INRAD RX7300 & retain ATU

Having seen the video on splitting the audio source from the main antenna and using a secondary ‘receive only’ antenna for the MFJ-1028 I thought this was an excelllent idea to deal with the QRM I have.

IC-7300 and RX7300 – no ATU tho

This video gives an excellent example of how to install the RX7300 and all the necessary connections. However, I use an MFJ-993B on 160m although my end-fed antenna is only designed to goto 80m. The internal ATU is good upto SWR of 3.0 approx, so an external ATU becomes essential.

My first ‘issue’ was getting the case off. I read comments that others had suffered this as well, beit from overight screws, or using the wrong screwdriver. I found a screwdriver that worked perfectly, but one screw (speaker screw, top left from the rfront) wouldn’t budge. In the end i relcutantly used a dremel and a small drill bit to remove the screw.

I do not understand why manufactures put screws in so tight. I wasnt happy about using a dremel on such a new piece of equipment.

I looked at the ATU cable and where it could fit. I wasn’t going to cut the case, thats for sure, and whilst i dont use the other sockets at the moment, i may do in the future. It felt like i was gaining one feature, i.e. to tap the RX circuit but had to lose another. The Instructions for the tap kit specify that the ATU cable be tucked away and kept away from the fan. However, this gave me an idea to look at could I route the cable around the fan enclouser and not-tighten the screws quite so much ?

I carefully fed the ATU wiring around the fan enclousre, not thru it, but between the fan case and the chasiss of the transceiver. I put on electrical tape onto the wire and the chassis to provide a degree of protection to the cable.

I was able to get te ATU cable and the RX Tap out of the casing nicely. The next step was to do some basic testing of the transcevier, firstly without the ATU to ensure receive was working correctly, then to test some low-wattage (WSPR) and then higher (FT8) transmissions.

I was able to receive WSPR no problem and also transmit and see my transmissions were being received via map. This was on 1W of power. I then proceeded to FT8 on 40m, as this is a popular frequency any time of day with generally good propergation. With 20W I was quickly able to make contacts and confirm my RX tap was working correctly and my TX was working correctly.

I attached the external ATU via the power and re-routed the antenna feeds to go via the ATU. I kept the RX tap still in a close loop to ensure my previous setup was working correctly.

I was pleased to see that I was reaching Europe on 80m and low SWR, so the transceiver was working well.

I will monitor the fan on the IC-7300 to ensure the the wire between the PCB and the ATU are not being ‘clipped’ or any other damage. Next step is to fit my receive only antenna and test the phasing/nulling of the MFJ-1026.

Until next time, 73.


Storm Alex. QRM

I can report that all the rigging and daily inspections insured that the end-fed antenna stayed up well despite storm alex lashing down wind and rain of epic proportion !

Whilst I have been enjoy several QSO’s on other digital modes (SSTV, BSPK) other than FT8, id thought I do an update on the next steps for the End-Fed antenna.

Whilst my signals are not bad, there is a noise floor present. Whilst I have largely removed alot of sources of QRM from ‘the shack’ (see earlier posts on QRM) my end-fed antenna seems particuarly good at picking up ‘noise’. Maybe its good to state what I think noise is as well.

When I tune the radio, I should be able to, ideally, hear all stations on that frequency (and mode). What noise brings is either man-made or remote interference to a weak signal. For noise that is ‘local’ the weak signals hide in a ‘noise’ band, this can be upto S9 for thinks like washing machines/VDSL/construction equipment.

With the ‘local’ noise its possible to use the an external antenna (lets call that a receive antenna) and transmit on the existing antenna, then between the two ‘phase’ the noise until it is no longer present.

I am going to use the MFJ-1028 noise canceller as I was using this already with my Kenwood and DX-Commander multi-band vertical, but as both a send and receive antenna making using of the ‘T/R Delay’ – The Icom 7300 doesnt come with its own ‘receive only’ port unlike its ‘bigger brothers’ in the Icom range, but is easily adapater to have one via the a plug-in kit from Inrad.

The installation looks simple enough as shown in the video below. I face the challenge that I am also using an external ATU (MFJ-993B) so getting both ports in will mean doing the install slightly differenty.

INRAD RX7300 mod

I have a number of antennas i could use as a receive only, but a recommended ‘noise gather’ is the ‘mini-whip’. I picked mine up off ebay and it arrived in a bout a week.

I have yet to install the miniwhip, but have all the necessary parts, including a rather impressive 4th ground pole ! I will be following the guidance from the following video

I will first try using the mini-whipa and end-fed combo and feedback on results !

Hopefully there will be less bad weather in the coming week allowing more ‘build’ work outside, for now i’m glad my masts have stayed up and we are all staying safe at home !

Until next post – 73 !