Dr. Ulrich Rohde: Electrically Short Antennas

Thanks for asking, you opened a Pandora box Most explanation are what I would call lying by omission.

The conventional receiver with a high first IF of
45 MHz or so is limited outside the first IF bandwidth by the mixer ( IP3 typically 40 dBm ) and the synthesizer noise. And the 45 MHz Filter IMD, if monolithic pretty bad.
Th input filters protect against second oder Image products, the third order IMD because of the very close spacing like a few KHz can not be improved, here the performance of mixer, amplifier and oscillator determine all ( In band intermodulation ).
The high end dual conversion transceiver are pretty much all state of the art and expensive.

In contrary the fully digital receivers using analog/ digital converters and they integrate power. In 1 Mhz bandwidth one million signals of 1 uV result in 1 V vector added voltage and will totals overload the A/D based receiver while the conventional analog receiver will not be impressed and all will be good.

This should be a technical discussion by its own
and many may not like an honest answer.

The best Version is a hybrid RX with the A/D Filter after first VHF crystal fiter.

 

You are absolutely correct !

73 de Ulrich

 

Bravo.

Thank Dr. Karl and Dr. Rohde for the enlightenment.

Kind of a Christmas gift; much appreciated.

 

I have experienced "overload" on my IC 7300 at least once, at night, on 40 meters, with all the Chinese broadcasters crashing in, besides hams. Full sized dipole. I don't have any large gain antennas for the ham bands. The issue with 40 meters was alleviated by turning the RF gain just slightly to the left. Turning that, and mic gain down, is a difficult task for many of us!

 

For many of us, AB4OJ is a pretty well known ham. His rig performance tests are epic.

https://www.ab4oj.com/icom/ic7300/7300notes.pdf

https://www.ab4oj.com/icom/ic7610/7610notes.pdf

 

Thanks to Dr. Rohde and SM0AOM.
It's always ultra interesting to read dr. Rohde on HF receivers.
And now with this wide diffusion of SDR receivers and transceivers we need really know if they will work well in a new solar maximum in 5 years.
I am the satisfied enought owner of an Elecraft K3S, with an analogue front end before the sdr, and dont thing for now to change my rig for a pure SDR. I will wait and see/listen...
Dr. Rohde, it would be a great thing an amateur radio transceiver from Rohde Schwartz, could we dream about it?
73 and hny, Ian IK4EWX

 

If I am allowed I would like to point out that some of the A/D preamplifier are not linear, reducing the gain may shift the distortion to the preamp, see Dualgate FETS , very pronounced.

I really wanted to touch the antenna issues here and not slide in a different topic as there is no very complete publications on active antennas.

I have a recent RX book with McGraw Hill that will guide you through the RX options.

73 de Ulrich

 

interesting topic. Collins burned their fingers with such a project. The R&S tactical radios use hi rel components, too expensive for the ham market.
My XK 2100 L is now used for 25 years trouble free but without a panoramic display the hams wouldn’t want it. Great transceiver though.
For QRP I use the M3TR, the 705 was not on the market then
Thanks, Ulrich

 

Here you find almost all the answers....
Have fun

 

He didn't ask for apology!

 

just for everyone's info, ISBN 0071843337

sample Amazon link: https://www.amazon.com/Communications-Receivers-Principles-Design-Fourth/dp/0071843337

 

Hi Ron.
Many thanks for your generous endorsement of my work. All my test reports (as well as links to articles) are accessible here:
https://www.ab4oj.com/test/reports.html

73, best holiday wishes,
Adam VA7OJ/AB4OJ

 

Happy holidays, Dr. Rohde. Always nice to work you on the bands. Best 73, Bob AK3Y

 

Very interesting article. Thanks for that, Dr. Rohde. I have been wanting to build an active antenna for a long time, there are a lot of designs to be found on the internet. But reading this, I begin to think that none of the designs I have seen to far, live up to the requirements depicted in this document. A supply voltage of 50V to reach the required IP3 levels.. wow. I wonder if any designs are available in the 'public domain' that do meets these requirements. I'd certainly be interested in one to build.

 

Good morning,

on a battleship with both aktive transmitters and receivers this dynamic range is a necessity and only since LD-MOS transistors are available and GaN Transistors it is possible to build such systems.
With no co-site operation most of the 24 V aktive Antennas are ok.

I am more afraid what will happen if the sun activity will be back full force.

The big mistake in selecting radios happens if the decision is price driven and not performance driven and the system must operate under high electric field field conditions. This to a high extends applies to a contest station.
Tough choices

Take a look at VE2AED’s Station or website. Thanks amongst the best well thought out places.