MB7TR – SSTV Repeater in Magor

Peter (MW0RPB) closed down the MB7TR 2m repeater in Cwmbran a year or so ago. I decided to start my own here in Magor. This time however, it would be on 70cm, using the same callsign.

MB7TR is now a 70cm, FM, regenerative sstv repeater based in Magor, S.Wales. It shares the Diamond X300n antenna with APRS station MB7UNE.

All details can be found HERE.

FM deviation using Bessel Zero method

I decided to try to work out the peak deviations in FM when transmitting from an IC-9700 and an IC-705 into a dummy load. The receiving transceiver is a SunSDR2 Pro without antenna connected. I used a software sig gen to feed both Icom radios with an audio tone via their USB audio interface.

This tone is adjusted whilst observing the FM transmission on another SDR receiver, or listening to the fundamental frequency with narrow CW filter. The injected tone’s frequency is adjusted to bring the main carrier frequency to the zero point (null) in the bessel function, the carrier at the fundamental will drop to zero on the sdr, and it will go silent on the receiver that is listening in CW mode.

Bessel Function

  • 1st fundamental crossing = 2.4048 modulation index
  • Deviation = 2.4048 * AF (where AF is the audio frequency applied that results in a null carrier at fundamental RF frequency)
  • Bandwidth = 2 * (max audio freq + peak deviation)
  • Assume 3k peak audio frequency for voice used in bandwidth calculations


1830 Hz FIL1 = ±4.4 kHz dev
913 Hz FIL2 = ±2.195 kHz dev

FIL1 BW : 14.8kHz
FIL2 BW : 10.39kHz


1762 Hz FIL1 = ±4.24 kHz dev
889 Hz FIL2 = ±2.13 kHz dev

FIL1 BW : 14.48kHz
FIL2 BW: 10.26kHz

FM from IC-705 with 1762 Hz tone applied
NFM from IC-705 with 889 Hz tone applied

Icom Remote Utility Issue and Hamlib

When running JTDX (version rc155 with the ic-705 supported) and the Icom Remote Utility I kept getting annoying errors from HamLib which made it unusable.

Hamlib error: Protocol error while getting current VFO frequency
Hamlib error: Command rejected by the rig while getting current mode

It seems that if you turn OFF the CI-V Transceive option in the Connectors->CI-V menu this fixes the issue. All problems went away, however I did need to restart the Icom Remote Utility.

I assume Hamlib wasn’t handling the returned ci-v commands with the ci-v transceive setting enabled. This may be the case on all Icom radios, not sure, however it is a default setting on the ic-705.

73 Richie.

Multi Band Vertical – Part 1

So, unless you have been living under a rock you will have heard of DX Commander. M0MCX, Callum, runs a micro antenna business producing mostly multiband vertical antennas. He also runs a very enjoyable YouTube channel.

Based on a ‘fan dipole’ idea, half of the the dipole is taken and turned on end, and driven elements for each band run up a vertical fibreglass flag pole. With a suitable ground system deployed a multiband HF vertical can be achieved very quickly. Research paper after research paper shows that diminishing returns are reached with roughly 4 times the amount of copper down as the wavelength of the lowest frequency band. So, if you want to reach those diminishing returns on 20m for example, you need something over 80m of ground radials, and don’t stress making them 1/4 wave or anything, just any old length, 20 to 30 radials of 4m each would be fantastic. Just chuck them down and get on the air !!!!

Anyway, with the ‘technomagic’ aside, I decided to built my own home brew version. I am using an aluminium plasterers hawk, upturned to act as the ground plate to attach all the radials to. Drilled and tapped, suitable bolts and an so239 attached, it is very easy to deploy. A couple of holes can be made to push tent pegs through.

I picked up a DX Commander 10m fibreglass pole. The end cap can be removed and it sits nicely over the handle from the plasterers hawk.

In Part 2 I will build the ‘spacer plates’ and get the elements cut for each band I want to operate on.

73 for now !

ICOM-7851 RFI issues

A quick follow up.

So, my friend had problems with his IC-7851 doing strange things. After hours of diagnostics the issue was found. The interlink cable between the STEP-iR control box and the CI-V port on the back of the radio seemed to be causing the USB disconnects and other gremlins. With the interconnect removed, all problems vanished.

We tried ferrite after ferrite on that cable to no avail. Either the early generation STEP-iR control box has insufficient RF attenuation, or there is some other issue, perhaps with the ic-7851 or the data/control cable from the tower to the STEP-iR control box. Either way, with the interconnect removed, and consequently no auto control of bands, then the problem goes ‘away’.


ICOM-7851 musings

A friend has been having some issues with his new, rather gorgeous, ICOM flag ship radio, the IC-7851. CAT issues, com port issue, cw keying issues, STEPir tracking issues. This post is really to act as a record, and perhaps help anyone else with similar problems. All related to configuration, possible conflicts and other such annoying gremlins.

