Essential website for any serious 11m DXer, Live Spot Log and personal logbook. See what stations are active on the bands right now!

https://www.ClusterDX.nl

Dean 26AM069 receiving my SSTV transmission on 27.025 Channel 6 Mids, TX Mode Scottie 1

https://youtu.be/lBZV9kGJrzw

Sunday 28th August 2021

This Mornings net was chaired by James 26JS07 on new frequency of 27.285 Usb and joined by the following stations:

1. CT3855 Pete – Allhallows
2. TE032 Adam – Two tree Island
3. TE11 Alan – Bushy hill radar
4. CT3699 Dave – Chatham
5. CT4051 Steve – High Halstow
6. Osprey Bill – Shenfield Brentwood
7. TE03 Colin – Langdon Hills
8. AB406 John – Bethersden
9. TE01 Jay – Southend
10. OT01 Ron – Allington
11. TE256 Steve - West Bergholt Colchester
12. HS1172 Pete – Maidstone
13. (No Call) Pete – Tonbridge
14. CT331 John – Rye harbour
15. AM101 Billy – Mobile
16. AM081 Will – Allington
17. TE310 Kevin – Leigh on sea
18. AM525 Dennis – Tonbridge
19. TE67 Jeff – Southend

Look forward to hearing everyone next weekend
Thanks to everyone that joined 73

I find many CB operators these days are not familiar with the understanding between "Modes and Bands". This is more prevalent here in the UK, as most operators are only familiar with the "Straight UK 40" or "One trick ponies". Namely the 27/81 radios that where legalized.

I've also found that even explaining the difference between modes and bands is recurring topic to the same operators who may not grasp the difference in these modulation types.

This has all probably stemmed for a previous miss-conception with broadcast radio receivers, which are kind of incorrect, namely small transistor radios with a band switch marked AM/FM. Although this does in-fact switch between bands, the labeling is written in "Modes".

Firstly AM is Amplitude Modulation, where the carrier intensity is increased with the audio frequency. The modulation is transmitted in DSB e.g. "Double Side Band" The carrier in essence is only there to prop up the modulation, and the intensity change is a product of the way the audio frequency is imposed onto the carrier. There are many ways to do this that I will not go into here, as it's beyond the scope of this topic for now.

Secondly FM is Frequency Modulation which is almost identical, but the carrier will deviate in sympathy with the modulation that has been imposed onto it. In essence the carrier is only there once again to prop up the modulation, with still the same DSB pattern.

Thirdly SSB or Single Side Band is basically AM with rectified audio, this will either be the "Upper" or "Lower" side. The way this is done is very simple and yet ingenious too. However now the carrier is suppressed, and is not technically part of the transmission.

There are many types of modes, all requiring a different approach to the way they are resolved at the receiver. For AM a simple diode detector is all that is required. For FM a "Discriminator" is needed, and finally for SSB a "Product Detector" is needed.

I hope this has shed some light on the topic of "Modes" and I'd be interested to hear from others who are finding the same operators on 11m especially with the same lack of understanding regarding modes.

Here's an image below giving an example to what I've explained.



73 DE Bill

This circuit for a simple Digi-Vox unit will allow easy connection between any CB or HF transceiver that is not VOX capable. Below shows how the digital signal from a PC or Laptop can trigger the PTT on the radio, and then hold it on until the digi transmission has completed, which-then-after it has completed will drop the PTT.

The digital signal, “which is technically just an audio frequency”  will first pass through the first stage amplifier and then onto a double diode detector stage to be rectified into a steady DC voltage. The use of a DC blocking capacitor between the detector stage and 1st stage amplifier is there to prevent false trigger, or permanently supplying voltage to the base of the TIP121.

The steady all-be-it small voltage applied to the base of the TIP121 Darlington transistor is just enough to conduct, thus switching on the transistor and passing the supply voltage to the relay, which in-turn will switch on the relay and close the PTT switch to your transceiver.

It’s important to use a “double pole” type relay here as some transceivers / CB’s require the RX connection to be closed when in receiving mode, otherwise you may not hear any digital signal being returned for you to decode.

At the same time the digital signal is also being passed over to the mic input connection on your radio to be sent. The use of a small variable potentiometer has been employed to set the correct level that’s needed. If you have a mic level control on your radio, you may wish to just use this instead. However switching from voice to digital may be a nuisance when adjusting for both types of transmission. 

Finally the Digi-Input must be DC blocked from the rest of the circuit and transceiver, this is very important and is easily achieved via the 2x 1uF capacitors that sit on both AF connections to your computer. If the 1uf from the AF+ was omitted, there would be a DC offset being sent back to your computer. This is also the same for the AF- which would more than likely cause an unwanted ground-loop.

The circuit is very simple, free from snags and odd behavior, and shouldn't be a problem for someone to build that is competent in doing so.

73’s DE Bill

 Download Link for MMSSTV 1.13a  MMSSTV113A.zip (2428.79 kB - downloaded 25 times.)

 Simply un-zip and run the installer.

https://youtu.be/ARmhkZaBuoM

I've defiantly experienced more bad than good from KamSat over the years. First instance was with the New Team Mutlimode transceiver, which is basically the same chassis as the CRT SS9900. They listed it very cheaply which was a good thing, so I snapped it up.

Sadly it took almost a month for it to finally arrive, and the process of constant messaging either way, I finally came to the conclusion it just wasn't in stock. Bang goes that order before 2pm for next day dispatch!

Most recently was my purchase of the Sunker Elite Four. Which turned out to be a second hand returned item. I wasn't pleased. None of the original packaging to protect the radio was in the box, so it rattle around terrible. There was scratches all over the top and bottom covers, plus someone has crimps dirty old spade connectors to the power lead. KamSat insisted it wasn't a return!

I think I'll give KamSat a wide berth in future.