last decade of my teaching career I taught (real) Physics to ALL 9th graders at Westtown School (Quaker coed boarding school). That taught me patience and trying to come up with good demos/labs and examples. Real physics with nothing beyond basic algebra was a challenge.

So, I came up with the idea that VARA is like a 20-speed mountain bike with hand brakes.

Packet is like a one-speed bike with a foot brake.

Which bike would you choose to tackle a rough mountain trail?

Maybe that is an unfair comparison, but it felt right at the time.

If you spot errors, let me know.

VARA on HF and VARA FM on VHF/UHF are two different modems.

You can NOT interchange them (I tried).

And remember - if you play with digital modes on an analog (voice) repeater, then get the permission of the repeater trustee/owner first.

De Barry k3eui
West Chester PA
Feb 08 2023