So, after removing the icom usb drivers, unplugging the usb cable, and reinstalling the drivers, then reconnecting the usb cable, the radio and computer seemed happy. COM7 and COM8 showed up in device manager. However, there does seem to be an issue where upon reboot, sometimes the USB devices will not be recognised. This issue is to be monitored and some more work perhaps required figuring out what is happening.

Moving on, we managed to get the radio talking to HRD and Logger32, at 19200 baud, 8n1, no handshaking, on COM7.

We then looked at CW keying over the USB cable, instead of running a separate cable and related serial interface. The IC-7851 presents two com ports as mentioned above, COM7 seemingly the CAT control, COM8 the keying port perhaps. Another friend did mention that COM8 might be second RX, but not entirely sure on that. Anyway, COM8 was used in the keying config of Logger32, and the 7851 was configured to use USB2 DTR as its CW keying source. All worked great, with CW and break-in selected on the radio.

We then looked into getting the STEPir auto tracking the vfo frequency. The STEPir control box is quite an old version, pre-dating the current SDA100’s. After much head scratching, we decided to use the remote (ci-v) port on the radio. The TIP of the 3.5mm jack, going to PIN9 (ttl rx) of the 9way d-type female that plugs into the STEPir box, and the RING to pin5 (gnd). A quick solder job and it was all working. Note: the pin out of the STEPir 9 way is not standard serial, certain pins are there to be connected to different makes of radios.

3.5mm mono – 9way d-type female – CI-V to STEPir

It has been noted that the STEPir will only track when the vfo on the radio is adjusted, and not when Logger32 tells the radio to move frequency. The IC-7851 needs to have CI-V transceive turned on.

Some configuration settings recorded here as a record.


current IC-7851 settings

MB7TR – SSTV repeater

We have a new local SSTV repeater, and as far as I know one of only two in the country. Classed as a ‘regenerative node’ it will relay/repeat a received image.

MB7TR is situated in Cwmbran, and maintained by MW0RPB (Peter). It operates on 144.500MHz using FM and outputs in the Martin1 sstv mode.

To get it to repeat your transmitted image, which incidentally can be transmitted in any SSTV mode, you need to do the following, all on 144.500MHz in FM :

  1. TX your CW ident (good practice)
  2. TX a 1750Hz tone burst for around 1-2 seconds and key off
  3. Listen and wait for MB7TR to reply with its CWid – this signifies it is ready to repeat
  4. TX your SSTV image
  5. Sit back and wait for your image to be repeated out

You can use your SSTV software of choice, MMSSTV being mine. It is working great, after a few teething problems Peter has ironed out all the gremlins. Give it a try, you never know who might reply !!

SSTV from the ISS

An SSTV image from a pass of the ISS @ 14:23z today as part of the “Expedition 55 Interkosmos” mission. I didn’t get set up in time so only managed to get the end of the last transmitted image. ISS was over north France at the time, at about 250 miles up. 145.800MHz +- some doppler. SunSDR2 Pro and the X510n vertical. 30dB over 9 signal.

The next pass at 15:50z ish was going right overhead, so I was all set up for this one. The first image (with the green noise) was received over the middle of the Atlantic (amazing 800-1000 miles away?), the second when overhead here in S.Wales and the third when passing over the east side of Poland.

The last pass of today, around 17:30z resulted in the following two images. Signal strength on the last was around S5-S7 with qsb. 

Most of the time signals were around s9+10 or so, with very little qsb. I did notice some flutter/phasing/qsb on the final image as can be seen by the noise lines over the image.

Anyway that is all for now. I will put any new images below.

73 Richie.

The (call)sign of things to come?

So, I decided to have a dabble on JT65 last night, had a listen to the bands and opted for 17m.

The frequency was quite busy but I found a spot where I could call some CQ’s. 7X3WPL came back to me, but as you can see he failed to give me a report. In fact, he ended the contact with a 73 and then started calling CQ.

So this station did not give me a signal report (look at the times), and he then went about calling CQ. I double checked back through the call/band history and could not see his call sign. Unless there was some serious QSB or some sporadic propagation openings he was not on that frequency calling cq prior to me.

So, this morning, I checked QRZ, and unsurprisingly there was a QSL waiting for my approval from 7X3WPL.

Now, as I am only a year or so on the air with this callsign, I would have liked to have had that QSO confirmed and add Algeria to my country’s worked, but no, I refuse to add something that has been so obviously made incomplete. Why bother even operating and trying to make contacts if you cant even be bothered to send a report ?  Obviously it could be, and probably is, an operating mistake but to then call CQ as well ? As it happens according to QRZ he gave me a -14 report.

Is this a sign of things to come, with more and more automation, and the 59 73 mentality ? I read about the up and runs where the last you hear from a station is R-02.

Please for the love of god, if you are operating a slow as hell mode (5-6 mins per qso) then at least send a report and see the qso through to completion. I am slowly getting fed up of wasting my time.